Medical instrumentation webster pdf

 
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  1. Medical Instrumentation Application and Design, 4th Edition by John G. Webster.pdf
  2. Medical Instrumentation Application and Design, 4th Edition by John G. Webster.pdf
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  4. Biomedical instrumentation webster 4th edition.pdf

MEDICAL INSTRUMENTATION. Application and Design. FOURTH EDITION. John G. Webster, Editor. Contributing Authors. John W. Clark, Jr. Rice University. 𝗣𝗗𝗙 | On Jan 1, , John Webster and others published Medical instrumentation: application and design, Fourth edition, John Wiley. Encylopedia of medical devices & instrumentation/by John G. Webster, PDE. Pregelled disposable electrodes. p.d.f.. Probability density function. PDL.

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Medical Instrumentation Webster Pdf

Medical Instrumentation Application and Design, 4th Edition by John G. Webster. pdf - Ebook download as PDF File .pdf), Text File .txt) or read book online. Hardcover 4th Edition - [Free] Medical Instrumentation Application And Design By Webster John. G Wiley Hardcover 4th Edition [PDF] [EPUB] -. MEDICAL. [PDF]Free All Ebooks/biomedical Instrumentation Webster 4th Edition download Book. All Ebooks/biomedical Instrumentation Webster 4th. taunipesetis.gq

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Diffeienl appli- calions of each piinciple can be used lo slienglhen undeislanding of each concepl; also, new applicalions may be ieadily appaienl. This appioach isolales all impoilanl measuiemenls foi specialisls whoneedlo know sensed and piinciples of liansduclion. This appioach is valuable foi medical peisonnel who aie inleiesled in special- ized insliumenls. Modifying inpuls can affecl piocessing of eilhei desiied oi inleifeiing inpuls.

Some undesiiable quanlilies can acl as bolh a modifying inpul and an inleifeiing inpul. A lypical elecliocaidiogiaphic iecoiding syslem, shown in Iiguie 1. The desiied inpul is lhe elecliocaidiogiaphic vollage ecg lhal appeais belween lhe lwo elecliodes on lhe body suiface. An example of a modifying inpul is lhe oiienlalion of lhe palienl cables.

We shall discuss seveial compensalion melhods foi eliminaling lhe effecls of inleifeiing and modifying inpuls.

Ioi lhe elecliocaidiogiaph an example is lhe lwisling of lhe elecliode wiies lo ieduce The vollage of lhe induced noise is piopoilional lo lhe aiea of lhal loop. The effecls of elecliode molion can be ieduced by lechniques desciibed in Seclion 5. This oulpul-dependenl signal is subliacled fiom lhe inpul, and lhe diffeience becomes lhe effeclive syslem inpul. Less inpul-signal powei is also needed foi lhis feedback scheme, so less loading occuis.

The sludy of feedback syslems is a well-developed discipline lhal cannol be puisued fuilhei heie Kuo and Golnaiaghi, 2OO3. Iilleis may be inseiled al lhe insliumenl inpul, al some poinl wilhin lhe insliumenl, oi al lhe oulpul of lhe insliumenl. Iillei elemenls may be dislincl devices lhal block oi pass all inpuls, oi lhey may be embodied in a single device lhal seleclively blocks only ciicuils bul use inslead mechanical, pneumalic, lheimal, oi elecliomagnelic piinciples lo block oul undesiied enviionmenlal inpuls.

Ioi example, insliu- insliumenl componenls. The seleclivily needed may be easiei lo achieve wilh highei-level oulpul signals. These exlia inlenlional inpuls may be lhe same as lhose lo be canceled. The lwo oulpuls musl cancel despile vaiialions in all lhe unavoidable inleifeiing inpuls and vaiialions in lhe desiied inpuls.

The aclual cancellalion of undesiied oulpul componenls can be implemenled eilhei befoie oi aflei lhe desiied and undesiied oulpuls aie combined. The melhod of opposing inpuls can also be used lo cancel lhe effecls of modifying inpuls. Aulomalic ieal-lime coiieclions aie implied foi lhe melhod of opposing inpuls usl desciibed.

Aclually, oulpul coiieclions aie oflen calculaled manu- ally oi by compulei melhods and applied aflei dala aie collecled. An example of using lhe opposing-inpul melhod is lo inlenlionally induce lhe oulpul is achieved.

An obvious disadvanlage of lhis melhod is lhal lhe Iiguie 1. These sludies aie wilhoul conliol sub ecls, in oidei only lo idenlify queslions foi fuilhei ieseaich.

Medical oulcome sludies show cosl-effeclive impiovemenls in palienl heallh aie incieasingly iequiied piioi lo adoplion and ieimbuisemenl foi new medical lechnologies Anonymous, 2OO1.

Desciiplive slalislics aie useful lo summaiize dala and lheii alliibules. Measuies of spiead oi dispeision of dala desciibe lhe vaiialion in lhe obseivalions. Oflen we need lo sludy ielalionships belween lwo numeiical chaiaclei- islics. Like lhe ielalionship, il may be small foi a sliong cuivilineai ielalionship. Melhods foi measuiing lhe accuiacy of a diagnoslic pioceduie use lhiee pieces of infoimalion.

Theie aie seveial melhods foi ievising lhe piobabilily lhal a palienl has a condiliononlhe basis of lhe iesulls of a diagnoslic lesl. Taking inlo consideialion lhe iesulls of a diagnoslic pioceduie is only one pail of lhe complex clinical decision-making piocess. Decision liee analysis and olhei foims of decision analysis lhal include economic implicalions aie also used in an effoil lo make oplimal decisions Webslei, 2OO4. These ciileiia musl cleaily specify how well an insliumenl measuies lhe desiied inpul and how much lhe oulpul depends on inleifeiing and modifying inpuls.

Chaiacleiislics of insliumenl peifoim- ance aie usually subdivided inlo lwo classes on lhe basis of lhe fiequency of lhe inpul signals. The piopeilies of lhe oulpul foi a wide iange of conslanl inpuls demonsliale lhe qualily of lhe measuiemenl, including non- lineai and slalislical effecls.

Some sensois and insliumenls, such as piezo- elecliic devices, iespond only lo lime-vaiying inpuls and have no slalic chaiacleiislics. Allhough dynamic chaiacleiislics usually depend on slalic chaiacleiislics, lhe nonlineaiilies and slalislical vaiiabilily aie usually ignoied foi dynamic inpuls, because lhe aie appioximaled by lhe sum of slalic and dynamic chaiacleiislics.

This ieal and ideal insliumenl peifoimance. This ialio is usually expiessed as a peicenl. The accuiacy usually vaiies ovei lhe noimal iange of lhe quanlily measuied, usually decieases as lhe full-scale value of lhe quanlily decieases on a mulliiange insliumenl, andalso oflen vaiies wilh lhe fiequency of desiied, inleifeiing, and modifying inpuls.

Accuiacy is a measuie of lhe lolal eiioi wilhoul iegaid lo lhe lype oi souice of lhe eiioi. The possibilily lhal lhe measuiemenl is low and lhal il is high aie assumed lo be equal. The accuiacy can be expiessed as peicenl of ieading, peicenl of full scale, numbei of digils foi digilal ieadouls, oi 1 2 lhe smallesl division on an analog scale. Oflen lhe accuiacy is expiessed as a sum of lhese, foi example, on a digilal device, O. O1' of ieading O.

O15' of full-scale 1 digil. Some insliumenl manu- facluieis specify accuiacy only foi a limiled peiiod of lime. Ioi example, a melei lhal displays a ieading of 2. High-piecision measuiemenls do nol imply high accuiacy, howevei, because piecision makes no compaiison lo lhe liue value. Resolulion expiesses lhe degiee lo which neaily equal values of a quanlily can be disciiminaled.

Repioduc- ibilily does nol imply accuiacy. Ioi example, a bioken digilal clock wilh an AMoi PMindicaloi gives veiy iepioducible values lhal aie accuiale only once a day. Making mulliple measuiemenls and aveiaging lhe iesulls can impiove lhe eslimale of lhe liue value. This one inpul is vaiied inciemenlally ovei lhe noimal opeialing iange, iesulling in a iange of inciemenlal oulpuls. The slalic sensilivily of an insliumenl oi syslem is lhe ialio of lhe inciemenlal oulpul quanlily lolhe inciemenlal inpul quanlily.

The inciemenlal slope can be oblained fiom eilhei lhe secanl belween lwo ad acenl poinls oi lhe langenl lo one poinl on lhe calibialion cuive. The slalic sensilivily may be conslanl foi onlypail of lhenoimal opeialing iange of lhe insliumenl, as shownin Iiguie 1. The slalic sensilivily foi modulaling sensois is usually given pei voll of excilalion, because lhe oulpul vollage is piopoilional lo lhe excilalion vollage.

Zeio diifl has occuiied when all oulpul values inciease oi deciease by lhe same absolule amounl. The slope of lhe sensilivily cuive is unchanged, bul lhe oulpul-axis inleicepl incieases oi decieases as showninIiguie 1.

The following faclois cancause zeiodiifl: A change in lhe de-offsel vollage al lhe elecliodes in lhe elecliocaidiogiaph example in Iiguie 1. Sensilivily diifl causes eiioi lhal is piopoilional lo lhe magnilude of lhe inpul. The slope of lhe calibialion cuive can eilhei inciease oi deciease, as indicaled in Iiguie 1.

Sensilivily diifl can iesull fiom manufacluiing loleiances, vaiialions in powei supply, nonlineaiilies, and changes in ambienl lempeialuie and piessuie. Slalic sensilivily may be conslanl foi only a limiled iange of inpuls. These lwo iequiiemenls foi syslem lineaiily aie ieslaled in Iiguie 1. Ioi small ieadings neai zeio, howevei, peicenlage of full scale is moie iealislic because il is nol feasible lo lesl foi small peicenl-of-ieading devialions neai zeio.

Ioi mosl insliumenls lhal aie essenlially lineai, if olhei souices of eiioi aie minimal, lhe accuiacy is equal lo lhe nonlineaiily. Minimal iesolvable inpuls impose a lowei bound on lhe quanlily lo maximal inpuls lhal give lineai oulpuls. The slalic lineai iange and lhe dynamic lineai iange may be diffeienl. The maximal opeialing iange is lhe laigesl inpul lhal does nol damage lhe insliumenl. Opeialion in lhe uppei pail of lhis iange is moie likely lo be nonlineai. Iinally, sloiage condilions specify enviionmenlal and inleifeiing inpul limils lhal should nol be exceeded when lhe insliumenl is nol being used.

These ianges aie nol always symmeliic wilh iespecl lo zeio inpul, pailiculaily foi sloiage condilions. This is necessaiy so lhal we can piopeily evaluale lhe degiee lo which insliumenls disluib lhe quanlily being measuied. Mosl medical insliumenls musl piocess signals lhal aie funclions of lime. Diffeienlial oi inlegial equalions aie iequiied lo ielale dynamic inpuls lo dynamic oulpuls foi conlinuous syslems.

Ioi example, an auloianging insliumenl may violale lhese condilions. Solulions foi is lhe mosl common liansienl inpul foi insliumenlalion. Sinusoids aie lhe mosl common peiiodic funclion lo use because, lhiough lhe Iouiiei-seiies expan- sion, any peiiodic funclion can be appioximaled by a sum of sinusoids.

Band- limiled while noise unifoim-powei speclial conlenl is a common iandom inpul because one can lesl insliumenl peifoimance foi all fiequencies in a pailiculai bandwidlh. The phase angle foi mosl insliumenls is negalive. The dynamic chaiacleiislics of insliumenls aie illuslialed below by sinusoidal inpuls. This zeio- oidei insliumenl has ideal dynamic peifoimance, because lhe oulpul is piopoilional lo lhe inpul foi all fiequencies and lheie is no amplilude oi phase disloilion.

Alineai polenliomelei is a good example of a zeio-oidei insliumenl. Iiguie 1. Also, low-iesislance ciicuils connecled lo lhe oulpul can load lhis simple zeio-oidei insliumenl. The slalic-sensilivily cuive given in Iiguie 1. The slep iesponse in Iiguie 1. Ioi sinusoids, 1. Ioi laigei lime conslanls, lhis deciease occuis al lowei fiequency.

The oidinale of lhe fiequency- iesponse magnilude in Iiguie 1. Iind lhe maximal sinusoidal inpul fiequency lhal will keep oulpul eiioi due lo fiequency iesponse less lhan 5'. Iind lhe phase angle al lhis fiequency. The slalic chaiacleiislic is zeio foi all values of inpul, andlhe slep iesponse umps immedialely lo lhe slep vollage bul decays exponenlially lowaid zeio as lime incieases.

Low-fiequency sinusoids aie seveiely allenualed, wheieas high-fiequency sinusoids aie lillle allenualed. Iuilhei- moie, many highei-oidei insliumenls can be appioximaled by second-oidei chaiacleiislics if some simplifying assumplions can be made. The foui con- slanls in 1. Then lhe sum of lhe foices equals lhe pioducl of mass and acceleialion.

The slep iesponse can have lhiee foims, depending on lhe damping ialio. Apiaclical compiomise belween iapid iise lime and minimal oveishool is a damping ialio of aboul O. The iale of decline in lhe amplilude fiequency iesponse is lwice lhe iale of lhal s.

Nole lhal iesonance phenomena can occui if lhe damping ialio is loo small. The oveiall liansfei funclion of lineai elemenls connecled in seiies is lhe pioducl of lhe liansfei funclions foi lhe individual elemenls. Many combinalions of nonlineai elemenls can pioduce lhe oveiall lineai liansfei funclion iequiied. The faclois lhal impose consliainls on lhe design aie of couise diffeienl foi each lype of insliumenl.

Howevei, some of lhe geneial iequiiemenls can be calegoiized as signal, enviionmenlal, medical, and economic faclois. Physicians, nuises, clinical engineeis, and sales peisonnel aie lheiefoie good souices of ideas.

Mosl companies have one oi moie people who aie iesponsible foi evalualing new ideas, so il is veiy impoilanl foi lhose who wanl lo piopose a new idea lo be in conlacl wilh a peison who can undeisland lhe idea and who has lhe aulhoiily lo pioceed wilh a delailed evalualion.

A simple, signed nondisclosuie agiee- menl is adequale bul essenlial lo piolecl palenl iighls when delailed ideas aie discussed.

Deleimin- ing medical feasibilily enlails examining lhe clinical need foi lhe pioducl, including palienl indicalions, numbei of palienls, clinical specially, and exaclly how, why, and by whom lhe device will be ulilized.

Maikeling ieseaich and analysis can be useful foi evolulionaiy pioducls bul aie nol ieliable foi ievolulionaiy pioducls, especially when a change in medical piaclice is iequiied. Technical feasibilily analysis should include a desciiplion of lhe nenls, bieaklhioughs oi invenlions iequiied, syslems analysis, and pieliminaiy cosl eslimales. A funclional piololype lhal includes lhe sensoi, piimaiy signal piocessing elemenls, and olhei new oi unique componenls should be buill and lesled on animals and humans as eaily as possible.

The manufacluiing feasibilily analysis should be done eaily, when ma oi alleinalive lechnologies peisonnel iequiiemenls, compelilion, palenls, slandaids, manufacluiing ie- quiiemenls, sales and seivice iequiiemenls, and lhe lime schedule foi lhe pio ecl.

Ioi mosl insliumenls, funclions musl be paililioned inlo haidwaie and soflwaie befoie delailed design can begin. Design ieviews focus on syslems issues and pioblems lhal lhe company may lesl, design assuiance, and manufacluiing engineeis.

These piololypes aie also lesled on animals oi human sub ecls lo veiify expecled opeialion and pei- foimance al a few clinical lesling cenleis.

Pioduclion engineeis musl be involved lhioughoul lhe design and devel- opmenl piocess lo avoid a iedesign foi manufacluiabilily. Special pioduclion be ieleased by lhe design and developmenl engineeis. Small pioduclion iuns aie usually needed lo discovei pioblems and high volume, as consumei pioducls aie, so full aulomalion of pioduclion is nol cosl-effeclive.

COs may be needed lo be documenled, along wilh lhe coiieclive aclion laken. Successful companies musl be commilled lo iepaiiing oi ieplacing lheii pioducls lhioughoul lhe enliie expecled lifelime of lhe pioducl. Second, seven calegoiies weie eslablished: The seven calegoiies inlo which medical devices aie divided aie desciibed used in medical devices has become an aiea of incieasing concein; seveial iequiiemenls foi mainlaining liaceabilily of devices lo lhe ullimale cuslomei, poslmaikeling suiveillance foi life-suslaining and life-suppoiling implanls, and hospilal iepoiling iequiiemenls foi adveise incidenls weie added lo lhe law in O.

These conliols apply lo all lhiee classes. The IDA has exlensively iegulaled lhese devices by iequiiing manufacluieis lo piove lheii safely and effecliveness piioi lo maikel ielease.

Devices aie assigned lo 1 of 3 classes. A manufacluiei may pelilion lhe IDA foi Analog elecliocaidiog- iaphy machine; elec- liohydiaulic lilholiiploi; conliaceplive inliauleiine device and accessoiies; infanl iadianl waimei; conliaceplive lubal occlusion device; aulomaled hepaiin analyzei; aulomaled diffeienlial cell counlei; aulomaled blood-cell sepaialoi; liansabdominal aminoscope. Poslamendmenl devices oi new devices Devices pul on lhe maikel aflei May 28, Subslanlially equivalenl devices Poslamendmenl devices lhal aie subslanlially equivalenl lo pieamendmenl devices.

Devices aie assigned lo lhe same class as lheii pieamendmenl counleipails and sub ecl lo lhe same iequiiemenls.

Digilal elecliocaidiogiaphy machines; YAG laseis foi ceilain uses; lampons;! Phienic-neive slimulaloi; pacemakei pulse geneialoi; inliacaidiac palch; vena cava clamp.

Medical Instrumentation Application and Design, 4th Edition by John G. Webster.pdf

Cuslom devices Devices nol geneially available lo olhei licensed piaclilioneis and nol available in Pioducl musl be designed foi a pailiculai palienl and may nol be offeied foi geneial commeicial disliibulion.

Devices aie exempl fiom piemaikeling lesling and peifoimance slandaids bul aie sub ecl lo geneial conliols. Denluies; oilhopedic shoes. Tiansilional devices Devices lhal weie iegulaled as diugs befoie enaclmenl of lhe slalule bul aie medical devices. Anlibiolic susceplibilily disks; bone heleiogiafls; gonoiihea diagnoslic pioducls; in eclable silicone; inliaoculai lenses; suigical suluies; sofl conlacl lenses. Sanla Monica, CA: Plymoulh Meeling, PA: New Yoik, NY: Monlvale, N1: Bionzino, 1.

Boca Ralon, IL: Biush, L. Biea, CA: Cobbold, R. New Yoik: Wiley, Cohen, B. Lippincoll, 2OO4. Ciomwell, L. Weibell, and!. Pienlice-Hall, O. Davis, N. Neil M. Davis Associales, 2OO1. Dawson-Saundeis, B. Noiwalk, CT: McGiaw-Hill, O. Doiland, N. Saundeis, 2OO3. Washinglon, DC: Nalional Academy Piess, Blanchaid, and 1. Academic, 2OO5. Iiikin, B.

Paik Ridge, N1: Pailhenon, Geddes, L. Habei, K. Raven Piess, Hamillon, B. Neal-Schuman, Heislei, R. Spiingei, Piscalaway, N1: Pienlice-Hall, Kesslei, D.

Kuo, B. Wiley, 2OO3. Pacela, A. Special Supplemenl No. Rabbill, 1. While Plains, NY: Ray, C. Yeai Book, Scoll, D. Slanaszek, M. Lancaslei, PA: Technomic Publishing Co. Tompkins, W. Webslei eds. Webslei, 1. Hoboken N1: Wiley, 2OO4. Wiley, 2OO6. Cook eds. An elecliic oulpul fiom lhe sensoi is noimally desiiable because of lhe advanlages il gives in fuilhei signal piocessing Pallas-Aieny and Webslei, 2OO1. As we shall see in lhis chaplei, lheie aie many melhods used lo conveil physiological evenls lo elecliic signals.

Dimensional changes may be measuied by vaiialions in iesislance, induclance, capacilance, and piezoelecliic effecl. Theimislois and lheimocouples aie employed lo measuie body lempeialuies. Displacemenl sensois can be used in bolh diiecl and indiiecl syslems of measuiemenl. Diiecl measuiemenls of displacemenl aie used lo deleimine lhe change indiamelei of blood vessels and lhe changes in volume and shape of caidiac chambeis. An example is lhe movemenl of a miciophone diaphiagm lhal delecls lhe movemenl of lhe heail indiieclly and lhe iesulling heail muimuis.

Heie we will desciibe lhe following lypes of displacemenl-sensilive measuiemenl melhods: The polenliomelei shown in Iiguie 2. The iesislance elemenls composed of wiie-wound, caibon-nlm, melal-nlm, conducling- plaslic, oi ceiamic maleiial may be exciled by eilhei dc oi ac vollages.

These polenliomeleis pioduce a lineai oulpul wilhinO. O1'of full scale as a funclion of displacemenl, piovided lhal lhe polenliomelei is nol elecliically loaded. The iesolulion of lhese polenliomeleis is a funclion of lhe consliuclion. Ioi giealei vaiialions in iesislance, fiom seveial ohms lo seveial megohms, lhe iesislance wiie is wound on a mandiel oi caid. The vaiialion in iesislance is lheieby nol conlinuous, bul ialhei slepwise, because lhe wipei moves fiom one luin of wiie lo lhe nexl.

The fiiclional and ineilial componenls of lhese polenliomeleis should be low in oidei lo minimize dynamic disloilion of lhe syslem. The iesulling sliain gages may be used lo measuie exliemely small displacemenls, on lhe oidei of nanomeleis.

Thus dividing membeis of 2. Subsliluling lhis inlo lhe cenlei leim of 2. Nole lhal lhe gage facloi foi semiconducloi maleiials is appioximalely 5O lo 7O limes lhal of lhe melals.

Also nole lhal lhe gage facloi foi melals is piimaiily a funclion of dimensional effecls. The desii- able fealuie of highei gage faclois foi semiconducloi devices is offsel by lheii giealei iesislivilylempeialuie coefncienl.

Designs foi insliumenls lhal use semiconducloi maleiials musl incoipo- iale lempeialuie compensalion. Sliain gages can be classined as eilhei unbonded oi bonded. An unbonded sliain-gage unil is shown in Iiguie 2. These wiies aie mounled undei sliess belween lhe fiame and lhe movable aimaluie such lhal pieload is giealei lhan any expecled exleinal compiessive load.

This is necessaiy lo avoid pulling lhe wiies in compiession. This lype of sensoi may be used foi conveiling blood piessuie lo diaphiagm movemenl, lo iesislance change, lhen lo an elecliic signal.

A bonded sliain-gage elemenl, consisling of a melallic wiie, elched foil, vacuum-deposiled nlm, oi semiconducloi bai, is cemenled lo lhe sliained suiface. Iiguie 2. The devialion fiom lineaiily is appioximalely 1'. One melhod of lempeialuie compensalion foi lhe naluial lempeialuie sensilivily of bonded sliain gages involves using a second sliain gage as a dummy elemenl lhal is also exposed lo lhe lempeialuie vaiialion, bul nol lo sliain.

When possible, lhe foui-aim biidge shown in Iiguie 2. Ioui bonded melal sliain gages can be used on canlilevei beams lo measuie bile foice in denlal ieseaich Dechow, 2OO6. Sliain-gage lechnology advanced in lhe Os wilh lhe inlioduclion of lhe semiconducloi sliain-gage elemenl, which has lhe advanlage of having a high gage facloi, as shown in Table 2. Howevei, il is moie lempeialuie sensilive and inheienlly moie nonlineai lhan melal sliain gages because lhe piezo- iesislive effecl vaiies wilh sliain.

Iiom R. Aiiows above unils show diieclion of maximal sensilivily lo sliain. The diaphiagm is diieclly coupled by an aimaluie lo an unbonded sliain-gage syslem. Wilh incieasing piessuie, lhe sliain on gage paii B and C is incieased, while lhal on gage paii A and D is decieased. The opposile-lype maleiial is diffused inlo lhe subsliale.

Medical Instrumentation Application and Design, 4th Edition by John G. Webster.pdf

A laige gage facloi can be allained wilh lighlly doped maleiial. The gages aie diffused diieclly onlolhe diaphiagm. When piessuie is applied lo lhe diaphiagm, a iadial sliess componenl occuis al lhe edge.

Some undesiiable quanlilies can acl as bolh a modifying inpul and an inleifeiing inpul. A lypical elecliocaidiogiaphic iecoiding syslem, shown in Iiguie 1. The desiied inpul is lhe elecliocaidiogiaphic vollage ecg lhal appeais belween lhe lwo elecliodes on lhe body suiface. An example of a modifying inpul is lhe oiienlalion of lhe palienl cables.

We shall discuss seveial compensalion melhods foi eliminaling lhe effecls of inleifeiing and modifying inpuls. Ioi lhe elecliocaidiogiaph an example is lhe lwisling of lhe elecliode wiies lo ieduce The vollage of lhe induced noise is piopoilional lo lhe aiea of lhal loop. The effecls of elecliode molion can be ieduced by lechniques desciibed in Seclion 5. This oulpul-dependenl signal is subliacled fiom lhe inpul, and lhe diffeience becomes lhe effeclive syslem inpul.

Less inpul-signal powei is also needed foi lhis feedback scheme, so less loading occuis. The sludy of feedback syslems is a well-developed discipline lhal cannol be puisued fuilhei heie Kuo and Golnaiaghi, 2OO3. Iilleis may be inseiled al lhe insliumenl inpul, al some poinl wilhin lhe insliumenl, oi al lhe oulpul of lhe insliumenl.

Iillei elemenls may be dislincl devices lhal block oi pass all inpuls, oi lhey may be embodied in a single device lhal seleclively blocks only ciicuils bul use inslead mechanical, pneumalic, lheimal, oi elecliomagnelic piinciples lo block oul undesiied enviionmenlal inpuls. Ioi example, insliu- insliumenl componenls.

The seleclivily needed may be easiei lo achieve wilh highei-level oulpul signals. These exlia inlenlional inpuls may be lhe same as lhose lo be canceled. The lwo oulpuls musl cancel despile vaiialions in all lhe unavoidable inleifeiing inpuls and vaiialions in lhe desiied inpuls. The aclual cancellalion of undesiied oulpul componenls can be implemenled eilhei befoie oi aflei lhe desiied and undesiied oulpuls aie combined.

The melhod of opposing inpuls can also be used lo cancel lhe effecls of modifying inpuls. Aulomalic ieal-lime coiieclions aie implied foi lhe melhod of opposing inpuls usl desciibed.

Aclually, oulpul coiieclions aie oflen calculaled manu- ally oi by compulei melhods and applied aflei dala aie collecled. An example of using lhe opposing-inpul melhod is lo inlenlionally induce lhe oulpul is achieved.

An obvious disadvanlage of lhis melhod is lhal lhe Iiguie 1. These sludies aie wilhoul conliol sub ecls, in oidei only lo idenlify queslions foi fuilhei ieseaich. Medical oulcome sludies show cosl-effeclive impiovemenls in palienl heallh aie incieasingly iequiied piioi lo adoplion and ieimbuisemenl foi new medical lechnologies Anonymous, 2OO1.

Desciiplive slalislics aie useful lo summaiize dala and lheii alliibules. Measuies of spiead oi dispeision of dala desciibe lhe vaiialion in lhe obseivalions. Oflen we need lo sludy ielalionships belween lwo numeiical chaiaclei- islics. Like lhe ielalionship, il may be small foi a sliong cuivilineai ielalionship. Melhods foi measuiing lhe accuiacy of a diagnoslic pioceduie use lhiee pieces of infoimalion. Theie aie seveial melhods foi ievising lhe piobabilily lhal a palienl has a condiliononlhe basis of lhe iesulls of a diagnoslic lesl.

Taking inlo consideialion lhe iesulls of a diagnoslic pioceduie is only one pail of lhe complex clinical decision-making piocess. Decision liee analysis and olhei foims of decision analysis lhal include economic implicalions aie also used in an effoil lo make oplimal decisions Webslei, 2OO4. These ciileiia musl cleaily specify how well an insliumenl measuies lhe desiied inpul and how much lhe oulpul depends on inleifeiing and modifying inpuls.

Chaiacleiislics of insliumenl peifoim- ance aie usually subdivided inlo lwo classes on lhe basis of lhe fiequency of lhe inpul signals. The piopeilies of lhe oulpul foi a wide iange of conslanl inpuls demonsliale lhe qualily of lhe measuiemenl, including non- lineai and slalislical effecls. Some sensois and insliumenls, such as piezo- elecliic devices, iespond only lo lime-vaiying inpuls and have no slalic chaiacleiislics.

Allhough dynamic chaiacleiislics usually depend on slalic chaiacleiislics, lhe nonlineaiilies and slalislical vaiiabilily aie usually ignoied foi dynamic inpuls, because lhe aie appioximaled by lhe sum of slalic and dynamic chaiacleiislics. This ieal and ideal insliumenl peifoimance. This ialio is usually expiessed as a peicenl. The accuiacy usually vaiies ovei lhe noimal iange of lhe quanlily measuied, usually decieases as lhe full-scale value of lhe quanlily decieases on a mulliiange insliumenl, andalso oflen vaiies wilh lhe fiequency of desiied, inleifeiing, and modifying inpuls.

Accuiacy is a measuie of lhe lolal eiioi wilhoul iegaid lo lhe lype oi souice of lhe eiioi. The possibilily lhal lhe measuiemenl is low and lhal il is high aie assumed lo be equal. The accuiacy can be expiessed as peicenl of ieading, peicenl of full scale, numbei of digils foi digilal ieadouls, oi 1 2 lhe smallesl division on an analog scale. Oflen lhe accuiacy is expiessed as a sum of lhese, foi example, on a digilal device, O.

O1' of ieading O. O15' of full-scale 1 digil. Some insliumenl manu- facluieis specify accuiacy only foi a limiled peiiod of lime. Ioi example, a melei lhal displays a ieading of 2. High-piecision measuiemenls do nol imply high accuiacy, howevei, because piecision makes no compaiison lo lhe liue value.

Resolulion expiesses lhe degiee lo which neaily equal values of a quanlily can be disciiminaled. Repioduc- ibilily does nol imply accuiacy. Ioi example, a bioken digilal clock wilh an AMoi PMindicaloi gives veiy iepioducible values lhal aie accuiale only once a day. Making mulliple measuiemenls and aveiaging lhe iesulls can impiove lhe eslimale of lhe liue value. This one inpul is vaiied inciemenlally ovei lhe noimal opeialing iange, iesulling in a iange of inciemenlal oulpuls.

The slalic sensilivily of an insliumenl oi syslem is lhe ialio of lhe inciemenlal oulpul quanlily lolhe inciemenlal inpul quanlily. The inciemenlal slope can be oblained fiom eilhei lhe secanl belween lwo ad acenl poinls oi lhe langenl lo one poinl on lhe calibialion cuive. The slalic sensilivily may be conslanl foi onlypail of lhenoimal opeialing iange of lhe insliumenl, as shownin Iiguie 1. The slalic sensilivily foi modulaling sensois is usually given pei voll of excilalion, because lhe oulpul vollage is piopoilional lo lhe excilalion vollage.

Zeio diifl has occuiied when all oulpul values inciease oi deciease by lhe same absolule amounl. The slope of lhe sensilivily cuive is unchanged, bul lhe oulpul-axis inleicepl incieases oi decieases as showninIiguie 1. The following faclois cancause zeiodiifl: A change in lhe de-offsel vollage al lhe elecliodes in lhe elecliocaidiogiaph example in Iiguie 1.

Sensilivily diifl causes eiioi lhal is piopoilional lo lhe magnilude of lhe inpul. The slope of lhe calibialion cuive can eilhei inciease oi deciease, as indicaled in Iiguie 1. Sensilivily diifl can iesull fiom manufacluiing loleiances, vaiialions in powei supply, nonlineaiilies, and changes in ambienl lempeialuie and piessuie.

Slalic sensilivily may be conslanl foi only a limiled iange of inpuls. These lwo iequiiemenls foi syslem lineaiily aie ieslaled in Iiguie 1. Ioi small ieadings neai zeio, howevei, peicenlage of full scale is moie iealislic because il is nol feasible lo lesl foi small peicenl-of-ieading devialions neai zeio. Ioi mosl insliumenls lhal aie essenlially lineai, if olhei souices of eiioi aie minimal, lhe accuiacy is equal lo lhe nonlineaiily.

Minimal iesolvable inpuls impose a lowei bound on lhe quanlily lo maximal inpuls lhal give lineai oulpuls. The slalic lineai iange and lhe dynamic lineai iange may be diffeienl. The maximal opeialing iange is lhe laigesl inpul lhal does nol damage lhe insliumenl. Opeialion in lhe uppei pail of lhis iange is moie likely lo be nonlineai.

Iinally, sloiage condilions specify enviionmenlal and inleifeiing inpul limils lhal should nol be exceeded when lhe insliumenl is nol being used. These ianges aie nol always symmeliic wilh iespecl lo zeio inpul, pailiculaily foi sloiage condilions. This is necessaiy so lhal we can piopeily evaluale lhe degiee lo which insliumenls disluib lhe quanlily being measuied.

Mosl medical insliumenls musl piocess signals lhal aie funclions of lime. Diffeienlial oi inlegial equalions aie iequiied lo ielale dynamic inpuls lo dynamic oulpuls foi conlinuous syslems. Ioi example, an auloianging insliumenl may violale lhese condilions. Solulions foi is lhe mosl common liansienl inpul foi insliumenlalion. Sinusoids aie lhe mosl common peiiodic funclion lo use because, lhiough lhe Iouiiei-seiies expan- sion, any peiiodic funclion can be appioximaled by a sum of sinusoids.

Band- limiled while noise unifoim-powei speclial conlenl is a common iandom inpul because one can lesl insliumenl peifoimance foi all fiequencies in a pailiculai bandwidlh. The phase angle foi mosl insliumenls is negalive. The dynamic chaiacleiislics of insliumenls aie illuslialed below by sinusoidal inpuls.

This zeio- oidei insliumenl has ideal dynamic peifoimance, because lhe oulpul is piopoilional lo lhe inpul foi all fiequencies and lheie is no amplilude oi phase disloilion. Alineai polenliomelei is a good example of a zeio-oidei insliumenl. Iiguie 1. Also, low-iesislance ciicuils connecled lo lhe oulpul can load lhis simple zeio-oidei insliumenl.

The slalic-sensilivily cuive given in Iiguie 1. The slep iesponse in Iiguie 1. Ioi sinusoids, 1. Ioi laigei lime conslanls, lhis deciease occuis al lowei fiequency. The oidinale of lhe fiequency- iesponse magnilude in Iiguie 1. Iind lhe maximal sinusoidal inpul fiequency lhal will keep oulpul eiioi due lo fiequency iesponse less lhan 5'.

Iind lhe phase angle al lhis fiequency. The slalic chaiacleiislic is zeio foi all values of inpul, andlhe slep iesponse umps immedialely lo lhe slep vollage bul decays exponenlially lowaid zeio as lime incieases. Low-fiequency sinusoids aie seveiely allenualed, wheieas high-fiequency sinusoids aie lillle allenualed. Iuilhei- moie, many highei-oidei insliumenls can be appioximaled by second-oidei chaiacleiislics if some simplifying assumplions can be made.

The foui con- slanls in 1. Then lhe sum of lhe foices equals lhe pioducl of mass and acceleialion. The slep iesponse can have lhiee foims, depending on lhe damping ialio.

Apiaclical compiomise belween iapid iise lime and minimal oveishool is a damping ialio of aboul O. The iale of decline in lhe amplilude fiequency iesponse is lwice lhe iale of lhal s. Nole lhal iesonance phenomena can occui if lhe damping ialio is loo small.

The oveiall liansfei funclion of lineai elemenls connecled in seiies is lhe pioducl of lhe liansfei funclions foi lhe individual elemenls. Many combinalions of nonlineai elemenls can pioduce lhe oveiall lineai liansfei funclion iequiied. The faclois lhal impose consliainls on lhe design aie of couise diffeienl foi each lype of insliumenl.

Howevei, some of lhe geneial iequiiemenls can be calegoiized as signal, enviionmenlal, medical, and economic faclois. Physicians, nuises, clinical engineeis, and sales peisonnel aie lheiefoie good souices of ideas. Mosl companies have one oi moie people who aie iesponsible foi evalualing new ideas, so il is veiy impoilanl foi lhose who wanl lo piopose a new idea lo be in conlacl wilh a peison who can undeisland lhe idea and who has lhe aulhoiily lo pioceed wilh a delailed evalualion.

A simple, signed nondisclosuie agiee- menl is adequale bul essenlial lo piolecl palenl iighls when delailed ideas aie discussed. Deleimin- ing medical feasibilily enlails examining lhe clinical need foi lhe pioducl, including palienl indicalions, numbei of palienls, clinical specially, and exaclly how, why, and by whom lhe device will be ulilized. Maikeling ieseaich and analysis can be useful foi evolulionaiy pioducls bul aie nol ieliable foi ievolulionaiy pioducls, especially when a change in medical piaclice is iequiied.

Technical feasibilily analysis should include a desciiplion of lhe nenls, bieaklhioughs oi invenlions iequiied, syslems analysis, and pieliminaiy cosl eslimales.

A funclional piololype lhal includes lhe sensoi, piimaiy signal piocessing elemenls, and olhei new oi unique componenls should be buill and lesled on animals and humans as eaily as possible. The manufacluiing feasibilily analysis should be done eaily, when ma oi alleinalive lechnologies peisonnel iequiiemenls, compelilion, palenls, slandaids, manufacluiing ie- quiiemenls, sales and seivice iequiiemenls, and lhe lime schedule foi lhe pio ecl.

Ioi mosl insliumenls, funclions musl be paililioned inlo haidwaie and soflwaie befoie delailed design can begin. Design ieviews focus on syslems issues and pioblems lhal lhe company may lesl, design assuiance, and manufacluiing engineeis. These piololypes aie also lesled on animals oi human sub ecls lo veiify expecled opeialion and pei- foimance al a few clinical lesling cenleis.

Pioduclion engineeis musl be involved lhioughoul lhe design and devel- opmenl piocess lo avoid a iedesign foi manufacluiabilily. Special pioduclion be ieleased by lhe design and developmenl engineeis. Small pioduclion iuns aie usually needed lo discovei pioblems and high volume, as consumei pioducls aie, so full aulomalion of pioduclion is nol cosl-effeclive.

COs may be needed lo be documenled, along wilh lhe coiieclive aclion laken. Successful companies musl be commilled lo iepaiiing oi ieplacing lheii pioducls lhioughoul lhe enliie expecled lifelime of lhe pioducl.

Second, seven calegoiies weie eslablished: The seven calegoiies inlo which medical devices aie divided aie desciibed used in medical devices has become an aiea of incieasing concein; seveial iequiiemenls foi mainlaining liaceabilily of devices lo lhe ullimale cuslomei, poslmaikeling suiveillance foi life-suslaining and life-suppoiling implanls, and hospilal iepoiling iequiiemenls foi adveise incidenls weie added lo lhe law in O.

These conliols apply lo all lhiee classes. The IDA has exlensively iegulaled lhese devices by iequiiing manufacluieis lo piove lheii safely and effecliveness piioi lo maikel ielease. Devices aie assigned lo 1 of 3 classes. A manufacluiei may pelilion lhe IDA foi Analog elecliocaidiog- iaphy machine; elec- liohydiaulic lilholiiploi; conliaceplive inliauleiine device and accessoiies; infanl iadianl waimei; conliaceplive lubal occlusion device; aulomaled hepaiin analyzei; aulomaled diffeienlial cell counlei; aulomaled blood-cell sepaialoi; liansabdominal aminoscope.

Poslamendmenl devices oi new devices Devices pul on lhe maikel aflei May 28, Subslanlially equivalenl devices Poslamendmenl devices lhal aie subslanlially equivalenl lo pieamendmenl devices. Devices aie assigned lo lhe same class as lheii pieamendmenl counleipails and sub ecl lo lhe same iequiiemenls.

Digilal elecliocaidiogiaphy machines; YAG laseis foi ceilain uses; lampons;! Phienic-neive slimulaloi; pacemakei pulse geneialoi; inliacaidiac palch; vena cava clamp. Cuslom devices Devices nol geneially available lo olhei licensed piaclilioneis and nol available in Pioducl musl be designed foi a pailiculai palienl and may nol be offeied foi geneial commeicial disliibulion. Devices aie exempl fiom piemaikeling lesling and peifoimance slandaids bul aie sub ecl lo geneial conliols.

Denluies; oilhopedic shoes. Tiansilional devices Devices lhal weie iegulaled as diugs befoie enaclmenl of lhe slalule bul aie medical devices. Anlibiolic susceplibilily disks; bone heleiogiafls; gonoiihea diagnoslic pioducls; in eclable silicone; inliaoculai lenses; suigical suluies; sofl conlacl lenses. Sanla Monica, CA: Plymoulh Meeling, PA: New Yoik, NY: Monlvale, N1: Bionzino, 1. Boca Ralon, IL: Biush, L. Biea, CA: Cobbold, R. New Yoik: Wiley, Cohen, B.

Lippincoll, 2OO4. Ciomwell, L. Weibell, and!. Pienlice-Hall, O. Davis, N. Neil M. Davis Associales, 2OO1. Dawson-Saundeis, B. Noiwalk, CT: McGiaw-Hill, O. Doiland, N. Saundeis, 2OO3. Washinglon, DC: Nalional Academy Piess, Blanchaid, and 1. Academic, 2OO5. Iiikin, B. Paik Ridge, N1: Pailhenon, Geddes, L. Habei, K. Raven Piess, Hamillon, B.

Neal-Schuman, Heislei, R. Spiingei, Piscalaway, N1: Pienlice-Hall, Kesslei, D. Kuo, B. Wiley, 2OO3. Pacela, A. Special Supplemenl No. Rabbill, 1. While Plains, NY: Ray, C.

Yeai Book, Scoll, D. Slanaszek, M. Lancaslei, PA: Technomic Publishing Co. Tompkins, W. Webslei eds. Webslei, 1. Hoboken N1: Wiley, 2OO4. Wiley, 2OO6. Cook eds. An elecliic oulpul fiom lhe sensoi is noimally desiiable because of lhe advanlages il gives in fuilhei signal piocessing Pallas-Aieny and Webslei, 2OO1.

As we shall see in lhis chaplei, lheie aie many melhods used lo conveil physiological evenls lo elecliic signals. Dimensional changes may be measuied by vaiialions in iesislance, induclance, capacilance, and piezoelecliic effecl. Theimislois and lheimocouples aie employed lo measuie body lempeialuies.

Displacemenl sensois can be used in bolh diiecl and indiiecl syslems of measuiemenl. Diiecl measuiemenls of displacemenl aie used lo deleimine lhe change indiamelei of blood vessels and lhe changes in volume and shape of caidiac chambeis. An example is lhe movemenl of a miciophone diaphiagm lhal delecls lhe movemenl of lhe heail indiieclly and lhe iesulling heail muimuis. Heie we will desciibe lhe following lypes of displacemenl-sensilive measuiemenl melhods: The polenliomelei shown in Iiguie 2.

The iesislance elemenls composed of wiie-wound, caibon-nlm, melal-nlm, conducling- plaslic, oi ceiamic maleiial may be exciled by eilhei dc oi ac vollages. These polenliomeleis pioduce a lineai oulpul wilhinO. O1'of full scale as a funclion of displacemenl, piovided lhal lhe polenliomelei is nol elecliically loaded. The iesolulion of lhese polenliomeleis is a funclion of lhe consliuclion.

Ioi giealei vaiialions in iesislance, fiom seveial ohms lo seveial megohms, lhe iesislance wiie is wound on a mandiel oi caid. The vaiialion in iesislance is lheieby nol conlinuous, bul ialhei slepwise, because lhe wipei moves fiom one luin of wiie lo lhe nexl. The fiiclional and ineilial componenls of lhese polenliomeleis should be low in oidei lo minimize dynamic disloilion of lhe syslem.

The iesulling sliain gages may be used lo measuie exliemely small displacemenls, on lhe oidei of nanomeleis. Thus dividing membeis of 2. Subsliluling lhis inlo lhe cenlei leim of 2. Nole lhal lhe gage facloi foi semiconducloi maleiials is appioximalely 5O lo 7O limes lhal of lhe melals.

Also nole lhal lhe gage facloi foi melals is piimaiily a funclion of dimensional effecls. The desii- able fealuie of highei gage faclois foi semiconducloi devices is offsel by lheii giealei iesislivilylempeialuie coefncienl. Designs foi insliumenls lhal use semiconducloi maleiials musl incoipo- iale lempeialuie compensalion.

Sliain gages can be classined as eilhei unbonded oi bonded. An unbonded sliain-gage unil is shown in Iiguie 2. These wiies aie mounled undei sliess belween lhe fiame and lhe movable aimaluie such lhal pieload is giealei lhan any expecled exleinal compiessive load. This is necessaiy lo avoid pulling lhe wiies in compiession.

This lype of sensoi may be used foi conveiling blood piessuie lo diaphiagm movemenl, lo iesislance change, lhen lo an elecliic signal. A bonded sliain-gage elemenl, consisling of a melallic wiie, elched foil, vacuum-deposiled nlm, oi semiconducloi bai, is cemenled lo lhe sliained suiface.

Iiguie 2. The devialion fiom lineaiily is appioximalely 1'. One melhod of lempeialuie compensalion foi lhe naluial lempeialuie sensilivily of bonded sliain gages involves using a second sliain gage as a dummy elemenl lhal is also exposed lo lhe lempeialuie vaiialion, bul nol lo sliain.

When possible, lhe foui-aim biidge shown in Iiguie 2. Ioui bonded melal sliain gages can be used on canlilevei beams lo measuie bile foice in denlal ieseaich Dechow, 2OO6. Sliain-gage lechnology advanced in lhe Os wilh lhe inlioduclion of lhe semiconducloi sliain-gage elemenl, which has lhe advanlage of having a high gage facloi, as shown in Table 2.

Howevei, il is moie lempeialuie sensilive and inheienlly moie nonlineai lhan melal sliain gages because lhe piezo- iesislive effecl vaiies wilh sliain. Iiom R. Aiiows above unils show diieclion of maximal sensilivily lo sliain. The diaphiagm is diieclly coupled by an aimaluie lo an unbonded sliain-gage syslem. Wilh incieasing piessuie, lhe sliain on gage paii B and C is incieased, while lhal on gage paii A and D is decieased.

The opposile-lype maleiial is diffused inlo lhe subsliale. A laige gage facloi can be allained wilh lighlly doped maleiial. The gages aie diffused diieclly onlolhe diaphiagm. When piessuie is applied lo lhe diaphiagm, a iadial sliess componenl occuis al lhe edge. The sign of lhis componenl is opposile lo lhal of lhe langenlial sliess componenl neai lhe cenlei. The placemenl of lhe eighl diffused sliain-gage unils shown in Iiguie 2. Silicon sliain-gage piessuie sensois can be placed on lhe lip of a calhelei and inseiled diieclly inlo lhe blood, iesulling in moie accuiale measuiemenls and faslei iesponse limes Koiiles, These syslems noimally consisl of a naiiow silicone-iubbei lube O.

Iiom R. Aiiows above unils show diieclion of maximal sensilivily lo sliain. The diaphiagm is diieclly coupled by an aimaluie lo an unbonded sliain-gage syslem. Wilh incieasing piessuie, lhe sliain on gage paii B and C is incieased, while lhal on gage paii A and D is decieased.

The opposile-lype maleiial is diffused inlo lhe subsliale. A laige gage facloi can be allained wilh lighlly doped maleiial. The gages aie diffused diieclly onlolhe diaphiagm. When piessuie is applied lo lhe diaphiagm, a iadial sliess componenl occuis al lhe edge. The sign of lhis componenl is opposile lo lhal of lhe langenlial sliess componenl neai lhe cenlei. The placemenl of lhe eighl diffused sliain-gage unils shown in Iiguie 2. Silicon sliain-gage piessuie sensois can be placed on lhe lip of a calhelei and inseiled diieclly inlo lhe blood, iesulling in moie accuiale measuiemenls and faslei iesponse limes Koiiles, These syslems noimally consisl of a naiiow silicone-iubbei lube O.

The ends of lhe lube aie sealed wilh elecliodes amalgamaled coppei, silvei, oi plalinum. As lhe lube slielches, lhe diamelei of lhe lube decieases and lhe lenglh incieases, causing lhe iesislance lo inciease. The iesislance pei unil lenglh of lypical gages is appioximalely O. These unils measuie much highei displacemenls lhan olhei gages. The elaslic sliain gage is lineai wilhin 1' foi 1O' of maximal exlension. As lhe exlension is incieased lo 3O'of maximum, lhe nonlineaiily ieaches 4' of full scale.

The silicon chip has a silicon diaphiagm wilh a foui-iesisloi Whealslone biidge diffused inlo il. This pievenls elecliic shock fiom lhe sensoi lo lhe palienl and pievenls desliuclive cuiienls duiing denbiillalion fiom lhe palienl lo lhe silicon chip. Long-leim cieep is a piopeily of lhe iubbei lubing. This is nol a pioblem foi dynamic measuiemenls. Opeialional pioblems include mainlaining a good conlacl belween lhe mei- cuiy and lhe elecliodes, ensuiing conlinuily of lhe meicuiy column, and conlioll- ing lhe diifl in iesislance due lo a ielalively laige gage lempeialuie coefncienl.

The low value of iesisl- ance means moie powei is iequiied lo opeiale lhese sliain-gage unils. Lawlon and Collins deleimined lhe slalic and dynamic iesponse of elaslic sliain gages.

They found lhal lhe amplilude and phase weie conslanl up lo 1O Hz. Signincanl disloilion occuiied foi fiequencies giealei lhan 3O Hz. Cobbold indicaled lhal a pioblem nol fully appiecialed is lhal lhe gage does nol dislend fully duiing pulsalions when diamelei of lhe vessel is being measuied. The mass of lhe gage and ils nnile mechanical iesislance can cause il lo dig inlo lhe vessel wall as lhe vessel expands, so il can give a ieading seveial limes lowei lhan lhal measuied using ulliasonic oi cineangiogiaphic melhods.

Lead-wiie eiiois aie common wilh lhese devices because of lhe low iesislance of lhe sliain gage. A conslanl-cuiienl souice causes an oulpul lhal is lineai foi laige changes in gage iesislance.

Pail a is based on D. Hokanson, D. Sumnei, and D. Sliandness, 1i. Resislance-lype sensois may be connecled in one oi moie aims of a biidge ciicuil. Nole lhal 2. Alleinaling-cuiienl ac balancing ciicuils aie moie complicaled because a ieaclive as well as a iesislive imbalance musl be compensaled. Nole in Iiguie 2. An induclive sensoi has an advanlage in nol being affecled by lhe dielecliic piopeilies of ils enviionmenl. Howevei, il may be affecled by exleinal magnelic nelds due lo lhe pioximily of magnelic maleiials.

The vaiiable-induclance melhod employing a single displaceable coie is shown in Iiguie 2. This device woiks on lhe piinciple lhal alleialions in lhe self-induclance of a coil may be pioduced by changing lhe geomeliic foim facloi oi lhe movemenl of a magnelic coie wilhin lhe coil. The change in induclance foi lhis device is nol lineaily ielaled lo displacemenl. The facl lhal lhese devices have low powei iequiiemenls and pioduce laige vaiialions in induclance makes lhem alliaclive foi iadiolelemeliy applicalions.

The mulual-induclance sensoi employs lwo sepaiale coils and uses lhe vaiia- lion in lheii mulual magnelic coupling lo measuie displacemenl Iiguie 2. Cobbold desciibes lhe applicalion of lhese devices in measuiing caidiac dimensions, moniloiing infanl iespiialion, and asceilaining aileiial diameleis. The induced vollage in lhe secondaiy coil is a funclion of lhe geomeliy of lhe coils sepaialion and axial alignmenl , lhe numbei of piimaiy and secondaiy luins, and lhe fiequency and amplilude of lhe excilalion vollage.

The induced vollage in lhe secondaiy coil is a nonlineai funclion of lhe sepaialion of lhe coils. The oulpul vollage is delecled wilh slandaid demodulaloi and amplinei ciicuils. As shown in Iiguie 2. The lwo secondaiy coils aie connecled in opposilion in oidei lo achieve a widei iegion of lineaiily.

The piimaiy coil is sinusoidally exciled, wilh a fiequency belween 6O Hz and 2O kHz. The alleinaling magnelic neld induces neaily equal vollages ce and de in lhe secondaiy coils. The oulpul vollage cd ce de. When lhe slug is symmeliically placed, lhe lwo secondaiy vollages aie equal and lhe oulpul signal is zeio.

A phase-sensilive demodulaloi is used lo deleimine lhe diieclion of displace- menl.

Iiguie 3. O foi aii Bowman and Meindl, Howevei, lhe melhod lhal is easiesl lo implemenl and lhal is mosl commonly used is lo change lhe sepaialion belween lhe plales. By subsliluling 2.

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Thus 2. This fiequency iesponse is quile adequale foi a miciophone lhal does nol measuie sound piessuies al fiequencies below 2O Hz. Howevei, il is inadequale foi measuiing mosl physiological vaiiables because of lheii low-fiequency componenls.

Complianl plaslics of diffeienl dielecliic conslanls may be placed belween foil layeis lo foima capacilive mal lo be placed ona bed. A capacilance sensoi can be fabiicaled fiom layeis of mica insulalois sandwiched belween coiiugaled melal layeis. Piezoelecliic maleiials geneiale an elecliic polenlial when mechanically sliained, and conveisely an elecliic polenlial can cause physical defoimalion of lhe maleiial. The piinciple of opeialion is lhal when an asymmeliical ciyslal lallice is disloiled, a chaige ieoiienlalion lakes place, causing a ielalive displacemenl of negalive and posilive chaiges.

The displaced inleinal chaiges induce suiface chaiges of opposile polaiily on opposile sides of lhe ciyslal. Suiface chaige can be deleimined by measuiing lhe diffeience in vollage belween elecliodes allached lo lhe suifaces. Then, by subslilulion of 2. Ioi a piezoelecliic sensoi of 1 cm 2 aiea and 1 mm lhickness wilh an applied foice due lo a 1O g weighl, lhe oulpul vollage is O. Theie aie vaiious modes of opeialion of piezoelecliic sensois, depending on lhe maleiial and lhe ciyslallogiaphic oiienlalion of lhe plale Lion, These modes include lhe lhickness oi longiludinal compiession, liansveisal compiession, lhickness-sheai aclion, and face-sheai aclion.

These nlms aie veiy lhin, lighlweighl and plianl, and lhey can be cul easily and adapled lo uneven suifaces.

The low mechanical qualily facloi does nol peimil iesonance appli- calions, bul il peimils acouslical bioadband applicalions foi miciophones and loudspeakeis. Piezoelecliic maleiials have a high bul nnile iesislance. Whal is lhe low- coinei fiequency? O5 lo 1OO Hz. Add lhe minimal numbei of exlia componenls lo achieve lhe design specincalions.

Allow foi a gain of 1O. The oulpul decays exponenlially because of lhe nnile inleinal iesislance of lhe piezoelecliic maleiial. Howevei, doing so ieduces lhe sensilivily in lhe midband fiequencies accoiding lo 2. Anolhei appioach lo impioving lhe low-fiequency iesponse is lo use lhe chaige amplinei desciibed in Seclion 3. Because of ils mechanical iesonance, lhe high-fiequency equivalenl ciicuil foi a piezoelecliic sensoi is complex.

Piezoelecliic sensois aie used quile exlensively in caidiology foi exleinal body-suiface and inleinal inliacaidiac phonocaidiogiaphy. They aie also used in lhe deleclion of Koiolkoff sounds in blood-piessuie measuiemenls Chaplei 7. Addilional applicalions of piezoelecliic sensois involve lheii use in measuiemenls of physiological acceleialions.

Seclion 8. McGiaw- Hill. Adiop in lhe big-loe lempeialuie is a good eaily clinical waining of shock. Aneslhesia decieases body lempeialuie by depiessing lhe lheimal iegulaloiy cenlei.

Also, enviionmenlal changes and ailifacls can cause misleading ieadings. The following lypes of lheimally sensilive melhods of measuiemenl will be desciibed heie: This phenomenon is due lo lhe sum of lwo independenl effecls. The nisl effecl, discoveied by Pelliei, is an emf due solely lo lhe conlacl of lwo unlike melals and lhe unclion lempeialuie. The nel Pelliei emf is ioughly piopoilional lo lhe diffeience belween lhe lempeialuies of lhe lwo unclions. The second effecl, ciediled lo Thomson Loid Kelvin , is an emf due lo lhe lempeialuie giadienls along each single conducloi.

The magniludes of lhe Pelliei and Thom- son emfs can be deiived fiom lheimodynamic piinciples Anonymous, , and eilhei may piedominale, depending on lhe melals chosen. The piaclical implicalion of lhis piinciple is lhal lead wiies may be allached lo lhe lheimocouple wilhoul affecling lhe accuiacy of lhe measuied emf, piovided lhal lhe newly foimed unclions aie al lhe same lempeialuie Iiguie 2.

This piinciple makes il possible foi calibialion cuives deiived foi a given iefeience- unclion lempeialuie lo be used lo deleimine lhe calibialion cuives foi anolhei iefeience lempeialuie. The sensilivilies of common lheimocouples iange fiom 6.

Tempeialuie-conliolled ovens can mainlain a iefeience lempeialuie lo wilhin O 4 C. Paiallel combinalions may be used lo measuie aveiage lempeialuie. Chail iecoidings may be secuied by using a self-balancing polenliomelei syslem. The lineaiily of lhis lallei device is dependenl only on lhe lheimocouple and polenliomelei; il is independenl of lhe olhei ciicuiliy.

Theimocouples have lhe following advanlages: Theii disadvanlages aie small oulpul vollage, low sensilivily, and lhe need foi a iefeience lempeialuie.

Numeious examples of lhe use of lheimocouples in biomedical ie- seaich aie given in lhe lileialuie Wien, 2OO6. Theimocouples can be made small in size, so lhey can be inseiled inlo calheleis and hypodeimic needles. These maleiials ieacl lo lempeialuie changes in a way lhal is opposile lo lhe way melals ieacl lo such changes. The iesislance of lheimislois decieases as lempeialuie incieases and incieases as lempeialuie decieases Melo, 2OO6. Sapoff ieviewed lhe vaiious lypes of lheimislois lhal have been found lo be mosl suilable foi biomedical use.

The iesislivily of lheimisloi semiconduclois used foi biomedical applicalions is belween O. These devices aie small in size lhey can be made less lhan O. The diagonal lines wilh a posilive slope give lineai iesislance values and show lhe degiee of lheimisloi lineaiily al low cuiienls. The inleiseclion of lhe lheimisloi cuives and lhe diagonal lines wilh negalive slope give lhe device powei dissipalion.

Howevei, lhis does nol piesenl a pioblem ovei lhe limiled lempeialuie spans foi biomedical woik 1O Clo 2O C. The vollage-veisus-cuiienl chaiacleiislics of lheimislois, as shown in Iiguie 2. When lheie is laige self-healing, lhe lheimisloi vollage diop de- cieases as lhe cuiienl incieases.

This poilion of lhe cuive displays a negalive- iesislance chaiacleiislic. The lempeialuie of lhe lheimisloi is lhal of ils suiioundings. Opeialions in lhis iegion iendei lhe device vulneiable lo lheimal desliuclion. The piinciple of vaiialion in lheimal iesislance can be used lo measuie blood velocily, as desciibed in Seclion 8. The lheimisloi lempeialuie is close loambienl. Calculale minimum lheimisloi iesislance. The lime delay foi lhe cuiienl lo ieach ils maximal value is a funclion of lhe vollage applied, lhe mass of lhe lheimisloi, and lhe value of lhe seiies-ciicuil iesisl- ance.

Time delays fiom milliseconds lo seveial minules aie possible wilh lheimisloi ciicuils. Similai lime delays occui when lhe lempeialuie suiiound- ing lhe lheimisloi is changed in a slep fashion. Modein insliumenls use miciocompuleis lo coiiecl foi nonlineaiilies, ialhei lhan lhe foimei ciicuil schemes.

The ciicuiliy used foi lheimisloi ieadoul is essenlially lhe same as foi conduclive sensois, and many of lhe same lechniques apply. Biidge ciicuils give high sensilivily and good accuiacy. The biidge ciicuil shown in Iiguie 2. An example is lhe need lo deleimine lhe lempeialuie diffeience belween lwo oigans oi belween mulliple siles in lhe same oigan. Opeialional-amplinei ciicuils may be used lo measuie lhe cuiienl in a lheimisloi as a funclion of lempeialuie.

The glass-encapsulaled bead lheimisloi is lhe one mosl commonly used in biomedical applicalions. The glass coaling piolecls lhe sensing elemenl fiom lhe hoslile enviionmenl of lhe body wilhoul signincanlly affecling lhe lheimal iesponse lime of lhe syslem. The small size of lhese lheimislois makes possible lheii placemenl al lhe lip of calheleis oi hypodeimic needles.

The lheimodilulion-calhelei syslem discussed in Seclion 8. An addilional applicalion of lheimislois is in lhe clinical measuiemenl of oial lempeialuie. Theimisloi piobes wilh disposable shealhs aie piesenlly used, bul lhese exhibil a nisl-oidei slep iesponse as shown in Iiguie 1.

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A pioblem wilh lheimisloi neonalal skin suiface lempeialuie-moniloiing insliumenls is lhal lhe piobes fall off. Theimal conlacl wilh lhe skin can be moniloied by applying a 14 s pulse eveiy 4. This piinciple makes il possible lo measuie lhe lempeialuie of a body wilhoul physical conlacl wilh il. Medical lheimogiaphy is a lechnique wheieby lhe lempeialuie disliibulion of lhe body is mapped wilh a sensilivily of a few lenlhs of a kelvin.

Theimogiaphy has been used foi lhe eaily deleclion of bieasl cancei, bul lhe melhod is conlioveisial. Heie we shall deal wilh lhe basic piinciples of lheimal iadialion and delecloi syslems. Ioi ob ecls al ioom lempeialuie, lhe speclium is piedominanlly in lhe fai- and exlieme-fai-infiaied iegions. A blackbody is an ideal lheimal iadialoi; as such, il absoibs all incidenl iadialion and emils lhe maximal possible lheimal iadialion.

Nole fiom 2. This paiamelei, plolled in Iiguie 2. The lenses used in infiaied insliumenls musl be caiefully selecled foi lheii infiaied speclial piopeilies. On lhe olhei hand, some maleiials such as aisenic liisulnde ieadily pass infiaied and nol visible lighl. These devices musl have a shoil iesponse lime and appiopiiale wavelenglhbandwidlh iequiiemenls lhal malch lhe iadialion souice.

Theimal and pholon deleclois aie used as infiaied deleclois. The deleclois aie of lwo lypes, bolh of which aie desciibed in Seclion 2. The lheimal delecloi has low sensilivily and iesponds lo all wavelenglhs, as shown in Iiguie 2. Suilable insliumenlalion musl be used lo amplify, piocess, and display lhese weak signals fiom iadialion deleclois. Mosl iadiomeleis make use of a beam-choppei syslemloinleiiupl lhe iadialion al a nxediale seveial hundied heilz.

This aiiangemenl allows lhe use of high-gain ac amplineis wilhoul lhe inheienl pioblems of slabilily associaled wilh dc amplineis. A miiioi focuses lhe iadialion on lhe delecloi.

Howevei, a blackenedchoppei inleiiupls lhe iadialion beamal a conslanl iale. The oulpul of lhe delecloi ciicuil is a seiies of pulses wilh amplilude dependenl on lhe slienglh of lhe iadialion souice. This ac signal is amplined, while lhe mean value, which is sub ecl lo diifl, is blocked. A iefeience-phase signal, used lo synchionize lhe phase-sensilive demodulaloi Seclion 3.

The signal is lhen nlleied lo piovide a dc signal piopoilional lo lhe laigel lempeialuie. This signal can lhen be displayed oi iecoided. The lympanic membiane and hypo- lhalamus aie peifused by lhe same vasculaluie. This appioach has advanlages ovei using meicuiy lheimomeleis, lheimocouples, oi lheimislois.

The slandaid lempeialuie-measuiing lechniques measuie lhe lempeialuie of lhe sensoi, nol lhal of lhe sub ecl. The sensoi musl be in conlacl wilh lhe palienl long enough foi ils lempeialuie lo become lhe same as, oi close lo, lhal of lhe sub ecl whose lempeialuie is being measuied. Howevei, lhe infiaied lheimomeliy device delecls emilled eneigy lhal is piopoilional lo lhe aclual lempeialuie of lhe sub ecl.

Theie is negligible lheimal lime conslanl foi lhe pyioelecliic sensoi Iiaden, The infiaied lympanic lempeialuie-moniloiing syslem has a iesponse lime in lhe oidei of O. A disposable sanilaiy piobe covei is used lo pievenl cioss-conlaminalion fiom palienl lo palienl. Iiom 1. Webslei ed. Asmall piism-shaped sample of single-ciyslal undoped GaAs is epoxied al lhe ends of lwo side-by-side oplical nbeis.

The sensois and nbeis can be quile small, compalible wilh biological implanlalion aflei being shealhed. One nbei liansmils lighl fiom a lighl-emilling diode souice lo lhe sensoi, wheie il is passed lhiough lhe GaAs and collecled by lhe olhei nbei foi deleclion in lhe ieadoul insliumenl. Some of lhe oplical powei liaveling lhiough lhe semiconducloi is absoibed, by lhe piocess of iaising valence-band eleclions, acioss lhe foibidden eneigy gap inlo lhe conduclion band.

This nonmelallic piobe is pailiculaily suiled foi lempeialuie measuie- menl in lhe sliong elecliomagnelic healing nelds used in healing lissue foi cancei lheiapy oi in palienl iewaiming. The mosl common use occuis in lhe clinical-chemisliy lab, in which lechnicians analyze samples of blood and olhei lissues iemoved fiom lhe body.

Oplical insliumenls aie also used duiing caidiac calheleiizalion lo measuie lhe oxygen saluialion of hemoglobin and lo measuie caidiac oulpul. The iemaindei of lhis chaplei is divided inlo seclions lhal deal wilh souices, geomeliical oplics, nlleis, deleclois, and combinalions lheieof.

Theii iadianl oulpul vaiies wilh lempeialuie and wave- lenglh, as given by 2. The ielalive-oulpul speclium shown in Iiguie 2. Al 2OOO K, oulpul is lowei al all wavelenglhs and peak oulpul shifls lo longei wavelenglhs. Monochiomalic oulpuls fiomcommon laseis aie shown by dashed lines: A Coining glass nllei passes a blue wavelenglh band. A Kodak 87 gelalin nllei passes infiaied and blocks visible wavelenglhs.

Geimanium lenses pass long wavelenglhs lhal cannol be passed by glass. The S4 iesponse is a lypical phololube iesponse. CdS plus a nllei has a iesponse lhal closely malches lhal of lhe eye.

PbS is a sensilive infiaied delecloi. These aie only ielalive iesponses. Peak iesponses of diffeienl deleclois diffei by 1O 7. The lolal iadialion is given by 2. Hence lhe iadianl oulpul incieases iapidly wilh lempeialuie, as do lhe efnciency, lhe evapoialion of lungslen, and lhe blackening of lhe glass bulb.

The life of lhe nlamenl is lhus diaslically shoilened by highei lempeialuies. Iilamenls aie usually coiled lo inciease lheii emissivily and efnciency. Ioi use in insliumenls, shoil lineai coils may be aiianged wilhin a compacl, neaily squaie aiea lying in a single plane. To pioduce a souice of unifoim iadianl oulpul ovei a subslanlial aiea, iibbon nlamenls may be used.

Tungslenhalogen lamps have iodine oi biomine added lo lhe gases noimally used lo nll lhe bulb. The small quailz bulbs opeiale al lempeialuies above 25O C and usually iequiie cooling by a blowei.

The halogen combines wilh lungslen al lhe wall. The iesulling gas migiales back lo lhe nlamenl, wheie il decomposes and deposils lungslen on lhe nlamenl. As a iesull, lhese lamps mainlain moie lhan 9O' of lheii inilial iadianl oulpul lhioughoul lheii life. The iadianl oulpul of a convenlional lamp, on lhe olhei hand, declines as much as 5O' ovei ils lifelime. A phosphoi on lhe inside of lhe glass bulb absoibs lhis ulliaviolel iadialion and emils lighl of longei, visible wavelenglhs.

Olhei low-piessuie dischaige lamps include lhe glow lamp such as lhe neon lamp , lhe sodium-vapoi lamp, and lhe lasei. High-piessuie dischaige lamps aie moie impoilanl foi oplical insliumenls because lhe aic is compacl and lhe iadianl oulpul pei unil aiea is high. The caibon aic has been in use foi lhe longesl lime, bul il has laigely been ieplaced by lhe meicuiy lamp bluish-gieen coloi , lhe sodium lamp yellowcoloi , and lhe xenon lamp while coloi.

These lamps usually have a cleai quailz bulb wilh elecliodes al bolh ends of lhe spheiical bulb. The ziiconium aic lamp piovides an inlense poinl souice. Sponlaneous iecombinalion of in ecled hole and eleclion paiis iesulls in lhe emission of iadialion. Because lhe silicon band gap is 1. The silicon device is nol efncienl.

Howevei, GaAs has a slighlly highei band gap, as shown in Iiguie 2. Allhough lhe oulpul is nol visible, lhe efnciency is high and lhe GaAs device is widely used.

The GaP L! D in Iiguie 2. D and pioduces a biighl ied lighl. The GaAsP L! Ds make use of a special phosphoi lhal absoibs lwo pholons al one wavelenglh and emils a single pholon al a shoilei wavelenglh.

The GaAs is Si doped lo emil iadialion al 94O nm. Powei al lhis wavelenglh is absoibed by lhe phosphoi coaling lhal emils gieen lighl al 54O nm, as shown in Iiguie 2. The decay lime of lhe phosphoi is aboul 1 ms. Lighl-emilling diodes aie compacl, iugged, economical, and neaily mono- chiomalic.

They aie widely used in a vaiiely of medical, lianspoilalion, and indusliial ciicuils. A vaiiely of ciicuils aie available foi L! Ds and pholo- deleclois using eilhei sleady oi modulaled iadialion. Oidinaiy silicondiodes have a band gap of 1. GaAs has a band gap of 1. GaP has a band gap of 2.

The foiwaid cuiienl pumps a laige populalion of lhe molecules lo an exciled eneigy level. Radialion incidenl on lhe molecules causes lhe pioduclion of addilional iadialion lhal is idenlical in chaiaclei. Lasei oulpul is highly monochiomalic, collimaled paiallel , and phase coheienl. The mosl common lasei is lhe HeNe lasei lhal opeiales al nm in lhe ied iegion, as shown in Iiguie 2.

The lasei is opeialed by a low-piessuie aic similai lo a neon sign and piovides up lo 1OO mW. Aigon laseis piovide lhe highesl conlinuous-powei levels W in lhe visible pail of lhe speclium al nm Iiguie 2. This high-powei oulpul peimils pholocoagulalion of blood vessels in lhe eyes of palienls suffeiing fiom diabelic ielinopalhy. The iuby lasei has a modeiale 1 m1 oulpul in lhe ied iegion of lhe speclium al nm, as shown in Iiguie 2.

The neodymium in ylliium aluminumgainel Nd: The mosl impoilanl medical use of lhe lasei has been lo mend leais in lhe ielina. A lypical pholocoagulaloi uses a pulsed iuby lasei wilh a conliollable oulpul.

The heal dissipaled by lhe pulse foims a buin, which, on healing, develops scai lissue lhal mends lhe oiiginal leai. Seclion

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