Doc 0000022007

- -- -- ... --· _ .. 7 . F - . ·"4 ... .·-· 1 .---------..} .. \ .... ·----~----l BIOQPOWER INTERIM REPORT ... -- ts; October' 1966 ; :~ ' Contract No: Prepared by: . -· ..... ·-.. .. J ~- --- w&*tt ri¥ a-x- •t'fi!ii'iPb+ Jwe·. e a ... TABLE OF COt\'TENTS Page STATEMENT OF OBJECTIVES 1 SUMMARY 2 m. CE:>l'E RA L DISCUSSION ·3 A. Directly Obtained Electricity . 3 1. Neuromuscular Potentials 3 a. Nervt:! Potentials 4 b •. Muscle Potentials 5 ,,.., c. Cardiac Potentials 6 ~ 2. .D irect Current Systems. . . . 7 1l. Physiologi~~~ Electrode Cell 7 b. Fuel Cell 11 . B. Thern;~oelectric Converter 12 c. Mechanoelectric Converter 14 1. ~ourc'es • 14 2. Transducers 19 a. Piezoelectric Crystals 19 b. Permanent Magnet Generators 24 3. Previous Work 25 \ ·rv. BIBLIOC RA PHY 28 ... ....... -~-- ~d~----------~------------------------------~ .......... ~- -1- t. STATEMENT OF OBJECTIVES '!'he object of this study is to survey past work in the area of body prod'uced electrical power as rep~rted in the literature, develop an ur.derstanding or the various methods and approaches which have been suggested as possible sources. and present this information in a useful !onn. This report is directed towarus the general problem of providing electriCal power to implanted electronic devices, such as artificial c~rdiac pacemakers, requiring less than 200 micro• wat-ts for an indefinite time from a completely self contained internal system. - " . . ·.. - · - .• -wn~~~._. .... __.._._. .. __..__.~. .- ----..--..---------------------------------~-------------- e --.---- _, --- I -z- I!. SUMMARY A general literature review was first undertaken to both dis· . cover previous experimental work and _to gather general impressions ot thinking on this subject •. The revi.ew indicated that there were few well documented conclustons available and that although a fresh start might be duplicative, it is ne·eded for a systematic study. Conceiv• able sources were listed and each has been ·brieny considered from t::,e physiological and instrumental viewpoints. In trying to evaluate t:otential usefulness of a source it was sometimes necessary to form conceptual d_esigns of mechanical syste:ns which could utilize that ar_e source. Comm:ents !ln these de,signs- 'included in the discussion as contextual in.f ormation becaus~ theyillustrate those asp~cts o£ ~ the systems which were considered and the design problems en- countered, not because these designs. are fe:t to be the The page features a digital graphic depicting the front of a sturdy vault, likely symbolizing the "Black Vault" mentioned in the text. The vault is gray with a circular door, featuring a complex locking mechanism with several gears and a central dial. A bright blue light emanates from the right side of the vault, casting a glow on its surface. To the right of the vault are lines of white text on a black background, explaining that the document was obtained from "The Black Vault," an online database of declassified government documents, specifically mentioning the MKULTRA/Mind Control Collection. Below this explanatory text, a yellow web address is prominently displayed. There are no photographs of people, handwritten annotations, official stamps, forms, diagrams, tables, redactions, or visual evidence of experimental procedures. The page is a standard report cover page. It features the title "BIO-POWER INTERIM REPORT" followed by the date "October 15, 1966." Below this, there is a line for "Contract No." and another line for "Prepared by:". There are no photographs, diagrams, or tables present. The page does have a handwritten annotation "273" circled in the bottom right corner. There's no visible evidence of experimental procedures or facilities. form conceptual d_esigns of mechanical syste:ns which could utilize that ar_e source. Comm:ents !ln these de,signs- 'included in the discussion as contextual in.f ormation becaus~ theyillustrate those asp~cts o£ ~ the systems which were considered and the design problems en- countered, not because these designs. are fe:t to be the proper ·s-olution. We concur with recent statements 'tiy investigators active in experimental work that the physiological Galvanic ;,:ell and mech• anoelectric conversion are the two roost premising systems. although m. uch work is ne .. cess ·~' a ,.. ry 'before I• either is ; usefu 't l for practical purposes. . . . Throughout this st~dy w.e repeatedly encountered unanswere.d questions or ·.ne possible effects of bio1og1cal adaptation on the total implanted system. These effects need not be entirely negative. Adapt'ion in a direction tending to increase power output is a possibility deserving or serious attention. / e - T - III. GENERAL DISCUSSION A. pirectly Obtained Electricity; Since our goal is electricity prod\:.ced from an energy so\!::-ce within the body, the siffiplest system instrumentally and the first which should be evaluated is the direct electrical tap. Th~ systems under CC?nsideration in this section are all those that contain electrodes that are in physical cont-act with the biological environo me:1t and in which electrical potentials betweeB electrodes can be measured. These potentials are due to, or at least intima.tely associated with, time and space variations in ionic concentrations and Oow. 'fhe ultimate _description; an~ expl~nat\ons and definitions ot these potent~ls are within the sci.enc~ of irreversible thermo rable- dynamics an<! t}!e subject or cons"i.~e controversy. (19) For the purpose of this discussior. we wU.l generally consider these - - potentials ope rationally, that is, according to what :you_ do to obtain a :neasurable potential and the characteristics of that potential. 1. · Neuromuscular Potentials ' The most st~di~d biologi.ca·l electrochemical phenomena.. are the neuromuscular action potentials. At the cellular lev~l micro electrodes of several microns diameter inserted throug,h neuron or o! muscle cell membrane i.ndicate potentials of tens mUlivolts between points within the cytoplaEm and betwe<!n cJtvplasm and extracelblar or \ fluid. The time course variations ~n these potentials is from :a millisecond to hours. These 11membrane potentials" in themselves are of no use !ol' oul' purposes because of the !anhstically low currents \and short ttre ora cell damagod hJ perforation or its membrane. But e -- ~· ----- This document appears to be a table of contents for a report. The main content is text organized into sections numbered with Roman and Arabic numerals, detailing various topics related to electricity generation and properties. There are no photographs, handwritten annotations, stamps, forms, diagrams, or redactions visible on this page. The layout is structured with a clear heading "TABLE OF CONTENTS" and a "Page" column aligned to the right, indicating the corresponding page numbers for each listed section. or \ fluid. The time course variations ~n these potentials is from :a millisecond to hours. These 11membrane potentials" in themselves are of no use !ol' oul' purposes because of the !anhstically low currents \and short ttre ora cell damagod hJ perforation or its membrane. But e -- ~· ----- \ the gl"oss extracellular ph~nomena associated with the summated effects of thousands or nearby active cell sections in nerve and muscle bundles deserve consideration. When a metal win or disc is placed near- a nerve. "compound action potenHals11 ar"e observed between that electrode and another placed in the body, and when a muscle is. used. the "electromyogram" .is observed. a. Nerve Potentials The use or neural electricity as an energy source can be dismissed as .not feasible on the grounds that drawing currents will cau~e stimulation of the excitable membrane's and dis~ . . ' rurtion or nor~al rw;ction. This col')clusion results from o~serving that whatever electric.al energy is prodUced is the result of neural - .. \. : . activity (by assumption) and that that level of electrical current must or necessity be sufficient to c~use stimulation since it was generated in ordEr to pro~uce (natural) st\mulation. There is no· way to avoid returning current to t.he e1ecttode whic? supplied it when the voltages tr:.volved .are less thaf\ the • 4 ~.olt minimum !o,r- germanium diodes. and • • wnile the two electro'de current distributions ~ill differ, it seems r-easonable to expect that at least some units will be stimulated. The . . or . loss even a few units in the PNS is undesirable. Also. since neural . or or potentials are the order of 100 millivolt, a source resistance 12 ohm is needed to obtain 200 microwatts. This requirement is not compatible with the source. Consider for example, the input im• pedances (to 8 ohm) or the amplifiers typically required ,to measure nerve compound action potentials •. ·--.... ~. • - --.-- ·- ... .....,_ ..., .. I _\ -s- b. Muscle· Potentials With muscles the situation differs in several respect!i that make power pick up from this system at least con• ceivable. Namely, the vo1um~ of muscle is la:-ge compared with neural_tissue and stimulation of a· few units should not seriously dis=-upt normal function. The large muscle areas may allow many electrodes to be used simultaneously in order to provide a lower electrical source resistance. For this system at least con• ceivable. Namely, the vo1um~ of muscle is la:-ge compared with neural_tissue and stimulation of a· few units should not seriously dis=-upt normal function. The large muscle areas may allow many electrodes to be used simultaneously in order to provide a lower electrical source resistance. For example. if one pair of electrodes prcvides a source resistance of 500 ohm, 40 pair will provide 12 ohm. In order to utUi:te this low VQ1t~ g:e ac s.ource a miniature trans 4 I. former can be ~.s ed to step up t.he voltage ber.,:-e rectification. From ; a power standpoint i~ shou1d '!:',;; \ilore eff~fient to uf··· on.e transformer and rectifier with each pair· or e:~ctrodes and sum .. . de outputs. !; Sir.ce skeletal muscle EMG signals <.;ontain most of -~heir power i i n o .frEquencies abo~e 100 cps, submi.nia~'-!r-e tran_srormers <1~ oz, in. 3 .1 can be used. Aflswers to imp?rtant biological questions were not found in the literature. No reports describing investigation oC EMG signals as power sourc~s we~e discov~red. althoug.'l ~se oC EMG signals for control purpose's have heel'\ frequently studied, Whether or not a low en-ough source resistance can be achieved and maintained and what tne of electrode and impla~tation is best are questions Yfhich will probably have to be answered by experiment. Careful technique may prevent electrodes embedded in muscles performing large movements from causing irritation and pain but this will also require study. Judging from the experience or clinical workers with implanted cardiac pacemakers, small electrodes can be talented but dislodg-~ment and lead breakage rr.ay be serious problems. -- ·- --.. u "1 \.. l e. Cardiae Potentials The strong rhythmic contractions of the myo cardium attract immediate attention but the characteristics of its elec e . trical potentials present particular d.iffi.culties. Unlike skele~al muscle v:hich maintains contraction with a high frequency train or "spikes'. . cardiac muscle !ibers depolarize and repola.rize only once per heart• beat. Thus. the energy is contained mostly in low frequency compon· ents (l-20 cps).· Since the contraction of all are as of the muscle is · synchronized, large electrode areas can be used without the losses which would be associated with large electrodes on skeletal m_uscle. {Cu . r rent from : a ctive .. non-synch.r o. nized. s keletal muscle fibers c . o uld ~ pass t~1ru a large electrode to inactiv~·tissue without The document contains text typed on a white background. There are some dark ink marks, possibly from a binder or staples, at the top of the page. There are also several small black dots scattered throughout the page, which could be artifacts from the scanning or printing process. A handwritten number "-1-" is visible near the top of the page, as is the heading "STATEMENT OF OBJECTIVES". The text discusses a study on body-produced electrical power for implanted electronic devices, such as artificial cardiac pacemakers. There are no photographs, diagrams, stamps, or any other visual elements beyond the typed text and minor visual artifacts. The image displays a page of a typed document. Visible elements include the page number "-2-" near the top center and the section title "II. SUMMARY" towards the left. There are some faint, dark circular markings at the top of the page, possibly from a binder or filing system. The text is primarily black type on a white background, with some light gray lines and what appear to be very faint, scattered dark specks. There are no photographs, handwritten annotations, official stamps, forms, diagrams, tables, or obvious redactions present on this page. · synchronized, large electrode areas can be used without the losses which would be associated with large electrodes on skeletal m_uscle. {Cu . r rent from : a ctive .. non-synch.r o. nized. s keletal muscle fibers c . o uld ~ pass t~1ru a large electrode to inactiv~·tissue without passing to the - \ . . second electrode of the pair.) But while this allows only one trans• former to be used on the heart with ·one pair of large electrodes, trans• formers which are designed for ve'7' low frequencies are relatively lar \e. he~vy and inefficient. Regardless of t}te differences in wave!onn, the ECG on the heart is }ess than.lOO mV (possib~y only 10 mV) and thus a maximum source tesistanc~ ~r ~2 ohm is 3~in required for 200 uv: power yie-ld {assuming the 100 mV peak figure). Unless a radically improved electrode material is developed this resistance is. not likely to be achieved. Effective source resistance figures for common elec· trode materials directly on muscle have not been found in the literature, an ·and experiment appears necessary to determine what resistance can be easily obtained and how this might change with time~ I Z!'HilF* - . . -- - - E±' - .. • l ·7· 2. Direct C'urrent Systems These systems are all those that produce electron flow in one direction only between the two elec~rodes.· This is un• like the neuromuscular potential electrode system in which a capacitor would be placed in the circuit to insure that no net c~arge flows from one electrode to the othe·r. In the neuromuscular system the electrical energy or interest i~ " l~emating current" in that charge flows from electrode A to electrode d and then, milliseconds later. returns to A. In the neuromuscular electrode sy:;tem net current flow would provide no •tseful work and undesired reactions might accumulate products on or near the electrodes- that result in "polarization" and/or e-lectrodedeteriora~ion\vhich interfe_res with the desired action, This type or electrode activity. how eyer, can· become the desired activity in . \. : cirect currenfsystems. a. ·Physiologic'at Elect!"'...ide Cell The Galvanic cell in its simplest and classical form consists ("inly in two different metals (or other conductors) dipping into a common..! i onic: . . solution; J An electric po • tential, characteristic ' c·f the metals, ·i~mperature, ionic species and concentration, can be m. easured between the non·imm.!rsed portions The page contains a typewritten document with section headings and numbered lists. There are no photographs, handwritten annotations, signatures, official stamps, forms, diagrams, schematics, organizational charts, or tables. There are no visual elements that suggest experimental procedures, equipment, or facilities. The document appears to be purely textual, with no visual aids or markings. Galvanic cell in its simplest and classical form consists ("inly in two different metals (or other conductors) dipping into a common..! i onic: . . solution; J An electric po • tential, characteristic ' c·f the metals, ·i~mperature, ionic species and concentration, can be m. easured between the non·imm.!rsed portions of the two metal ' electrodes, Since the fluids existing within the body are ionic solu~ ti.ons inter· electrode potentials can be prod~ by inserting two Cissimi.lar conductors anywhere, Because of the complexity or the body fluid composition, variation in compos:tion at different points. induced effects from the presence or foreign material, presence or many membranes with unknown properties, acti.vc processes, etc,, etc., the actual ehemical reactions and inter-electroce potential can not be pre· '~dieted, in fact such potentials are not strictly defined, (Nims, p. S). __, • • a -- - 4-l ~ I \ ·8- We can consider that there are two general types or reaction wh.ich occur with implanted electrodes. 'l'he first. which we will call type 1, is like that iri the classical Galvanic cell described above in which one or both electrode materials enters into the reaction and··· becomes irreversibly altered or lost. The second type of· reaction is possible when membranes are present and the chemical environ• ment differs at the two electrodes. In this type 2 reaction, which in i':s simplest form is the classical concentration cell, irreversible change to the electrode surfaces need not occur and the electrodes need not be cis similar. The rate of the .chemical reactions may be much improved by dissimilar surfaces:. however, for example by catalytic action, in· creased effective area, ·inducement o( lo . c .al environmental chang.e, etc. .. " ~ ~ This second type oC activity can be col)sidered as a fuel cell with the .,_ . "'· . . . phys'iological system maw,a'ning aU the reactants and removing the" end products. A special u ;dcation ·or the type 2 system is when similar electrodes or 11\nert metals" or of "non-polarizable11 liquid filled tubes are used in conjunction with very high i~pedance voltage measuring cir cuits which insure that the pot~ntial chemical ,reactions do not occur .~... ! . : ... - at '.he electrodes. This arrangem~nt is used ~or investigating so called· na~ural de potential gradients within and on the sunace or the body (4). Such measurements necessal"ily must draw virtually no power cir cuits which insure that the pot~ntial chemical ,reactions do not occur .~... ! . : ... - at '.he electrodes. This arrangem~nt is used ~or investigating so called· na~ural de potential gradients within and on the sunace or the body (4). Such measurements necessal"ily must draw virtually no power from. the chemical energy sources responsible~ for the electrode potentials. for as soon a!: current is drawn reactions occur and the natural concentrations change. Thus any de current producing electrode generator scheme use ful for our purposes will have inter-electrode potentials which are more · or less unnatural physiologic~lly. That is, the potential difference be· tween electrodes or any type dra~ving current will be different from that measure,j between "non-polarizable" electrodes drawing no current, and the local chemical environment surrounding the electrodes may be grossly -· •• iiillll& • .,., -. I -9· different. :For these reasons the type 1 system tn which electrode material change occurs and the type 2 system in which it need not are considered here as two special cases of the general physiological electrode cell system. ~e general case or which the type 1 and 2 systems are ex amples, is when dissimilar metals. which produce a potential when dipped into a coq~mon ionic solution. are place:i in a nonhomogeneous environment that produces a potential between similar electrodes. This is probably a fair description of the situation prevailing in the electrode materiai, electrode placement comb"~ations with whkh Dr. John Koni~ort and others produ~e ~he best results. The Konikort wor:k is a significan~ source or'experimental data and has stimulated much or the recent int~rest in t~~ _physiological electrode cell powa - so1.:.rce. For these reasons a brief ~_ummary oC the work reported in ; "~ reference 12 is included here. The reader is referred to the original pape~ for details. . John Konikoff and Luthe.r Reynolds wer!! the principal workers ' at the General tlect;ic Comp~ny'~ Space Sci~nces Laboratory under a c.ontract with NASA in 1963- 64 to investigate the. use of what is re~e rred to here as physiological electrode cell· potentials as a biologically derived power source, Many combinations 'of electrode matedals in several anatomical locations in several species o£ labor atory animals were tried •. Their final choice or electrode materials w~s uhigh speed steel (75'ro Fe. 6'Vo Cr,. 18o/o W, • 3~ V, • '1% C)11 and a specially prepared "plntinum platinum·black'1 The page is dominated by typed text, discussing neural potentials and electricity. There are several abstract line drawings in the upper portion of the page, possibly representing schematics or diagrams, but they are too abstract to identify specific equipment or procedures. The text mentions electrodes, stimulation, and amplifiers, hinting at experimental setups, but no direct visual representations of these are present. There are no photographs, stamps, or formal markings visible on this page. derived power source, Many combinations 'of electrode matedals in several anatomical locations in several species o£ labor atory animals were tried •. Their final choice or electrode materials w~s uhigh speed steel (75'ro Fe. 6'Vo Cr,. 18o/o W, • 3~ V, • '1% C)11 and a specially prepared "plntinum platinum·black'1 combinntion. The f'irial choice o£ location was as follows, ...... the PPb electrode was located in the abdominal cavity dorsal to the peritoneal membrane·, and HSS situ::tted s·Jbcutaneously but phys~~atly adj::~cent to the abdominal incision." The = nwee -- .J ._____, , I \ longest conHnuous implant was· 128 days. ele~'trodes and sites were as above. 'The animal .was a·. rabbit, and a constant resistive load of - 10,000 ohiO\ was applied between electrodes. Arter 15 days the output stabilized and thereafter remained at ~4 micr:Jwatts ·and • 5 volt, The highest power reported in short term studies was 308 microwatt. No new work from either Konikoff or Reynolds has been published since 1954. Telep!'lone conversations with both men indicate that work is co.:1tinuing, and that recent improvements in the platinum-black elec· trode matertal have increased the power output threefold for the same ehctrode area •. Reynolds who is now at Hahnemann Medical College, Philadelpr1ia reports that 200 microwatts ·has'been obtained when each . . 2 . . . electrode is ot;t/2 ~ area. 1'h:fs elec.tr~de power generation scheme has the advantages, ~·according to, the ~·riginatc·rs. of simple .sv.rgical pr:>cedure and ~o harmful tissue i-eaction or loss of output at least !or 4 months in the OM long ~.::rm rabbit experiment. According to the data in the Konikoff report and especially ~he recent report of Strohl et. al: (29), when "biologically inert'' metals such as plat i.num and type 316'; stainless are tin planted. power levels 'I ·,f!'. 1 - greater than 10 ~W have not been obtained and the output dr-ops signifi· cantly below this after a few ~ays. Strohl's comments on the inevitable growth oC a fibrous membrane around implanted electro~es suggests that the electrodes become isolat~d from the original. dissimilar ionic {.mvironments as this membrane grows. The better power outputs and longevity have been obtained in con_iunction with an elect~ode which actively reacts with species present in the extracellular fluids. Even when covered with (hypothetical) cells tending to maintain identical ionic coocentrations around the two electrodes. a reactive elechode can ~ontinue to provide current, tn evaluating :1n The page features a typed excerpt from a document, numbered "-5-" at the top. The text discusses "Muscle Potentials" and appears to be a scientific or technical description of using muscle signals as a power source, referencing electrodes, transformers, and the properties of EMG signals. There are no photographs, handwritten annotations, official stamps, or forms visible on this page. The content is entirely text-based, with no visual elements like diagrams, tables, or redactions. The page is a black-and-white, typed document with a faint speckled texture and a vertical crease down the left side. At the top, there are several small, irregular black marks that appear to be abstract shapes or smudges. The page is numbered "-6-" on the right-hand side, indicating it is part of a larger document. The text content discusses "Cardiac Potentials" and the challenges of measuring them, mentioning "electrodes," "ECG," and "experimental procedures." There are no photographs, diagrams, stamps, or handwritten annotations visible on this page. better power outputs and longevity have been obtained in con_iunction with an elect~ode which actively reacts with species present in the extracellular fluids. Even when covered with (hypothetical) cells tending to maintain identical ionic coocentrations around the two electrodes. a reactive elechode can ~ontinue to provide current, tn evaluating :1n electrode cell sys~em con· or_ -t.::~_iniug reactive electrodes important conside:-ations are toxicity ;J --- L...-_..J ; ~- ·-\,.. I .- 1 -11- p,..oducts and deterioration oC performance with time. As Strohl notes, Faraday's first law predicts the electrode weight loss due to ionic solution when the electrode reactions are known G_uantitatively. For example, • 91 of iron will be needed to supply 100 uA for 1 year. But at least as important are the hard to predict effects such as loss or effective surface area "catalyst poisoning", uneven surface deterioration and long term local tissue reaction.- In conclusion, it appears that ther-e is a reasonable possibility that physiological elec• trode cells can provide 200 uW for e:ctended periods, but careful. long term studies.and an understanding of the actiye phenomena, which, hopefully. will p.r ovide the basis. !or ~ptimizing the electrode . materials, are~ necessary. But the sun.p le surgery in low risk areas . Which haS been~ USed', the mechatl_~CS -• 00 moving partS, the nOQM dependence on any bodily motion, lhe inherent freedom from en-_ capsulation problems, and the short term results already achiev7d· combine to make this a most promising syste'm at this time. b. Fuel Cell : ~ ~ ~ ··sophisti.c:a,ted direct current systems have been speculated on for producing relatively large quantities of electrical power for running proposed artificial hearts. These systems are usually referred to as ruel cells and usually are considered in ref· erenca to known chemical energy sources such as glucose- or ATP. These systems are very appealing, largely because the proposed energy source is Caidy well understood, Molecular energy yields, available C9ncen trations and naturally occuring reactions can be stated. The develop or ment physical systems to \ltilize these sources then"appears to be a problem amenable to present technological capability since t.he avail• · able raw materials .and necessary operations are known, at least ______ ___,l -·- _,- --- 0 ...--- __,_. - I ~ -12- i.n broad outline. This is in contrast to the simpler Galvanic cell systems discussed earlier in which the present state of the art has been reached The image is a scanned page of a declassified document, likely a research paper or report, given the typed text and numbered sections. There are no photographs, diagrams, or stamps visible. The text is densely typed and discusses direct current systems and physiological electrode cells, specifically mentioning neuromuscular potential and Galvanic cells. There are some handwritten annotations in the margins, including numbers and possibly brief notes, but they are difficult to decipher clearly. The page appears to be a scanned copy of a typed document, with no visual evidence of experimental procedures or facilities. avail• · able raw materials .and necessary operations are known, at least ______ ___,l -·- _,- --- 0 ...--- __,_. - I ~ -12- i.n broad outline. This is in contrast to the simpler Galvanic cell systems discussed earlier in which the present state of the art has been reached largely by trial and error without benefit or thorough un:ierstanding of the detailed p_rocesses involved. Approaching the problem from basic principles and pro·ceeding in accordance with established theory will no doubt achieve practical success in time. The National Institutes of Health recently circulated a Reque:>t For Proposal to;undertake feasibility studies of ir:lplanted biological fuel cells. When these initial studies are completed we will have a statement of the problem and outline of needed research. For the immediate future. however. th~ simpler ~ proposed system is. the g..·eater appears its chance of success. . • ' .;: ... .i: : ~ ~ B. Thennoelectric Converterp -· ' Temperature gradients w. ithin the body theoretically can be exploited as a source of electrical energy. In recent years -considerable research on thermoelectric compositions for use with nuclear reactor heat sources has produced materials with thermoelectric properties much' i . m proved ov~r those of conventional t.'lermocouplefl. .. ·~ ~ : For example. a c.o nventional copper-constantin couple will produce 23 microvolt per fahrenheit degree temperature difference while a material 0 of Bismuth-Antimony-Telluride composition produces 77 microvolt/F 0 (ll, 8). Simple calculations using this second figure indicate that with a 5 F0 temperature difference and 1 ohm resistance for every element 2soo elements connected in series will yield 200 uW at.$ volt. A Japanese group (32) has published a report of a 150 element thermo~lectric · &ener~tor for use on the extem~l body surface. Their device used t~e Bi-Sb·Te material and the size of the thermoelectric array appears-~ to be about 2. 5 em x tern x •. Scm.. The d~ta pre