Thermal energy harvesting on the bodily surfaces of arms and legs through a wearable thermo-electric generator

senso s A icle The mal Ene gy Ha es ing on he Bodily Su aces o A ms and Legs h ough a Wea able The mo-Elec ic Gene a o An onino P o o 1ID , Daniele Bibbo 2, Ma in Ce ny 1ID , Da id Vala 1, Vladimi Kasik 1, Lukas Pe e 1, Sil ia Con o o 2, Mau izio Schmid 2and Ma ek Penhake 1,*ID 1Depa men o Cybe ne ics and Biomedical Enginee ing, VŠB-Technical Uni e si y o Os a a, 17. lis opadu 15, 70833 Os a a-Po uba, Czech Republic; an onino.p [email p o ec ed] (A.P.); [email p o ec ed] (M.C.); [email p o ec ed] (D.V.); ladimi [email p o ec ed] (V.K.); [email p o ec ed] (L.P.) 2Depa men o Enginee ing, Uni e si y o Roma T e, Via Vi o Vol e a, 62, 00146 Rome, I aly; [email p o ec ed] (D.B.); sil ia.con o o@uni oma3.i (S.C.); mau izio.schmid@uni oma3.i (M.S.) *Co espondence: ma [email p o ec ed]; Tel.: +420-897-325-853 Recei ed: 19 Ma ch 2018; Accep ed: 11 June 2018; Published: 13 June 2018   Abs ac : This wo k analyzes he esul s o measu emen s on he mal ene gy ha es ing h ough a wea able The mo-elec ic Gene a o (TEG) placed on he a ms and legs. Fou la ge skin a eas we e chosen as loca ions o he placemen o he TEGs. In o de o place he gene a o on he body, a special manu ac u ed band gua an eed he p ope con ac be ween he skin and TEG. P elimina y measu emen s we e pe o med o ind ou he alue o he esis o load which maximizes he powe ou pu . Then, an expe imen al in es iga ion was conduc ed o he measu emen o ha es ed ene gy while use s we e pe o ming daily ac i i ies, such as si ing, walking, jogging, and iding a bike. The gene a ed powe alues we e in he ange om 5 o 50 µ W. Mo eo e , a p elimina y hypo hesis based on he ob ained esul s indica es he possibili y o use TEGs on leg o he ecogni ion o locomo ion ac i i ies. I is due o he a he high and di e en biomechanical wo k, p oduced by he gas ocnemius muscle, while he use is walking a he han jogging o iding a bike. This esul e lec s a di e ence be ween empe a u es associa ed wi h he pe o mance o di e en ac i i ies. Keywo ds: body empe a u e; ene gy ha es ing; human daily ac i i ies; he moelec ici y; wea able de ice 1. In oduc ion Nowadays, ha es ing he ene gy on he human body is becoming a popula means o powe wea able de ices [ 1 – 4 ]. Wea ables a e inc easingly being used in di e en heal h- ela ed applica ions, hanks o he a ailabili y o minia u ized echnologies. By in eg a ing da a p ocessing in o wea ables, i is possible o cap u e a a ie y o a iables associa ed wi h he heal h and sa e y o human beings [ 5 – 8 ]. Un o una ely, he ba e y size de e mines he ope a ing ime o wea ables, hus limi ing applicabili y o long- e m moni o ing [9,10]. Among all echnologies used o ha es ene gy om en i onmen al sou ces, eco e ing he ene gy associa ed o he hea p oduced by he human body is an in e es ing op ion om an ene gy pe spec i e [ 11 ]. In he ollowing sec ion, i s he aspec s ela ed o he physiological p ocesses and he body hea exchange wi h he en i onmen will be analyzed. Then, he p e ious solu ions le e aging on he human hea ene gy ha es ing will be e iewed. The Ma e ials and Me hods sec ion shows he p oposed solu ion, and ob ained esul s will be analyzed in he Discussion sec ion. Conclusions will comple e he wo k. Senso s 2018,18, 1927; doi:10.3390/s18061927 www.mdpi.com/jou nal/senso s Senso s 2018,18, 1927 2 o 17 1.1. Physiological and En i onmen al Aspec s Human body physiological pa ame e s, and en i onmen al condi ions a ec he amoun o he mal ene gy ha can be ha es ed om body su aces [ 12 ]. The o me include he posi ion and he numbe o subcu aneous blood essels, he cha ac e is ics o he li ing issue ( hickness o he a laye , dep h o he muscle issue, and ana omy o he skin su ace), and he physiological s a e o he body (me abolism, blood pe usion and swea sec e ion). The Pennes’ biohea equa ion includes all hese pa ame e s, and i has been used o cha ac e ize he in luence o he blood low on he body empe a u e dis ibu ion [ 13 , 14 ]. Rega ding en i onmen al condi ions, which in luence he hea ans e be ween li ing issues, he main ac o s a e he empe a u e and he humidi y o he medium be ween wo li ing issues. In addi ion, body physiological s a es may change based on a numbe o si ua ional a iables, such as wea he , and ac i i ies pe o med by people (e.g., wo king a a desk, as compa ed o pe o ming spo ac i i ies): blood pe usion and me abolic hea gene a ion signi ican ly inc ease when a pe son is aking mul iple physiological ac i i ies [ 15 ]. The mos e ec i e si ua ion o ha es ing he human hea ene gy is hus when he body is unde an exci ed physiological s a e. F om he abo e conside a ions, i is s aigh o wa d ha skin empe a u e is non-uni o m on he body su ace: Table 1shows he a e age alues o skin empe a u es measu ed a di e en body posi ions. Resul s a e summa ized based on he wo ks p oposed by Yang e al. [ 16 ], Zap oudina e al. [ 17 ] and Webb [ 18 ]. In he i s wo s udies, body empe a u es we e measu ed by means o in a ed he mog aphy, while Webb collec ed da a h ough mul iple he mis o p obes. Simila alues o body empe a u es a e epo ed in o he wo ks [19,20]. Table 1. Skin empe a u e o di e en body posi ions. Body Posi ions Yang e al. [16] (Tai = 17 ◦C) Zap oudina e al. [17] (Tai = 23.5 ◦C) Webb [18] (Tai = 27 ◦C) Fo ehead 29.5 ◦C 34.1 ◦C 35.2 ◦C Neck 31.1 ◦C 33.2 ◦C 35.1 ◦C Back 30.6 ◦C 32.5 ◦C 34.4 ◦C Ches 30.3 ◦C 32.3 ◦C 34.4 ◦C A m an e io 30.3 ◦C 31.7 ◦C 33.2 ◦C Fo ea m 29.5 ◦C 31.5 ◦C 34.0 ◦C Thigh 28.3 ◦C 30.8 ◦C 33.0 ◦C Cal 29.4 ◦C 31.3 ◦C 31.6 ◦C Foo do sal 27.1 ◦C 28.6 ◦C 30.4 ◦C F om hese da a, i is clea ha being unde low en i onmen empe a u es leads o he mos bene icial si ua ions o ha es was ed human hea : a ise o abou 10 ◦ C in he ai empe a u e p oduces an a e age inc ease o abou 4 ◦C o he skin empe a u e. 1.2. The moelec ic Gene a o s In 1821, Seebeck disco e ed he moelec ici y [ 21 ]. I can be summa ized by saying ha a ol age di e ence ac oss wo dissimila me als o semiconduc o s appea s in he p esence o a empe a u e di e ence be ween hem. Thus, in he middle o he 20 h cen u y, scien is s a ound he wo ld deepened he s udy on semiconduc o s as he moelec ic elemen s, hus c ea ing he i s The mo-elec ic Gene a o (TEG) [ 22 ]. A TEG consis s o mul iple pai s o p- and n- ype elemen s ha a e elec ically connec ed in se ies by wo me al conduc o s. In addi ion, wo ce amic pla es encapsula e he he moelec ic elemen s o hei elec ical insula ion, bu making he TEG he mally conduc ing. The e o e, by placing a TEG on he body su ace, i is possible o ha es he elec ical ene gy by exploi ing he he moelec ici y, i.e., he Seebeck e ec , which occu s due o he empe a u e di e ence Senso s 2018,18, 1927 3 o 17 be ween he wo opposing sides o he TEG: he one in con ac wi h he skin, and he one acing he en i onmen . In eg a ion o TEGs in o de ices g ew in he la e nine ies: he Seiko Company de eloped he i s w is wa ch powe ed by a TEG [ 23 ]. The TEG powe ou pu was app oxima ely 22.5 µ W. This amoun o powe could d i e a wa ch and simul aneously echa ge i s ba e y, since he alue o he powe ou pu was well in excess o he amoun needed o powe ing he wa ch (1 µ W). A e ha , many esea che s designed au onomous de ices: be ween 2004 and 2008 he IMEC g oup de eloped wea ables powe ed by he human hea . A i s , Leono e al. [ 24 ] designed a wa chs ap wi h a single laye TEG, made o 128 he mocouples connec ed in se ies: hey s udied he he mal ea u es o he human body. Then, a 4-laye TEG wi h 5000 he mocouples was designed o powe a con en ional pulse oxime e [ 25 ]. This 4-laye TEG gene a ed up o 200 µ W when a empe a u e di e ence o abou 8 ◦ C occu ed be ween i s wo sides. In addi ion, in 2008 he esea che s de eloped a sel -powe ed 2-channel elec oencephalog aphy sys em [ 26 ], by ealizing a ho side a ea o app oxima ely 64 cm 2 . The sys em could gene a e a powe ou pu o app oxima ely 2.2 mW. Based on hese, he o ehead has been iden i ied as he bes posi ion o ha es ing human hea , since he o ehead p o ides he la ges hea low on a qui e la ge a ea. Again, in 2009, he same esea ch g oup p oposed he i s shi o ha es ing body he mal ene gy while people a e pe o ming no mal daily ac i i ies [ 27 , 28 ]: 14 TEG modules placed in he shi gene a ed up o 1 mW when he use was wo king a he desk, whe eas while walking on a sunny day, he powe ou pu eached up o 2–3 mW. Fo ha es ing body he mal ene gy di ec ly om he a m, Lossec e al. [ 29 ] p oposed a sys em made by s acking wo TEGs wi h a black hea sink on he cold su ace. The black su ace inc eased he emissi i y o he cold side, and he coe icien alue abou he TEG hea ans e / adia ion pa ame e . Wi h a empe a u e di e ence o abou 15 ◦ C, he powe ou pu eached up o 7 µ W/cm 2 du ing es , and 30 µ W/cm 2 while he use was walking. In addi ion, Voss e al. [ 30 ] placed a Velc o s ap, wi h an in eg a ed TEG, on he uppe a m, o p oduce elec ical ene gy while use s we e pe o ming locomo ion ac i i ies, such as walking and jogging. The alues o powe ou pu eached up o 0.5 mW o a empe a u e di e ence o abou 8.5 ◦ C. In all o he a o emen ioned sys ems, he hea sink was placed on he cold side o he TEG o imp o ing he he mal coupling be ween TEG and en i onmen , hus esul ing in an inc ease o he powe ou pu [ 31 ]. Howe e , he hea sink placemen hinde s wea abili y, and i makes he de ice uncom o able o he human daily use. Nowadays, in he comme cial ma ke , a sma wa ch, i.e., he Ma ix Powe Wa ch, is ully powe ed by a TEG. The wa ch is able o p o ide accu a e in o ma ion abou calo ie coun , s ep coun , and sleep ack. Howe e , i s p ice is s ill e y high since i cos s is app oxima ely $250. Anyway, despi e he a he la ge amoun o solu ions p esen ed in he li e a u e, which p ominen ly ocus on he TEG placemen on he uppe body pa s, o he au ho s’ knowledge he e is a no able lack o s udies a ge ing he placemen o TEGs on he lowe limbs. Fo his eason, he p oposed wo k ocuses on he compa a i e analysis o he powe ha es ed on a m and leg, by means o a TEG, wi hou making discom o o he use . We would a i m ha he TEG placemen on legs is a p omising and di e en way o design and de elop new sel -powe ed, wea able, de ices. 2. Ma e ials and Me hods 2.1. The moelec ic E ec A TEG p oduces measu able elec ical ene gy by exploi ing he he moelec ic e ec , i.e., Seebeck e ec . A quan i a i e cons an desc ibes he Seebeck e ec , and he ollowing equa ion de ines i , as ollows: α=−∆V ∆T, (1) whe e ∆ V is he elec ical ol age di e ence, and ∆ T is he empe a u e di e ence be ween he wo dissimila me als o semiconduc o s. αis measu ed in µV/K. Senso s 2018,18, 1927 4 o 17 The moelec ic igu e o me i (ZT), deno es ansduc ion e iciency alue o he moelec ic ma e ials. I is a dimensionless quan i y, and he ollowing equa ion de ines i , as ollows: ZT =σα2T κ, (2) whe e α is he Seebeck coe icien , T is he a e age empe a u e, and σ and κ a e he elec ical and he mal conduc i i y o ma e ials, espec i ely. In o de o de ine he wo king e iciency o TEG, he ollowing equa ion combines he igu e o me i ZT and he exp ession abou he Ca no cycle (TH−TC TH). I is as ollows: η=TH−TC TH √1+ZT −1 √1+ZT +TC TH , (3) whe e η can assume a alue be ween ze o and one. The ZT alue is he mos c i ical pa ame e o a TEG. In oday’s bes comme cial TEGs, ZT is abou 1 a 25 ◦ C [ 32 ]. I means ha TEGs ope a e a only 10% o he Ca no e iciency [ 33 ]. The 30% o Ca no e iciency, compa able o home e ige a ion, could be eached by a TEG wi h a ZT equal o 4, bu his alue canno be achie ed wi h cu en TEG modules [34]. 2.2. The moelec ic Gene a o Chosen In his s udy, we chose he TES1-12704 Pel ie module as TEG. I is low-cos , and in eg a es a la ge numbe o couples o p- and n- ype elemen s in o a small a ea o 9 cm 2 . Table 2lis s he main ea u es o he TES1-12704 module. Table 2. P ope ies o he TES1-12704 module. P ope y Value Dimension, (l ×w× ) 30 mm ×30 mm ×3.2 mm Weigh 0.015 g Ce amic subs a e ma e ial Aluminum oxide (Al2O3) Me al conduc o s ma e ial Coppe (Cu) Numbe o p-n couples 127 p- and n- ype elemen s Bismu h ellu ide (Bi2Te3) Elec ical conduc i i y, σ800–13,501/(cm·Ω) The mal conduc i i y, κ0.016–0.02 W/(cm·K) Seebeck coe icien , α160–200 µV/K Coe icien o me i , Z 0.002695–0.0031/K Figu e 1shows he s uc u e o he TEG module and i s equi alen , simpli ied elec ical ci cui . Senso s 2018, 18, x FOR PEER REVIEW 4 o 17 ZT= σαT κ, (2) whe e α is he Seebeck coe icien , T is he a e age empe a u e, and σ and κ a e he elec ical and he mal conduc i i y o ma e ials, espec i ely. In o de o de ine he wo king e iciency o TEG, he ollowing equa ion combines he igu e o me i ZT and he exp ession abou he Ca no cycle ( ). I is as ollows: η= T−T T √ 1+ZT−1 √ 1+ZT+T T, (3) whe e η can assume a alue be ween ze o and one. The ZT alue is he mos c i ical pa ame e o a TEG. In oday’s bes comme cial TEGs, ZT is abou 1 a 25 °C [32]. I means ha TEGs ope a e a only 10% o he Ca no e iciency [33]. The 30% o Ca no e iciency, compa able o home e ige a ion, could be eached by a TEG wi h a ZT equal o 4, bu his alue canno be achie ed wi h cu en TEG modules [34]. 2.2. The moelec ic Gene a o Chosen In his s udy, we chose he TES1-12704 Pel ie module as TEG. I is low-cos , and in eg a es a la ge numbe o couples o p- and n- ype elemen s in o a small a ea o 9 cm2. Table 2 lis s he main ea u es o he TES1-12704 module. Table 2. P ope ies o he TES1-12704 module. P ope y Value Dimension, (l × w × ) 30 mm × 30 mm × 3.2 mm Weigh 0.015 g Ce amic subs a e ma e ial Aluminum oxide (Al2O3) Me al conduc o s ma e ial Coppe (Cu) Numbe o p-n couples 127 p- and n- ype elemen s Bismu h ellu ide (Bi2Te3) Elec ical conduc i i y, σ 800–13,501/(cm·Ω) The mal conduc i i y, κ 0.016–0.02 W/(cm·K) Seebeck coe icien , α 160–200 μV/K Coe icien o me i , Z 0.002695–0.0031/K Figu e 1 shows he s uc u e o he TEG module and i s equi alen , simpli ied elec ical ci cui . Figu e 1. S uc u e o he TEG module and i s equi alen , simpli ied elec ical ci cui . In Figu e 1, a esis o (RTEG) in se ies wi h a ol age gene a o is he simpli ied elec ical ci cui o he TEG module. The TEG p oduces an elec ical cu en low in an ex e nal ci cui i a empe a u e di e ence (ΔT) be ween i s wo sides is applied. The ΔT alue de e mines he magni ude o he TEG ol age (VTEG) and he di ec ion o he hea low de e mines he ol age pola i y. Fu he mo e, a ΔT change, ac oss he TEG sides, causes a a ia ion o he esis ance alue, RTEG [35– Figu e 1. S uc u e o he TEG module and i s equi alen , simpli ied elec ical ci cui . In Figu e 1, a esis o (R TEG ) in se ies wi h a ol age gene a o is he simpli ied elec ical ci cui o he TEG module. The TEG p oduces an elec ical cu en low in an ex e nal ci cui i a empe a u e Senso s 2018,18, 1927 5 o 17 di e ence ( ∆ T) be ween i s wo sides is applied. The ∆ T alue de e mines he magni ude o he TEG ol age (V TEG ) and he di ec ion o he hea low de e mines he ol age pola i y. Fu he mo e, a ∆ T change, ac oss he TEG sides, causes a a ia ion o he esis ance alue, R TEG [ 35 – 37 ]. Thus, in he applica ion ield o human hea ene gy ha es ing, i is di icul ob ain a s able alue o R TEG , since he empe a u e ac oss he wo sides o TEG changes o e ime, as he esul o modi ica ions o he physiological s a e o he body, and om he ex e nal unp edic able en i onmen al condi ions. Figu e 2 shows he elec ical ci cui o measu e he powe gene a ed by he TEG. Senso s 2018, 18, x FOR PEER REVIEW 5 o 17 37]. Thus, in he applica ion ield o human hea ene gy ha es ing, i is di icul ob ain a s able alue o RTEG, since he empe a u e ac oss he wo sides o TEG changes o e ime, as he esul o modi ica ions o he physiological s a e o he body, and om he ex e nal unp edic able en i onmen al condi ions. Figu e 2 shows he elec ical ci cui o measu e he powe gene a ed by he TEG. Figu e 2. Elec ical ci cui o he measu emen s o powe gene a ed by he TEG, wi h he co esponding g aph abou he ack o he powe ou pu while measu ing he closed ci cui ol age. Fo a gi en empe a u e di e ence be ween he wo sides o TEG, i he impedance ma ching is ob ained (RLOAD = RTEG), he maximum alue o he powe ou pu (PMAX) is ob ained o a ol age alue (VLOAD) equals o he hal o he open ci cui ol age alue (VTEG/2) [38]. The ollowing equa ions desc ibe he ela ion be ween VLOAD and PLOAD: V =V R  R  + R  ⇒ P = V  R , (4) dP d R  = d󰇧V  R 󰇨 d R  =0 ⇔ R  = R , (5) Du ing he execu ion o he expe imen , he alues o he ol age ou pu (VLOAD) we e measu ed and acqui ed by he NI-USB-6210 da a acquisi ion sys em (DAQ) (see Supplemen a y Ma e ials, Figu e S1). 2.3. Sys em o Tempe a u e Measu emen s In o de o acqui e empe a u e da a on bo h sides o he TEG, NTC 10K3MBD1 he mis o p obes we e connec ed o a mul ichannel eco ding sys em (see Supplemen a y Ma e ials, Figu e S2). The empe a u e senso has a ime esponse o abou 400 ms, wi h a esolu ion alue o ±0.2 °C in he empe a u e ange om 0 °C o +70 °C. Two channels o he de ice we e used o acqui e he empe a u e da a on bo h sides o he TEG, and a hi d one was used o he oom empe a u e measu emen . The p oposed sys em elies on a 4-wi e schema ic con igu a ion wi h a 100 μA cu en sou ce based on REF200 in eg a ed ci cui . An OPA335 in eg a ed ci cui ampli ies he measu ed signals o app oxima ely 100 imes, and an A/D con e e wi h a sampling equency o 10 samples/s con e s hem o ha e a display isualiza ion. Tempe a u e senso s we e calib a ed by means o a Fluke 1523 e e ence he mome e , which uses a Haa 5611T empe a u e senso ( esolu ion ± 0.01 °C, ange 0–100 °C). 2.4. Fab ic Band o Suppo ing he TEG In o de o place he TEG di ec ly on o he skin, a ab ic band made o PVC and gauze ac ed as a suppo o he TES1-12704 module. PVC ab ic is a nonwo en ab ic made up o a g oup o long ibe s wi h a andom pa e n. I gua an ees excellen he mal insula ion. The e o e, i was chosen as he bo om laye o he band o he mally insula e he con ac a ea be ween skin and TEG. Con e sely, he gauze was used o he op laye o he band, as i is a s uc u e wi h a loose open wea e, a hin ne ing, wi h a good ea u e o b ea habili y. Figu e 2. Elec ical ci cui o he measu emen s o powe gene a ed by he TEG, wi h he co esponding g aph abou he ack o he powe ou pu while measu ing he closed ci cui ol age. Fo a gi en empe a u e di e ence be ween he wo sides o TEG, i he impedance ma ching is ob ained (R LOAD = R TEG ), he maximum alue o he powe ou pu (P MAX ) is ob ained o a ol age alue (V LOAD ) equals o he hal o he open ci cui ol age alue (V TEG /2) [ 38 ]. The ollowing equa ions desc ibe he ela ion be ween VLOAD and PLOAD: VLOAD =VTEG RLOAD RTEG +RLOAD ⇒PLOAD =V2 LOAD RLOAD , (4) dPLOAD dRLOAD = dV2 LOAD RLOAD  dRLOAD =0⇔RLOAD =RTEG, (5) Du ing he execu ion o he expe imen , he alues o he ol age ou pu (V LOAD ) we e measu ed and acqui ed by he NI-USB-6210 da a acquisi ion sys em (DAQ) (see Supplemen a y Ma e ials, Figu e S1). 2.3. Sys em o Tempe a u e Measu emen s In o de o acqui e empe a u e da a on bo h sides o he TEG, NTC 10K3MBD1 he mis o p obes we e connec ed o a mul ichannel eco ding sys em (see Supplemen a y Ma e ials, Figu e S2). The empe a u e senso has a ime esponse o abou 400 ms, wi h a esolu ion alue o ± 0.2 ◦ C in he empe a u e ange om 0 ◦ C o +70 ◦ C. Two channels o he de ice we e used o acqui e he empe a u e da a on bo h sides o he TEG, and a hi d one was used o he oom empe a u e measu emen . The p oposed sys em elies on a 4-wi e schema ic con igu a ion wi h a 100 µ A cu en sou ce based on REF200 in eg a ed ci cui . An OPA335 in eg a ed ci cui ampli ies he measu ed signals o app oxima ely 100 imes, and an A/D con e e wi h a sampling equency o 10 samples/s con e s hem o ha e a display isualiza ion. Tempe a u e senso s we e calib a ed by means o a Fluke 1523 e e ence he mome e , which uses a Haa 5611T empe a u e senso ( esolu ion ± 0.01 ◦ C, ange 0–100 ◦C). 2.4. Fab ic Band o Suppo ing he TEG In o de o place he TEG di ec ly on o he skin, a ab ic band made o PVC and gauze ac ed as a suppo o he TES1-12704 module. PVC ab ic is a nonwo en ab ic made up o a g oup o long Senso s 2018,18, 1927 6 o 17 ibe s wi h a andom pa e n. I gua an ees excellen he mal insula ion. The e o e, i was chosen as he bo om laye o he band o he mally insula e he con ac a ea be ween skin and TEG. Con e sely, he gauze was used o he op laye o he band, as i is a s uc u e wi h a loose open wea e, a hin ne ing, wi h a good ea u e o b ea habili y. Figu e 3shows he manu ac u ing s eps o de eloping he ab ic band. A i s , he PVC ab ic was cu o o m a ec angula shee , wi h a ea size o app oxima ely 350 cm 2 . A gap o he con ac a ea be ween skin and TEG was made by cu ing he PVC shee in i s cen al pa (a squa e hole wi h a ea size o abou 2.5 cm × 2.5 cm). Thus, he TEG, i.e., 3 cm × 3 cm, was encapsula ed be ween he men ioned PVC shee and a second PVC laye , which is also wi h a hole in i s cen al pa , bu wi h a la ge a ea size (2.9 cm × 2.9 cm). Finally, a anspi ing laye , made o gauze was placed on he PVC ab ic o enhance he s abili y o he sys em, bu no o he mally isola e he TEG om he en i onmen . All he ab ic laye s we e kni ed by using co on ya ns. To comple e i , ou laces we e sewn on i s ends. In he Supplemen a y Ma e ials, Figu es S3 and S4 show he chosen ma e ials and he de eloped band, espec i ely. Senso s 2018, 18, x FOR PEER REVIEW 6 o 17 Figu e 3 shows he manu ac u ing s eps o de eloping he ab ic band. A i s , he PVC ab ic was cu o o m a ec angula shee , wi h a ea size o app oxima ely 350 cm 2 . A gap o he con ac a ea be ween skin and TEG was made by cu ing he PVC shee in i s cen al pa (a squa e hole wi h a ea size o abou 2.5 cm × 2.5 cm). Thus, he TEG, i.e., 3 cm × 3 cm, was encapsula ed be ween he men ioned PVC shee and a second PVC laye , which is also wi h a hole in i s cen al pa , bu wi h a la ge a ea size (2.9 cm × 2.9 cm). Finally, a anspi ing laye , made o gauze was placed on he PVC ab ic o enhance he s abili y o he sys em, bu no o he mally isola e he TEG om he en i onmen . All he ab ic laye s we e kni ed by using co on ya ns. To comple e i , ou laces we e sewn on i s ends. In he Supplemen a y Ma e ials, Figu es S3 and S4 show he chosen ma e ials and he de eloped band, espec i ely. Figu e 3. The manu ac u ing s eps o he band de elopmen . 2.5. Human Body Posi ions o he Placemen o TEG The placemen o he TEG on human body occu ed on ou body posi ions, wo in he uppe and wo in he lowe body pa s. In o de o imp o e he i o he TEG on o he skin, he ou di e en body pa s we e chosen wi h su icien ly la ge skin a eas, and in co espondence o he supe icial muscles o a m and leg. Biceps b achii o he a m an e io , and lexo ca pi adialis o he o ea m we e he muscles co esponding o he placemen o he TEG in he uppe body pa , while g acilis o he high and gas ocnemius o he cal we e he chosen muscles o he leg (see Supplemen a y Ma e ials, Figu es S5 and S6). 3. Expe imen al Sec ion We pe o med h ee expe imen al es s: (1) p elimina y measu emen s; (2) execu ion o human daily ac i i ies in a con olled en i onmen ; (3) execu ion o human daily ac i i ies in a eal scena io. 3.1. P elimina y Maesu emen s Two heal hy male olun ee s s ayed in es ing posi ion o mo e han 20 min, in which he ol age alues we e acqui ed in acco dance o he ollowing ime-in e als: i s minu e, i h minu e, en h minu e, and wen ie h minu e. These p elimina y measu emen s we e made o ind ou he alue o he esis i e load ha maximizes he powe ou pu . To ind ou he op imum esis o load, he ol age da a we e acqui ed by a ying he ex e nal load in he ange: 1–32 Ω. Pa icula ly, he ange o esis o loads is as ollows: 1.12 Ω, 3.88 Ω, 4.68 Ω, 5.71 Ω, 7.61 Ω and 31.84 Ω. The TEG was placed on each o he ou a o emen ioned skin a eas. Figu e 3. The manu ac u ing s eps o he band de elopmen . 2.5. Human Body Posi ions o he Placemen o TEG The placemen o he TEG on human body occu ed on ou body posi ions, wo in he uppe and wo in he lowe body pa s. In o de o imp o e he i o he TEG on o he skin, he ou di e en body pa s we e chosen wi h su icien ly la ge skin a eas, and in co espondence o he supe icial muscles o a m and leg. Biceps b achii o he a m an e io , and lexo ca pi adialis o he o ea m we e he muscles co esponding o he placemen o he TEG in he uppe body pa , while g acilis o he high and gas ocnemius o he cal we e he chosen muscles o he leg (see Supplemen a y Ma e ials, Figu es S5 and S6). 3. Expe imen al Sec ion We pe o med h ee expe imen al es s: (1) p elimina y measu emen s; (2) execu ion o human daily ac i i ies in a con olled en i onmen ; (3) execu ion o human daily ac i i ies in a eal scena io. 3.1. P elimina y Maesu emen s Two heal hy male olun ee s s ayed in es ing posi ion o mo e han 20 min, in which he ol age alues we e acqui ed in acco dance o he ollowing ime-in e als: i s minu e, i h minu e, en h minu e, and wen ie h minu e. These p elimina y measu emen s we e made o ind ou he alue o he esis i e load ha maximizes he powe ou pu . To ind ou he op imum esis o load, he ol age da a we e acqui ed Senso s 2018,18, 1927 7 o 17 by a ying he ex e nal load in he ange: 1–32 Ω . Pa icula ly, he ange o esis o loads is as ollows: 1.12 Ω , 3.88 Ω , 4.68 Ω , 5.71 Ω , 7.61 Ω and 31.84 Ω . The TEG was placed on each o he ou a o emen ioned skin a eas. Du ing all he pe o med es s, a he mis o p obe measu ed he oom empe a u e, which was 25.0 ◦ C. Mo eo e , wo p obes we e connec ed o he op and bo om sides o he TEG o measu e he empe a u e di e ence alues. Figu e 4a shows he powe ou pu gene a ed by he TEG when i was placed on he a m an e io , whe eas Figu e 4b shows he ela i e empe a u e di e ence be ween he wo sides o he TEG. In he diag am o Figu e 4a he powe ou pu eached up o 5 µ W a e 1 min, and i dec eased up o 4 µ W a he end o he measu emen s. The disc epancy o app oxima ely 1 µ W is based on he dec ease o he empe a u e di e ence. As i can be clea ly seen in Figu e 4b, he empe a u e di e ence dec eases om 2.4 ◦C o a ound 2.0 ◦C. Senso s 2018, 18, x FOR PEER REVIEW 7 o 17 Du ing all he pe o med es s, a he mis o p obe measu ed he oom empe a u e, which was 25.0 °C. Mo eo e , wo p obes we e connec ed o he op and bo om sides o he TEG o measu e he empe a u e di e ence alues. Figu e 4a shows he powe ou pu gene a ed by he TEG when i was placed on he a m an e io , whe eas Figu e 4b shows he ela i e empe a u e di e ence be ween he wo sides o he TEG. In he diag am o Figu e 4a he powe ou pu eached up o 5 μW a e 1 min, and i dec eased up o 4 μW a he end o he measu emen s. The disc epancy o app oxima ely 1 μW is based on he dec ease o he empe a u e di e ence. As i can be clea ly seen in Figu e 4b, he empe a u e di e ence dec eases om 2.4 °C o a ound 2.0 °C. Figu e 4. The powe ou pu gene a ed by he TEG on he an e io a m an e io (biceps b achii) (a); and he ela i e empe a u e di e ence (b). E o ba s ep esen s anda d de ia ions. Figu e 5a shows he powe ou pu gene a ed by he TEG when i was on he o ea m, whe eas Figu e 5b shows he ela i e di e ence o empe a u es be ween he skin and he en i onmen . In he diag am o Figu e 5a, he powe ou pu eached up o 4.8 μW a e 1 min, and i dec eased o 3.3 μW a he end o he measu emen . Again, he a ia ion o app oxima ely 1.5 μW was in acco dance o he dec ease o empe a u e di e ence. As i can be clea ly seen om Figu e 5b, i dec eased om 2.4 °C o 1.8 °C. Figu e 6a shows he powe ou pu gene a ed by he TEG when i was on he high, and Figu e 6b shows he ela i e empe a u e di e ences be ween skin and en i onmen . In his case, he powe ou pu eached up o 2.6 μW a e 1 min, and dec eased o 2.1 μW a he end o he measu emen . I is depic ed by he dec ease o he empe a u e di e ence om 1.4 °C o 1.2 °C. A simila beha iou was ound o he powe ou pu gene a ed by he TEG placed on he cal (see Figu e 7a): he powe ou pu eached up o 4.4 μW a e 1 min, and i dec eased o 3.35 μW a he end o he measu emen . In his case, he dec ease o he empe a u e di e ence was om 2.20 °C o 1.80 °C (see Figu e 7b). Figu e 4. The powe ou pu gene a ed by he TEG on he an e io a m an e io (biceps b achii) ( a ); and he ela i e empe a u e di e ence (b). E o ba s ep esen s anda d de ia ions. Figu e 5a shows he powe ou pu gene a ed by he TEG when i was on he o ea m, whe eas Figu e 5b shows he ela i e di e ence o empe a u es be ween he skin and he en i onmen . In he diag am o Figu e 5a, he powe ou pu eached up o 4.8 µ W a e 1 min, and i dec eased o 3.3 µ W a he end o he measu emen . Again, he a ia ion o app oxima ely 1.5 µ W was in acco dance o he dec ease o empe a u e di e ence. As i can be clea ly seen om Figu e 5b, i dec eased om 2.4 ◦ C o 1.8 ◦C. Figu e 6a shows he powe ou pu gene a ed by he TEG when i was on he high, and Figu e 6b shows he ela i e empe a u e di e ences be ween skin and en i onmen . In his case, he powe ou pu eached up o 2.6 µ W a e 1 min, and dec eased o 2.1 µ W a he end o he measu emen . I is depic ed by he dec ease o he empe a u e di e ence om 1.4 ◦C o 1.2 ◦C. Senso s 2018,18, 1927 8 o 17 Senso s 2018, 18, x FOR PEER REVIEW 8 o 17 Figu e 5. The powe ou pu gene a ed by he TEG on he o ea m, ( lexo ca pi adialis) (a); and he ela i e empe a u e di e ence (b). E o ba s ep esen s anda d de ia ions. Figu e 6. The powe ou pu gene a ed by he TEG on he high, (g acilis muscle) (a); and he ela i e empe a u e di e ence (b). E o ba s ep esen s anda d de ia ions. Figu e 5. The powe ou pu gene a ed by he TEG on he o ea m, ( lexo ca pi adialis) ( a ); and he ela i e empe a u e di e ence (b). E o ba s ep esen s anda d de ia ions. Senso s 2018, 18, x FOR PEER REVIEW 8 o 17 Figu e 5. The powe ou pu gene a ed by he TEG on he o ea m, ( lexo ca pi adialis) (a); and he ela i e empe a u e di e ence (b). E o ba s ep esen s anda d de ia ions. Figu e 6. The powe ou pu gene a ed by he TEG on he high, (g acilis muscle) (a); and he ela i e empe a u e di e ence (b). E o ba s ep esen s anda d de ia ions. Figu e 6. The powe ou pu gene a ed by he TEG on he high, (g acilis muscle) ( a ); and he ela i e empe a u e di e ence (b). E o ba s ep esen s anda d de ia ions. Senso s 2018,18, 1927 9 o 17 A simila beha iou was ound o he powe ou pu gene a ed by he TEG placed on he cal ( see Figu e 7a ): he powe ou pu eached up o 4.4 µ W a e 1 min, and i dec eased o 3.35 µ W a he end o he measu emen . In his case, he dec ease o he empe a u e di e ence was om 2.20 ◦ C o 1.80 ◦C (see Figu e 7b). Senso s 2018, 18, x FOR PEER REVIEW 9 o 17 Figu e 7. The powe ou pu gene a ed by he TEG on he cal , (gas ocnemius muscle) (a); and he ela i e empe a u e di e ence (b). E o ba s ep esen s anda d de ia ions. Fo all he pe o med measu emen s, esul s ela ed o he bes powe alues sugges a esis o load in he ange om 4 o 6 Ω, as isible om he uppe panels o Figu es 4–7. 3.2. Execu ion o Human Daily Ac i i ies in a Con olled En i onmen Si ing, walking and jogging we e he ac i i ies pe o med by use s o measu e he amoun o elec ical powe gene a ed by he TEG. We pe o med measu emen s in a con olled en i onmen . Based on he esul s ob ained in he p e ious expe imen al s age, he 5.71 Ω esis o load was used in he measu emen ci cui . Fou heal hy male olun ee s (age: 25 ± 5 yea s; body weigh : 69 ± 10 kg; heigh : 174 ± 6 cm) pe o med o h ee imes he ollowing cycle o mul iple ac i i ies: si ing posi ion ( wo minu es), walking ( wo minu es), again si ing posi ion ( wo minu es), jogging ( wo minu es), again si ing posi ion ( wo minu es). Each olun ee has epea ed his cycle o mul iple ac i i ies h ee imes. Du ing es s, he TEG was only placed on he biceps b achii and he gas ocnemius, because hese body pa s gene a ed, in he p elimina y measu emen s, he la ges amoun o powe on a m and leg, espec i ely. Figu e 8 shows he mean alues o powe ou pu , wi h he s anda d de ia ion alues. The measu ed empe a u e in he con olled en i onmen was always a ound 23 °C. A i s , i is impo an o a i m ha he measu ed alue o oom empe a u e du ing he execu ion o hese ac i i ies was 23 °C. I is 2 °C lowe han he measu ed oom empe a u e in he i s s age o he expe imen s (25 °C). The e o e, in Figu e 8 he powe alues ela ed o he i s wo minu es o he si ing (5.5 μW o he biceps b achii and 6.5 μW o he gas ocnemius) esul ed qui e highe han he alues in Figu e 4a o he biceps b achii (4.5 μW), and in Figu e 7a o he gas ocnemius (4 μW). Figu e 7. The powe ou pu gene a ed by he TEG on he cal , (gas ocnemius muscle) ( a ); and he ela i e empe a u e di e ence (b). E o ba s ep esen s anda d de ia ions. Fo all he pe o med measu emen s, esul s ela ed o he bes powe alues sugges a esis o load in he ange om 4 o 6 Ω, as isible om he uppe panels o Figu es 4–7. 3.2. Execu ion o Human Daily Ac i i ies in a Con olled En i onmen Si ing, walking and jogging we e he ac i i ies pe o med by use s o measu e he amoun o elec ical powe gene a ed by he TEG. We pe o med measu emen s in a con olled en i onmen . Based on he esul s ob ained in he p e ious expe imen al s age, he 5.71 Ω esis o load was used in he measu emen ci cui . Fou heal hy male olun ee s (age: 25 ± 5 yea s; body weigh : 69 ± 10 kg; heigh : 174 ± 6 cm) pe o med o h ee imes he ollowing cycle o mul iple ac i i ies: si ing posi ion ( wo minu es), walking ( wo minu es), again si ing posi ion ( wo minu es), jogging ( wo minu es), again si ing posi ion ( wo minu es). Each olun ee has epea ed his cycle o mul iple ac i i ies h ee imes. Du ing es s, he TEG was only placed on he biceps b achii and he gas ocnemius, because hese body pa s gene a ed, in he p elimina y measu emen s, he la ges amoun o powe on a m and leg, espec i ely. Figu e 8shows he mean alues o powe ou pu , wi h he s anda d de ia ion alues. The measu ed empe a u e in he con olled en i onmen was always a ound 23 ◦ C. A i s , i is impo an o a i m Senso s 2018,18, 1927 16 o 17 13. Pennes, H.H. Analysis o issue and a e ial blood empe a u es in he es ing human o ea m. J. 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