Pressure and humidity detector based on textile integrated waveguide

sciendo Jou nal o ELECTRICAL ENGINEERING, VOL 73(2022), NO1, 57–61 COMMUNICATIONS P essu e and humidi y de ec o based on ex ile in eg a ed wa eguide Ma in Kokolia, Zbynek Raida1 In he pape , a p essu e senso and a humidi y senso a e designed as supplemen a y componen s o a ex ile in eg a ed wa eguide (TIW) based on an a i icial magne ic conduc o (AMC) consis ing o hexagonal elemen s. Thanks o AMC, sewing o elec ically conduc i e side walls can be elimina ed. Since ope a ing in he s op-band o TIW, he senso s do no in luence ansmission pa ame e s o TIW, and p o ide an addi ional unc ionali y. Fo ab ica ion, a h ee-dimensional kni ed ab ic was used as a subs a e and conduc i e su aces we e c ea ed om a sel -adhesi e coppe oil. The senso s we e simula ed, manu ac u ed and measu ed in he equency ange om 10 GHz o 12 GHz wi h a easonable ag eemen . Since he designed componen s a e sensi i e on manu ac u ing ole ances, a highe measu ed inse ion loss in TIW can be obse ed compa ed o simula ions. Ne e heless, he inse ion loss can be educed when manu ac u ing accu acy is imp o ed. K e y w o d s: ex ile-in eg a ed wa eguide (TIW), a i icial magne ic conduc o (AMC), p essu e senso , humidi y senso 1 In oduc ion In he las decade, a en ion has been gi en o he in e- g a ion o a ious elec onic componen s and senso s in o ex ile ma e ials [1]-[3]. This app oach p omises seamless blending o unc ionali y and com o in bo h wea able applica ions and echnical ex iles, used inside ehicles ypically [4]-[5]. Applica ions usually comp ise DC and low equency elec onics, high equency and mic owa e s uc u es o e en op oelec onical ci cui s o sonic sen- so s [6]-[11]. The RF sensing is he app oach discussed in his pape . Since ex ile-in eg a ed wa eguides (TIW) con- s uc ed om a i icial magne ic conduc o s (AMC) ha e al eady been used o a powe ansmission in ehicles, non-con en ional senso s exploi ing hose s uc u es a e a ac i e being implemen ed wi h minimum cos s [12]. Since TIW can be di ec ly p in ed on a echnical ex- ile a uphols e y o ehicles, sa ings o con en ional coope wi ing and weigh a e associa ed wi h. TIW, which was p esen ed in [13], ope a es a equencies om 10 GHz o 12 GHz. I an op imal sensing sys em is going o be designed, no addi ional losses should be caused in powe ansmission on one hand, and a good sensing eliably should be ensu ed on he o he hand. A p esen , he e a e se e al app oaches o sense phys- ical changes inside and a ound he ma e ial adop ing mic owa es ene gy. Those app oaches ange om de- o med wa eguides [14], an ennas ecei ing signal ac oss he changing space [15], RFID sys ems [16] and ela ed me hods. Some wo k in his ield was p esen ed bu mos o de ices a e ei he oo complex o be manu ac u ed o only a single-pu pose ope a ion is p o ided. In pape s [14] and [17], he p inciple o sensing me- chanical de o ma ion caused by mechanical p essu e is p esen ed. In [14], au ho s p esen ed a ca i y esona o made o me al which wall was de o med a a ce ain le el o high p essu e ou side he ca i y. Thus, a dimension o he esona o and i s esonan equency we e changed. In [15], au ho s desc ibed a coplana wa eguide made on a lexible subs a e wi h se e al ing esona o s. Once a ce ain mechanical de o ma ion o he subs a e occu ed, p ope ies o di e en esona o s al e ed and he o e all ansmission o he s uc u e was changed in a p edic able way. Ano he p omising app oach o implemen a senso s uc u e u ilizing mic owa e bands is desc ibed in [17] and [18]. In bo h pape s, some kind o a ca i y o a es- ona o is used. In he base s a e, he cu -o equency o he esonan equency can be obse ed om he iew- poin o equency dependence o ansmission coe icien . Gi en by known ela i e pe mi i i y o an expec ed liq- uid and a a ia ion o e ec i e pe mi i i y on he senso , ei he he p esence o di e en liquids can be de ec ed o a change o liquids composi ion can be sensed. The p esen ed pape is aimed o u ilize an a i i- cial magne ic conduc o (AMC)-based ex ile in eg a ed wa eguide (TIW) desc ibed in [13] o sensing. This TIW was designed o be used o powe ansmission in up- hols e y inside ca s o ai planes. The s aigh sec ion o he TIW is con e ed in o a p ac ical senso wi h mini- mal modi ica ions o he TIW while p ese ing he ease o manu ac u ing, low cos s and he p ima y RF powe ansmission. Thus, he dual-pu pose s uc u e is c ea ed. As an example, wo ypes o senso s we e designed, man- u ac u ed, and es ed in a con olled en i onmen : 1B no Uni e si y o Technology, FEEC, Depa men o Radio Elec onics, Technick´a 12, 616 00 B no, Czechia, [email p o ec ed], [email p o ec ed] h ps://doi.o g/10.2478/jee-2022-0008, P in ( ill 2015) ISSN 1335-3632, On-line ISSN 1339-309X c This is an open access a icle licensed unde he C ea i e Commons A ibu ion-NonComme cial-NoDe i s License (h p: //c ea i ecommons.o g/licenses/by-nc-nd/3.0/). 58 M. Kokolia, Z. Raida: PRESSURE AND HUMIDITY DETECTOR BASED ON TEXTILE INTEGRATED WAVEGUIDE Fig. 1. AMC-based TIW. Side walls a e eplaced by wo ows o hexagonal elemen s. The senso is o be connec ed ia he coupling slo s in he TIW cen e . The s uc u e is comple ed by SMA- o- mic os ip ansi ion a he inpu and he ou pu •The i s senso measu es a a ia ion o a ex ile hick- ness. Such a senso can play he ole o a use -in e ace bu on o can egis e he p esence o a pe son on a sea . •The second senso de ec s he a ia ion o ela i e pe - mi i i y. Such a de ice can sense he p esence o wa e inside he ex ile. Tha way, he humidi y inside he ex ile can be de ec ed. 2 AMC based TIW senso s Con en ional ex ile-in eg a ed wa eguides (TIW) con- sis o a op and bo om conduc i e laye manu ac u ed om a conduc i e ab ic ma e ial, sc een-p in ed sil e pas e, o a sel -adhesi e coppe oil. Side walls can be sewed by a conduc i e h ead. In o de o elimina e he need o cos ly, ime-demanding and inaccu a e sewing, side walls can be eplaced by an a i icial magne ic con- duc o (AMC) as explained in [12]. The TIW was op imized o ope a e in he equency ange om 10 GHz o 12 GHz. The layou o he TIW was e ched in a sel -adhesi e coppe oil o be ixed o he 3D kni ed ex ile SINTEX 3D097 (h= 3.4 mm, ε = 1.2). P op ie ies o his ma e ial we e in es iga ed in [19]. Ob- iously, he manu ac u ed TIW shows addi ional losses in compa ison wi h he simula ion o he lossless s uc- u e. A signi ican pa o losses is due o he undesi ed adia ion and dispe sion a he edges o AMC cells a he ansi ion om he eeding sec ion o he s aigh sec ion o TIW. L1 L2 W1 D1 A1 Fig. 2. De ail o coupling slo s in he cen e o TIW In o de o ind he esonance equency, a esona o composed o a single hexagonal cell can be app oxima ed by a ec angula ca i y. The physical leng h o he cell is 17.4 mm bu he e ec i e leng h is smalle since he i ual elec ical wall is no pe ec ly hin and causes an ex ension wi hin <0.50 mm; 0.75 mm>inwa ds. Hence, he app oxima e esonance equency is = 8.6 GHz. The AMC-based wa eguide ope a es wi h TE00 mode and he ca i y esona o ope a es wi h TE001 mode. In Fig. 3, ab- solu e alue o E- ield in ensi y is shown a he ope a ion equency = 8.6 GHz. P og essi ely changing shape o he wa e a eling hough he wa eguide is he esul o he changing eloci y o p opaga ion a di e en angles o coincidence wi h he AMC cell walls. A equencies be ween 10 GHz and 12 GHz, he TE002 mode is exci ed inside he ca i y esona o wi h minima placed a ound eeding slo s. Thus, he minimal ene gy e u ns o he wa eguide and he p opaga ing wa e is no in e e ing wi h. Fig. 3. Absolu e alue o E- ield in ensi y a = 8.63 GHz inside TIW (le ). De ail o coupling slo s ( igh ) Jou nal o ELECTRICAL ENGINEERING 73(2022), NO1 59 Table 1. Dimensions o coupling slo s o TIW Va iable Value Uni A1 12.5 deg ees D1 5.8 mm W1 2.0 mm L1 1.5 mm L2 6.0 mm Table 2. Dimensions o sensing slo s o humidi y de ec o Va iable Value Uni D2 2.50 mm L2 12.00 mm W2 2.50 mm Fig. 4. AMC-TIW p essu e senso a maximum de o ma ion (le ). AMC-TIW humidi y de ec o ( igh ) S21 (dB) 8 9 1210 F equency (GHz) -10 0 -20 -30 Base s a e Max. p ess 1 mm p ess Fig. 5. Simula ed equency esponse o ansmission coe icien o he p essu e senso The senso s o be coupled o TIW ia coupling slo s a e concei ed as ca i y esona o s consis ing o a single AMC cell. Side walls o he esona o s a e c ea ed by a single ow o AMC cells o elimina e he need o sewing. Bo h he senso s a e shown in Fig. 4. The p ecise align- men o eeding slo s in TIW and he ca i y esona o o he senso is c i ical o an e icien ope a ion o he sys- em. In eal si ua ions, andom s op bands o a sligh e- quency shi o he s op band migh appea . Since he neg- ligible in luence on he communica ion wi hin he band om 10 GHz o 12 GHz is eques ed, he change o losses in he s op band should be consis en ac oss he whole ange o de o ma ions and pe mi i i y a ia ions. L2 D2 W2 Fig. 6. Dimensions o sensing slo s o he humidi y de ec o S21 (dB) 8 9 1210 F equency (GHz) -10 0 -20 -30 Epsilon = 5 Epsilon = 3 Base s a e Fig. 7. Simula ed equency esponse o ansmission coe icien o he humidi y de ec o Fig. 8. Manu ac u ed p o o ypes o he p essu e senso (le ) and he humidi y de ec o ( igh ) Figu e 7 shows simula ed losses be ween po s o he wa eguide wi h he humidi y de ec o . The di e ence be- ween equency cha ac e is ics o he ini ial s a e wi h 60 M. Kokolia, Z. Raida: PRESSURE AND HUMIDITY DETECTOR BASED ON TEXTILE INTEGRATED WAVEGUIDE S21 (dB) 8 9 1210 F equency (GHz) -10 0 -20 -30 Maximum de o ma ion Base s a e Fig. 9. Measu ed equency esponse o ansmission coe icien o he p essu e senso he d y ex ile and an expec ed h eshold humidi y in- side he ex ile is ob ious. The mos signi ican and eli- able a ia ion in he ange o pa ame ic analysis can be seen a 8.65 GHz. In he simula ed ange o ela i e pe - mi i i y inside he ca i y, he peak o he s op band a his equency was only diminishing wi h no o he peak ha could be misin e p e ed. 3 Manu ac u ing and es ing Resul s show ha he desi ed s op band is less p o- nounced and appea s a a sligh ly lowe equency 8.25 GHz. When p essed, he losses a 8.25 GHz a e lessened by 20 dB, making his change qui e signi ican (a e y na ow equency band). Fo example, he change is only abou 10 dB a 8.20 GHz. On he o he hand, he com- munica ion band om 10.0 GHz o 12.0 GHz is no dis- u bed a all. %Fig. 10 Measu ed equency esponse o ansmission coe icien o he humidi y de ec o . S21 (dB) 8 9 1210 F equency (GHz) -10 0 -20 -30 Base s a e We ex ile Fig. 10. Measu ed equency esponse o ansmission coe icien o he humidi y de ec o Few d ops o a pu e wa e we e d opped a he cen al elemen o he de ec o o es he unc ionali y. Resul s show ha he eal esponse o he humidi y de ec o is e y simila o simula ion. Roughly a 8.2 GHz, he e is a p onounced peak o losses a he ini ial s a e. When he humidi y was p esen , he losses a his equency signi ican ly diminished and he s op band disappea ed. This makes he e ec o he humidi y ha d o mis ake and p o es he concep o he senso . The communica ion band om 10.0 GHz o 12.0 GHz is isibly dis u bed in i s lowe pa , and he e is a easonably small inc ease in losses om 10.8 GHz o 12.0 GHz. This could be con- ibu ed o wa e ge ing in o he wa eguide in he lowe laye o he ex ile. The es ed p o o ype was d ied na - u ally and es ed again. When enough wa e was added o be de ec able clea ly, he esul s we e simila . 4 Conclusions In he pape , he concep o he p essu e senso and he humidi y de ec o coupled o he ex ile in eg a ed wa eguide is p esen ed. The AMC-based wa eguide was used o he communica ion in he equency band om 10.0 GHz o 12.0 GHz. Fo sensing and de ec ion, a lowe equency band om 8.0 GHz o 10.0 GHz was used. Hence, a dual-pu pose sys em was designed. A lowe equencies, senso applica ions we e implemen ed while minimizing e ec s on powe ansmission wi hin he com- munica ion equency band. The design comp ises a ca - i y esona o o be pu on he op o he wa eguide. Res- onan equency o he esona o is a ied by he change o hickness o he ex ile subs a e (in case o he p es- su e senso ) o by he change o pe mi i i y (in case o he humidi y de ec o ). The senso s we e manu ac u ed and es ed in ealis ic condi ions. T ansi ions o ex ile in eg a ed wa eguides we e measu ed by a ec o ne - wo k analyze while sensing was applied. The p essu e senso was used as a bu on. The ealis ic maximal de- o ma ion was abou hal o he hickness o he ex ile wi hou he pe manen damage. Due o highe losses in he communica ion band, he s op band used o sensing is e y p onounced. A 8.25 GHz, he e was a s op band peak e y p onounced comple ely absen , when he sen- so was p essed. Resul s p o ided by es ing o humidi y de ec o a e also somewha di e en om he expec ed e- sponse since he con ol o he p ecise dis ibu ion o he wa e inside he desi ed sensing sec ion is di icul . This could be mi iga ed in u he de elopmen . 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