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 . Ne e heless,
he de ec ion capabili y a 8.2 GHz was e y s ong and
eliable.
Acknowledgmen
The p esen ed esea ch was suppo ed by he In e -
nal G an Agency o B no Uni e si y o Technology ( he
p ojec no. FEKT-S-20-6526). The esea ch is pa o
he p ojec FV40385 Tex ile elec onics o homeca e and
p o essional use (TED) unded by Czech Minis y o In-
dus y and T ade.
Jou nal o ELECTRICAL ENGINEERING 73(2022), NO1 61
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