research article a wearable wireless energy link for thin-film...

Research ArticleA Wearable Wireless Energy Link forThin-Film Batteries Charging

Giuseppina Monti Laura Corchia Egidio De Benedetto and Luciano Tarricone

Department of Engineering for Innovation University of Salento Via Monteroni 73100 Lecce Italy

Correspondence should be addressed to Giuseppina Monti giuseppinamontiunisalentoit

Received 26 November 2015 Accepted 28 February 2016

Academic Editor Jaume Anguera

Copyright copy 2016 Giuseppina Monti et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

A wireless charger for low capacity thin-film batteries is presentedThe proposed device consists of a nonradiative wireless resonantenergy link and a power management unit Experimental data referring to a prototype operating in the ISM band centered at434MHz are presented and discussed In more detail in order to facilitate the integration into wearable accessories (such ashandbags or suitcases) the prototype of the wireless energy link was implemented by exploiting a magnetic coupling betweentwo planar resonators fabricated by using a conductive fabric on a layer of leather From experimental data it is demonstrated thatat 434MHz the RF-to-RF power transfer efficiency of the link is approximately 693 As for the performance of the system as awhole when an RF power of 75 dBm is provided at the input port a total efficiency of about 297 is obtained Finally experimentsperformed for calculating the charging time for a low capacity thin-film battery demonstrated that for RF input power higher than6 dBm the time necessary for recharging the battery is lower than 50 minutes

1 Introduction

In recent years wearable electronics have gained muchresearch interest with applications that range from health-care monitoring [1 2] to public safety [3 4] and mobilecomputing [5ndash7]Thedesign and fabrication ofwearable elec-tronics require that the embedding of electronic componentsinside clothes andor other wearable accessories must notcompromise the appearance and usability of the product Infact in the fashion industry any new wearable technologymust be useful but also comfortable Additionally it must notbe intrusive to the user whomust be able to carry out his dailyactivities without anymovement limitation andor additionalburden

Considering these requirements either near-field [8ndash13]or far-field [14ndash21] wireless technologies may successfullyserve the purpose for both data and power transmission Stillto guarantee a seamless integration of electronic devices andantennas in wearable and portable accessories it is crucialto select appropriate materials and fabrication techniquesTo this purpose the use of nonconventional materials such

as textile materials conductive threads electrotextile fabricsand nonwoven conductive fabrics should be preferred

Accordingly some wearable antennas for far-field Wire-less Power Transmission (WPT) links have been proposed inthe literature [15ndash17] Among these in [16] numerical datareferring to a multifrequency rectifying antenna (rectenna)are reported the multiband behavior is obtained by using aslotted annular-ring microstrip antenna The overall systemis a multilayer structure using two layers of pile the GlobalEMC shielding fabric for the conductive parts a layer ofKapton for the rectifying circuit and a thermoadhesive layerat each interface between pile and conductive fabric

Additionally in [17] two textile logo antennas fabricatedbymeans of a self-adhesive nonwoven conductive fabric havebeen presented

As for near-field WPT links for wearable applications asystem using two resonators on a layer of leather has beenproposed in [22]

In this paper starting from the prototype presented in[22] a wireless battery charger for application in clothingindustry is presented In more detail the wireless resonant

Hindawi Publishing CorporationInternational Journal of Antennas and PropagationVolume 2016 Article ID 9365756 9 pageshttpdxdoiorg10115520169365756

2 International Journal of Antennas and Propagation

Primary resonator

Secondary resonator

Power management unit

MEC201Source

S

Cprimary

Lprimary

CSecondary

LSecondary

PRE-IN PRF-OUT PDC-OUT

(a)

Secondary resonator

Primaryresonator

(b)

Figure 1 Proposed wireless charger (a) Schematic representation the link consists of a wireless resonant energy link and of a powermanagement unit (b) Example of application the secondary resonator is embedded into a leather bag while the primary resonator is ona pad where the bag should be placed on for charging the battery

energy link (WREL) proposed in this work was exploitedfor implementing a wireless charger [8 9] for low capacitythin-film batteries The proposed system consists of (1) twoplanar resonators that were optimized and fabricated to beembedded in portable leather accessories and (2) a powermanagement unit (PMU)

Figure 1(a) shows a schematic representation of theproposed WPT link which exploits a magnetic couplingbetween two planar resonators namely a primary resonatorand a secondary resonator The former is embedded intoa pad and is connected to an external power source thatprovides it with an AC input power whereas the latter isconnected to the rechargeable battery by means of the PMUFigure 1(b) shows a sketch of a possible practical applicationthe secondary resonator is embedded into a bag while theprimary resonator is embedded into a pad where the bagshould be placed on for charging battery

As will be detailed in the following section for theresonators fabrication a self-adhesive nonwoven fabric wasused for the conductive parts while a layer of leatherwas usedas support

Numerical and experimental results referring to a pro-totype working in the ISM band (43305ndash43479MHz) arereported and discussed

The paper is structured as follows Numerical and exper-imental data obtained for the proposed WPT link are illus-trated in Section 2 Section 3 describes each single block of thePMU Experimental results related to the proposed wirelesscharging system as a whole are reported in Section 4 Finallyconclusions are drawn in Section 5

2 Wearable Resonators Geometry and Results

21 Resonators Geometry and Numerical Results The pro-posed WPT link is comprised of two identical resonatorseach one consisting of a distributed inductance loaded bya lumped capacitor [22] Figure 2(a) shows a sketch of aperspective view of the configuration adopted for the WPTlink while Figure 2(b) illustrates the resonator geometry

From Figure 2(a) it can be noticed that each resonatorconsists of an elliptical loop loaded by a smaller oneThe two

Port 2 Port 1

(a)

h

d

x

y

z

Lsub

W

Hsu

b

C2

C1

R1

r2

R2

r1

(b)

Figure 2 Geometry of the proposed wireless energy link (a)perspective view (b) front view It can be seen that the secondaryresonator is overlapped to the primary resonator

resonators are rotated by 180∘ with respect to each other (onthe 119909-119910 plane) and they are also alignedwith the center of theexternal elliptical loop Additionally to tune the resonancefrequency two lumped capacitors 119862

1and 119862

2 are also used

The geometry of the resonators was optimized by meansof full-wave simulations to obtain (1) an operating frequencyin the ISM band (43305ndash43479MHz) and (2) an inputimpedance of 50Ω In the following the main steps of thedesign process are briefly described

The starting geometry was a simple elliptical loop with amajor axis of 36mm a width of 2mm and an eccentricityclose to zero thus corresponding to a nearly circular geom-etry These initial values were chosen in order to obtain acompact structure suitable to be fabricated with the facilities

International Journal of Antennas and Propagation 3

200 300 400 500 600 700 800

0

minus5

minus10

minus15

minus20

minus25minus30minus40minus50minus60

Scat

terin

g pa

ram

eter

(dB)

f0

fm fe

|S11| (single loop)|S11| (WREL)

|S22| (WREL)|S21| (WREL)

f (MHz)

Figure 3 Simulated reflection coefficient of the single loop com-pared to the scattering parameters of the WREL consisting of twoloops configured as in Figure 2(a)

at hand To tune the resonance frequency in the ISM band aseries 11 pF lumped capacitor was added

The scattering parameters corresponding to this initialgeometry are illustrated in Figure 3 which shows (1) thereflection coefficient of the primary resonator and (2) thescattering parameters of the wireless resonant energy link inthe configuration of Figure 2(a)

It can be seen that the resonance frequency 1198910 of

the single resonator is approximately 427MHz It can bealso noticed that when the two resonators are coupled theresonance frequency 119891

0splits into two different frequencies

(ie the magnetic resonance 119891119898and the electric resonance

119891119890) which correspond to two relative maxima of the power

transfer efficiency From the coupled mode theory it can bederived that these frequencies are given by [23]

119891119898=

1198910

(radic1 + 119896)

119891119890=

1198910

(radic1 minus 119896)

(1)

where 119896 is themagnetic coupling between the two resonatorsIn practical applications 119896 assumes small values and thetwo resonance frequency values are so mutually close thatby acting on the resonators parameters a bandwidth centeredat 1198910can be obtained where the link can be used for WPT

applicationsStarting from these results the geometry of the resonators

was optimized in order to obtain a bandwidth suitable forWPT applications around119891

0(ie flat transmission scattering

parameters in the frequency range between 119891119898and 119891

119890) and

in order to center 119891119890at the center of the ISM band of interest

The first step of the design process was the optimizationof the eccentricity (119890) of the ellipse In this regard somefull-wave simulation results are illustrated in Figure 4(a) in

Table 1 Dimensions in millimeters of the geometry illustrated inFigure 2

119867sub 119871 sub 119882 1198771

1199031

1198772

1199032

ℎ 119889

547 476 24 152 95 113 37 119 39

the frequency range of interest the best results were obtainedfor an eccentricity of about 087

The design process was carried out by optimizing thewidth (119882) of the loop the corresponding results are givenin Figure 4(b) The parameter 119882 mainly influences thedistributed equivalent inductance and capacitance of eachloop and thus 119891

0 As a consequence a variation of119882 leads to

a shift of the entire useful bandwidth of the link Accordingto full-wave simulation results119882 was set at 2mm

Later on in order to improve the flatness of 11987821parameter

the possibility of improving the matching at 1198910by loading

the elliptical loop with LC distributed elements was inves-tigated Satisfactory results were obtained by loading theexternal loop with a smaller loop In Figure 5 the scatteringparameters obtained for the final geometry are comparedwith the ones obtained for the simple elliptical resonatorsAs shown in Figure 5(b) the transmission coefficient (ie11987821

parameter) is higher than minus3 dB in the 263ndash582MHzfrequency range corresponding to a relative bandwidth ofapproximately 755 The geometric parameters of the finalgeometry simultaneously optimized by means of full-wavesimulations are summarized in Table 1 After optimizationthe values of the lumped capacitors (119862

1and 119862

2) are 68 pF

and 10 pF respectively

22 Experimental Results A prototype of the proposedWPTlink was fabricated by using an adhesive nonwoven con-ductive fabric [24] on a layer of leather Figure 6(a) showsa picture of the two realized resonators while Figure 6(b)shows the setup adopted for experimental tests

The conductive fabric has a surface resistivity of004Ωsq With reference to the fabrication of devices forwearable applications this fabric has several advantages suchas low cost mechanical resistance and no fraying problemsThis last feature makes it particularly suitable also for thefabrication of complicated geometries [15 17 22 25 26]

As for the leather substrate a layer with a thickness of165mm and a relative dielectric permittivity (120576

119903) of 3 was

usedThe value of 120576119903was determined by fitting numerical and

experimental results obtained for some simple rectangularpatches As for the lumped capacitors 119862

1and 119862

2 surface

mounted capacitors were usedThe 119878-parameters were measured through a vector net-

work analyzer RampS ZVA50 the obtained results are reportedin Figure 7 An overall good agreement can be noticedbetween the measurement results and the numerical dataillustrated in Figure 5 In more detail the measured trans-mission coefficient is higher than minus3 dB in the frequencyrange 319ndash524MHz corresponding to a relative bandwidthof about 486 The slight degradation of the measuredperformance with respect to the simulated one is most likely


100 200 300 400 500 600 700 800f (MHz)

0

minus10

minus20

minus30

minus40

Scat

terin

g pa

ram

eter

(dB)

|S11| (e = 0)

|S21| (e = 0)

|S11| (e = 075)

|S21| (e = 075)

|S11| (e = 087)

|S21| (e = 087)

(a)

100 200 300 400 500 600 700 800

0

minus10

minus20

minus30

minus40

minus50

minus60

Scat

terin

g pa

ram

eter

(dB)

f (MHz)

|S11| (W = 2mm)|S21| (W = 2mm)|S11| (W = 3mm)

|S21| (W = 3mm)|S11| (W = 4mm)|S21| (W = 4mm)

(b)

Figure 4 Scattering parameters calculated bymeans of full-wave simulations during the optimization process of the resonators Optimizationof (a) the eccentricity 119890 and (b) the width119882 of the loop

100 200 300 400 500 600 700 800f (MHz)

0

minus5

minus10

minus15

minus20

minus25

minus30

minus35

minus40

Refle

ctio

n sc

atte

ring

para

met

er (d

B)

|S11| (no smaller loop)|S22| (no smaller loop)

|S11| (with smaller loop)|S22| (with smaller loop)

(a)

100 200 300 400 500 600 700 800f (MHz)

00

minus05

minus10

minus15

minus20

minus25

minus30minus10

minus20

minus30

minus40Tran

smiss

ion

scat

terin

g pa

ram

eter

(dB)

|S21| (no smaller loop)|S21| (with smaller loop)

(b)

Figure 5 Comparison between the scattering parameters calculated by means of full-wave simulations for the proposed wireless energylink obtained with and without the smaller loop (a) reflection scattering parameters (b) transmission scattering parameters

(a) (b)

Figure 6 Picture of the fabricated prototype (a) the two resonators (b) measurements setup


100 200 300 400 500 600 700 800

0

minus5

minus10

minus15

minus20

minus25

minus30

minus35

minus40

Scat

terin

g pa

ram

eter

(dB)

f (MHz)

|S11|

|S12||S21||S22|

Figure 7 119878-parameters measured by using the experimental config-uration shown in Figure 6(b)

100 200 300 400 500 600 700 8000

10

20

30

40

50

60

70

80

f (MHz)

120578RF

-RF

()

Figure 8 Experimental results obtained for the power transferefficiency (120578RF-RF) of the proposed wireless energy link

due to the SMA connectors which do not allow a perfectoverlap between the two resonators

With reference to the schematization shown in Figure 1by denoting by119875RF-IN the power available from the source andby 119875RF-OUT the power delivered by the secondary resonator tothe PMUunit the RF-to-RF power transfer efficiency (120578RF-RF)can be defined as follows

120578RF-RF =119875RF-OUT119875RF-IN=

119875RF-IN sdot100381610038161003816100381611987821

1003816100381610038161003816

2

119875RF-IN=100381610038161003816100381611987821

1003816100381610038161003816

2

(2)

Figure 8 shows the power transfer efficiency calculated forthe proposedWPT link by using experimental data accordingto (2) A maximum of 713 was obtained at 40397MHzIt can also be noticed that 120578RF-RF is higher than 50 inthe frequency range 31870ndash52367MHz corresponding to arelative bandwidth of approximately 487 Furthermore itcan be seen that in the ISM band (43305ndash43479MHz) theproposed link exhibits values of 120578RF-RF higher than 693

3 Power Management Unit

To assess the feasibility of using the proposed WPT link forimplementing a wireless charger a PMU that converts theRF power received by the secondary resonator into a DCpower that can be directly delivered to a battery was alsodesigned As can be seen from the schematic representationgiven in Figure 9 the PMU consists of three major blocks(A) a voltage doubler rectifier (B) a boost circuit and (C) abattery charger A photograph of a prototype fabricated on adouble side FR4 board (relative dielectric permittivity equalto 41 and thickness of 04mm) is shown in Figure 10The sizeof the PMU board is 55 times 55mm2

In the following paragraphs each single block will bedescribed in detail

31 Voltage Doubler Rectifier A voltage doubler rectifier wasused as RF-to-DC rectifier the corresponding schematic rep-resentation is reported in Figure 11The design of the rectifierwas developed by means of the software NI AWR DesignEnvironment by National Instruments [27] the design goalswere (1) to maximize the RF-to-DC conversion efficiency(120578RF-DC) and (2) to obtain an input impedance of 50Ω

First of all experimental tests were performed in order todetermine the input impedance of the boost converter whichis the load impedance of the rectifier (ie 119885LOAD) This waya value of 119885LOAD of about 20 kΩ was derived As for thevalue assumed for 119875RF-OUT which is the power delivered bythe secondary resonator to the rectifier a value of 5 dBm at434MHz was assumed Considering that from experimentalresults the RF-to-RF efficiency of the WREL link presentedin the previous section is equal to 693 assuming a valueof 5 dBm for 119875RF-OUT corresponds to assuming a value ofabout 65 dBm for the power 119875RF-IN delivered to the primaryresonator (see Figure 1) which is a reasonable value forWPTapplications

As can be seen from Figure 11 an Input MatchingNetwork (IMN) consisting of two shunt varactors and a seriesinductorwas used tomatch the rectifier to 50ΩThe varactors119862VAR1 and 119862VAR2 have a capacitance range of 065ndash25 pFand of 25ndash65 pF respectively They were exploited duringexperimental tests to adjust the level of matching betweenthe wireless energy link and the rectifier As for the inductorits value is 39 nH The Schottky diodes are the HSMS-2820by Avago Technologies [28] The capacitors 119862

3and 119862

4of the

voltage doubler rectifier were set at 01 120583FThe performance of the voltage doubler rectifier in terms

of 120578RF-DC was experimentally evaluated Measurements wereperformed for different values of the load (119885LOAD) and ofthe input power at the rectifier (119875RF-OUT) The followingdefinition was used to calculate 120578RF-DC values

120578RF-DC =119875Rect-OUT119875RF-OUT

=

(1198812

Rect-OUT119885LOAD)

119875RF-OUT (3)

where 119881Rect-OUT is the DC voltage at the output port of therectifier (see Figure 11) Experimental tests were performedby using the Vector Signal Generator (VSG) RampS FSW26 togenerate the RF signal at the input port of the rectifier (ie


GNDLM2767

NTC

LBSEL

ADJ BAT

GND

LTC4071

VCC

MEC201

Rectifier

(b) Battery charger(a) Boost circuit

V+

CAP+CAPminus

C5

RIN

ICHG

VBA

T

VOUT

D3

C6

C7C8

PRF-OUT

VBo

ost-O

UT

VRe

ct-O

UT

To system load VCC

Figure 9 Schematic representation of the power management unit (see Figure 1(a)) In particular the external lumped elements and the pinsconnection used for implementing the boost circuit (a) and the battery charger (b) are illustrated

Figure 10 Prototype of the proposed power management circuit

Voltage doubler rectIMN

L

C3

C4D2

D1

CVAR2CVAR1

PRF-OUT

VRect-OUT

PRect-OUT

ZLO

AD

Figure 11 Schematic representation of the voltage doubler rectifierused for rectifying the RF signal

119875RF-OUT) Results are reported in Figure 12 which shows themeasured 120578RF-DC values as a function of the resistive load (119877)for different values of 119875RF-OUT It can be seen that a maximumof 54 was obtained for 119877 = 33 kΩ and 119875RF-OUT = 10 dBmFurthermore values of 120578RF-DC higher than 30were obtainedfor 119875RF-OUT equal to 5 dBm and values of 119877 in the range of 1ndash22 kΩ

32 Boost Circuit The core of the boost circuit is the TexasInstruments LM2767 switched capacitor voltage converter[29] This chip operates as a voltage doubler for an input

10 100 1k 10k 100 k 1MR (Ω)

minus50dBmminus25dBm00dBm25dBm

50dBm75dBm100 dBm

05

10152025303540455055

PRF-OUT values

120578RF

-DC

()

Figure 12 RF-to-DC conversion efficiency of the rectifier asfunction of the resistive load (119877) for different values of the RF powerat the input port of the rectifier (119875RF-OUT)

voltage in the range of 18 V to 55 V and a supply currentof 40 120583A From specifications the LM2767 guarantees anoperating efficiency greater than 90 with most loads

In Figure 9(a) a schematic representation of the circuitalconfiguration adopted for implementing the boost converteris shownThe working mechanism is as follows a DC voltageapplied at the input pin (ie 119881+) is doubled at the output pin(119881OUT) In the intended application 119881+ is the voltage at theoutput port of the rectifier

As recommended by the manufacturer three lumpedcapacitors with low ESR (Equivalent Series Resistance) wereused to maximize efficiency and reduce the output voltagedrop and voltage ripple In particular three 10 120583F ceramiccapacitors were employed for 119862

5 1198626 and 119862

7 The aim of

the Schottky diode 1198633is to prevent malfunctions caused by

possible internal latch-up


1

2

3

4

5

6

7

8

9

10

LM2767

1050minus5minus10minus15minus20

PRF-OUT (dBm)

0

VRe

ct-O

UT

(V)

1kΩ18 kΩ33kΩ10kΩ

15kΩ18kΩ22kΩ150kΩ

Figure 13 119881Rect-OUT as function of 119875RF-OUT for different resistiveloads are compared with the one obtained when the rectifier isconnected with the boost circuit (see Figure 9)

In Figure 13 the curves obtained for 119881Rect-OUT as afunction of 119875RF-OUT for different resistive loads are comparedwith the one obtainedwhen the rectifier is connectedwith theboost circuit (see Figure 9) This comparison demonstratesthe validity of the initial assumptions and in particular thatrectifier sees the boost circuit as a resistive load of kilohmsorder of magnitude

33 Battery Charger The battery charger whose circuit dia-gram is given in Figure 9(b) was implemented by using theLTC4071 chip by Linear Technologies [30] The main featureof the LTC4071 is the charging of low capacity Li-ion or thin-film batteries from very low current For a correct operationthe LTC4071 requires just two external lumped componentsnamely a resistor and a capacitor (see Figure 9(b)) Theaim of the capacitor is to decouple the VCC and the GNDpins according to specifications (which recommend using acapacitor higher than 01 120583F) a 10 120583F capacitor was used for1198628 As for 119877IN a resistor of 180Ω was usedThe VCC pin is connected to the source by means of the

series resistor119877IN in presence of a system load this must alsobe connected to VCC pin as shown in Figure 9 The batteryis connected to the BAT pin

The LTC4071 chip has two different operation modes theldquorecharge moderdquo and the ldquouser moderdquo The recharge modeallows recharging a battery connected between the GND andthe BAT pin in this case the power source is on and thepower provided by the source is used to recharge the batteryIn the user mode the power source is off and the system loadconnected to the VCC pin is powered through the battery Inthe user mode the DC voltage on the VCC pin is controlledby the ADJ pin in this work the pin ADJ is floating whichcorresponds to a voltage of 41 V on the VCC pin

The LTC4071 implements also a battery protection fromboth overcharge and overdischarge In particular to protectthe battery the voltage on the BAT pin (119881BAT) is monitoredand the power flow from the battery to the system load isinterruptedwhen119881BAT is lower than a threshold voltage119881LBDIn turn 119881LBD is set through an appropriate connection of thepin LBSEL More specifically connecting the LBSEL pin toground corresponds to set 119881LDB at 32 V while connectingthe LBSEL pin to VCC corresponds to set 119881LDB at 27 V Asfor the protection from overcharge when a source is presentthe battery charges until the battery voltage rises above thelow battery connect voltage (119881LBC) Also 119881LBC depends onthe state of the LBSEL pin but its value varies with respectto other parameters such as charge current (for more detailsrefer to [30]) In this work the LBSEL pin was connected toground

As for the battery a THINERGY MEC201 by InfinitePower Solutions (IPS) having a battery capacity of 07mAhwas chosen In the following section the experimental resultsfor the charging time are presented and discussed

4 Wireless Charger for Thin-Film BatteriesExperimental Results

The performance of the proposed battery charger consistingof the WREL illustrated in Figure 6 connected to the PMUof Figure 10 was experimentally investigated In more detailexperimental tests were performed in order to evaluate boththe total efficiency of the wireless charger (120578TOT) and thetime necessary to recharge the THINERGY MEC201 battery(119905CHG)

As for the total efficiency 120578TOT we refer to the followingdefinition

120578TOT =119875DC-OUT119875RF-IN

=

119881BAT sdot 119868CHG119875RF-IN

(4)

where 119881BAT and 119868CHG are the charge voltage and the chargecurrent respectively

Referring to Figure 1 experimental tests were performedthrough the VSG RampS FSW26 to generate the RF inputpower (119875RF-IN) The input port of the WREL configuredas illustrated in Figure 6(b) was connected to the VSG bymeans of a flexible coaxial cable while the output port wasconnected to the PMU by means of a 50Ω SMA connectorAs input RF signal a 434MHz sinusoidal signal was used

Figures 14(a) and 14(b) show the results for 120578TOT and119905CHG respectively From Figure 14(a) it can be seen that theproposed wireless charger exhibits a maximum 120578TOT of about297 for an RF input power of 75 dBm

As for the charging time experimental tests demon-strated that values of119875RF-IN higher than 15 dBm are necessaryto recharge the THINERGYMEC201 battery

Figure 14(b) shows results obtained for the charging time(ie 119905CHG) of the low capacity thin-film battery THINERGYMEC201 as a function of the power delivered to the primaryresonator It can be seen that for 119875RF-IN higher than 6 dBmthe time necessary to recharge the THINERGY MEC201battery is shorter than 50 minutes


0 1 2 3 4 5 6 7 8 9 10 11 125

10

15

20

25

30120578

TOT

()

PRF-IN (dBm)

(a)

0 1 2 3 4 5 6 7 8 9 10 11 120

100

200

300

400

500

600

t CH

G(m

in)

PRF-IN (dBm)

(b)

Figure 14 Experimental results obtained for the proposed wireless battery charger (a) total efficiency as function of the input power (119875RF-IN)at the primary resonator (see Figure 1) (b) charging time necessary to recharge the battery THINERGYMEC201 as function of input power(119875RF-IN) at the primary resonator (see Figure 1)

5 Conclusion

In this work a wireless charger for low capacity thin-filmbatteries was presented The proposed device exploits anonradiative wireless resonant energy link for power trans-mission A prototype operating in the ISM band centered at434MHz was presented and discussed The power link wasfabricated by using an adhesive conductive nonwoven fabricon a leather substrate thus resulting in a device suitable to beembedded in wearable accessories (such as handbags) Fromexperimental data it was demonstrated that the fabricatedpower link exhibits a maximum of the RF-to-RF powertransfer efficiency of about 693

As for the battery charger a total efficiency of approxi-mately 297 was demonstrated

It was also shown that by providing an input powerhigher than 6 dBm a time charging shorter than 50 minutesis required for recharging a thin-film battery THINERGYMEC201

Overall the obtained results demonstrate the feasibilityof using the proposed wearable WPT link for implementinga wireless charger

Competing Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] MA ROsmanMKA RahimNA Samsuri HAM Salimand M F Ali ldquoEmbroidered fully textile wearable antenna formedical monitoring applicationsrdquo Progress in ElectromagneticsResearch vol 117 pp 321ndash337 2011

[2] Y Li R Vyas A Rida J Pan and M M Tentzeris ldquoWearableRFID-enabled sensor nodes for biomedical applicationsrdquo inProceedings of the 58th Electronic Components and Technology

Conference (ECTC rsquo08) pp 2156ndash2159 IEEE Lake Buena VistaFla USA May 2008

[3] C Hertleer H Rogier and L Van Langenhove ldquoA textileantenna for protective clothingrdquo in Proceedings of the IETSeminar on Antennas and Propagation for Body-CentricWirelessCommunications pp 44ndash46 April 2007

[4] L Vallozzi P Van Torre C Hertleer H Rogier MMoeneclaeyand J Verhaevert ldquoWireless communication for firefightersusing dual-polarized textile antennas integrated in their gar-mentrdquo IEEE Transactions on Antennas and Propagation vol 58no 4 pp 1357ndash1368 2010

[5] Z Chun-Qing W Jun-Hong and H Yu-Nan ldquoCoupled pla-nar dipole UWB antenna design for wearable computerrdquo inProceedings of the International Conference on Microwave andMillimeter Wave Technology (ICMMT rsquo07) pp 1ndash4 April 2007

[6] W Thompson R Cepeda G Hilton M A Beach and SArmour ldquoAn improved antenna mounting for ultra-widebandon-body communications and channel characterizationrdquo IEEETransactions on Microwave Theory and Techniques vol 59 no4 pp 1102ndash1108 2011

[7] B Sanz-Izquierdo J A Miller J C Batchelor and M ISobhy ldquoDual-band wearable metallic button antennas andtransmission in body area networksrdquo IETMicrowaves Antennasand Propagation vol 4 no 2 pp 182ndash190 2010

[8] H Marques and B V Borges ldquoContactless battery chargerwith high relative separation distance and improved efficiencyrdquoin Proceedings of the 33rd International TelecommunicationsEnergy Conference (INTELEC rsquo11) pp 1ndash8 Amsterdam TheNetherlands October 2011

[9] K-C Wan Q Xue X Liu and S Y Hui ldquoPassive radio-frequency repeater for enhancing signal reception and trans-mission in a wireless charging platformrdquo IEEE Transactions onIndustrial Electronics vol 61 no 4 pp 1750ndash1757 2014

[10] A N Laskovski M R Yuce and T Dissanayake ldquoStackedspirals for biosensor telemetryrdquo IEEE Sensors Journal vol 11 no6 pp 1484ndash1490 2011

[11] K Jung Y-HKim E J ChoiH J Kim andY-J Kim ldquoWirelesspower transmission for implantable devices using inductive


component of closed magnetic circuitrdquo Electronics Letters vol45 no 1 pp 21ndash22 2009

[12] G Monti L Tarricone M Dionigi and M Mongiardo ldquoMag-netically coupled resonant wireless power transmission anartificial transmission line approachrdquo in Proceedings of the 42ndEuropeanMicrowaveConference (EuMC rsquo12) pp 233ndash236 IEEEAmsterdam The Netherlands October-November 2012

[13] A Costanzo M Dionigi D Masotti et al ldquoElectromagneticenergy harvesting and wireless power transmission a unifiedapproachrdquo Proceedings of the IEEE vol 102 no 11 pp 1692ndash17112014

[14] S Riviere A Douyere F Alicalapa and J D Lan Sun LukldquoStudy of complete WPT system for WSN applications at lowpower levelrdquo Electronics Letters vol 46 no 8 pp 597ndash598 2010

[15] GMonti L Corchia and L Tarricone ldquoUHFwearable rectennaon textile materialsrdquo IEEE Transactions on Antennas and Prop-agation vol 61 no 7 pp 3869ndash3873 2013

[16] D Masotti A Costanzo and S Adami ldquoDesign and realizationof a wearable multi-frequency RF energy harvesting systemrdquoin Proceedings of the 5th European Conference on Antennas andPropagation pp 517ndash520 April 2011

[17] G Monti L Corchia and L Tarricone ldquoTextile logo antennasrdquoin Proceedings of the 14th Mediterranean Microwave Symposium(MMS rsquo14) pp 1ndash5 Marrakech Morocco December 2014

[18] G Monti and F Congedo ldquoUHF rectenna using a bowtieantennardquo Progress in Electromagnetics Research C vol 26 pp181ndash192 2012

[19] G Monti L Corchia and L Tarricone ldquoA microstrip antennawith a reconfigurable pattern for RFID applicationsrdquo Progress InElectromagnetics Research B no 45 pp 101ndash116 2012

[20] G Monti L Corchia and L Tarricone ldquoPlanar bowtie antennawith a reconfigurable radiation patternrdquo Progress in Electromag-netics Research C vol 28 pp 61ndash70 2012

[21] F Congedo G Monti L Tarricone and M Cannarile ldquoBroad-band bowtie antenna for RF energy scavenging applicationsrdquoin Proceedings of the 5th European Conference on Antennas andPropagation (EUCAP rsquo11) pp 335ndash337 Rome Italy April 2011

[22] G Monti L Corchia and L Tarricone ldquoA wearable wirelessenergy linkrdquo in Proceedings of the 45th European MicrowaveConference (EuMC rsquo15) pp 143ndash146 Paris France September2015

[23] M Dionigi A Costanzo and M Mongiardo ldquoNetworkmethods for analysis and design of resonant wireless powertransfer systemsrdquo in Wireless Power TransfermdashPrinciples andEngineering Explorations K Y Kim Ed InTech 2012 httpwwwintechopencombookswireless-power-transfer-princi-ples-and-engineering-explorationsnetworks-methods-for-the-analysis-and-design-of-wireless-power-transfer-systems

[24] ADFORS Saint-Gobain httpwwwsg-adforscomTechnol-ogiesFabricsGlassmat

[25] G Monti L Corchia and L Tarricone ldquoFabrication techniquesfor wearable antennasrdquo in Proceedings of the European RadarConference (EuRAD rsquo13) Nuremberg Germany October 2013

[26] GMonti L Corchia and L Tarricone ldquoLogo antenna on textilematerialsrdquo inProceedings of the EuropeanMicrowave Conference(EuMC rsquo14) pp 516ndash519 Rome Italy October 2014

[27] httpwwwawrcorpcomproducts[28] ldquoHSMS-282x Surface Mount RF Schottky Barrier Diodesrdquo

httpwwwavagotechcomdocsAV02-1320EN[29] httpwwwticomgeneraldocslitgetliteraturetspgeneric-

PartNumber=lm2767ampfileType=pdf[30] httpwwwlinearcomproductLTC4071

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014


Active and Passive Electronic Components

Control Scienceand Engineering

Journal of



RotatingMachinery


Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design



Shock and Vibration


Civil EngineeringAdvances in

Acoustics and VibrationAdvances in



Electrical and Computer Engineering

Journal of

Advances inOptoElectronics


Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of


Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014


Chemical EngineeringInternational Journal of Antennas and

Propagation




Navigation and Observation



DistributedSensor Networks



Primary resonator

Secondary resonator

Power management unit

MEC201Source

S

Cprimary

Lprimary

CSecondary

LSecondary

PRE-IN PRF-OUT PDC-OUT

(a)

Secondary resonator

Primaryresonator

(b)

Figure 1 Proposed wireless charger (a) Schematic representation the link consists of a wireless resonant energy link and of a powermanagement unit (b) Example of application the secondary resonator is embedded into a leather bag while the primary resonator is ona pad where the bag should be placed on for charging the battery

energy link (WREL) proposed in this work was exploitedfor implementing a wireless charger [8 9] for low capacitythin-film batteries The proposed system consists of (1) twoplanar resonators that were optimized and fabricated to beembedded in portable leather accessories and (2) a powermanagement unit (PMU)

Figure 1(a) shows a schematic representation of theproposed WPT link which exploits a magnetic couplingbetween two planar resonators namely a primary resonatorand a secondary resonator The former is embedded intoa pad and is connected to an external power source thatprovides it with an AC input power whereas the latter isconnected to the rechargeable battery by means of the PMUFigure 1(b) shows a sketch of a possible practical applicationthe secondary resonator is embedded into a bag while theprimary resonator is embedded into a pad where the bagshould be placed on for charging battery

As will be detailed in the following section for theresonators fabrication a self-adhesive nonwoven fabric wasused for the conductive parts while a layer of leatherwas usedas support

Numerical and experimental results referring to a pro-totype working in the ISM band (43305ndash43479MHz) arereported and discussed

The paper is structured as follows Numerical and exper-imental data obtained for the proposed WPT link are illus-trated in Section 2 Section 3 describes each single block of thePMU Experimental results related to the proposed wirelesscharging system as a whole are reported in Section 4 Finallyconclusions are drawn in Section 5

2 Wearable Resonators Geometry and Results

21 Resonators Geometry and Numerical Results The pro-posed WPT link is comprised of two identical resonatorseach one consisting of a distributed inductance loaded bya lumped capacitor [22] Figure 2(a) shows a sketch of aperspective view of the configuration adopted for the WPTlink while Figure 2(b) illustrates the resonator geometry

From Figure 2(a) it can be noticed that each resonatorconsists of an elliptical loop loaded by a smaller oneThe two

Port 2 Port 1

(a)

h

d

x

y

z

Lsub

W

Hsu

b

C2

C1

R1

r2

R2

r1

(b)

Figure 2 Geometry of the proposed wireless energy link (a)perspective view (b) front view It can be seen that the secondaryresonator is overlapped to the primary resonator

resonators are rotated by 180∘ with respect to each other (onthe 119909-119910 plane) and they are also alignedwith the center of theexternal elliptical loop Additionally to tune the resonancefrequency two lumped capacitors 119862

1and 119862

2 are also used

The geometry of the resonators was optimized by meansof full-wave simulations to obtain (1) an operating frequencyin the ISM band (43305ndash43479MHz) and (2) an inputimpedance of 50Ω In the following the main steps of thedesign process are briefly described

The starting geometry was a simple elliptical loop with amajor axis of 36mm a width of 2mm and an eccentricityclose to zero thus corresponding to a nearly circular geom-etry These initial values were chosen in order to obtain acompact structure suitable to be fabricated with the facilities


200 300 400 500 600 700 800

0

minus5

minus10

minus15

minus20


Scat

terin

g pa

ram

eter

(dB)

f0

fm fe



f (MHz)










119891119898=

1198910

(radic1 + 119896)

119891119890=

1198910


(1)






119890) and




119867sub 119871 sub 119882 1198771

1199031

1198772

1199032

ℎ 119889

547 476 24 152 95 113 37 119 39









1and 119862

2) are 68 pF





119903) of 3 was



1and 119862

2 surface




100 200 300 400 500 600 700 800f (MHz)

0

minus10

minus20

minus30

minus40

Scat

terin

g pa

ram

eter

(dB)

|S11| (e = 0)

|S21| (e = 0)

|S11| (e = 075)

|S21| (e = 075)

|S11| (e = 087)

|S21| (e = 087)

(a)

100 200 300 400 500 600 700 800

0

minus10

minus20

minus30

minus40

minus50

minus60

Scat

terin

g pa

ram

eter

(dB)

f (MHz)

|S11| (W = 2mm)|S21| (W = 2mm)|S11| (W = 3mm)

|S21| (W = 3mm)|S11| (W = 4mm)|S21| (W = 4mm)

(b)


100 200 300 400 500 600 700 800f (MHz)

0

minus5

minus10

minus15

minus20

minus25

minus30

minus35

minus40

Refle

ctio

n sc

atte

ring

para

met

er (d

B)



(a)

100 200 300 400 500 600 700 800f (MHz)

00

minus05

minus10

minus15

minus20

minus25

minus30minus10

minus20

minus30

minus40Tran

smiss

ion

scat

terin

g pa

ram

eter

(dB)


(b)


(a) (b)



100 200 300 400 500 600 700 800

0

minus5

minus10

minus15

minus20

minus25

minus30

minus35

minus40

Scat

terin

g pa

ram

eter

(dB)

f (MHz)

|S11|

|S12||S21||S22|


100 200 300 400 500 600 700 8000

10

20

30

40

50

60

70

80

f (MHz)

120578RF

-RF

()




120578RF-RF =119875RF-OUT119875RF-IN=

119875RF-IN sdot100381610038161003816100381611987821

1003816100381610038161003816

2

119875RF-IN=100381610038161003816100381611987821

1003816100381610038161003816

2

(2)








3and 119862

4of the




=

(1198812

Rect-OUT119885LOAD)

119875RF-OUT (3)



GNDLM2767

NTC

LBSEL

ADJ BAT

GND

LTC4071

VCC

MEC201

Rectifier


V+

CAP+CAPminus

C5

RIN

ICHG

VBA

T

VOUT

D3

C6

C7C8

PRF-OUT

VBo

ost-O

UT

VRe

ct-O

UT

To system load VCC




L

C3

C4D2

D1

CVAR2CVAR1

PRF-OUT

VRect-OUT

PRect-OUT

ZLO

AD




10 100 1k 10k 100 k 1MR (Ω)


50dBm75dBm100 dBm

05

10152025303540455055

PRF-OUT values

120578RF

-DC

()





5 1198626 and 119862

7 The aim of




1

2

3

4

5

6

7

8

9

10

LM2767


PRF-OUT (dBm)

0

VRe

ct-O

UT

(V)













120578TOT =119875DC-OUT119875RF-IN

=


(4)







0 1 2 3 4 5 6 7 8 9 10 11 125

10

15

20

25

30120578

TOT

()

PRF-IN (dBm)

(a)

0 1 2 3 4 5 6 7 8 9 10 11 120

100

200

300

400

500

600

t CH

G(m

in)

PRF-IN (dBm)

(b)


5 Conclusion





Competing Interests


References



































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










200 300 400 500 600 700 800

0

minus5

minus10

minus15

minus20


Scat

terin

g pa

ram

eter

(dB)

f0

fm fe



f (MHz)










119891119898=

1198910

(radic1 + 119896)

119891119890=

1198910


(1)






119890) and




119867sub 119871 sub 119882 1198771

1199031

1198772

1199032

ℎ 119889

547 476 24 152 95 113 37 119 39









1and 119862

2) are 68 pF





119903) of 3 was



1and 119862

2 surface




100 200 300 400 500 600 700 800f (MHz)

0

minus10

minus20

minus30

minus40

Scat

terin

g pa

ram

eter

(dB)

|S11| (e = 0)

|S21| (e = 0)

|S11| (e = 075)

|S21| (e = 075)

|S11| (e = 087)

|S21| (e = 087)

(a)

100 200 300 400 500 600 700 800

0

minus10

minus20

minus30

minus40

minus50

minus60

Scat

terin

g pa

ram

eter

(dB)

f (MHz)

|S11| (W = 2mm)|S21| (W = 2mm)|S11| (W = 3mm)

|S21| (W = 3mm)|S11| (W = 4mm)|S21| (W = 4mm)

(b)


100 200 300 400 500 600 700 800f (MHz)

0

minus5

minus10

minus15

minus20

minus25

minus30

minus35

minus40

Refle

ctio

n sc

atte

ring

para

met

er (d

B)



(a)

100 200 300 400 500 600 700 800f (MHz)

00

minus05

minus10

minus15

minus20

minus25

minus30minus10

minus20

minus30

minus40Tran

smiss

ion

scat

terin

g pa

ram

eter

(dB)


(b)


(a) (b)



100 200 300 400 500 600 700 800

0

minus5

minus10

minus15

minus20

minus25

minus30

minus35

minus40

Scat

terin

g pa

ram

eter

(dB)

f (MHz)

|S11|

|S12||S21||S22|


100 200 300 400 500 600 700 8000

10

20

30

40

50

60

70

80

f (MHz)

120578RF

-RF

()




120578RF-RF =119875RF-OUT119875RF-IN=

119875RF-IN sdot100381610038161003816100381611987821

1003816100381610038161003816

2

119875RF-IN=100381610038161003816100381611987821

1003816100381610038161003816

2

(2)








3and 119862

4of the




=

(1198812

Rect-OUT119885LOAD)

119875RF-OUT (3)



GNDLM2767

NTC

LBSEL

ADJ BAT

GND

LTC4071

VCC

MEC201

Rectifier


V+

CAP+CAPminus

C5

RIN

ICHG

VBA

T

VOUT

D3

C6

C7C8

PRF-OUT

VBo

ost-O

UT

VRe

ct-O

UT

To system load VCC




L

C3

C4D2

D1

CVAR2CVAR1

PRF-OUT

VRect-OUT

PRect-OUT

ZLO

AD




10 100 1k 10k 100 k 1MR (Ω)


50dBm75dBm100 dBm

05

10152025303540455055

PRF-OUT values

120578RF

-DC

()





5 1198626 and 119862

7 The aim of




1

2

3

4

5

6

7

8

9

10

LM2767


PRF-OUT (dBm)

0

VRe

ct-O

UT

(V)













120578TOT =119875DC-OUT119875RF-IN

=


(4)







0 1 2 3 4 5 6 7 8 9 10 11 125

10

15

20

25

30120578

TOT

()

PRF-IN (dBm)

(a)

0 1 2 3 4 5 6 7 8 9 10 11 120

100

200

300

400

500

600

t CH

G(m

in)

PRF-IN (dBm)

(b)


5 Conclusion





Competing Interests


References



































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










100 200 300 400 500 600 700 800f (MHz)

0

minus10

minus20

minus30

minus40

Scat

terin

g pa

ram

eter

(dB)

|S11| (e = 0)

|S21| (e = 0)

|S11| (e = 075)

|S21| (e = 075)

|S11| (e = 087)

|S21| (e = 087)

(a)

100 200 300 400 500 600 700 800

0

minus10

minus20

minus30

minus40

minus50

minus60

Scat

terin

g pa

ram

eter

(dB)

f (MHz)

|S11| (W = 2mm)|S21| (W = 2mm)|S11| (W = 3mm)

|S21| (W = 3mm)|S11| (W = 4mm)|S21| (W = 4mm)

(b)


100 200 300 400 500 600 700 800f (MHz)

0

minus5

minus10

minus15

minus20

minus25

minus30

minus35

minus40

Refle

ctio

n sc

atte

ring

para

met

er (d

B)



(a)

100 200 300 400 500 600 700 800f (MHz)

00

minus05

minus10

minus15

minus20

minus25

minus30minus10

minus20

minus30

minus40Tran

smiss

ion

scat

terin

g pa

ram

eter

(dB)


(b)


(a) (b)



100 200 300 400 500 600 700 800

0

minus5

minus10

minus15

minus20

minus25

minus30

minus35

minus40

Scat

terin

g pa

ram

eter

(dB)

f (MHz)

|S11|

|S12||S21||S22|


100 200 300 400 500 600 700 8000

10

20

30

40

50

60

70

80

f (MHz)

120578RF

-RF

()




120578RF-RF =119875RF-OUT119875RF-IN=

119875RF-IN sdot100381610038161003816100381611987821

1003816100381610038161003816

2

119875RF-IN=100381610038161003816100381611987821

1003816100381610038161003816

2

(2)








3and 119862

4of the




=

(1198812

Rect-OUT119885LOAD)

119875RF-OUT (3)



GNDLM2767

NTC

LBSEL

ADJ BAT

GND

LTC4071

VCC

MEC201

Rectifier


V+

CAP+CAPminus

C5

RIN

ICHG

VBA

T

VOUT

D3

C6

C7C8

PRF-OUT

VBo

ost-O

UT

VRe

ct-O

UT

To system load VCC




L

C3

C4D2

D1

CVAR2CVAR1

PRF-OUT

VRect-OUT

PRect-OUT

ZLO

AD




10 100 1k 10k 100 k 1MR (Ω)


50dBm75dBm100 dBm

05

10152025303540455055

PRF-OUT values

120578RF

-DC

()





5 1198626 and 119862

7 The aim of




1

2

3

4

5

6

7

8

9

10

LM2767


PRF-OUT (dBm)

0

VRe

ct-O

UT

(V)













120578TOT =119875DC-OUT119875RF-IN

=


(4)







0 1 2 3 4 5 6 7 8 9 10 11 125

10

15

20

25

30120578

TOT

()

PRF-IN (dBm)

(a)

0 1 2 3 4 5 6 7 8 9 10 11 120

100

200

300

400

500

600

t CH

G(m

in)

PRF-IN (dBm)

(b)


5 Conclusion





Competing Interests


References



































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










100 200 300 400 500 600 700 800

0

minus5

minus10

minus15

minus20

minus25

minus30

minus35

minus40

Scat

terin

g pa

ram

eter

(dB)

f (MHz)

|S11|

|S12||S21||S22|


100 200 300 400 500 600 700 8000

10

20

30

40

50

60

70

80

f (MHz)

120578RF

-RF

()




120578RF-RF =119875RF-OUT119875RF-IN=

119875RF-IN sdot100381610038161003816100381611987821

1003816100381610038161003816

2

119875RF-IN=100381610038161003816100381611987821

1003816100381610038161003816

2

(2)








3and 119862

4of the




=

(1198812

Rect-OUT119885LOAD)

119875RF-OUT (3)



GNDLM2767

NTC

LBSEL

ADJ BAT

GND

LTC4071

VCC

MEC201

Rectifier


V+

CAP+CAPminus

C5

RIN

ICHG

VBA

T

VOUT

D3

C6

C7C8

PRF-OUT

VBo

ost-O

UT

VRe

ct-O

UT

To system load VCC




L

C3

C4D2

D1

CVAR2CVAR1

PRF-OUT

VRect-OUT

PRect-OUT

ZLO

AD




10 100 1k 10k 100 k 1MR (Ω)


50dBm75dBm100 dBm

05

10152025303540455055

PRF-OUT values

120578RF

-DC

()





5 1198626 and 119862

7 The aim of




1

2

3

4

5

6

7

8

9

10

LM2767


PRF-OUT (dBm)

0

VRe

ct-O

UT

(V)













120578TOT =119875DC-OUT119875RF-IN

=


(4)







0 1 2 3 4 5 6 7 8 9 10 11 125

10

15

20

25

30120578

TOT

()

PRF-IN (dBm)

(a)

0 1 2 3 4 5 6 7 8 9 10 11 120

100

200

300

400

500

600

t CH

G(m

in)

PRF-IN (dBm)

(b)


5 Conclusion





Competing Interests


References



































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










GNDLM2767

NTC

LBSEL

ADJ BAT

GND

LTC4071

VCC

MEC201

Rectifier


V+

CAP+CAPminus

C5

RIN

ICHG

VBA

T

VOUT

D3

C6

C7C8

PRF-OUT

VBo

ost-O

UT

VRe

ct-O

UT

To system load VCC




L

C3

C4D2

D1

CVAR2CVAR1

PRF-OUT

VRect-OUT

PRect-OUT

ZLO

AD




10 100 1k 10k 100 k 1MR (Ω)


50dBm75dBm100 dBm

05

10152025303540455055

PRF-OUT values

120578RF

-DC

()





5 1198626 and 119862

7 The aim of




1

2

3

4

5

6

7

8

9

10

LM2767


PRF-OUT (dBm)

0

VRe

ct-O

UT

(V)













120578TOT =119875DC-OUT119875RF-IN

=


(4)







0 1 2 3 4 5 6 7 8 9 10 11 125

10

15

20

25

30120578

TOT

()

PRF-IN (dBm)

(a)

0 1 2 3 4 5 6 7 8 9 10 11 120

100

200

300

400

500

600

t CH

G(m

in)

PRF-IN (dBm)

(b)


5 Conclusion





Competing Interests


References



































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










1

2

3

4

5

6

7

8

9

10

LM2767


PRF-OUT (dBm)

0

VRe

ct-O

UT

(V)













120578TOT =119875DC-OUT119875RF-IN

=


(4)







0 1 2 3 4 5 6 7 8 9 10 11 125

10

15

20

25

30120578

TOT

()

PRF-IN (dBm)

(a)

0 1 2 3 4 5 6 7 8 9 10 11 120

100

200

300

400

500

600

t CH

G(m

in)

PRF-IN (dBm)

(b)


5 Conclusion





Competing Interests


References



































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










0 1 2 3 4 5 6 7 8 9 10 11 125

10

15

20

25

30120578

TOT

()

PRF-IN (dBm)

(a)

0 1 2 3 4 5 6 7 8 9 10 11 120

100

200

300

400

500

600

t CH

G(m

in)

PRF-IN (dBm)

(b)


5 Conclusion





Competing Interests


References



































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation









research article a wearable wireless energy link for thin-film...

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