6º CONGRESSO DO COMITÉ PORTUGUÊS DA URSI 1

SUMMARY — This paper presents a novel eco-friendly

battery-less remote control system based on wireless power

transmission and passive UHF RFID. The proposed remote

controller is a fully passive device that does not require the use of

batteries or other installed power source. The controlled device

(e.g. a TV, a game console or a garage door) incorporates a reader

system that remotely powers up the remote controller device and

communicates with it using UHF radio waves. The battery-less

remote controller incorporates a plurality of N passive RFID

chips/tags, N keys/switches and a novel N-port microstrip

network specially conceived to interconnect the various RFID

chips. Each remote controller’s key is associated with a RFID

with an Unique IDentifier (UID), which allows the device to be

controlled to identify the key pressed by the user. The microstrip

network combined with the switches ensures proper

interconnection between the chips and allow them to share the

same antenna in such way that only the chip associated with the

pressed key is read.

First of all, a brief description of the system is presented and

an analytical model of the novel N-port microstrip network is

provided. The proper arrangement of the network along with the

tags and the switches is also proposed. Several controller units

with 3, 4 and 5 keys are simulated, prototyped and measured.

Finally, the complete battery-free system is implemented,

including the controller and the device to be controlled. A

functional demonstration prototype is successfully tested and

validated. The remote control system is integrated in a TV and

some basic control functionalities (CH +, CH -, Vol + and Vol -)

are implemented as a proof of concept.

Index Terms—Remote Control Systems, Battery-less Systems,

Wireless Power Transmission, Passive UHF RFID, Low-Cost,

Efficient, Eco-friendly.

I. INTRODUCTION

EMOTE CONTROL systems are used to wirelessly

control a variety of devices such as TV’s, doors, game

consoles and air-conditioning equipment. Conventionally,

remote control systems are based on infrared (IR) technology

and the controller unit requires batteries as power source. Such

IR battery-powered systems present two major drawbacks.

First of all, optical communication using IR signals requires

line-of-sight, otherwise the communication fails. More

important, the remote controller uses disposable chemical

batteries which leads to several problems: first, there is a cost

related to battery maintenance. Second, the limited lifetime of

batteries is a constant source of frustration. More important,

disposable batteries at the end of lifetime generate huge

amounts of toxic waste that release heavy metals. Beyond

monetary cost, there is thus a tremendous environmental price

to pay. Fig. 1 might not look nice, but it is what actually

happens with disposable batteries. They take hundreds of years

to decompose in the nature and if not properly treated they can

present a serious threat to the public health and to the

environment.

As an illustrative example, consider the case of Portugal.

According to the last population census of the National

Institute of Statistics [1], there existed 4 Million habitual

residences in Portugal in 2011. Assuming that 75% of those

residences have a TV equipment, 40% have a cable TV Box

and 30% have a Hi-Fi equipment, we end up with an average

of 5.8 Million remote control devices. Considering two

batteries per remote and a battery replacement each six

months, we have a total of 23.2 Million batteries being wasted

every year. It should be noticed that this figure is very

conservative since it only takes into account the traditional

entertainment equipments. This figure drastically increases if

we consider other equipments such as air-conditioning

equipment, game consoles and battery-powered toys, garage

doors, wireless keyboards. I happens that if not properly

treated this huge amount of waste generates toxic residues that

can seriously put in risk the public health and the environment.

In this sense efficient and eco-friendly solutions must be

found.

In order to overcome the communication problems of IR

technology (short range and need for line of sight), recently,

manufactures started to adopt radio-frequency remote control

systems instead of the traditional IR-based technology [2][3].

Nowadays, a significant number of high-end TV and audio

equipments are equipped with RF remote controls. While in

the past the IR technology was preferred and became

widespread thanks to its cost effectiveness and low complexity

implementation compared with past RF solutions, nowadays as

A Novel Battery-less Remote Control System

based on Low Cost Passive RFID Technology

Alírio Jesus Soares Boaventura and Nuno Borges Carvalho

Instituto de Telecomunicações, Departamento de Electrónica, Telecomunicações e Informática,

Universidade de Aveiro, 3810-193 Aveiro, Portugal.

R

6º CONGRESSO DO COMITÉ PORTUGUÊS DA URSI 2

the RF/microwave industry has grown and reached massive

production, the price per unit has been considerably reduced.

Thus, the trend for the next years is the replacement of IR

technology by radio even in low-end equipments.

Nevertheless, both in the conventional IR technology and

in the current radio-frequency approach, there is a need for

disposable batteries, that as mentioned before lead to several

problems. In this work we propose in this work is inspired and

based on a very peculiar class of radio technology, passive

RFID. In such technology the mobile devices that carry

information (RFID tags) have no self-battery to power up their

electronics. Instead, all the energy needed is wirelessly

delivered by a fixed RFID reader [4][5]. In order to provide a

cost-effective solution, a commercially available low cost

passive technology is selected for this work (UHF Global EPC

Gen2 Class1 [6]).

The battery-less remote controller proposed in this work

incorporates an antenna, a plurality of N passive RFID

chips/tags, N keys/switches and a novel N-port microstrip

network specially conceived to interconnect the various chips

(details are found in the next section). Each remote controller’s

key is associated with an RFID chip and an Unique IDentifier

(UID) which allows the device to be controlled to identify the

key pressed by the user. The proposed implementation

requires the use of multiple RFID chips/tags wherein only one

is active each time. Nevertheless, RFID tags were originally

thought to operate separately and independently and their

application is typically limited to the unique identification of

people, animals and objects. Furthermore, due to energy and

computational limitations, passive RFID tags have no external

control or sensing capabilities neither have exposed digital

input/output terminals – commercially available passive RFID

chips only have two external RF terminals for antenna

connection. For these reasons the proposed implementation

imposes two challenging requirements: controllability and

interconnection/routing. First of all, it is necessary to add

control to the individual chips in order to allow the user to

activate and deactivate them. Second and most important, it is

necessary to guarantee proper interconnection between the

various tags so that they can share the same antenna. This must

be done in such manner that only the active chip is routed to

the antenna without being interfered by inactive chips. In [7]

and [8] some external control capabilities have been added to

an RFID chip. However, in both cases only a single chip

scenario is considered and the proposed solutions are not

suitable for multi-tag environment. In [7] an external

functionality is added to a single RFID tag to allow the user to

activate/deactivate the tag by opening/closing a switch. When

closed the switch simply short-circuits the tag antenna

terminals which prevents the tag to respond to the reader

commands. In [8] beyond activation/deactivation, an extra

functionality is added to control the communication distance.

This is done by introducing an attenuation through the use a

resistor in series with a switch. Again, no strategy for multi-tag

operation is covered.

In this work we disclose an UHF multi-tag remote control

scheme and we propose both control and interconnection

strategies. We also propose the ways to integrate the remote

control receiver in the device to be controlled (e.g. a TV).

Finally, we present a strategy and system to guarantee

compatibility with already installed equipments that use IR. In

order to protect the invention presented in this work, a patent

application has already been filled by University of Aveiro [9].

Fig. 1 Disposable batteries at the end of lifetime

II. PROPOSED SYSTEM

In this work, a completely passive remote control system is

proposed and designed wherein the remote controller (RC)

requires no battery to operate and it is based on a passive

RFID technology. The device to be controlled (DC), e.g. a TV,

a game device, a garage door or other, wirelessly energizes the

battery-less RC using radio waves. For this purpose, the DC

incorporates internally or externally an RFID reader that

remotely energizes the RC. Also, the reader accesses the

memory of the passive RFID tags in order to identify the key

pressed by the user. Compared with conventional infrared (IR)

remote control systems, this system presents several

advantages namely the use of an efficient, clean, and eco-

friendly form of energy transference using radio waves; no

need for batteries; elimination of costs related to battery

maintenance and treatment of toxic waste; long range and no

line of sight communication thanks to the use of radio waves;

and very low cost solution thanks to the use of a very mature

passive RFID technology (the UHF EPC technology [6]).

The system is composed by the RC (Fig. 2a) that is made

up with passive UHF RFID chips/tags and the DC (Fig. 2b or

Fig. 2c). To access the information on the memory of the tags,

an RFID reader is internally (as in Fig. 2b) or externally (as in

Fig. 2c) mounted on the DC. Additionally, in order to

guarantee compliance with already installed equipment (e.g.

old TV’s) an RFID-IR adapter can be used as in Fig. 2c. The

controller is composed by N passive RFID tags associated with

N keys/switches. A novel N-port microstrip network (Fig. 3),

specially designed for this purpose, guarantees that: by default

all the tags are inactive (silent); once a key is pressed by the

user the respective tag goes to active mode and is read by the

RFID reader to identify the pressed key; and the inactive tags

do not interfere with the active one. The RC communicates

6º CONGRESSO DO COMITÉ PORTUGUÊS DA URSI 3

with the reader and receives power to operate the tags through

an antenna via RF waves, precisely in the UHF band (860-

960MHz).

RFID 2 RFID 4 RFID 6 RFID N

… ...

N-Port Microstrip Network

Switch+ Resonant

CircuitCR 1

RFID 1

CR 3

RFID 3 RFID 5 RFID N-1

… ...

CR 5 CR N-1

CR NCR 6CR 4CR 2

(a)

Embedded RFID reader

RFID Front-End

RFID TX

RFID RX

Control Unit

of RFID and

Device to be

controlled

Device to be controlled

(e.g. TV, door)

(b)

RFID Reader

RFID TX

RFID RX

RFID

Control Unit

RFID-IR

Adapter

InfraRed

communication

No electrical connection

External RFID-InfraRed Interface

Device to be

controlled

(e.g. TV, door)

(c)

Fig. 2 Proposed battery-less remote control system: a) diagram of the multi-

tag passive RC, b) DC with embedded RFID reader and c) DC with external

RFID reader plus RFID-IR adaptor to guarantee compliance with already

installed IR equipments.

A. The Novel N-port Microstrip Network

A novel N-port microstrip network (Fig. 3) has been

proposed to interconnect the N RFID chips and the respective

N switch-controlled resonant circuits. This network combined

with the switch-controlled resonant circuits must guarantee

that only one RFID tag (the active one) is connected to the

antenna (port ZIN’). Moreover, all other inactive tags should

not interfere with the active one. This is, the port ZIN’ must see

at each moment only the active tag port Zi=n, while all other

ports must remain invisible. Accordingly, with respect to Fig.

3, the following requirements must be followed:

Only one impedance Zi=n, corresponding to the active port

n, should be routed to the input port (antenna port)

Active port (active RFID tag) is selected by the user

through a switch

All other ports remain invisible to the antenna port

All other ports do not interfere with port n

Insertion loss between antenna port and active port n is

ideally 0dB

Cross-talking between antenna port and all inactive ports

is ideally null

Cross-talking between active port and all other is ideally

null

Each impedance Zi attached to port i assumes two values:

Zi = 0 or Zi = ZTAG_MATCHED

By default the impedance of all ports is Zi = 0,

superimposed by a switch–controlled resonant circuit

resonating at the operating frequency

By acting on the switch n the user sets Zi=n =

ZTAG_MATCHED =Z0

The lossless model of the proposed N-port microstrip

network is shown in Fig. 3 and its analytical description is

presented next.

Z1

…

Z0

Z0

Z3 Z4

Z2

β2l2

β1l1

β1l1β1l1

β1l1

Z0

Z0

Z0

β3l3Z2

'

Z4'

Z3'

Z1' ZAZA

'

ZIN' ZIN

Z0

Fig. 3 Model of the N-port microstrip network. The port Zin corresponds to

the common antenna port and the ports Zi correspond to the N keys of the

remote control.

Considering the lossless model of a microstrip transmission

line, the input impedance seen when looking into each branch i

of the network is given by:

)tan(

)tan(

110

1100

'

ljZZ

ljZZZZ

i

ii

(1)

6º CONGRESSO DO COMITÉ PORTUGUÊS DA URSI 4

where i=1,2,…n…N, N is the total number of ports in the

network, corresponding to the total number of keys of the RC,

Zi is the load attached to each branch i, Z0 is the characteristic

impedance of the system, β1 is the phase propagation constant

and l1 is the physical length of the line. Similarly, the

impedance ZA’ can be obtained from ZA as follows:

)tan(

)tan(

220

2200

'

ljZZ

ljZZZZ

A

AA

(2)

If the central transmission line (β2l2) is forced to produce a

delay equal to a multiple of a half wavelength, by doing β2l2 =

k.180º, and assuming lossless transmission lines, then

0)tan( 22 lk and consequently:

AA ZZ '

(3)

The consequence of (3) is that if lossless lines are

considered then the central lines have no impact in the circuit.

However, from the structural point of view such lines are

important since they give a degree of freedom in the design of

the circuit layout. In practice, the lines are not completely

lossless but if a substrate with an acceptable loss is used the

previous approximation is valid. Considering (3) and the

parallel association of impedances the input impedance ZIN is

given by:

1

43214321

'

1

'

1

'

1

'

1'//'//'//'

ZZZZZZZZZ IN

(4)

Using (1), (3) and (4) the input impedance can be generalized

for a N-port network as:

1

1 1100

110

1

1)tan(

)tan(

'

1

N

i i

iN

i i

INljZZZ

ljZZ

ZZ

(5)

wherein the phase shift of each branch is set to be a quarter

wavelength plus a multiple of a half wavelength:

º180.º9011 kl ,

(6)

and each terminal impedance of each branch, Zi, can assume

two different impedance values corresponding to the cases

where the tag is activated or deactivated:

Zn=ZTAG_MATCHED=Z0 , if the key (n) is pressed

Zi =

01, by default, if no action is performed

(7)

The tag activation and deactivation methods will be

discussed with more details in the next subsection. Only one

tag is expected to be active each time, while the rest remain in

idle state. Consider a N-port network in which the port n

corresponds to the active tag, matched to the characteristic

impedance of the system (Zi=n=ZTAG_MATCHED=Z0). Consider

also that all other ports are terminated with a short circuit (Zi≠n

= 0, superimposed by a resonant circuit in parallel with the tag

as in Fig. 5). According to (5) and (6), the input impedance is

given by:

0

1

00

0

00

0

020

20

010

10

)º90tan(

)º90tan(...

)º90tan(

)º90tan(...

)º90tan(

)º90tan(

)º90tan(

)º90tan(

ZZ

jZZZ

jZZ

jZZZ

jZZ

jZZZ

jZZ

jZZZ

jZZ

Z

n

N

N

n

nIN

(8)

Using again the model of a lossless microstrip transmission

line terminated with the same impedance as the characteristic

one (Z0), the input impedance seen by the antenna (ZIN’) is

equal to the network input impedance (ZIN).

Previous results fulfill all the requirements presented in the

beginning of this subsection for the N-port microstrip network

and can be summarized as follows: if only one tag is activated

and matched to the characteristic impedance of the lines, while

all other tags are short-circuited to ground, presenting a null

impedance, then only the active tag matched impedance (equal

to Z0) is seen by the antenna and all other are invisible.

In order to better understand the dynamic routing

mechanism involved in the RC circuit, an illustrative example

is presented in Fig. 4. In this case a 5-key RC is considered

and the user has pressed the key number four, forcing the

normally-closed switch number four to be open. Consequently,

the impedance termination of branch four becomes equal to Z0

(corresponding to the impedance of the matched chip RFID4).

On the other hand, all other tags are in parallel with a short

circuit, imposed by a resonant circuit at the operating

frequency, so that the impedance seen by deactivated branches

is always zero. These null impedances are transformed into

open circuits by the 90º phase shift imposed by the quarter

wavelength lines. In this sense, the short-circuited tags are

deactivated and don´t interfere with the rest of the circuit as

can be seen in Fig. 4 (where the crosses represent infinite

impedances that do not have impact in a parallel impedance

association). Consider a different scenario, where, for instance,

1 Ideally this should be a null impedance, however in practice an

approximate short-circuit is used.

6º CONGRESSO DO COMITÉ PORTUGUÊS DA URSI 5

RFID1 or RFID2 is activated and RFID3, RFID4 and RFID5

are deactivated (by parallel short-circuits). In this case, the

infinite impedance (open circuit) appearing at the right

crossover node would be transposed to the left crossover node

by the central half wavelength line (180º phase shift). Again

the infinite impedance would have no effect on the parallel

association of impedances and would not interfere with the rest

of the circuit. This is in perfect agreement with previously

presented mathematical model and proves its validity.

Key 2 Key 4

Key 5

RFID 1

RFID 2

RFID 3

RFID 4

RFID 5

Z0, 180ºZ0

Z0

90º

Z0, 90º

Z0

90º

Z0

90º

Z0

90º

Key 1 Key 3

Fig. 4 Illustrative example of a 5-key RC in which chip RFID4 is active and

all other are inactive. Active chip is routed to the antenna port. The crosses

represent no connection, meaning that inactive chips do not interfere with the

active one.

B. Port termination and Tag activation/deactivation

In the previous mathematical formulation it has been shown

that it is possible to design a certain network that allows the

coexistence of multi-tags. This network guarantees that only

one tag accesses the antenna each time (according to the user

selection) without interference from the other tags. For this

purpose the termination of each port must allow dynamic

adjustment by the user and must obey the condition imposed

by (7): each port termination should present an impedance

equal to the characteristic impedance of the system if the

respective key is pressed by the user and should be zero

otherwise. Fig. 5 depicts a port termination configuration that

approximates the condition (7) and permits the user to activate

the desired RFID chip by acting on a switch. For this purpose

a switch-controlled series resonant circuit is inserted in parallel

with the matched chip. Such resonant circuit is formed by a

capacitor Cres, an inductor Lres and a normally closed switch.

By default the switch is closed (a normally-closed switch is

used) exhibiting an inductive behavior and closing the series

circuit. The capacitor Cres and the inductor Lres are

dimensioned in such way that the series circuit (capacitor,

inductor and inductive-switch) resonates and imposes a null

impedance in parallel with the matched chip at the operating

frequency (866.6Mhz):

resres

cCL

f2

1

(9)

Consequently, Zi is forced to be approximately zero. This

satisfies the second part of condition (7) and sets the RFID

chip to its inactive state. In this state the chip cannot respond

to the reader commands neither it interferes with the rest of the

circuit as proved in the previous subsection. It should be

noticed that in the closed position the switch presents an

inductive component that is absorbed by Lres and is taken into

account in the calculations.

Otherwise, if the switch is pressed by the user it goes to its

open position forcing the series circuit (capacitor, inductor and

capacitive-switch) to present a very high impedance. Such high

impedance in parallel with the matched chip has practically no

effect, reason why Zi approximates Z0. This satisfies the first

part of condition (7). In this active state, the matched RFID

chip is seen by the RC antenna (see Fig. 4) allowing the RFID

reader to read its ID.

Lres

NC

Switch

Chip

RFID i

Matching

Network

Cres

Resonant

circuit

Zi’=Z0

Zi

Fig. 5 Port termination i composed by a parallel association of the switch-

controlled series resonant circuit and the matched RFID chip.

III. SIMULATION AND MEASUREMENT RESULTS

In this section, simulations and measurements are presented.

First of all, the characterization of the switches and the RFID

chips is addressed, followed by the chip matching procedure.

The previously described N-port microstrip network is

simulated and measured and a remote control prototype is also

measured.

6º CONGRESSO DO COMITÉ PORTUGUÊS DA URSI 6

A. Measurement and characterization of the RFID tag

and switch and tag impedance matching

In order to match the chip impedance power-dependent

measurement of the RFID chip is required, precisely the

knowledge of the large signal S-parameters is needed. Details

of UHF RFID chip measurements can be found in [10]. It is

also important to characterize the RF behavior of the switches.

The switch S-parameters model is extracted and exported to

simulations for further evaluation and design.

In order to have accurate measurements both for the RFID

chips and switches, first a proper calibration procedure is

conducted. Since we are dealing with non-insertable Devices

Under Test (DUT’s) and the reference plan must be exactly at

the pins of the DUT’s, a commercial SOL calibration kit is not

suitable. For this reason, we have built a custom SOL

calibration kit (Fig. 6). In such kit SMA connectors are used

as the fixture both for the DUT and for the calibration

standards (mounted on the edge of such SMA connectors).

This allows the definition of a precise reference plan since

both the calibration standards and the DUT are placed at the

same physical location. Moreover, since the reference plan is

set at the edge of the SMA connectors, the characterization

and specification of the standards in the Vector Network

Analyzer (VNA) is straightforward (see reference [11]). To

perform calibration and measurements the calibration

standards and DUT are mounted/soldered at the top of the

SMA connectors (Fig. 6). The short standard is obtained by

short-circuiting the inner SMA conductor to the outer

conductor, the open standard is realized by an open-circuit

SMA connector and the load standard is build up with a high

quality 50 Ohms termination [12] on the top of an SMA

connector.

Fig. 6 Custom calibration standards and DUT’s mounted on the SMA fixtures

After proper calibration, the desired measurements were

conducted. In Fig. 7 is depicted the input impedance of an

RFID chip. As can be observed the non-linear impedance

varies with the input power level. Thus the matching circuit

should consider the desired input power level, precisely the

chip activation point – minimum input power level required to

activate the tag electronics. Activation point information can

also be drawn from Fig. 7. The activation point is

characterized by an accentuated fluctuation in the real part of

the chip input impedance [13]. The knowledge of the

unmatched activation point (near -5dBm) and the measured

reflection coefficient allows the calculation of the actual

activation level or chip sensitivity, given by (10). The chip

matching is then optimized for this specific power level. The

return loss of the matched chip is presented in Fig. 8.

)||1( 2unmatchedunmatchedmatched PP

(10)

Fig. 7 Measured input impedance of an RFID chip.

Fig. 8 Return loss of the matched RFID chip. The RFID chip is matched to

50Ω using a L-match circuit as in [10], with Lmatch=22nH and Cmatch=2.2pF.

In Fig. 9 is depicted the measured input impedance of the

switch. The measured S-parameter model is used in the

simulations with the entire RC circuit. In Fig. 9, point A

corresponds to the default closed position in which the switch

behaves predominantly as an inductor. Point B corresponds to

Open Short Load DUT1 DUT2

(switch) (chip)

chip activation point

Real

(Ω)

Im

(Ω)

6º CONGRESSO DO COMITÉ PORTUGUÊS DA URSI 7

the open position in which the switch has a predominant

capacitive behavior. Next, the entire port termination is

measured. This termination is formed by the switch and a

series LC circuit in parallel with a 50Ω load. The pure resistive

impedance Z0 (50Ω) is used to simulate the matched chip

impedance in parallel with the switch-controlled resonant

circuit (Fig. 5). As can be seen in Fig. 10 the series circuit

resonates at 866.6Mhz imposing a short circuit (point C) when

the switch is closed. When the switch is open the impedance is

approximately 50Ω (point D), meaning that the series circuit

has no significant impact. The inductance Lres is the series

inductance of the switch and the capacitance Cres (10pF) is

inserted to achieve resonance.

Fig. 9 Measured input impedance of the switch. Point A corresponds to the

closed position in which the switch has a predominant inductive behavior.

Point B corresponds to the open position in which the switch has a

predominant capacitive behavior.

Fig. 10 Series circuit formed by the series circuit (switch plus LC circuit) in

parallel with a 50Ω load. When the switch is closed the series circuit

resonates at 866.6Mhz imposing an approximate short circuit (point C).

When the switch is open the input impedance is approximately 50Ω (point

D).

B. N-Port Microstrip Network Simulation and Measurement

In this subsection, the proposed N-port microstrip network

is simulated, prototyped and measured. The N-port network is

modeled in Advanced Design System (ADS) using micrsostrip

line components. Fig. 11 shows the simulation model. In order

to reduce the overall circuit size, meandering technique is

used. However, since meandering can cause inter-coupling

between the lines, an electromagnetic simulation is also carried

out using Momentum electromagnetic simulator. Fig. 12 shows

the measurement setup used to validate the proposed N-port

network scheme. Return loss of the antenna port S11 (P1), and

of one of the key ports S22 (P2) are measured and compared

with simulations. Also, the transmission coefficient (insertion

loss) between the antenna port and one key port is evaluated

(S21). Both the simulation and measurement scenarios

consider that only one of the keys is pressed by the user. For

this purpose the active port is terminate with 50Ω both in

simulations and measurements2 and the remaining ports are

terminated with a short circuit to ground imposed by using a

via-to-ground. This represents the ideal case in which the

series circuit exhibit infinite impedance when the switch is

open and zero impedance when the switch is closed. Results

are presented in Fig. 13. Simulated and measured return loss

values agree well and indicate a good performance in the band

of interest (return loss below -14dB in the 800-900MHz band).

Transmission coefficient (S21) also achieves an acceptable

value around -1dB (Fig. 13c).

Fig. 11 ADS model of the N-port microstrip network model. Ports P1 and P2

are added to provide return loss information (S11,S22) and insertion loss

information (S21,S12).

2 In the measurements, the VNA port itself provides the 50Ω termination.

A

B

C

D

P1

P2

6º CONGRESSO DO COMITÉ PORTUGUÊS DA URSI 8

Fig. 12 Measurement setup used to validate the proposed N-port network

scheme. The circuit is fabricated in low cost FR4 substrate in a 50Ω

environment. Antenna port and one of the key ports are probed in order to

evaluate the return loss and transmission coefficient. All other ports are short-

circuited to ground in order to simulate the inactive port condition.

(a)

(b)

(c)

Fig. 13 N-port network simulations (solid line) and measurement (circles): a)

return loss of port 1, b) return loss of port 2 and c) insertion loss between port

2 and port 1.

C. Final prototypes and measurements

The aim of this subsection is to prototype and measure the

complete RFID RC circuit. For this purpose, several RC

circuits with 3, 4 and 5 keys are simulated and prototyped. Fig.

14 shows the final prototypes of a 3-key, 4-key and 5-key

remote control units. Nevertheless, the proposed concept can

be extended to any number of keys simply by designing the

adequate N-port network. Moreover, the layout of the network

can assume a variety of shapes by using the degrees of

freedom expressed by equation (6) combined with meandering

techniques. This allows to place the keys in the desired

physical location of the board.

In order to simulate the entire RC circuit, the model of the N-

port network and the extracted/measured models of the RFID

chips and switches are used. In the measurements a 4-key RC

(Fig. 14b) is connected to the VNA in order to evaluate the

return loss of the controller when each key is pressed. It is

assumed that only one key is pressed each time. The VNA is

connected to the RC antenna port. The results depicted in Fig.

15 indicate good performance in the band of interest. These

measurements validate the previous mathematical formulation

of section II and the simulation results of previous subsection.

Only one RFID chip is active and routed to the antenna port

and the other chips remain in idle mode and do not interfere

with the active one.

P1

P2 via-to-ground

via-to-ground via-to-ground

via-to-ground

6º CONGRESSO DO COMITÉ PORTUGUÊS DA URSI 9

(a)

(b)

(c)

Fig. 14 Final remote controller prototypes fabricated in low cost FR4

substrate: a) 3 keys, b) 4 keys, c) 5 keys. The concept can be extended to any

number of keys. The layout of the network can assume a variety of shapes by

combining the condition expressed by equation (6) with meandering

techniques.

Fig. 15 Measured return loss of a 4-key remote controller when a key is

pressed by the user: key 1 pressed (circles), key 2 pressed (crosses), key 3

pressed (squares), key 4 pressed (triangles).

IV. A REAL SCENARIO DEMONSTRATION PROTOTYPE

In this section a functional demonstration prototype of the

battery-free system is described, including the developed

RFID RC device and the DC (in this case a TV). As a proof of

concept the remote control system is integrated in a TV

equipment and some control functionalities are implemented

and successfully tested. To do so, the 4-key RC prototype (Fig.

14b) is used to implement channel up (CH +), channel down

(CH -), volume up (Vol +) and volume down (Vol -)

functionalities.

Concerning the communication between the proposed RFID

RC and the DC, two options exist as exemplified in Fig. 2b

and Fig. 2c: in the first case an RFID reader front-end is

embedded in the DC during the manufacturing process. Such

RFID front-end consists of a transmitter that sends data (RFID

commands) and wireless power to the RC device, and a

receiver responsible for receiving the backscattered data from

the RC. In this case both the transmitter and receiver should be

embedded in the DC and a common control unit can serve the

RFID reader and the DC. Alternatively, as illustrated in Fig.

2c, an interface/adaptor unit can be externally mounted in the

DC. Such interface unit comprises an RFID reader and

antennas and an RFID-to-infrared converter that acts as a

bridge between the RFID reader and the DC. In this case the

RFID reader has an independent control unit. In this scenario

there is no direct electrical contact between the RFID reader

and DC. Instead, the communication between the RC and the

DC is made in two steps: the RC communicates with the

interface unit by RF backscattering (RFID) and the

communication between the interface unit and the DC is

implemented using infrared. This is especially useful to

incorporate the proposed scheme into already installed system

that use conventional infrared technology (e.g. old TV’s), thus

ensuring backward-compatibility.

Since the first option – RFID reader embedded in the DC –

is a quite more time demanding implementation and because

we are only interested in provide a simple prove of concept, in

this work the second solution is followed. To do so, a

commercial RFID reader kit [14][15] is combined with an

universal IR remote controller to implement the above

mentioned RFID-IR interface (Fig. 16). The RFID reader kit is

controllable by a computer which allows the implementation

of our own application software (Fig. 18-19). The used RFID

kit provides a set of commands [15], namely to perform tags’

inventory, to read tags’ ID and to access tags’ memory. Such

commands are accessible through TCP-IP interface by using a

custom software application3. The RFID reader also provides

digital I/O interfaces equally controlled by software

application. These I/O interfaces are used to interface with the

universal IR remote control. The use of an universal remote

control for the demo prototype is quite useful since it allows

3 Several options exist, JAVA has been used in this work to develop the

Demo application.

Return

Loss

(dB)

6º CONGRESSO DO COMITÉ PORTUGUÊS DA URSI 10

the prototype to be adaptable to any equipment covered by the

universal remote control.

The flowchart of the developed demo application is shown

in Fig. 19: the JAVA application sets the RFID reader to be

continuously scanning its field searching for RFID tags. Once

a tag is read, the application determines whether the read ID is

valid or not. If it is a valid key ID then the application

activates the corresponding key in the universal IR remote

controller through the reader I/O interface. The universal IR

remote controller is placed in the proximity of the equipment

to be controlled, allowing line-of-sight IR communication

between the RFID-IR interface and the TV.

Fig. 16 shows the complete transmitter/receiver setup

including a TV, a commercial RFID reader and antennas, a

computer running the demo application software and a

universal IR remote control. Details of the RFID-IR interface

are depicted in Fig. 17, precisely the universal IR controller

can be observed. In Fig. 18 is depicted the developed software

interface. The application allows the configuration of the RFID

reader (e.g. set output power level, start and stop scanning the

field), displays the ID’s of the tags being read by the reader

and also provides information of the control actions being

performed (CH-,CH+,VOL-, VOL+).

Fig. 16 Demonstration prototype of the complete battery-free remote control

receiver using an external RFID-IR interface unit: 1 – TV, 2 – RFID reader, 3

– reader antennas, 4 – RFID-IR interface and universal IR remote control,

detailed in the next figure, 5 – computer running application. In a final

industrial implementation all the external hardware (RFID reader and

antennas) would be miniaturized and integrated in the TV equipment. The

control software, now running in a computer, would be implemented in the

TV control unit.

Fig. 17 RFID-IR interface including a universal IR remote controller. In this

prototype it acts as a bridge between the RFID reader and the TV: it receives

information from the reader via a digital I/O interface and it sends this

information to the TV via IR signals.

Fig. 18 Demo application software that controls the RFID reader. In this case

the channel up icon is red indicating that the corresponding key is being

pressed in remote controller.

SET TCP-IP Connection

(Connect to RFID reader)

INIT RFID Reader

CONFIGURE Reader

(e.g. SET Output power level)

SCAN Reader’s Filed

IS THERE A TAG

IN THE FIELD?

NO

YES

READ Tag

(Access Tag ID)

VALID Key-ID?

YES

NO

DISPLAY Info

(e.g. CH UP icon gets red)

SET I/O Port according

to read Key-ID

TV operation

is performed(CH+,CH-,

Vol+, Vol-)

Fig. 19 Simplified flowchart of the developed JAVA application software.

IR LED

Cable from the RFID reader

1

2

3 3

4

5

6º CONGRESSO DO COMITÉ PORTUGUÊS DA URSI 11

V. CONCLUSION

A battery-less remote control system has been proposed and

prototyped. Several versions of the control unit with 3, 4 and 5

keys have been fabricated. Nevertheless, the concept can be

extended to any number of keys. A complete prototype of the

battery-free remote control system has been implemented and

tested. The system has been integrated in a TV and, as a proof

of concept, four basic control functionalities were successfully

implemented: CH-,CH+,VOL- and VOL+. Although the

prototype has been tested with a TV equipment, this remote

control scheme can be applied to a variety of other systems

specially in scenarios where the use of batteries is undesirable.

The proposed approach is based on a commercially available

low cost RFID technology and can be integrated in old systems

that use conventional infrared technology. Moreover, the

remote controller unit can be manufactured at very low cost.

This makes the solution quite affordable and cost-effective.

The main drawback of the proposed approach is related to the

need of having the RFID reader always turned on. Future work

will focus on this issue by combining passive RFID with other

energy harvesting technologies. A strategy can be followed in

which the RFID reader is turned off by default. The

mechanical strain energy generated when the user presses a

key can be used to generate a beacon pulse solely to wake up

the RFID reader while further communication is still made by

backscattering (RFID) mechanism as proposed in this work.

ACKNOWLEDGMENT

The authors would like to thank Portuguese Science and

Technology Foundation (FCT) for the financial support

provided under Project PTDC/EEA-TEL/099646/2008

TACCS.

First Author would like to thank FCT for the doctoral

scholarship SFRH/ BD/ 80615/ 2011

REFERENCES

[1] www.ine.pt, INE – Censos 2011

[2] Introducing ZigBee RF4CE,

http://www.daintree.net/downloads/whitepapers/zigbee-rf4ce-intro.pdf

[3] Texas Instruments, ZigBee RF4CE,

www.ti.com/ww/en/analog/bluetooth/zigbee_4_jan12.pdf

[4] Finkenzeller, Klaus, RFID Handbook, 2nd Edition ed. Wiley

[5] Daniel M. Dobkin, The RF in RFID: Passive UHF in Practice

[6] EPC Radio-Frequency Identity Protocols Class-1 Generation-2 UHF

RFID, Protocol for Communications at 860 MHz – 960 MHz, Version

1.2.0

[7] Swarup Mumar Mohalik, Method and Apparatus for Tag Activation,

United States Patent, US2007152828A1, Jul 2006

[8] William R. Sweeney, Controlable RFID Card, United Stated Patent

US2006187040A1, Feb. 2005

[9] Alírio J.S. Boaventura and Nuno B. Carvalho, Controlo Remoto Passivo

RFID e Sistema e Método de Compatibilização com a Tecnologia

Convencional. Patent application submitted to INPI – Intituto Nacional

de Propriedade Intelectual

[10] Pavel V. Nikitin, K. V. Seshagiri Rao, Rene Martinez, and Sander F.

Lam, “Sensitivity and Impedance Measurements of UHF RFID Chips”,

IEEE TRANSACTIONS ON MICROWAVE THEORY AND

TECHNIQUES, VOL. 57, NO. 5, MAY 2009

[11] Michael Hiebel, Fundamental of Vector Network Analysis,

RHODE&SCHWARZ

[12] Bourns, CHF1206CNT Series 20 W Power RF Chip Termination

[13] Rainer Kronberger, Alexander Geissler and Barbara Friedmann, “New

Methods to determine the Impedance of UHF RFID Chips”, IEEE

RFID 2010

[14] Alien technology, Hardware Setup Guide ALR-8800

[15] Alien technology, Reader Interface Guide, September 2007

Alírio Soares Boaventura was born in Cape Verde in 1985. He received

the Master degree in Electronics and

Telecommunication Engineering from the

University of Aveiro, Portugal, in 2009. From

2008 to 2010 his was with Acronym-IT, a

Portuguese manufacturing company devoted to

RFID, WSN and consumer electronics. In 2010

he joined the Institute of Telecommunications,

Aveiro, as a researcher and currently he is a PhD

student at the University of Aveiro. His main

research interests include passive RFID and

sensors, low power wireless systems, wireless

power transmission and energy harvesting, and CAD/Modeling for RFID.

From 2004 to 2009, Alírio received a merit scholarship for graduation from

the Gulbenkian Foundation. In 2011 Alírio Boaventura was a finalist of the

Student Paper Competition of the IEEE-International Microwave

Symposium. Recently, Alírio was the ex-aequo recipient of the 2011

URSI/ANACOM Prize, awarded by URSI-Portugal section and ANACOM.

Alírio is co-inventor of a patent and the author and co-author of a book

chapter and several articles in international conferences and journals. Alírio

Boaventura has also served as invited reviewer for the IEEE Transactions

on Microwave Theory and Techniques (TMTT) and the IEEE Journal on

Emerging and Selected Topics in Circuits and Systems (JETCAS).

Nuno Borges Carvalho, was born in Luanda in 1972. He received the

diploma and doctoral degrees in Electronics and

Telecommunications Engineering from the

Universidade de Aveiro, Aveiro, Portugal in

1995 and 2000 respectively. He is an Associate

Professor with “Agregação” at the same

University, and a Senior Research Scientist at

the Instituto de Telecomunicações. His main

research interests include CAD for nonlinear

circuits/systems, nonlinear distortion analysis in

microwave/wireless circuits and systems and

measurement of nonlinear phenomena, recently

he has also been involved in design of dedicated radios and systems for newly

emerging wireless technologies. He was the recipient of the 1995 University

of Aveiro and the Portuguese Engineering Association Prize for the best 1995

student at the Universidade de Aveiro, the 1998 Student Paper Competition

(third place) presented at the IEEE International Microwave Symposium, the

2000 IEE Measurement Prize. He is also the co-inventor of four registered

patents. He is a reviewer and author of more than 100 papers in several

magazines and conferences and the vice-chair of the IEEE MTT-11 Technical

Committee and the chair of the URSI-Portugal Metrology group. Dr. Borges

Carvalho is co-author of the book “Intermodulation in Microwave and

Wireless Circuits” from Artech House, 2003.