**6. Simulations**

In this chapter different two antenna types are designed for the conductive textile material.The two designed antennas are H-slot antennas for RFID having an IC chip EM4222 at 869 MHz with the impedance 128-j577, microstrip patch antenna for RFID having T-match. Manual calculations and simulation results for all the antennas are presented below.

#### **6.1. Simulation of H-slot patch RFID tag antenna**

The wearable tags are designed on IE3D, fabricated and tested in real conditions. The overall size of the H-slot antennas is 180 mm x 200 mm. This big dimension of the antennas can be smaller by using a substrate which has a high dielectric constant, because the antenna size depends on the dielectric constant εr of the substrate and also the design frequency. In this design a fleece fabric is used as a substrate which has a dielectric constant of 1.25. This fabric is chosen because of its better radiation performance. When a substrate has low dielectric constant and small thickness then the designed antenna has good radiation performance. But if a small tag is requested then a substrate with high dielectric constant can be used.

Three different substrate materials are used for comparison. The first substrate is Polyethylene (εr = 2.25, thickness h =1.7 mm). This design gives smaller dimensions (145 mm x 160 mm) then fleece fabric.

Later on this substrate replaces with the fleece fabric to increase the radiation performance because of fleece's low dielectric constant.

Third design is made by a substrate material which has a very high dielectric constant εr, to reduce the antenna size. The material is silicone slab. Silicone slab is chosen because it is elastic, hydrophobic material and this property gives an advantage of avoiding the water absorption into the substrate, this is important property of silicone slab because when water absorbed into the substrate, the dielectric constant of the substrate changes. This also gives homogeneous connection between the substrate and radiating patch. The antenna design with silicone slab is giving as a size of 57 mm x 78 mm, much smaller than other designs. But a decreasing in the radiation performance is achieved. Thus there is a trade of between antenna performance and size of the antenna.

In this work, two different conductive textiles are used to design and fabricate two different tags, TAG1 and TAG2.


**Table 5.** Specifications for the conductive textile radiating element


**Table 6.** Specification for simulating antenna (TAG1 and TAG2)

#### *6.1.1. Antenna layouts and designs*

**5.3. Resistance measurement**

184 Radio Frequency Identification from System to Applications

the modelling results.

**6. Simulations**

fleece fabric.

size of the antenna.

tags, TAG1 and TAG2.

10 A). The measurement setup is depicted in Figure 13.

**6.1. Simulation of H-slot patch RFID tag antenna**

because of fleece's low dielectric constant.

The Betex sample is measured by RLCG bridge with respect to its calculated resistance. DC power source can cause sample damage at low voltage values (10 V corresponds to approx.

The measurement of Betex sample shows the resultant resistance is approx. 4Ω which confirms

In this chapter different two antenna types are designed for the conductive textile material.The two designed antennas are H-slot antennas for RFID having an IC chip EM4222 at 869 MHz with the impedance 128-j577, microstrip patch antenna for RFID having T-match. Manual

The wearable tags are designed on IE3D, fabricated and tested in real conditions. The overall size of the H-slot antennas is 180 mm x 200 mm. This big dimension of the antennas can be smaller by using a substrate which has a high dielectric constant, because the antenna size depends on the dielectric constant εr of the substrate and also the design frequency. In this design a fleece fabric is used as a substrate which has a dielectric constant of 1.25. This fabric is chosen because of its better radiation performance. When a substrate has low dielectric constant and small thickness then the designed antenna has good radiation performance. But

Three different substrate materials are used for comparison. The first substrate is Polyethylene (εr = 2.25, thickness h =1.7 mm). This design gives smaller dimensions (145 mm x 160 mm) then

Later on this substrate replaces with the fleece fabric to increase the radiation performance

Third design is made by a substrate material which has a very high dielectric constant εr, to reduce the antenna size. The material is silicone slab. Silicone slab is chosen because it is elastic, hydrophobic material and this property gives an advantage of avoiding the water absorption into the substrate, this is important property of silicone slab because when water absorbed into the substrate, the dielectric constant of the substrate changes. This also gives homogeneous connection between the substrate and radiating patch. The antenna design with silicone slab is giving as a size of 57 mm x 78 mm, much smaller than other designs. But a decreasing in the radiation performance is achieved. Thus there is a trade of between antenna performance and

In this work, two different conductive textiles are used to design and fabricate two different

if a small tag is requested then a substrate with high dielectric constant can be used.

calculations and simulation results for all the antennas are presented below.

Cu-Ni conductive textile has high conductivity and the designing with this conductivity gives better radiation performance then Betex textile which has low conductivity. The simulation of two antennas with two different materials having same dielectric substrate and the same dielectric constant is shown in Figure 14.

**Figure 14.** Simulated H-slot antenna for radiating element having surface resistivity = 0.02(a), and surface resistivity =1.19(b)

As expected, the tag with high conductive material is giving better radiation performance. When a comparison made between this two tag's simulations, a high reading distance and high radiation efficiency are achieved from TAG1 which is designed with high conductive textile. This can be shown by the plot obtained from the simulation, Figure 15.

**Figure 15.** Radiation efficiency Vs Frequency plot for TAG 1 and TAG 2 respectively

It can be seen that radiation efficiency obtained for TAG1 is 57.1% and that for TAG 2 is 3.05%. As it is concluded before that the radiation efficiency is directly proportional to the surface resistivity of the radiating patch. Therefore, higher radiation efficiency is obtained for the TAG having lower surface resistivity. If the antenna were designed from copper material the simulated efficiency would be very high because copper has high conductivity then these conductive textiles. This is shown in later case. Therefore, this value of 57% radiation efficiency is quite good result for this conductive textile.

**@869Mhz** TAG1 TAG2 **Radiation Efficiency,** 57.1% 3.05% **Conjugate Match Efficiency** 28.5% 1.52% **CMF** 0.975 0.874 **Gain** -8.46dBi -15.25 dBi **Directivity** 7.89dBi 8.47 dBi **Size of the Tag Lg x Wg** 180x200mm 180x200mm **Antenna impedance, Za** 100+j597 206+j472

RFID Textile Antenna and Its Development http://dx.doi.org/10.5772/53521 187

**Figure 18.** Conjugate match factor plot for TAG 1 and TAG 2 respectively

**Figure 17.** pattern of TAG2

**Table 7.** The combined results obtained from the simulation of two tag antenna

**Figure 16.** pattern of TAG1

The value of CMF is used to find how good the matching is in between the antenna impedance and chip impedance. The plot obtained for TAG 1 and TAG 2 is depicted in Figure 18.

From the above figure it can be observed that the CMF for TAG1 is 0.975 and that for TAG2 is 0.874. It can be considered that both of the tag antennas has good matching with the chip, however TAG 1 shows better match among the two.

**Figure 17.** pattern of TAG2

**Figure 15.** Radiation efficiency Vs Frequency plot for TAG 1 and TAG 2 respectively

is quite good result for this conductive textile.

186 Radio Frequency Identification from System to Applications

however TAG 1 shows better match among the two.

**Figure 16.** pattern of TAG1

It can be seen that radiation efficiency obtained for TAG1 is 57.1% and that for TAG 2 is 3.05%. As it is concluded before that the radiation efficiency is directly proportional to the surface resistivity of the radiating patch. Therefore, higher radiation efficiency is obtained for the TAG having lower surface resistivity. If the antenna were designed from copper material the simulated efficiency would be very high because copper has high conductivity then these conductive textiles. This is shown in later case. Therefore, this value of 57% radiation efficiency

The value of CMF is used to find how good the matching is in between the antenna impedance

From the above figure it can be observed that the CMF for TAG1 is 0.975 and that for TAG2 is 0.874. It can be considered that both of the tag antennas has good matching with the chip,

and chip impedance. The plot obtained for TAG 1 and TAG 2 is depicted in Figure 18.

**Figure 18.** Conjugate match factor plot for TAG 1 and TAG 2 respectively


**Table 7.** The combined results obtained from the simulation of two tag antenna

#### *6.1.2. Reading range calculation*

The read range is obtained as:

$$\mathbf{d}\_{\max} = \frac{c}{4\pi f} \sqrt{\frac{EIRP\_R}{P\_{chip}}} \mathbf{\tau} \,\mathbf{G}\_{\text{tag}} \tag{8}$$

$$\tau = \frac{4R\_{chip}R\_s}{\|Z\_{chip} + Z\_s\|^2} \le 1\tag{9}$$

Here, chip sensitivity is -10 dBm and the maximum radiated power by the reader is 3.2 W EIRP. Thus from the formula the transmission power coefficient for TAG1 and TAG2 is equal to,

$$
\tau\_1 = 0.97 \tag{10}
$$

$$
\pi\_2 = 0.87 \tag{11}
$$

**Figure 19.** Simulation result of Radiation efficiency plot for Cu-Ni, with the height of dielectric substrate 2 mm, 2.56

RFID Textile Antenna and Its Development http://dx.doi.org/10.5772/53521 189

**Figure 20.** Antenna with Dielectric substrate fleece and antenna with dielectric substrate silicone slab respectively

mm and 4 mm.

Thus the maximum range obtained is dmax= 2 m for TAG1 and dmax= 1.2 m for TAG2.

#### **6.2. Comparison when different dielectric substrate used**

A comparison is performed in simulation to compare the radiation efficiency of H-slot antenna, when the conductive textile (Cu-Ni) is used as radiating element. The comparison is made by changing the thickness of dielectric substrate (fleece fabric) to 2 mm, 2.56 mm and 4 mm. The simulation is performed for the conductor having the surface resistivity 0.02 Ω/sq to resonate at the frequency 869 MHz. For three different thickness values, three different antenna geometry and CMF and radiation pattern is achieved. The CMF for all the designs were measured to be more than 0.95 when measured in linear scale.

Figure 19 depicts the radiation efficiency obtained from 4 mm thick dielectric substrate is the highest and obtained to be 57.1 %, for 2.56 mm thick dielectric substrate is 43.4 % and that for 2 mm thick dielectric substrate is 35.8 %. The better performance is achieved with the antenna having thicker dielectric substrate.

#### **6.3. Comparison when different dielectric material used**

In this case the two dielectric materials are used. One is the fleece fabric with the dielectric constant 1.25 and the other is silicone slab with dielectric constant 11.9. The silicone slab with high dielectric constant is used to reduce the size of antenna and also hydrophobic in nature. This is very useful characteristics of silicon slab. The two antennas with two different materials are depicted in Figure 20 and 21.

As seen from the graph, the radiation efficiency of antenna using silicone slab and having higher dielectric constant, is reduced compared with the one using fleece fabric. Though the

*6.1.2. Reading range calculation*

188 Radio Frequency Identification from System to Applications

The read range is obtained as:

to,

*dmax* <sup>=</sup> *<sup>c</sup>* 4*πf*

*<sup>τ</sup>* <sup>=</sup> <sup>4</sup>*RchipRa*

Thus the maximum range obtained is dmax= 2 m for TAG1 and dmax= 1.2 m for TAG2.

A comparison is performed in simulation to compare the radiation efficiency of H-slot antenna, when the conductive textile (Cu-Ni) is used as radiating element. The comparison is made by changing the thickness of dielectric substrate (fleece fabric) to 2 mm, 2.56 mm and 4 mm. The simulation is performed for the conductor having the surface resistivity 0.02 Ω/sq to resonate at the frequency 869 MHz. For three different thickness values, three different antenna geometry and CMF and radiation pattern is achieved. The CMF for all the designs were

Figure 19 depicts the radiation efficiency obtained from 4 mm thick dielectric substrate is the highest and obtained to be 57.1 %, for 2.56 mm thick dielectric substrate is 43.4 % and that for 2 mm thick dielectric substrate is 35.8 %. The better performance is achieved with the antenna

In this case the two dielectric materials are used. One is the fleece fabric with the dielectric constant 1.25 and the other is silicone slab with dielectric constant 11.9. The silicone slab with high dielectric constant is used to reduce the size of antenna and also hydrophobic in nature. This is very useful characteristics of silicon slab. The two antennas with two different materials

As seen from the graph, the radiation efficiency of antenna using silicone slab and having higher dielectric constant, is reduced compared with the one using fleece fabric. Though the

**6.2. Comparison when different dielectric substrate used**

measured to be more than 0.95 when measured in linear scale.

**6.3. Comparison when different dielectric material used**

having thicker dielectric substrate.

are depicted in Figure 20 and 21.

*EIRP <sup>R</sup>*

Here, chip sensitivity is -10 dBm and the maximum radiated power by the reader is 3.2 W EIRP. Thus from the formula the transmission power coefficient for TAG1 and TAG2 is equal

*Pchip <sup>τ</sup>Gtag* (8)

<sup>|</sup>*Zchip* <sup>+</sup> *Za*|2 <sup>≤</sup><sup>1</sup> (9)

*τ*<sup>1</sup> =0.97 (10)

*τ*<sup>2</sup> =0.87 (11)

**Figure 19.** Simulation result of Radiation efficiency plot for Cu-Ni, with the height of dielectric substrate 2 mm, 2.56 mm and 4 mm.

**Figure 20.** Antenna with Dielectric substrate fleece and antenna with dielectric substrate silicone slab respectively

**Frequency(869 MHz)** TAG3 **Radiation Efficiency** 41.82% **Conjugate Match Efficiency** 20.91% **CMF** 0.956 **Gain** -7.99dBi **Directivity** 8.162dBi **Size LxW** 150x190 **Imput Impedance , Za** 92+j547

RFID Textile Antenna and Its Development http://dx.doi.org/10.5772/53521 191

**Reading distance** 2m

**Figure 23.** Radiation Efficiency Vs frequency plot for the tag antenna

material also attached to the substrate by using glue.

Figure 23 shows the radiation efficiency obtained is 41.8 %.

**7.1. Results of fabrication and measurements of TAG1 and TAG2**

**7. Fabrication and measurement of H-Slot and patch RFID antenna**

For fabrication of these two tag antenna, the available fleece fabric had a thickness of 2 mm, so to have 4 mm thickness two layer of fleece is overlapped by using glue. The conductive

**Table 8.** Simulated output results for TAG 3

**Figure 21.** Radiation efficiency of antenna using dielectric substrate fleece (43.4%) and silicone slab (32.7%)

size of antenna was reduced, the efficiency was also decreased drastically. It is due to this reason fleece fabric is preferred.

#### **6.4. Simulation of microstrip patch antenna for RFID application**

This is another technique of designing RFID tag antenna. A rectangular parch antenna is used as a tag antenna for RFID. The microstrip patch antenna for RFID is designed for 869 MHz. The manual calculation of microstrip patch is calculated in the similar ways as for the rectan‐ gular microstrip patch in chapter 3, however the feeding is different. A T-match is used to match the impedance of the antenna to the chip. The calculated length is 150 mm and the width is 190 mm.

The dielectric material used is Fleece fabric with dielectric constant 1.25 and dielectric height of the substrate 2 mm. The radiating element is simulation of conductive textile material having surface resistivity 0.02 Ω/sq.

**Figure 22.** Microstrip patch antenna using T match


**Table 8.** Simulated output results for TAG 3

size of antenna was reduced, the efficiency was also decreased drastically. It is due to this

**Figure 21.** Radiation efficiency of antenna using dielectric substrate fleece (43.4%) and silicone slab (32.7%)

This is another technique of designing RFID tag antenna. A rectangular parch antenna is used as a tag antenna for RFID. The microstrip patch antenna for RFID is designed for 869 MHz. The manual calculation of microstrip patch is calculated in the similar ways as for the rectan‐ gular microstrip patch in chapter 3, however the feeding is different. A T-match is used to match the impedance of the antenna to the chip. The calculated length is 150 mm and the width

The dielectric material used is Fleece fabric with dielectric constant 1.25 and dielectric height of the substrate 2 mm. The radiating element is simulation of conductive textile material having

**6.4. Simulation of microstrip patch antenna for RFID application**

reason fleece fabric is preferred.

190 Radio Frequency Identification from System to Applications

surface resistivity 0.02 Ω/sq.

**Figure 22.** Microstrip patch antenna using T match

is 190 mm.

**Figure 23.** Radiation Efficiency Vs frequency plot for the tag antenna

Figure 23 shows the radiation efficiency obtained is 41.8 %.

#### **7. Fabrication and measurement of H-Slot and patch RFID antenna**

#### **7.1. Results of fabrication and measurements of TAG1 and TAG2**

For fabrication of these two tag antenna, the available fleece fabric had a thickness of 2 mm, so to have 4 mm thickness two layer of fleece is overlapped by using glue. The conductive material also attached to the substrate by using glue.

**Figure 27.** Fabricated antenna for TAG 2 and chip connection

**Figure 28.** Fabrication and Chip connection for TAG 3

not done with TAG 1, as it was not necessary.

sent to the computer for further processing of the signal.

task. The reader is manufactured by METRA BLANSKO a.s.

As can be seen from the Figure 27 TAG 2 is constructed from Betex and being very difficult to connect chip by soldering, an alternative way is used. First a copper tape is attached, similar to that with microstrip patch and then the chip is soldered on top of it as shown in Figure. This

RFID Textile Antenna and Its Development http://dx.doi.org/10.5772/53521 193

The reader shown in the above figure generates the frequency signal which is captured by the tag antenna, and retransmit signal back to reader. This signal is received by the reader and is

The RFI21 RFID Reader Demo application program is used in the computer to read the reader. This application uses Python 2.6 programming language in the computer to accomplish this

To measure the tag performance, an RFID reader is connected to the computer.

**Figure 24.** Conjugate match vs frequency for TAG 3 (CMFmax=0.956)

**Figure 25.** radiation pattern for TAG 3

**Figure 26.** Fabricated antenna (a), chip connection to slot arm (b) for TAG 1

**Figure 27.** Fabricated antenna for TAG 2 and chip connection

**Figure 28.** Fabrication and Chip connection for TAG 3

**Figure 26.** Fabricated antenna (a), chip connection to slot arm (b) for TAG 1

**Figure 24.** Conjugate match vs frequency for TAG 3 (CMFmax=0.956)

192 Radio Frequency Identification from System to Applications

**Figure 25.** radiation pattern for TAG 3

As can be seen from the Figure 27 TAG 2 is constructed from Betex and being very difficult to connect chip by soldering, an alternative way is used. First a copper tape is attached, similar to that with microstrip patch and then the chip is soldered on top of it as shown in Figure. This not done with TAG 1, as it was not necessary.

To measure the tag performance, an RFID reader is connected to the computer.

The reader shown in the above figure generates the frequency signal which is captured by the tag antenna, and retransmit signal back to reader. This signal is received by the reader and is sent to the computer for further processing of the signal.

The RFI21 RFID Reader Demo application program is used in the computer to read the reader. This application uses Python 2.6 programming language in the computer to accomplish this task. The reader is manufactured by METRA BLANSKO a.s.

During the measurement, the reading distance of the TAG1 and TAG2 is measured. Tags are moved towards the reader's antenna till the reader detects the signal from the tag.

EM4222 chip is used in the tag antenna. When the tag is detected by the reader the tag ID is displayed in the computer. This can be seen in the figure which is the ID of the chip in red

From the measurement results, the reading distance for TAG1 is measured to be 50 cm. This is quite smaller then simulated results because of the change in dielectric material due to non-

The reading distance for TAG2 is quite close the simulation results, 90 cm. The simulated reading distance for this tag is 1.2 m. Thus TAG 2 gave better performance and was very close

A short experiment was done to compare working of the fabricated tag and the tag available in the market. To make a comparison of reading distance, two different UHF RFID tag's reading distance were measured. The tags used were UPM Hammer 258-1 and UMP short dipole 211\_2.

RFID tag

H-slot TAG2

RFID Textile Antenna and Its Development http://dx.doi.org/10.5772/53521 195

precise determination of permittivity and also soldering process.

**Table 9.** Measured read range from the three designed tag

These are the commercially available tag in the market.

**Figure 31.** UPM Hammer 258-1RFID tag (a), UMP short dipole 211\_2 RFID tag (b)

**Parameter** UPM Hammer 258-1 RFID tagUMP short dipole 211\_2

**Reading Distance** 98 cm 152cm 90cm **Chip Protocol** EPS S1 Gento EPS S1 Gento IP-X

**Table 10.** Comparison of read range of manufactured tag with commercially available tag

The measurement was performed in open space in the lab.

**Range** TAG1 TAG2 TAG3 **Reading range** 50 cm 90 cm 60 cm

color.

to simulated values.

**Figure 29.** Measuring Reading distance of TAG1

As soon as RFID tag is detected by reader's antenna, the information is displayed on the computer.


**Figure 30.** Application program detecting the EM4222 chip ID (in red)

EM4222 chip is used in the tag antenna. When the tag is detected by the reader the tag ID is displayed in the computer. This can be seen in the figure which is the ID of the chip in red color.

From the measurement results, the reading distance for TAG1 is measured to be 50 cm. This is quite smaller then simulated results because of the change in dielectric material due to nonprecise determination of permittivity and also soldering process.

The reading distance for TAG2 is quite close the simulation results, 90 cm. The simulated reading distance for this tag is 1.2 m. Thus TAG 2 gave better performance and was very close to simulated values.


**Table 9.** Measured read range from the three designed tag

During the measurement, the reading distance of the TAG1 and TAG2 is measured. Tags are

As soon as RFID tag is detected by reader's antenna, the information is displayed on the

moved towards the reader's antenna till the reader detects the signal from the tag.

**Figure 29.** Measuring Reading distance of TAG1

194 Radio Frequency Identification from System to Applications

**Figure 30.** Application program detecting the EM4222 chip ID (in red)

computer.

A short experiment was done to compare working of the fabricated tag and the tag available in the market. To make a comparison of reading distance, two different UHF RFID tag's reading distance were measured. The tags used were UPM Hammer 258-1 and UMP short dipole 211\_2. These are the commercially available tag in the market.

**Figure 31.** UPM Hammer 258-1RFID tag (a), UMP short dipole 211\_2 RFID tag (b)


**Table 10.** Comparison of read range of manufactured tag with commercially available tag

The measurement was performed in open space in the lab.

### **8. Conclusion**

Implementation of textile antennas for RFID tags represents a realistic developmental assign‐ ment, and as shown and practically proved, this arrangement yields good results. The successful operation of such textile antennas mainly requires the mechanical stability of the textile composite, which realizes a RFID tag antenna. A good function of the antenna and thus the sensitivity of the complete tag can be provided for just compliance with the mechanical construction and stability of required dimensions. A good choice of textile material for both electrically conductive structures and the insulating layer of the resultant fabric composite is the most important prerequisite for the successful implementation.

[3] Lozano-Nieto A. RFID Design Fundamental and Application. Boca Raton: CRC Press;

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[4] Occhiuzzi C. et al. Modeling, Design and Experimentation of Wearable RFID Sensor Tag, IEEE Transactions on Antennas and Propagation 2010; 58(8) 2490-2498.

[5] Aniolczyk H. et al., Application of Electrically Conductive Textile as Electromagnetic Shields in Physiotherapy, Fıbers and Textiles in Eastern Europe 2004; 12(4) 47-50. [6] Vojtěch, L. and Neruda, M. Application of Shielding Textiles for Increasing Safety Airborne Systems - Limitation of GSM Interference. In The Ninth International Conference on Networks (ICN 2010). Los Alamitos: IEEE Computer Society 2010,

[7] Constantine A.B. Antenna Theory Analysis and Design. New York: John Wiley; 1997. [8] Maryniak W.A., Uehara T., Noras M. A. Surface Resistivity and Surface Resistance Measurements Using a Concentric Ring Probe Technique, Trek Application Note 2003; 1005: 1–4. www.trekinc.com/pdf/1005\_Resistivity\_Resistance.pdf (accessed 16 August

[9] IEC 61340-5-1 Standard. Electrostatics – part 5-1: Protection of Electronic Devices from

[10] ASTM Standard D 257-99. Standard Test Methods for D-C Resistance or Conductance

[11] Neruda, M. and Vojtěch, L. Verification of Surface Conductance Model of Textile Materials. Journal of Applied Research and Technology 2012; 10(4), 579-585.

[12] Dahal, R. and D. Mercan. Design and performance analysis of purely textile antenna for wireless applications. Sweden, 2012. 64 p. Diploma thesis. Czech Technical Unive‐ sity, University of Gävle, Sweden. hig.diva-portal.org/smash/get/diva2:504525/

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Textile RFID tags find its use at both person marking (marking of athletes, protective clothing and other functional ready-made textile products) and stock-in-trade marking in hospitals, packaging, etc.
