Ultrawide-band Wearable Antenna with Uniplanar Compact Electromagnetic Band Gap

Ultrawide-band technology, commonly known as UWB, sends data over a wide frequency range for many applications. WBAN applications use wearable antennas because they have flexible materials and are suitable for telemedicine technology and have many advantages such as small size, lightweight, able to work at a wide enough frequency, easy fabrications, and affordable costs. In this research, the hexagonal patch ultrawide-band monopole planar wearable antenna was designed using Cordura Delinova 2000 textile material for the substrate and copper tape for the groundplane and patch. The Uniplanar Compact Electromagnetic Band Gap (UC-EBG) as a metamaterial was added to the design of the monopole planar antenna in this final project which aims to improve antenna parameters, increase efficiency, and reduce the effects of radiation on the body. From the measurement results on the antenna with the addition of the UC-EBG structure at the bottom of the patch, it produces a 6% fractional bandwidth increase and able to work in the frequency range of 3-10 GHz off-body conditions and 2-11 GHz on-body conditions. In the SAR test at 45 mm, it was found that the value decreased from previously 1.535 W/Kg to 1.31 W/Kg at a frequency of 3.5 GHz and previously from 1.421 to 1.267 W/Kg at a frequency of 5 GHz on a wrist phantom object which is a good value for SAR. The resulting increase in antenna gain after the addition of the UC-EBG structure. The radiation pattern on the antenna is bidirectional.


Introduction
In our rapidly evolving technological landscape, the shift from wired to wireless technology has become ubiquitous, profoundly impacting various facets of modern life, spanning home appliances, lifestyle, and even healthcare.The advent of wireless communication technology has unleashed a myriad of possibilities, notably in the realm of monitoring and data transmission.This is achieved through the utilization of wireless sensor networks (WSN), wherein sensors communicate vital information via radio waves [1].Within the expansive domain of WSN, a particularly intriguing subset emerges, known as Wireless Body Area Network (WBAN).Unlike standard WSN, WBAN is uniquely tailored to interface with the human body [2].The realm of WBAN is rife with groundbreaking developments that enable the monitoring of crucial physiological parameters, thereby contributing to the maintenance of human health.Beyond basic monitoring, WBANs offer the tantalizing prospect of remote health services, accurate disease diagnosis, and a plethora of other applications [3].
One integral component that empowers the efficacy of WBANs is the wearable antenna.These antennas possess a multitude of advantages that render them indispensable in this context.Notably, they are characterized by their small form factor, lightweight design, ease of fabrication, and costeffectiveness.Moreover, wearable antennas boast the capacity to operate across a wide frequency spectrum [4].Their flexible and thin construction allows them to bend and adapt to changes in body shape, ensuring optimal performance in WBAN applications.
Building upon these principles, the focus of this study is to engineer a planar ultrawide-band monopole wearable antenna.In a quest to further enhance its functionality, we intend to integrate a Uniplanar Compact Electromagnetic Band Gap (UC EBG) structure into the antenna's design.This strategic integration aims to bolster the antenna's performance by maintaining gain values, expanding bandwidth, and reducing Specific Absorption Rate (SAR) values.By selecting the optimal positioning of the UC EBG structure, we seek to create a wearable antenna that not only excels in performance but also upholds safety standards in wireless healthcare applications.In essence, this research endeavors to contribute to the evolution of wireless healthcare technology by advancing the capabilities of wearable antennas, thereby facilitating more effective and secure monitoring of human health through WBANs.The significance of this work lies in its potential to improve the quality of healthcare delivery and enhance the overall well-being of individuals in this increasingly wireless-dependent era.

Ultrawide-Band
Ultrawide-band technology or commonly known as UWB is a wireless technology used to send data at a rate over short distances using relatively little power.Frequency on UWB has been regulated in several bodies such as the Infocomm Development Authority (IDA) by setting in the frequency range of 3.1 GHz -10.6 GHz with the lowest bandwidth of 500 MHz [4].To make an antenna has UWB criteria, the antenna must have a Fractional Bandwidth Concept value of ≥ 50% [6].

Wearable Antenna
Wearable antennas are widely used today, especially in Wireless Body Area Network (WBAN) applications.They are easily placed on the body's surface for off-body communication with remote networks.The commonly used working frequency is the Industrial, Science, and Medical (ISM-Band), both globally and in Indonesia [7].

Phantom
A Phantom is a human limb model used for simulating Wireless Body Area Network (WBAN) technology.It mimics human body characteristics like muscle, bone, skin, and fat, ensuring simulation results match antenna measurements.Currently, a wrist phantom is used for research simulations especially for Wireless Body Area Networks [8][9].The following table is an electrical property that includes bone, muscle, skin, and fat used in the Phantom thigh, Phantom chest, and Phantom wrist [10].The Ultrawide-band antenna in this study was designed using a planar monopole antenna.The structure of the planar monopole antenna is similar to that of a microstrip antenna, but the groundplane uses the Defected Ground Structure method and the choice of patch shape is the difference between the two.A microstrip antenna is a small antenna that is shaped like a PCB plate.The microstrip antenna has a structure composed of three elements, namely radiation (patch), substrate, and defense (groundplane).
The structure of the microstrip antenna is shown in Figure 1.[14]

Electromagnetic Band Gap
EBG or Electromagnetic Band Gap is one type of metamaterial that is a renewal in communication systems and microwaves.By utilizing the suppression of waves on a surface of a particular metamaterial, the use of EBG aims to improve the performance of communication and microwave system devices.In its implementation, the EBG structure can increase gain value, reduce back radiation, increase efficiency value, and reduce the effect of mutual coupling.Currently, the development of EBG structures has been widely carried out [11] 2.6.Uniplanar Compact Electromagnetic Band Gap (UC-EBG) EBG, or Electromagnetic Band Gap, is an advanced metamaterial used in communication systems and microwaves.By exploiting surface wave effects, EBG enhances device performance by increasing gain values, reducing back radiation, improving efficiency, and mitigating mutual coupling effects.Its development is currently booming.[11].One popular form of EBG is the Uniplanar Compact EBG (UC-EBG), which stands out for its lack of vertical vias, simplifying fabrication compared to the mushroomlike EBG.The UC-EBG replaces the LC resonance series with gaps between unit cells.Additionally, UC-EBG offers the advantage of being sensitive to polarization.[12].

Specific Absorption Ratio (SAR)
Specific Absorption Ratio (SAR) is a measure of the level of energy received and absorbed by the body when exposed to radiation from electromagnetic waves by wireless devices or Radio Frequency (RF).The calculation of SAR is caused by wearable antennas.SAR is measured in watts per kilogram or W/kg.The value of SAR has a safe limit set by the International Commission on Non-Ionising Radiation Protection (ICNIRP), which is based in Europe and is valued at 2.0 W/kg.The American institutions, Federal Communication Commission (FCC) and Cellular Telecommunication Industry Association (CTIA), have set a safe limit value of 1.6 W/kg.[13]  The design of the Wearable Antenna was carried out using 3D modeling software, resulting in the wearable antenna and wrist phantom design shown in Figure 2. The antenna dimensions designed in the 3D modeling software are listed in Table 2 below.Following the design process in the 3D modeling software, the fabrication of the wearable antenna was performed using textile material and copper tape, with dimensions as specified in the previously determined parameter list.Figure 4. shows the fabrication result of the front design of the antenna, it consists of the antenna patch and 2 components of the Uniplanar Compact EBG structure.Figure 5.

Wearable Antenna Design on Simulation
shows the back side of the antenna, it has a defected ground structure which is a monopole planar characteristic.In this stage, on-body testing was conducted, measuring antenna parameters such as Gain, Return Loss, and Fractional Bandwidth directly on the human wrist, at a distance of 45mm from the wearable antenna, in accordance with the phantom simulation.

Frequency (GHz) SAR (Gap 45mm) 3,5
1,31 W/Kg 5 1,267 W/Kg SAR values were obtained from the antenna simulation with the UC-EBG structure.At the operating frequency of 3.5 GHz, with the antenna 45 mm away from the phantom, the SAR value was found to be 1.31 W/Kg, while at 5 GHz, the SAR value was 1.267 W/Kg.These SAR values comply with the standard requirement of being below 1.6 W/Kg.After conducting the measurements, the obtained gain values were compared with the simulated gain values.At the frequency of 3.5 GHz, the measured gain was 4.19 dBi, while the simulated gain at the same frequency was 2.615 dBi.At the working frequency of 5 GHz, the measured gain was 6.01 dBi, and the simulated gain was 2.594 dBi.Under on-body conditions, specifically on the wrist, the tested antenna operated in the frequency range of 2-11 GHz.The return loss measured at 3.5 GHz was -15.51 dB, at 5 GHz was -15.909 dB, and at 5 GHz was -13.05 dB.Under off-body conditions, the antenna operated in the frequency range of 3-10 GHz, with measured return losses of -14.09 dB at 3.5 GHz and -13.05 dB at 5 GHz.The Fractional Bandwidth (FBW) results from simulation and measurement were compared.There was an increase in FBW under on-body conditions, with a 110% increase in simulation and a 138% increase in measurement.Conversely, under off-body conditions, there was a decrease in FBW from 117% in simulation to 107%.The change in FBW values between simulation and measurement may be attributed to human error during measurement, location instability during testing, and limited tools and equipment.

Conclusion
The addition of the UC-EBG structure to both simulation and measurement enabled the antenna to operate in the ultrawide-band frequency range.Under on-body conditions, the antenna worked in the 2-11 GHz frequency range, while under off-body conditions, it operated in the 3-10 GHz ultrawide-band frequency range as proposed.Both simulation and measurement demonstrated excellent performance at the specified frequencies of 3.5 GHz and 5 GHz, with return loss below -10 dB and VSWR below 2.
The fractional bandwidth was 107% under off-body conditions and 138% under on-body conditions.The incorporation of the UC-EBG structure in the conventional antenna significantly reduced SAR values.Initially, SAR values were 1.535 W/Kg at 3.5 GHz and 1.421 W/Kg at 5 GHz.After adding the UC-EBG structure, the SAR values decreased to 1.31 W/Kg at 3.5 GHz and 1.267 W/Kg at 5 GHz.Moreover, the gain values increased from 2.615 dBi at 3.5 GHz and 2.594 dBi at 5 GHz to 4.19 dBi at 3.5 GHz and 6.01 dBi at 5 GHz in the simulation.
Differences between simulation and measurement results can be attributed to unstable and nonconducive measurement environments, manual antenna fabrication leading to variations from the simulation, and suboptimal calibration of measurement tools.

Suggestion
In the pursuit of the perfect wearable antenna, researchers explored new metamaterials beyond the conventional UC-EBG.Their goal: achieve the most optimal reduction in Specific Absorption Rate (SAR) values.Utilizing cutting-edge software, they designed a lifelike phantom to simulate real-life scenarios.The hands-on fabrication process required precision and care with textile materials and electronic tools.For accurate measurements, anechoic chambers provided the ideal testing environment.Diverse planar monopole patch antennas were tested against the traditional hexagonal design.Pushing boundaries, the researchers ventured into alternative substrates like denim, lycra, rubber, and foam, leaving no stone unturned in their pursuit of excellence.

Figure 3 .
Figure 3. Wearable Antenna and Phantom Design on Simulation

Table 1 .
Phantom Tissue Specification Figure 1.Monopole Planar Antenna Structure

Table 4 .
Gain Values Comparison

Table 5 .
Return Loss Values Comparison

Table 6 .
Fractional Bandwidth Values Comparison