A dual-band, low profile, high gain, and low specific absorption rate (SAR) triangular slotted monopole antenna backed with a $4\times 4$ artificial magnetic conductor (AMC) array is presented for wireless body area network (WBAN) applications. The antenna is printed on a Rogers ULTRALAM 3850 substrate, whereas the AMC array is printed on a RO3003 substrate. The design operates at 3.5 GHz, for WiMAX wireless applications, and at 5.8 GHz for the ISM Band. The proposed antenna preserved the dual-band resonance and exhibited acceptable gain and SAR at a separation of 15 mm from the human body model. To reduce such separation and achieve enhancements to gain and SAR, an AMC array was utilized. In free space, gain enhancements by 6.8 and 3.7 dBi were achieved at both frequencies, respectively. Furthermore, over a gap of 1 mm from the human body, gain enhancements by 23.3 and 13.9 dBi were achieved at both frequencies, respectively. In addition, SAR reductions by almost 99% were attained. The antenna was fabricated and measured where a very good agreement was observed between simulated and measured results, with and without the incorporated AMC array. With such results, the proposed design can be highly recommended for wearable medical applications, specifically for diabetic patients.

A Wearable Dual-Band Low Profile High Gain Low SAR Antenna AMC-Backed for WBAN Applications

The field of flexible antennas is witnessing an exponential growth due to the demand for wearable devices, Internet of Things (IoT) framework, point of care devices, personalized medicine platform, 5G technology, wireless sensor networks, and communication devices with a smaller form factor to name a few. The choice of non-rigid antennas is application specific and depends on the type of substrate, materials used, processing techniques, antenna performance, and the surrounding environment. There are numerous design innovations, new materials and material properties, intriguing fabrication methods, and niche applications. This review article focuses on the need for flexible antennas, materials, and processes used for fabricating the antennas, various material properties influencing antenna performance, and specific biomedical applications accompanied by the design considerations. After a comprehensive treatment of the above-mentioned topics, the article will focus on inherent challenges and future prospects of flexible antennas. Finally, an insight into the application of flexible antenna on future wireless solutions is discussed.

Flexible Antennas: A Review.

A planar, compact, dual-band antenna on a semiflexible substrate is proposed for 2.45/5.85 GHz wireless body-area network applications. The proposed antenna is comprised of an I-shaped monopole embedded with an inverted L-shaped slit and an inductive meander line on the front side of the substrate, which excites the higher resonant mode at 5.85 GHz. On the backside, an inverted U-shaped stripline embedded with another inductive meander line is attached to the ground plane to excite the lower resonant mode at 2.45 GHz. The key to the miniaturization procedure is increasing the inductance and the capacitance by loading the inductive meander lines and slit line. The overall size of the proposed antenna is 0.15λ × 0.1λ × 0.004λ at 2.45 GHz. The measured results of the proposed antenna show the impedance bandwidths of 5.7% (2.4–2.54 GHz) and 3.78% (5.72–5.94 GHz) and the maximum peak gains of 2.1 dBi and 3.5 dBi, respectively. The simulated specific absorption rate values satisfy both the U.S. and EUR standards of under 1 g average and under 10 g average, respectively.

Miniaturization of a Dual-Band Wearable Antenna for WBAN Applications

This paper presents a novel approach to design compact wearable antennas based on metasurfaces. The behavior of compact metasurfaces is modeled with a composite right-left handed transmission line (CRLH TL). By controlling the dispersion curve, the resonant modes of the compact metasurface can be tuned efficiently. A printed coplanar waveguide (CPW) monopole antenna is used as the feed structure to excite the compact metasurface, which will result in a low profile antenna with low backward radiation. Following this approach, two compact antennas are designed for wearable applications. The first antenna is designed to operate at its first negative mode (−1 mode), which can realize miniaturization, but maintain the broadside radiation as for a normal microstrip antenna. The proposed prototype resonates around 2.65 GHz, with a matching bandwidth of 300 MHz. The total dimensions of the antenna are 39.4 × 33.4 mm2 (0.1 λ02), and its maximum gain is 2.99 dBi. The second antenna targets dual-band operation at 2.45 and 3.65 GHz. A pair of symmetric modes (±1 modes) are used to generate similar radiation patterns in these two bands. The size of the antenna is 55.79 × 52.25 mm2 (0.2 λ02), and the maximum gains are 4.25 and 7.35 dBi in the two bands, respectively. Furthermore, the performance of the antennas is analyzed on the human body. The results show that the proposed antennas are promising candidates for Wireless Body Area Networks (WBAN).

A Novel Design Approach for Compact Wearable Antennas Based on Metasurfaces

The recent advancement in the wireless technology has led to the advent of wearable antennas. These antennas are utilized for Wireless Body Area Networks (WBANs) purposes such as health-care, military sportive activities and identification systems. Compared to conventional antennas, wearable antennas operate in an environment which is in highly near proximity to the curved human body. Therefore, the wearable/flexible antenna performance parameters, including reflection coefficient, bandwidth, directivity, gain, radiation characteristic, Specific Absorption Rate (SAR), and efficiency are anticipated to be influenced by the coupling and absorption by the human body tissues. In addition, an electromagnetic band-gap structure is introduced in the wearable/flexible antenna designs to enable and give a high degree of isolation from the human body which also decreases the SAR dramatically. This paper reviews the state-of-the-art wearable/flexible antennas integrated with the electromagnetic band-gap structure on flexible materials concentrating on single and dual-band designs. Besides, it also highlights the challenges and considerations for an appropriate wearable/flexible antenna.

/pdf/an-overview-of-electromagnetic-band-gap-integrated-wearable-1qt5853icu.pdf

An Overview of Electromagnetic Band-Gap Integrated Wearable Antennas

A high gain, low specific absorption rate, oval-shaped monopole antenna is presented. It is backed by an all-textile 3 × 3 array of electromagnetic bandgap (EBG) unit cells. The antenna is printed on the thin Rogers ULTRALAM 3850 substrate, while the EBG array is composed of the conductive ShieledIT Super and dielectric substrate felt. The design operates at 2.45 GHz of the Industrial, Scientific, and Medical band. Due to the close distance between the extended grounds of the co-planar waveguide feeding configuration and the oval-shaped monopole antenna, current-coupling was achieved, leading to gain enhancement. However, with body-loading cases, resonance at 2.45 GHz was attained at a separation of 30 mm. By incorporating the EBG array, as an isolator, this issue was resolved. In free space and over a gap of 3 mm from the human body, gain enhancements by 2.68 and 11.54 dB were achieved at 2.45 GHz, respectively. Simulated and measured results are benchmarked. Furthermore, SAR simulation study showed reductions by 99.5%, averaged over 1 and 10 g of tissue.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-map.2019.1089

Wearable high gain low SAR antenna loaded with backed all-textile EBG for WBAN applications

The compact and robust high-impedance surface (HIS) integrated with the antenna is designed to operate at a frequency of 2.45 GHz for wearable applications. They are made of highly flexible fabric material. The overall size is $45\times \,\,45\times 2.4$ mm3 which equivalent to $0.37\lambda \text{o}\times 0.37\lambda \text{o}\times 0.02$ mm3. The value of using HIS lies in protecting the human body from harmful radiation and maintaining the performance of the antenna, which may be affected by the high conductivity of the human body. Besides, setting the antenna on the human body by itself detunes the frequency, but by adding HIS, it becomes robust and efficient for body loading and deformation. Integrated antenna with HIS demonstrates excellent performance, such as a gain of 7.47 dBi, efficiency of 71.8% and FBR of 10.8 dB. It also reduces the SAR below safety limits. The reduction is more than 95%. Therefore, the presented design was considered suitable for wearable applications. Further study was also performed to show the useful of placing antenna over HIS compared to the use of perfect electric conductor (PEC). The integrated design was also investigated with the worst case of varying the permittivity of body equivalent model which shows excellent performance in term of reflection coefficient and SAR levels. Hence, the integrated antenna with HIS is mechanically robust to human body tissue loading, and it is highly appropriate for body-worn applications.

Fully Fabric High Impedance Surface-Enabled Antenna for Wearable Medical Applications

An ultrathin, compact, and highly efficient antenna based on the $\Pi $ -section composite right/left-handed (CRLH) methodology is presented. It operates at 2.45 GHz of the Industrial, Scientific and Medical (ISM) band with a physical size of 25 mm $\times25$ mm, a realized gain of 2.34 dBi, and a total efficiency of 87% in free space. Nevertheless, to maintain resonance at 2.45 GHz with body-loading scenarios, a high separation was required, leading to an overall large size. To circumvent that, an all-textile $2 \times 2$ artificial magnetic conductor (AMC) array was placed in-between the antenna and the human body. In free space, the low-profile integrated design exhibited a gain of 7.63 dBi (enhancement of 5.29 dBi) and total efficiency of 96.4%. The integrated design achieved a gain and total efficiency enhancements by 14.88 dBi and 72.4%, respectively, as well as, lower specific absorption rate (SAR) levels, in comparison with the CRLH antenna alone, for human loading cases. Results are achieved through circuit model and full-wave electromagnetic simulations. In addition, the CRLH antenna and AMC array structure were fabricated and measurements were undertaken, which agreed well with the simulated ones. Therefore, the integrated design is highly suggested to be recognized in wireless body area network (WBAN) and medical applications.

A Compact Highly Efficient Π-Section CRLH Antenna Loaded With Textile AMC for Wireless Body Area Network Applications

A compact, flexible, coplanar waveguide-fed, U-shaped reflector surrounded asymmetric meander line antenna operating at 2.4 GHz is presented for wrist wearable applications. The antenna is printed on flexible Rogers Ultralam 3850 substrate. Size reduction of 67.7% was attained by employing the meandering methodology, in comparison with the printed straight monopole. The design displays a gain of around 3 dB by incorporating a U-shaped reflector, on the same level as the radiator, which is considered as the main contribution of the proposed design. Bending scenarios were studied proving the antenna robustness against bending. The proposed antenna was bent over a human body model with optimum separation distance, where enhancement of the specific absorption rate (SAR) level has been achieved, compared to the symmetric meander line antenna. The antenna was fabricated and measured where a high agreement was met in terms of simulated and measured return loss and radiation pattern polar plots, as well as, simulated and measured gain.

Mohamed El Atrash

Papers

A Wearable Dual-Band Low Profile High Gain Low SAR Antenna AMC-Backed for WBAN Applications

Wearable high gain low SAR antenna loaded with backed all-textile EBG for WBAN applications

Fully Fabric High Impedance Surface-Enabled Antenna for Wearable Medical Applications

A Compact Highly Efficient Π-Section CRLH Antenna Loaded With Textile AMC for Wireless Body Area Network Applications

Gain enhancement of a compact thin flexible reflector‐based asymmetric meander line antenna with low SAR