A Novel Design Approach for Compact Wearable Antennas Based on Metasurfaces

Design and SAR Analysis of an AMC-Integrated Wearable Cavity-Backed SIW Antenna

Wearable communication technologies necessitate antenna designs that harmonize ergonomic compatibility, reliable performance, and minimal interaction with human tissues. However, high specific absorption rate (SAR) levels, limited radiation efficiency, and challenges in integration with flexible materials have significantly constrained widespread deployment. To address these limitations, this manuscript introduces a novel wearable cavity-backed substrate-integrated waveguide (SIW) antenna augmented with artificial magnetic conductor (AMC) structures. The proposed architecture is meticulously engineered using diverse textile substrates, including cotton, jeans, and jute, to synergistically integrate SIW and AMC technologies, mitigating body-induced performance degradation while ensuring safety and high radiation efficiency. The proposed design demonstrates significant performance enhancements, achieving SAR reductions to 0.672 W/kg on the spine and 0.341 W/kg on the forelimb for the cotton substrate. Furthermore, the AMC-backed implementation attains ultra-low reflection coefficients, as low as -26.56 dB, alongside a gain improvement of up to 1.37 dB, culminating in a total gain of 7.09 dBi. The impedance bandwidth exceeds the ISM band specifications, spanning 150 MHz (2.3-2.45 GHz). The design maintains remarkable resilience and operational stability under varying conditions, including dynamic bending and proximity to human body models. By substantially suppressing back radiation, enhancing directional gain, and preserving impedance matching, the AMC integration optimally adapts the antenna to body-centric communication scenarios. This study uniquely investigates the dielectric and mechanical properties of textile substrates within the AMC-SIW configuration, emphasizing their practicality for wearable applications. This research sets a precedent for wearable antenna innovation, achieving an unprecedented balance of flexibility, safety, and electromagnetic performance while establishing a foundation for next-generation wearable systems.

Efficient polarization conversion metasurface for scattered beam control and RCS reduction

This study proposes and experimentally validates a multifunctional, ultra-wideband polarization conversion metasurface. The design integrates polarization conversion and electromagnetic scattering functions into a single structure, enabling applications in polarization conversion, beam control, and effective reduction of the radar cross-section (RCS). The metasurface achieves linear-to-circular polarization conversion with an axial ratio (AR) of less than 3 dB across dual-band ranges of 14.6-26.8 GHz and 31-33.5 GHz. Additionally, by adjusting metallic resonant rings within the unit structure, cross-polarization conversion with a polarization conversion ratio (PCR) greater than 0.9 is realized in the 13.6-29.8 GHz frequency range, maintaining excellent stability even at oblique incidence angles up to 50°. Leveraging the phase cancellation principle, various coding arrays are designed to precisely control the scattered beams, reducing the RCS by more than 10 dB. The comparison of simulation and experimental results further validates the wide application potential of this polarization converter in fields such as wireless communication, antenna engineering, and radar stealth.

Design and performance investigation of metamaterial-inspired dual band antenna for WBAN applications

This paper presents the design and analysis of a metamaterial-based compact dual-band antenna for WBAN applications. The antenna is designed and fabricated on a 0.254 mm thick semi-flexible substrate, RT/Duroid® 5880, with a relative permittivity of 2.2 and a loss tangent of 0.0009. The total dimensions of the antenna are 0.26λo×0.19λo×0.002λo, where λo corresponds to the free space wavelength at 2.45 GHz. To enhance overall performance and isolate the antenna from adverse effects of the human body, it is backed by a 2×2 artificial magnetic conductor (AMC) plane. The total volume of the AMC integrated design is 0.55λo×0.55λo×0.002λo. The paper investigates the antenna's performance both with and without AMC integration, considering on- and off-body states, as well as various bending conditions in both E and H-planes. Results indicate that the AMC-integrated antenna gives improved measured gains of 6.61 dBi and 8.02 dBi, with bandwidths of 10.12% and 7.43% at 2.45 GHz and 5.80 GHz, respectively. Furthermore, the AMC integrated antenna reduces the specific absorption rate (SAR) to (>96%) and (>93%) at 2.45 GHz and 5.80 GHz, meeting FCC requirements for low SAR at both frequencies when placed in proximity to the human body. CST Microwave Studio (MWS) and Ansys High-Frequency Structure Simulation (HFSS), both full-wave simulation tools, are utilized to evaluate the antenna's performance and to characterize the AMC unit cell. The simulated and tested results are in mutual agreement. Due to its low profile, high gain, adequate bandwidth, low SAR values, and compact size, the AMC integrated antenna is considered suitable for WBAN applications.

Materials, Designs, and Implementations of Wearable Antennas and Circuits for Biomedical Applications: A Review

The intersection of biomedicine and radio frequency (RF) engineering has fundamentally transformed self-health monitoring by leveraging soft and wearable electronic devices. This paradigm shift presents a critical challenge, requiring these devices and systems to possess exceptional flexibility, biocompatibility, and functionality. To meet these requirements, traditional electronic systems, such as sensors and antennas made from rigid and bulky materials, must be adapted through material science and schematic design. Notably, in recent years, extensive research efforts have focused on this field, and this review article will concentrate on recent advancements. We will explore the traditional/emerging materials for highly flexible and electrically efficient wearable electronics, followed by systematic designs for improved functionality and performance. Additionally, we will briefly overview several remarkable applications of wearable electronics in biomedical sensing. Finally, we provide an outlook on potential future directions in this developing area.

A monopole antenna with cotton fabric material for wearable applications

A monopole antenna operated at 2.45 GHz and embedded with artificial magnetic conductor (AMC) for wearable communication systems is investigated in this article. The proposed antenna is composed of a metalized loop radiator with a coplanar waveguide microstrip feedline which is affixed on a cotton fabric material substrate. As well, a cotton-based AMC surface is utilized to eliminate the body's absorbed radiation and enhance the gain of the antenna. It is composed of 5 × 5 array unit cells etched with I-shaped slots. Using this configuration, simulations show that the specific absorption rate (SAR) level was significantly reduced. Considering flat and rounded body parts, it was found that the SAR values averaged over 10 g at a distance of 1 mm away from the tissues model were only 0.18 W/kg and 0.371 W/kg, respectively. Additionally, the antenna gain was improved up to 7.2 dBi with an average radiation efficiency of 72%. Detailed analysis with experimental measurements of the cotton-based antenna for different operation scenarios is introduced. The measured data show a good correlation with the electromagnetic simulation results.

Compact Wearable Antenna with Metasurface for Millimeter-Wave Radar Applications

Three metasurfaces (MTS) are designed to be combined with a series end-fed 1 × 10 array antenna with a modified Dolph-Chebyshev distribution for imaging applications in the millimeter frequency range, 24.05-24.25 GHz. A reduction in secondary lobes and an increase in FTBR can be achieved while preserving gain, radiation efficiency, SLL and size using an MTS-array combination. Moreover, as a result of each single-layer MTS-array combination, operation bandwidth is widened, with gain and radiation efficiency enhancement. The overall devices' size is 86.8 × 12 × 0.762 mm³. The envisioned application is collision avoidance in aid to visually impaired people at a medium-long distance.

Wearable Polarization Conversion Metasurface MIMO Antenna for Biomedical Applications in 5 GHz WBAN

This paper presents a wearable metasurface multiple-input multiple-output (MIMO) antenna for biomedical applications in a 5 GHz wireless body area network (WBAN) with broadband, circular polarization (CP), and high gain. The physical properties of the MIMO antenna element and the principles of polarization conversion are analyzed in-depth using characteristic mode analysis. For the proposed MIMO antenna, the measured -10 dB impedance bandwidth is 34.87% (4.76-6.77 GHz), and the 3 dB axial ratio bandwidth is 22.94% (4.9-6.17 GHz). By adding an isolation strip, the measured isolation of the two antenna elements is greater than 19.85 dB. The overall size of the MIMO antenna is 1.67λ₀ × 0.81λ₀ × 0.07λ₀ at 5.6 GHz, and the maximum gain is 7.95 dBic. The envelope correlation coefficient (ECC) is less than 0.007, with the maximum diversity gain greater than 9.98 dB, and the channel capacity loss is less than 0.29 b/s/Hz. The specific absorption rate (SAR) of the wearable MIMO antenna is simulated by the human tissue model, which proves that the proposed antenna conforms to international standards and is harmless to humans. The proposed wearable metasurface MIMO antenna has CP, broadband, high gain, low ECC, and low SAR, which can be used in wearable devices for biomedical applications.

Low-profile Button Sensor Antenna Design for Wireless Medical Body Area Networks

A button sensor antenna (BSA) for wireless medical body area networks (WMBAN) is presented, which works through the IEEE 802.11b/g/n standard. Due to strong interaction between the sensor antenna and the body, a new robust system is designed with a small footprint that can serve on- and off-body healthcare applications. The measured and simulated results are matched well. The design offers a wide range of omnidirectional radiation patterns in free space, with a reflection coefficient (S₁₁) of -29.30 (-30.97) dB in the lower (upper) bands. S₁₁ reaches up to -23.07 (-27.07) dB and -30.76 (-31.12) dB on the body chest and arm, respectively. The Specific Absorption Rate (SAR) values are below the regulatory limitations for both 1-gram (1.6 W/Kg) and 10-gram tissues (2.0 W/Kg). Experimental tests of the read range validate the results of a maximum coverage range of 40 meters. Clinical Relevance- WMBAN technology allows for continuous monitoring and analysis of patient health data to improve the quality of healthcare services.

Design of a Compact Dual-Band Textile Antenna Based on Metasurface

This paper presents a compact textile antenna design based on a metasurface for wearable applications. It operates in the 2.45 GHz and 5.5 GHz industrial, scientific, and medical bands. A two-dimensional equivalent circuit model is proposed to provide insight into the working principle of the metasurface. The tuning of the radiator's resonant frequencies can be easily performed by adjusting the dispersion curve of the metasurface unit cell. The metasurface in this work consists of a 4 × 4 array of unit cells fed by a printed coplanar waveguide structure with a slot in its reverse side to maintain its low profile structure. The main innovations of this work are: (i) the -2^nd mode is employed to significantly miniaturize the antenna dimensions; (ii) the simultaneous excitation of the +1^st mode to enable dual-band operation; (iii) an integrated back reflector to reduce back radiation and lower SAR; and (iv) the use of full textile materials to guarantee user comfort, ease of fabrication and low cost. The proposed antenna's footprint is 44.1 × 44.1 mm² (0.12 λ² at 2.45 GHz), with an impedance bandwidth of 10.2% centered at 2.45 GHz and 22.5% at 5.5 GHz. The maximum gain is -0.67 dBi and 7.4 dBi in free space, and 9% of power gain attenuation is generated when used on the body, and is suitable as a miniaturized antenna for wearable applications.

Design and Evaluation of a Button Sensor Antenna for On-Body Monitoring Activity in Healthcare Applications

A button sensor antenna for on-body monitoring in wireless body area network (WBAN) systems is presented. Due to the close coupling between the sensor antenna and the human body, it is highly challenging to design sensor antenna devices. In this paper, a mechanically robust system is proposed that integrates a dual-band button antenna with a wireless sensor module designed on a printed circuit board (PCB). The system features a small footprint and has good radiation characteristics and efficiency. This was fabricated, and the measured and simulated results are in good agreement. The design offers a wide range of omnidirectional radiation patterns in free space, with a reflection coefficient (S11) of −29.30 (−30.97) dB, a maximum gain of 1.75 (5.65) dBi, and radiation efficiency of 71.91 (92.51)% in the lower and upper bands, respectively. S11 reaches −23.07 (−27.07) dB and −30.76 (−31.12) dB, respectively, with a gain of 2.09 (6.70) dBi and 2.16 (5.67) dBi, and radiation efficiency of 65.12 (81.63)% and 75.00 (85.00)%, when located on the body for the lower and upper bands, respectively. The performance is minimally affected by bending, movement, and fabrication tolerances. The specific absorption rate (SAR) values are below the regulatory limitations for the spatial average over 1 g (1.6 W/Kg) and 10 g of tissues (2.0 W/Kg). For both indoor and outdoor conditions, experimental results of the range tests confirm the coverage of up to 40 m.

A Low-Profile Ultrawideband Antenna Based on Flexible Graphite Films for On-Body Wearable Applications

This paper presents a low-profile ultrawideband antenna for on-body wearable applications. The proposed antenna is based on highly conductive flexible graphite films (FGF) and polyimide (PI) substrate, which exhibits good benefits such as flexibility, light weight and corrosion resistance compared with traditional materials. By introducing flaring ground and an arrow-shaped slot, better impedance matching is achieved. The wearable antenna achieves a bandwidth of 122% from 0.34 GHz to 1.4 GHz, with a reflection coefficient of less than −10 dB, while exhibiting an omnidirectional pattern in the horizontal plane. To validate the proposed design, the wearable antenna with a profile of ~0.1 mm was fabricated and measured. The measured results are in good agreement with simulated ones, which indicates a suitable candidate for on-body wearable devices.

C-shaped antenna based artificial magnetic conductor structure for wearable IoT healthcare devices

A wearable C-shaped antenna based on a fabric material operating at 2.4 GHz frequency is proposed for use in flexible/wearable IoT medical systems. The wearable IoT device plays a key role in medical applications, and the antenna is a key part of it. Loading the presented antenna on the body models showed a frequency detuned with the gain and efficiency reduced from 1. 28 to −9 dB and 90% to 10%. In addition, the SAR did not meet the safety health requirement defined by the FCC or ICNIRP standards. Therefore, an “Artificial Magnetic Conductor” structure (AMC) is added to the C-shaped antenna to overcome these problems. The AMC acts as shielding material between the human skin and the presented antenna because of its 0° reflection phase, which mimics the action of the Perfect Magnetic Conductor (PMC). The overall size of the proposed design was 54 × 54 × 3.9 mm³. Numerical and experimental findings indicated that integrating the AMC structures with a C-shaped antenna was robust for body deformation and load. The C-shaped antenna worked equally well with the AMC, whether positioned in free space or on the chest or the arm of the human body. The integrated antenna with AMC structures has excellent performances. The gain and efficiency without loading on the chest were 6.49 dB and 84%, respectively. While for loaded on the chest were 6.21 dB and 81%, respectively. It also decreased the back radiation and raised the Front to Back Ration (FBR) by 13.8 dB. SAR levels have been reduced by more than 90% between the FCC and ICNIRP standards compared to the C-shaped antenna alone, which does not comply with the standards. As a result, the C-shaped integration with AMC structures is highly suitable for assembly in any wearable system.

Meta-Wearable Antennas-A Review of Metamaterial Based Antennas in Wireless Body Area Networks

Wireless Body Area Network (WBAN) has attracted more and more attention in many sectors of society. As a critical component in these systems, wearable antennas suffer from several serious challenges, e.g., electromagnetic coupling between the human body and the antennas, different physical deformations, and widely varying operating environments, and thus, advanced design methods and techniques are urgently needed to alleviate these limitations. Recent developments have focused on the application of metamaterials in wearable antennas, which is a prospective area and has unique advantages. This article will review the key progress in metamaterial-based antennas for WBAN applications, including wearable antennas involved with composite right/left-handed transmission lines (CRLH TLs), wearable antennas based on metasurfaces, and reconfigurable wearable antennas based on tunable metamaterials. These structures have resulted in improved performance of wearable antennas with minimal effects on the human body, which consequently will result in more reliable wearable communication. In addition, various design methodologies of meta-wearable antennas are summarized, and the applications of wearable antennas by these methods are discussed.