Wearable, small, and robust: the circular quarter-mode textile antenna

A miniaturized wearable antenna, entirely implemented in textile materials, is proposed that relies on a quarter-mode substrate integrated waveguide topology. The design combines compact dimensions with high body-antenna isolation, making it excellently suited for off-body communication in wearable electronics/smart textile applications. The fabricated antenna achieves stable on-body performance. A measured on-body impedance matching bandwidth of 5.1% is obtained, versus 4.8% in free space. The antenna gain equals 3.8 dBi in the on-body and 4.2 dBi for the free-space scenario. High radiation efficiency, measured to be 81% in free space, is combined with a low calculated specific absorption rate of 0.45 mW/g, averaged over 1 g of tissue, with 500 mW input power

Coupled eighth-mode substrate integrated waveguide antenna: small and wideband with high-body antenna isolation

A novel antenna design for wideband operation is presented, consisting of a system of two coupled miniaturized eighth-mode resonant radiating cavities with a low-complexity feeding network. The design methodology relies on the virtual magnetic boundaries along the symmetry planes of a rectangular waveguide resonator, for size reduction, and the frequency bifurcation of two tightly coupled resonators, for bandwidth enhancement. After discussing its operating principle, a prototype targeting wearable applications is designed, manufactured, and validated. Multiband operation is achieved with simultaneous coverage of the 2.4-GHz ISM band and the LTE-7 up- and downlink-bands. Measurements in free-space and on-body scenarios validate the antenna's performance. A bandwidth of 414 MHz (16.2%) is measured, as well as a maximal gain of 4.7 dBi. The directive patch-like radiation pattern and the ground plane topology lead to high body-antenna isolation and good on-body performance. Impedance bandwidth and radiation pattern remain stable when the antenna is worn by a person and bent around a cylinder to mimic deformation

The next generation textile antennas based on substrate integrated waveguide technology

Textile antennas for body-worn applications have some very specific requirements and needs. From an electrical engineer's point of view, good radiation characteristics and impedance matching to the active electronics are important. From the wearer's perspective, the antenna should be unobtrusively integrated into the clothing, and the smart textile comfortable to wear. New techniques offer the potential to fulfill these different needs. One new approach consists of applying metalized eyelets to implement substrate integrated waveguide technology on textile materials. This results in high-performance on-body antennas with excellent behavior in close proximity of the human body. Two realizations are discussed: a wideband design and a miniaturized half mode substrate integrated waveguide dual-band design. Both yield excellent free-space and on-body performance, and superb antenna-body isolation, automatically resulting in very robust characteristics when deployed on-body

Textile SIW antennas as hybrid energy harvesting and power management platforms

A compact, highly-integrated and unobtrusive wearable textile antenna system, able to establish a reliable and energy-efficient wireless body-centric communication link in the [2.4-2.4835]-GHz Industrial, Scientific and Medical band and enabling energy harvesting from three different energy sources, is presented. Our design approach relies on further extending the functionality of a carefully selected textile antenna by exploiting its surface as an energy scavenging and power management platform. More specific, two different ultra-flexible solar cells, a micro-energy cell and a flexible power management system are integrated onto a wearable substrate integrated waveguide cavity-backed textile slot antenna to enable energy harvesting from both solar and artificial light. Furthermore, thermal body energy harvesting, via an externally connected thermoelectric generator, is enabled by including an ultra-low voltage step-up converter. Measurements in four well-chosen indoor scenarios demonstrate that a hybrid energy-harvesting approach is necessary to obtain a more continuous flow and a higher amount of scavenged energy, leading to a higher system autonomy and/or reduced battery size

Recent advances in materials and technologies for body-centric and IoT antenna systems

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Compact half diamond dual-band textile HMSIW on-body antenna

A novel wearable dual-band textile antenna, designed for optimal on-body performance in the 2.4 and 5.8 GHz Industrial, Scientific and Medical bands, is proposed. By using brass eyelets and a combination of conducting and non-conductive textile materials, a half-mode substrate integrated waveguide cavity with ground plane is realized that is very compact and flexible, while still directing radiation away from the wearer. Additional miniaturization is achieved by adding a row of shorting vias and slots. Beside excellent free space performance in the 2.4 and 5.8 GHz bands, respectively, with measured impedance bandwidth of 4.9% and 5.1%, maximal measured free-space gain of 4.1 and 5.8 dBi, and efficiency of 72.8% and 85.6%, very stable on-body performance is obtained, with minimal frequency detuning when deploying the antenna on the human body and when bent around cylinders with radii of 75 and 40 mm. At 2.45 and 5.8 GHz, respectively, the measured on-body gain is 4.4 and 5.7 dBi, with sufficiently small calculated SAR values of 0.55 and 0.90 W/kg. These properties make the proposed antenna excellently suited for wearable on-body systems

Circularly-polarised cavity-backed wearable antenna in SIW technology

This study presents a circularly-polarised substrate-integrated waveguide (SIW) antenna implemented using a textile substrate and operating at 2.45GHz, in the industrial, scientific, and medical frequency band. The antenna topology is based on a folded cavity with an annular ring as a radiating element, and it permits to obtain compact size and low sensitivity to the environment, without deteriorating the radiating performance. These characteristics, together with the choice of adopting a textile substrate, make the SIW antenna suitable for the integration in wearable systems for body-centric applications. The electromagnetic performance of the proposed antenna achieved in simulations was verified through the measurement of the device in an anechoic chamber. The circularly-polarised antenna exhibits a maximum gain of 6.5dBi, a radiation efficiency of 73% and a very high front-to-back ratio

Ultra-wideband cork substrate-integrated-waveguide cavity-backed slot antenna

An ultra-wideband (UWB) substrate-integrated-waveguide (SIW) cavity-backed slot antenna covering the lower part of the 3.1-10.6 GHz block allocated to UWB transmission systems, being 3.1-3.6 GHz, is designed, constructed and validated. Owing to its planar topology, low profile and the use of cork substrate material, the proposed antenna may be integrated unobtrusively in any cork surface. Prior to the antenna design, the cork substrate material was characterized in the frequency band of interest. The design is conducted based on the average properties, while maintaining some impedance bandwidth margins to allow for varying cork material properties. A prototype is validated in free space conditions, confirming the high performance observed in simulation. An impedance bandwidth of 700 MHz (20.9%) is measured. At the center frequency 3.35 GHz, a radiation efficiency of 78%, a front-to-back ratio of 17.2 dB, and a maximum gain of 4.9 dBi are obtained. The maximum gain varies only by 1.4 dB within the frequency band of interest. The other far-field properties also vary only negligibly, which is the most important requirement to UWB antennas

Robust, wearable, on-body antenna relying on half mode substrate integrated waveguide techniques

A compact, robust, wearable antenna for body-worn applications in the 2.4 GHz Industrial Medical and Scientific band is designed, fabricated and tested. This novel compact textile cavity backed slot antenna combines a half-mode substrate integrated waveguide topology with an additional row of shorting vias for miniaturization. Excellent free space performance is achieved with a measured 4.6 % impedance bandwidth, maximal gain of 4.7 dBi and radiation efficiency of 81.3 %. On-body measurements reveal minimal frequency detuning when the antenna is worn by a test subject as well as a negligible impedance bandwidth reduction to 4.5 %. The low calculated Specific Absorption Rate of 0.51 W/kg averaged over 1 g of tissue demonstrates high antenna body isolation. Therefore, this design is an attractive option as antenna in smart textile systems