Thijs Castel

Threefold Rotationally Symmetric SIW Antenna Array for Ultra-Short-Range MIMO Communication

A high-performance, three-element substrate-integrated-waveguide (SIW) cavity-backed slot antenna array that covers the (5.15-5.85) GHz band is designed for integration inside or underneath the worktop of a desk, to set up a stable, high data-rate ultra-short-range 3 × 3 multiple-input multiple-output (MIMO) wireless communication link with a mobile user (MU) positioned on top of that worktop. The antenna topology and array geometry are carefully selected to maximally exploit the multiplexing capabilities of the ultra-short-range 3 × 3 MIMO channel over a wide bandwidth, yielding an increased channel capacity and/or reduced power consumption. In addition, special care was taken to guarantee a channel capacity that is less dependent on the relative orientation of the MU. Furthermore, the SIW implementation technology is combined with innovative antenna materials to guarantee a low-profile, low-cost, stable, and high-performance broadband array design that maintains its excellent performance after integration. A prototype of the antenna array was fabricated, integrated according to two different integration scenarios, and validated. Measurements prove that the antenna array allows integration into a worktop with only a minor influence on its return loss and mutual coupling, guaranteeing a bandwidth of at least 1.078 GHz and a minimum isolation between antenna elements of 30 dB within the entire (5.15-5.85) GHz band.

Improved reception of in-body signals by means of a wearable multi-antenna system

High data-rate wireless communication for in-body human implants is mainly performed in the 402–405 MHz Medical Implant Communication System band and the 2.45 GHz Industrial, Scientific and Medical band. The latter band offers larger bandwidth, enabling high-resolution live video transmission. Although in-body signal attenuation is larger, at least 29 dB more power may be transmitted in this band and the antenna efficiency for compact antennas at 2.45 GHz is also up to 10 times higher. Moreover, at the receive side, one can exploit the large surface provided by a garment by deploying multiple compact highly efficient wearable antennas, capturing the signals transmitted by the implant directly at the body surface, yielding stronger signals and reducing interference. In this paper, we implement a reliable 3.5 Mbps wearable textile multi-antenna system suitable for integration into a jacket worn by a patient, and evaluate its potential to improve the In-to-Out Body wireless link reliability by means of spatial receive diversity in a standardized measurement setup. We derive the optimal distribution and the minimum number of on-body antennas required to ensure signal levels that are large enough for real-time wireless endoscopy-capsule applications, at varying positions and orientations of the implant in the human body.

RSS-based secret key generation for indoor and outdoor WBANs using on-body sensor nodes

Given that the market of wearables is in so-called hypergrowth mode, more and more of these on-body devices will interact with each other. These body-to-body, device-to-device links should not only provide reliable but also secure communication of personal user data. Therefore, we have analyzed the potential of using the unique reciprocal body-to-body channel between two legitimate parties, to create a high-level security key that is unknown to an eavesdropper. Both randomly moving legitimate parties, typically called Alice and Bob, were equipped with low-power wireless on-body sensor nodes, which collect the Received Signal Strength values. Additionally, the eavesdropper Eve, who is continuously sniffing the body-to-body channel using a third sensor node, collects her own sequence of RSS values, which are expected to be highly decorrelated from the RSS values from both Alice and Bob. Based on a statistical analysis, applied to Received Signal Strength values to verify the correlation, entropy and mutual information, the body-to-body link seems very suitable for RSS-based secret key generation in indoor and outdoor Wireless Body Area Networks. Moreover, this practical and lightweight alternative for secret key generation ensures low on-chip complexity and, hence, low computational power consumption.

LTE as a potential standard for public safety indoor body-to-body networks

In this paper, a wideband indoor body-to-body communication channel is characterized and analyzed into detail by means of the RMS delay spread and the 50% correlation bandwidth. These body-to-body channel parameters are calculated based on high-resolution power delay profiles, directly provided by the Elektrobit channel sounder, and are further analyzed using a ray tracing algorithm. We have replicated a real-life rescue operation, performed by two firefighters as part of the Rapid Intervention Team searching for potential victims, operating at the same floor of an office block. Both firefighters, who were simultaneously moving around in the vicinity of each other, were equipped with two cavity-backed Substrate Integrated Waveguide textile antennas unobtrusively integrated in the front and back section of their jackets, allowing us to analyze four independent body-to-body links. Furthermore, we prove that the Long Term Evolution (LTE) and, by extension, the LTE - Device to Device (LTE-D2D) standard is compatible with this indoor body-to-body channel. This could provide high data rate indoor communication between rescuers, enabling multimedia broadcast and realtime communication of on-body sensor data in public safety networks.

On-Body Characterization of Planar Differential Antennas for Multiple, Wide, and Narrow Bands

This paper reports the results of the on-body experimental tests of a set of four planar differential antennas, originated by design variations of radiating elements with the same shape and characterized by the potential for covering wide and narrow bands. All the antenna designs have been implemented on low-cost FR4 substrate and characterized experimentally through on-body measurements. The results show the impact of the proximity to the human body on antenna performance and the opportunities in terms of potential coverage of wide and narrow bands for future ad hoc designs and implementations through wearable substrates targeting on-body and off-body communication and sensing applications.