IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 61, NO. 5,MAY 2013 2253 A Smart Wearable Textile Array System for Biomedical Telemetry Applications Ping Jack Soh, Student Member, IEEE, Bertold Van den Bergh, Hantao Xu, Student Member, IEEE, Hadi Aliakbarian, Member, IEEE, Saeed Farsi, Student Member, IEEE, Purna Samal, Guy A. E Vandenbosch, Fellow, IEEE, Dominique M. M.-P. Schreurs, Fellow, IEEE, and Bart K. J. C. Nauwelaers, Senior Member, IEEE Abstract—A smart wearable textile array system (SWTAS) with direction of arrival (DoA) estimation and beamforming is proposed and developed for biomedical telemetry applications. This conformal system enables effective and continuous patient monitoring when combined with one or more health sensors, as information about the subject’s health condition is received adap- tively to guarantee link reliability. This operation is facilitated by a receiver front-end and a digital baseband beamforming network, which enables scalability and flexibility. The proposed SWTAS also features flexible antenna arrays made using textiles, which are arbitrarily located on a cylindrically shaped body phantom to ensure wide spatial DoA estimation capability. Besides being designed to suit on-body placement, the system performance is also characterized for on-body usage using a commercial body-emulating liquid, and placed at a realistic distance from the body, considering user clothing. Investigation indicated a good performance in the system’s 80 forward plane with a DoA accuracy of 3 . Finally, a practical evaluation is presented using two transmitters placed at distinct locations and distances. The system successfully estimated both DoAs and received the telemetry signals using beamforming. Index Terms—Antenna arrays, biomedical communication, biomedical monitoring, biomedical telemetry, conformal an- tennas, direction of arrival (DoA) estimation, smart antennas. I. INTRODUCTION T HE RECENT development in wireless body area net- works (WBANs) necessitates the integration of various features onto the conformal radiating systems. WBAN appli- cations, which range from medical monitoring and sensing, emergency response, military, sports, and even consumer electronics, require features such as power efficiency and self-sustainability [1], [2]. The use of low-profile conformal Manuscript received October 10, 2012; revised January 29, 2013; accepted January 31, 2013. Date of publication February 26, 2013; date of current ver- sion May 02, 2013. This work was supported in part by the IEEE Antennas and Propagation Society (AP-S), the Malaysian Ministry of Higher Education (MOHE), and the European COST-VISTA IC1102 (Versatile, Integrated and Signal-Aware Technologies for Antennas) STSM Initiative. P. J. Soh is with ESAT-TELEMIC, Department of Electrical Engineering, Katholieke Universiteit Leuven, 3001 Leuven, Belgium, and also with the School of Computer and Communication Engineering, Universiti Malaysia Perlis (UniMAP), 02000 Kuala Perlis, Perlis, Malaysia (e-mail: e-mail: ping- jack.soh@esat.kuleuven.be). B. Van den Bergh, H. Xu, H. Aliakbarian, S. Farsi, P. Samal, G. A. E. Vandenbosch, D. M. M.-P. Schreurs, and B. K. J. C. Nauwelaers are with ESAT-TELEMIC, Department of Electrical Engineering, Katholieke Univer- siteit Leuven, 3001 Leuven, Belgium. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TMTT.2013.2247051 radiators in body-worn systems is crucial in guaranteeing user’s comfort without limiting regular movements. Textile antennas are regarded as one of the most realistic candidates in achieving these users’ requirements, offering sufficient flexibility, confor- mality, and ergonomicity [3]–[6]. Such wearable health monitoring systems are not new, as they have been previously realized for the biomedical appli- cations domain. Several examples are the smart shirt, VTAM (Clothes for Teleassistance in Medicine) Project, the European Wearable Healthcare System (WEALTHY) [7], LifeShirt [8], and the in-shoe plantar pressure measurement system [9]. Such vests and worn clothing are integrated with various sensors, ei- ther made using textile and/or conventional materials, and fea- ture various health monitoring functions, including electrocar- diography (ECG), respiration activities, and temperature and shock/fall sensors. Each of these wearable health monitoring so- lutions also features a mechanism to channel information back to the health personnel through the use of existing telecommu- nication infrastructures and protocols, i.e., global system for mobile communication (GSM), Bluetooth, wireless local area netowrk (WLAN), 802.15.4, etc. This feature is crucial, as all gathered health information from the patient would be rendered useless if a reliable telemetry link cannot be guaranteed. This work implements and analyzes a low-cost and flexible smart wearable textile array system (SWTAS) designed to be worn on the body, e.g., by health-monitoring personnel for a reliable telemetry signal reception. Similarly, the described tex- tile antennas can also be used on patients to transmit telemetry information. The term “smart” refers to the signal processing capability that combines antenna signals with different phases and amplitudes to determine transmitting sensor’s direction of arrival (DoA), and consequently adapt its radiation pattern to- wards it [10]–[12]. This DoA capability realized using a digital baseband beamforming (DBBF) network enables an effective nonobtrusive biomedical monitoring and telemetry when com- bined with a wearable textile array and wireless health sensor. This proposed system can communicate health conditions for home-bound patients or outpatients to their medical monitoring personnel by searching for nearby-transmitting medical sensor nodes through DoA estimation, and consequently, beamforming toward the intended direction, once a transmission is detected. This allows for a self-sustaining and continuous patient mon- itoring, both with the monitored patient in static and dynamic conditions. To our knowledge, such an arbitrary flexible array system with a combined DoA estimation and beamforming ca- pability has yet to be reported in the open literature. 0018-9480/$31.00 © 2013 IEEE