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IEEE TRANSACTIONS ON BIOMEDICAL CIRCUITS AND SYSTEMS, VOL. 1, NO. 4, DECEMBER 2007

Numerical and Experimental Evaluation of a Compact Sensor Antenna for Healthcare Devices Akram Alomainy, Member, IEEE, Yang Hao, Senior Member, IEEE, and Frank Pasveer

Abstract—The paper presents a compact planar antenna designed for wireless sensors intended for healthcare applications. Antenna performance is investigated with regards to various parameters governing the overall sensor operation. The study illustrates the importance of including full sensor details in determining and analysing the antenna performance. A globally optimized sensor antenna shows an increase in antenna gain by 2.8 dB and 29% higher radiation efficiency in comparison to a conventional printed strip antenna. The wearable sensor performance is demonstrated and effects on antenna radiated power, efficiency and front to back ratio of radiated energy are investigated both numerically and experimentally. Propagation characteristics of the body-worn sensor to on-body and off-body base units are also studied. It is demonstrated that the improved sensor antenna has an increase in transmitted and received power, consequently sensor coverage range is extended by approximately 25%. Index Terms—Body-worn device, compact planar antenna, efficiency, electromagnetic modeling, medical sensor.

I. INTRODUCTION

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IRELESS medical sensor technologies are heading towards a future with patient-specific information accessible at the doctor’s fingertips whenever and wherever required with radio and antenna systems playing a major role in defining such technologies. Wireless body area networks (WBAN) provide promising applications in medical sensing systems [1]–[4]. They present an apparent option for efficient, flexible systems with constant availability, reconfigurability and unobtrusiveness. Commonly, sensors are placed on the human body to measure specified physiological data and also location-based information if required. Antennas are essential parts of body-centric networks and their complexity depend on the radio transceiver requirements as well as the propagation characteristics of the surrounding environments. For current and future wireless devices, the antenna is required to perform more than one task or in other words the antenna needs to operate at different frequencies to account for the increasing new technologies and services available to the user, e.g., systems on pills [5] and miniaturized sensors [6]. For wireless sensor applications, antennas need to be efficient and immune from frequency and polarization detuning.

Manuscript received June 8, 2007; revised November 15, 2007. This paper was recommended by Associate Editor T. Falck. A. Alomainy and Y. Hao are with Department of Electronic Engineering, Queen Mary University of London, London E1 4NS, U.K. (e-mail: akram. [email protected]; [email protected]). W. F. Pasveer is with the System in Package Devices Group, Philips Research, Eindohoven 5656, The Netherlands (e-mail: [email protected]). 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/TBCAS.2007.913127

Understanding the antenna radiation pattern for wireless sensors, specifically when applied for body-worn applications, is vital in determining the sensor performance [7]–[11]. Performance evaluations of body-worn antennas for consumer applications have been intensively studied in the open literature [5]–[11]. Due to the increased demand on multifrequency and multifunction antennas to be utilized in future consumer and medical communication technologies, compact and easily integrated antenna designs have received a vast amount of attention in the last few years. Slightly modified conventional antennas were applied in sensor designs to enable energy radiation; however, with low efficiency and very limited coverage range due to lack of attention given to the antenna performance degredation [5], [6]. In [8], Salonen et al. introduced the application of the planar inverted F antenna as a wearable antenna that can be placed on the human with maximum functionality. The analyzed antenna is considered bulky for sensing applications, and surrounding circuitry and environment effects on the performance are neglected. To the authors’ knowledge, a thorough investigation on the causes of inefficiency in wireless medical sensors due to antenna performance and the effect of full sensor structure (including ICs and lumped elements) on the antenna operation has not been presented. This paper demonstrates extended investigations on a compact healthcare sensor (the sensor is presented in [12]) operating in the unlicensed industrial, scientific and medical 2.4-GHz band. Modeling and characterization issues of the antenna deployed in the full sensor are discussed and investigated to highlight potential enhancement techniques for healthcare applications. The rest of the paper is organized as follows. Section II presents various antenna designs applied for the proposed sensor structure and different matching techniques adopted to improve performance. Section III illustrates through numerical calculations the body-worn sensor performance applying a digital male phantom with electrical properties at 2.4 GHz to demonstrate the body influence on general antenna parameters and hence the sensor. Radio channel characterization of the proposed sensor antennas in wireless personal area network (WPAN) scenarios is detailed in Section IV. Section V draws the main conclusions of the presented work. II. PROPOSED SENSOR ANTENNA A. Design Requirements The compact sensor structure introduces many restrictions on the antenna design including the sensor size, chips placement, lumped element locations and flexibility of the sensor various

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Fig. 1. Compact sensor module applied in the presented study. (a) Schematic of the sensor structure including antenna and other components applied in the numerical analysis. (b) Photograph of the sensor transceiver layer. (c) Fabricated prototype sensor.( a) Sensor model applied in numerical analysis. (b) Top view of the fabricated transceiver layer. (c) Photograph of the manufactured prototype sensor.

layers to be shuffled with minimum cost and changes to antenna performance. Fig. 1(a) presents a schematic of the sensor model applied in the numerical investigation with the printed monopole antenna around the circumference of the sensor upper layer and all other components included in the module. Photographs of the sensor transceiver layer and the prototype module fabricated are shown in Fig. 1(b) and (c), respectively. monopole The initial antenna deployed in the sensor is a etched on the edge of the circular PCB board. Hence, the antenna is designed with the printed wire wrapping the transceiver chip and other components. The antenna is derived from the circumference monopole, which is similar to the bent and inverted L antenna [13]. The sensor antenna performance is sensitive to the presence of lumped components, pins and copper routings. The surrounding and adjacent components are modeled as perfect conductor blocks around which the antenna is printed. The printed circuit board includes an embedded ground plane. One major difference, with an antenna in free space that can be identified directly when placing an antenna on a dielectric material is the deviation in wavelength value from the free space at the specified freone [7], [14]. The guided wavelength quency will become shorter since the wave travels slower in a dielectric and lossy medium. In addition, the metal pins and copper lines provide a parasitic extension to the antenna which increases the impedance value expected; however, due to the capacitive coupling between the antenna and surrounding components the antenna impedance tends to decrease. Therefore,

the radiation characteristics of the antenna are directly affected; hence changes in antenna gain and efficiency with respect to free space, are expected. B. Numerical Analysis of Antenna Performance The antenna design deployed in the proposed sensor is numerically analyzed using the finite integral technique (FIT) [15] utilized in the CST, Microwave Studio [16]. The printed cir, cular monopole antenna is modeled on FR4 substrate ( and thickness of 0.3 mm). The printed antenna thickness is 35 m and the width of the line is 150 m. The ground and supply voltage layers added have a radius of 5.5 mm, thickness of 17.5 m each, and separation between the layers of 80 m. The actual antenna length is 31.5 mm (approximately quarter wavelength at the required frequency, 2.4 GHz). The complex impedance at the RF transceiver differential output is 115 180 , therefore a matching circuit is applied in order to match the output to the single-ended monopole. Fig. 2(a) presents the return loss of the sensor antenna when only one layer is modeled and for full sensor modeling. The one layer model includes the printed antenna, the transceiver chip and PCB board. The figure illustrates the significance of considering full structure modeling in characterizing small antenna designs integrated with radio systems. The presence of the connectors in close proximity to the printed antenna causes strong coupling between them which in return increases the path of the produced current and hence shifting the resonance frequency of

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Fig. 3. 3-D gain function pattern of the capacitor-matched sensor antenna numerically calculated at 2.4 GHz.

Fig. 2. Comparison of matched sensor antenna performance for one layer and full sensor model. (a) Return loss of sensor antenna for the investigated scenarios. (b) Circuit schematic of the matching section between the transceiver and the antenna to provide matching to sensor antenna impedance of 10 . (a) Return loss of the one layer and full sensor models. (b) Lumped element circuit for matching the tranceiver output with the antenna input.

the antenna. The calculated antenna gain is ation efficiency of 48% at 2.4 GHz.

1.2 dBi with radi-

C. Performance Enhancement Techniques The impedance of the printed monopole is numerically analyzed and the real part of the antenna impedance is calculated as 10 . The curvature of the antenna causes the reactance part to be more inductive. Therefore, the matching circuit between the transceiver output and the antenna port needs to be modified, Fig. 2(b). The initial monopole antenna (not matched at frequency of operation) has a calculated complex impedance of at 2.4 GHz. Introducing a 0.2 pF capacitor at the antenna input cancels the reactive part of the impedance and provides a reasonable match to 50 (reflection coefficient approximately 15 dB). The 3-D radiation pattern at 2.4 GHz of the capacitor matched antenna is shown in Fig. 3. The pattern is different from that of a conventional vertical monopole due to the antenna curvature and also the effect of surrounding elements. The calculated capacitor matched antenna gain is around 1.6 dBi with radiation efficiency of 77%. This illustrates the potential extended coverage area served by the sensor with simple and reliable performance enhancement techniques. The modeled sensor structure includes

Fig. 4. Dipole antenna applied for sensor design to provide efficient and easily fabricated antennas without the need for matching circuitry.

two layers of circuitary components in comparison to four illustrated in the prototype photograph in Fig. 1. Two layers proved to be sufficient enough for obtaining reliable data in comparison to wavelength and total sensor size. D. Dipole for Compact Sensor In addition to the monopole, the dipole antenna is one of the most widely used antennas in wireless communication both practically and theoretically for various studies and applications [14]. The most common type is the half-wavelength dipole antenna due to its low real impedance (around 75 ) in addition to its simplicity, cost-effectiveness and efficiency. In order to design a dipole with complex input impedance that matches the output impedance of the transceiver chip , the length of the dipole arms have to be trimmed and optimized to achieve the desired complex impedance at the proposed frequency which leads to total antenna length different at 2.4 GHz (30 mm when printed on FR4 board). Fig. 4 from illustrates the modified sensor transceiver layer with the dipole arms printed on both sides of the board with each arm measuring 21 mm in length. In addition to features such as the ease of design and cost-effectiveness of the dipole, the antenna gain and radiation efficiency are improved by 2.3 dBi and 28% in comparison to the printed monopole without matching ( 1.2 dBi and initial

ALOMAINY et al.: NUMERICAL AND EXPERIMENTAL EVALUATION OF A COMPACT SENSOR ANTENNA FOR HEALTHCARE DEVICES

TABLE I PARAMETRIC COMPARISON OF THE PROPOSED SENSOR ANTENNA DESIGNS. (INITIAL =4 MONOPOLE, MONOPOLE WITH MODIFIED MATCHING CIRCUIT, MONOPOLE WITH CAPACITOR MATCHING AND DIPOLE)

48%). Table I compares antenna gain, radiation and total efficiency (total efficiency takes into account radiated power and accepted power of the antenna [14]) of the different antennas proposed for the sensor structure. III. WEARABLE SENSOR MODELING The sensor with a capacitor matched antenna is placed on the human chest of the digital male phantom [18], as shown in Fig. 5, with the radiating element normal and parallel to the body to numerically investigate the effect of human presence on performance. The used model is the commonly available detailed multilayer human model, namely the visible male model developed by the US air force [18]. All the tissues included in the digital phantom have electric properties at 2.4 GHz as presented in Table II [19], [20]. The simulated return loss of the body-worn sensor antenna shows the slight detuning due to presence of lossy tissues for the sensor sensor placed 2 mm away from the body which directly affects the effective permittivity of the medium surrounding the antenna, Fig. 6. Although the detuning effect is minimum (in this case 1.2%), the narrowband nature of the antenna (with capacitor used for matching) dramatically increases the influence of this detuning on the radiated energy. The attenuation of a wave propagating in lossy biological tissue is commonly defined in terms of penetration depth [22] (1) where is the angular frequency of the wave and is the real part of the permittivity of the medium. The penetration depth is therefore dependent on frequency and tissue parameters. It represents the distance a wave must travel in the dielectric before it times the field strength at the starting point is attenuated to (refer to Table II for penetration depths of various human tissues). The antenna gain when placed on the body is increased to 2.4 dB caused by partial reflections of waves incident on the human body. At 2.4 GHz, the human body behaves neither as good absorber nor a good reflector and a certain amount of the electromagnetic energy is absorbed by the body while some energy is reflected. The azimuth plane radiation patterns shown in Fig. 7 illustrate the effect of the human body on the antenna performance and the reduced radiated power in the backward direction with front to back ratio of around 22 dB. Since the average penetration depth of human tissues (specifically high water content tissues) is 20–30 mm, waves propagating through the human body would attenuate (considering the source

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is placed on the front and the receiving node is at the back of the body) by approximately 60–70 dB, which makes the signal negligible from the system point of view. Since the front-to-back ratio is around 22 dB, this indicates the existence of different wave propagation mechanism around the human body, bearing in mind that the human is placed in free space, therefore multipath reflections from the surrounding environment are ignored). Fig. 8 demonstrates the electric field distribution around the body at 2.4 GHz. The field distribution clearly shows the diffraction of free space waves originating from the antenna caused by the curvature of the human body and therefore introducing creeping waves that follow the human body shape and travel along the body surface. Hence, the received signal at the back contains contributions from creeping waves travelling from the transmitter along the surface at opposite directions, which corresponds to predictions from the General Theory of Diffraction (GTD) along and around cylindrical and elliptical bodies [21]. IV. PROPAGATION CHARACTERISTICS OF THE SENSOR ANTENNA IN WPAN SCENARIOS A. Sensor With a Planar Monopole Antenna The spatial performance of the sensor with monopole antenna is analyzed experimentally in free space (anechoic chamber measurements). The sensor is placed on a turn-table with angular variations of 0 –360 . The sensor is used as transmitting unit and a microstrip patch antenna connected to a spectrum analyzer acts as a receiving node. The measurement is performed in the far-field of the sensor antenna. The sensor is placed on the turn-table in horizontal and vertical orientations to investigate polarization effect on the propagation channel. Similar settings are used when the sensor is worn by the user, Fig. 5. Fig. 9 shows normalized measured co-polar and cross-polar patterns of the sensor antenna radiation performance in free space and also when placed on the body with the antenna normal to the body. When the body shadows the communication link between the transmitter and receiver, at around 180 the loss due to the body shadowing is around 20 dB, which agrees with results from the aforementioned numerical analysis. The angular patterns in Fig. 9 present reasonable omnidirectional behavior of the sensor antenna with a maximum variation of 8–10 dB for free space cases (off-body). Following the setup described above, path loss analysis of the radio channel between the transmitting sensor and the patch for cases where the sensor is placed in free space and on the body in the anechoic chamber and in an indoor environment is performed. Many theoretical and measurement-based studies presented in literature have shown that the average received signal decreases logarithmically with distance (for both indoor and outdoor environments) [23], [24]. Therefore, the average path loss for a distance between transmitter and receiver is expressed in decibels as (2) where is the path loss exponent that indicates the rate at which the path loss increases with distance and is a reference distance (normally set to 1 m for indoor channels).

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Fig. 5. Sensor placed on the male model provided by the visible US human project [18]. (a) Sensor placed on the chest. (b) Horizontal cut through the male model applied in the study. TABLE II ELECTRIC PROPERTIES OF SPECIFIC HUMAN TISSUES USED WITHIN THE VISIBLE MAN MODEL AT 2.4 GHz [19], [20] ( IS THE TISSUE CONDUCTIVITY,  IS THE DIELECTRIC CONSTANT AND  IS THE PENETRATION DEPTH IN mm)

Fig. 10 demonstrates the path loss measured in an office environment. The directivity of the antenna increases when the antenna is placed on the body due to reflections at 2.45 GHz from the human tissues which leads to an increase in the received power for the same distances applied in the stand alone sensor scenario. In order to evaluate the improvement achieved by applying the modified matched planar monopole, the received signal

Fig. 6. Return loss for capacitor-matched sensor antenna with resonance at 2.4 GHz when placed in free space and on the body horizontally (see Fig. 5).

power at a distance of 1.5 m away from the sensor when placed on the body in an indoor environment is investigated for different antenna cases. Fig. 11 presents the received monopole over spectrum when using an external vertical ground plane attached to the sensor transceiver, initial printed monopole design and the matched planar monopole. A higher

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Fig. 7. Normalized radiation pattern of capacitor matched sensor antenna when placed in free space and on the body.

Fig. 8. Normalized electric field distribution around the human body induced by the sensor antenna.

received signal power is apparent when applying the matched design compared to the unmatched antenna. Also very close performance to the external vertical monopole maybe observed. B. Dipole Antenna for Healthcare Sensor Based on the analysis presented in Section II with regards to the printed dipole applied for the proposed sensor structure, a modified wireless sensor for healthcare applications is fabricated with a total diameter of 30 mm and height of 6.5 mm (9.8 mm including packaging which might be extended, depending on the required functionalities and number of layers), Fig. 12. The board size is increased to accommodate more chips with a higher number of functions into a compact slim sensor. The applied antenna is the dipole antenna demonstrated in Fig. 4. The sensor performance is experimentally investigated in a manner similar to the procedures described earlier for the printed monopole case. With the sensor placed on the human body, the radiation performance of the sensor with the dipole

Fig. 9. Normalized received power pattern when the monopole antenna sensor is placed in the far-field of a receiving patch antenna (refer to Fig. 5).

antenna is investigated (Fig. 13). Due to the increased radiating area hence increase in effective antenna area, the overall radiation performance is improved because of more propagating wave launched, reflected from the body and diffracted along the body curvature. Fig. 14 shows the received spectrum when the sensor dipole antenna is placed on the body at 1.5 m away from the receiving antenna. Improvements in received signal power compared to the initial design (approximately 15 dB increase) has been realized. Therefore, inherently better coverage capability when the sensor is applied in healthcare applications is achieved

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Fig. 10. Indoor measured path loss when the sensor is placed on the body with modeled path loss using the least fit square technique for cases when the user is sitting and standing.

Fig. 13. Normalized received power pattern when the dipole antenna sensor is placed in the far-field of a receiving antenna.

Fig. 11. Measured received power spectrum when the sensor is placed on the body with the antenna normal to the body applying the initial printed unmatched monopole, matched monopole and an external vertical monopole at the transmitter and a patch at the receiver that is placed 1.5 m away in an indoor environment (office).

Fig. 12. Photograph of the new compact sensor applying dipole antenna to be deployed in healthcare applications.

for various scenarios with a less complicated antenna system (matching circuit is not required).

Fig. 14. Measured received power spectrum when the sensor dipole antenna is placed on the body with the antenna normal to the body (horizontally, see Fig. 5) at 1.5 m away from the receiving antenna.

V. CONCLUSION A study of a compact antenna used in sensors aimed at healthcare applications in the 2.4 GHz ISM band was presented. The antenna performance was investigated numerically considering the effect of full sensor structure. The investigation demonstrated the significance of considering the detailed sensor design in analysing the antenna and radio propagation performance due to the compact size of the proposed sensor. The limited and the careful placement of components surrounding the antenna introduced many challenges in determining and improving the antenna performance with regards to impedance matching, gain, efficiency and front to back ratio of radiated energy. Increased antenna gain by around 2.4–2.8 dB and improved radiation efficiency of approximately 28% in comparison to the intial planar monopole strip is achieved by applying simple matching techniques. Enhancement in sensor performance was demonstrated by replacing the radiating element with a dipole antenna to maximize radiated energy and hence sensor operation coverage area (25% extended coverage). The antenna

ALOMAINY et al.: NUMERICAL AND EXPERIMENTAL EVALUATION OF A COMPACT SENSOR ANTENNA FOR HEALTHCARE DEVICES

performance evaluation and radio propagation characterization provided promising indications of potential optimum sensor designs to be deployed in wireless personal area networks. ACKNOWLEDGMENT The authors would like to thank Y. Zhao and J. Dupuy from the Department of Electronic Engineering, Queen Mary, University of London, London, U.K., for their assistance with measurement setting and procedures. REFERENCES [1] J. Bernardhard, P. Nagel, J. Hupp, W. Strauss, and T. von der Grun, “BAN-body area network for wearable computing,” presented at the 9th Wireless World Research Forum Meeting, Zurich, Switzerland, Jul. 2003. [2] E. Jovanov, A. O’Donnell-Lords, D. Raskovic, P. Cox, R. Adhami, and F. Andrasik, “Stress monitoring using a distributed wireless intelligent sensor system,” IEEE Eng. Med. Biol. Mag., vol. 22, no. 3, pp. 49–55, May/Jun. 2003. [3] C. Kunze, U. Grossmann, W. Stork, and K. Muller-Glaser, “Application of ubiquitous computing in personal health monitoring systems,” in Proc. Biomedizinische Technik: 36th Annu. Meeting German Soc. Biomed. Eng., 2002, pp. 360–362. [4] N. F. Timmons and W. G. Scanlon, “Analysis of the performance of IEEE 802.15.4 for medical sensor body area networking,” in Proc. 2004 First Annu. IEEE Commun. Soc. Conf. Sensor Ad Hoc Commun. Netw. (SECON), Oct. 4–7, 2004, pp. 16–24. [5] E. A. Johannessen, L. Wang, C. Wyse, D. R. S. Cumming, and J. M. Cooper, “Biocompatibility of a lab-on-a-pill sensor in artificial gastrointestinal environments,” IEEE Trans. Biomed. Eng., vol. 53, no. 11, pp. 2333–2340, Nov. 2006. [6] J. Miettinen, M. Mantysalo, K. Kaija, and E. O. Ristolainen, “System design issues for 3-D system-in-package (SiP),” in Proc. 54th Electron. Compon. Technol. Conf. , Jun. 1–4, 2004, vol. 1, pp. 610–615. [7] W. G. Scanlon and N. E. Evans, “Numerical analysis of bodyworn UHF antenna systems,” Electron. Commun. Eng. J., vol. 13, no. 2, pp. 53–64, Apr. 2001. [8] P. Salonen, L. Sydanheimo, M. Keskilammi, and M. Kivikoski, “A small planar inverted-F antenna for wearable applications,” in Proc. 3rd Int. Symp. Wearable Comp., Oct. 18–19, 1999, pp. 95–100. [9] P. Salonen, Y. Rahmat-Samii, H. Hurme, and M. Kivikoski, “Dualband wearable textile antenna,” in Proc. IEEE Antennas Propaga. Soc. Int. Symp., Jun. 20–25, 2004, vol. 1, pp. 463–466. [10] H. R. Chuang and W. T. Chen, “Computer simulation of the humanbody effects on a circular-loop-wire antenna for radio-pager communications at 152, 280, and 400 MHz,” IEEE Trans. Veh. Technol., vol. 46, no. 3, pp. 544–559, Aug. 1997. [11] Z. N. Chen, Ed., Antennas for Portable Devices. New York: Wiley, 2007. [12] A. Alomainy, Y. Hao, and F. Pasveer, “Modelling and characterization of a compact sensor antenna for healthcare applications,” in Proc. 4th Int. Workshop Wearable Implantable Body Sensor Netw., Aachen, Germany, Mar. 26–28, 2007, pp. 3–8. [13] J.-Y. Jan, L.-C. Tseng, W.-S. Chen, and Y.-T. Cheng, “Printed monopole antennas stacked with a shorted parasitic wire for Bluetooth and WLAN applications,” in Proc. IEEE 2004 Antennas Propaga. Soc. Int. Symp., Jun. 2004, vol. 3, pp. 2607–2610. [14] C. Balanis, Antenna Theory Analysis and Design. New York: Wiley, 1997. [15] T. Weiland, AEU, “A discretization method for the solution of Maxwell’s equations for six-component fields,” Eletron. Commun., vol. 31, pp. 116–120, 1977. [16] Computer Simulation Technology, Microwave Studio [Online]. Available: http://www.cst.com [17] Chipcon CC2420 Transceiver Chip, 2.4 GHz IEEE 802.15.4/ZigBeeReady RF Transceiver. [Online]. Available: http://www.chipcon.com [18] “Electronic imaging: Board of regents,” National Institute of Health National Library of Medicine (USA), Board of Regents, Bethesda, MD, Tech. Rep. NIH 90-2197, 1990 [Online]. Available: http://www.brooks.af.mil/AFRL/HED/hedr/ [19] “Calculation of the dielectric properties of body tissues,” Institute for Applied Physics, Italian National Research Council. [Online]. Available: http://www.niremf.ifac.cnr.it/tissprop/

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[20] C. Gabriel and S. Gabriel, “Compilation of the dielectric properties of body tissues at RF and microwave frequencies,” [Online]. Available: http://www.brooks.af.mil/AFRL/HED/hedr/reports/dielectric/Title/Title.html [21] D. A. McNamara, C. W. I. Pistorius, and J. A. G. Malherbe, Introduction to the Uniform Geometrical Theory of Diffraction. Norwood, MA: Artech House. [22] A. D. Olver, Microwave and Optical Transmission. Chichester, U.K.: Wiley, 1997. [23] A. Alomainy, Y. Hao, A. Owadally, C. G. Parini, Y. Nechayev, P. S. Hall, and C. C. Constantinou, “Statistical analysis and performance evaluation for on-body radio propagation with microstrip patch antennas,” IEEE Trans. Antennas Propag., vol. 55, no. 1, pp. 245–248, Jan. 2007. [24] P. S. Hall and Y. Hao, Eds., Antennas and Propagation for Body-Centric Wireless Networks. Norwood, MA: Artech House, Sep. 2006.

Akram Alomainy (S’99–M’07) received the M.Eng. degree in communication engineering and the Ph.D. degree in electrical and electronic engineering (specialized in antennas and radio propagation) from Queen Mary, University of London (QMUL), London, U.K. in July 2003 and July 2007, respectively. His current research interests include small and compact antennas for wireless body area networks, radio propagation characterization and modeling for body-centric networks, antenna interactions with human body, computational electromagnetic (time domain and frequency domain methods) and advanced antenna enhancement techniques for mobile and personal wireless communications. He has authored and co-authored three book chapters, many journal and established conference papers. He is a reviewer for IEEE VTC biAnnual conferences, IET Communications Proceedings and Wiley book proposals. Dr. Alomainy was selected as a finalist in the Best Young Investigator award sponsored by CorScience in Body Sensor Networks 2007, Aachen, Germany.

Yang Hao (M’00–SM’06), received the Ph.D. degree from the Centre for Communications Research (CCR) at the University of Bristol, Bristol, U.K., in 1998. From 1998 to 2000, he was a Postdoctoral Research Fellow at the School of Electrical and Electronic Engineering, University of Birmingham, Birmingham, U.K. In May 2000, he joined the Antenna Engineering Group, Queen Mary College, University of London, London, U.K. first as a Lecturer and was promoted to Reader in 2005 and to Professor in 2007. He is active in a number of areas including computational electromagnetics, electromagnetic bandgap structures and microwave metamaterials, antennas and radio propagation for body centric wireless networks, active antennas for millimeter/submillimeter applications and photonic integrated antennas. His work on metamaterials and body-centric wireless communications has been reported in the Engineer, Electronics Times and Microwave Engineering. He is a co-editor of book Anntennas and Radio Propagation for Body-Centric Wireless Communications (Artech House, 2006). He has published over 200 technical papers including three book chapters and served as an invited (ISAP07) and keynote speaker (ANTEM05), a conference organizer and session chair at many international conferences. Prof. Hao is an Associate Editor for IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, and a Guest Editor for IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION. He is a member of Technical Advisory Panel of IET Antennas and Propagation Professional Network.

Frank Pasveer received the M.Sc. degree in physics at the University of Leiden, Leiden, Germany, in 2000, and the Ph.D. degree from the Department of Theoretical Physics at the Technical University, Eindhoven, The Netherlands, in 2004 Since 2005, he has been a Senior Scientist in the group “System in package devices” of the Philips Research Laboratory, Eindhoven, The Netherlands.