Wireless body sensor networks for health-monitoring applications

This is an author-created, un-copyedited version of an article accepted for publication in Physiological Measurement. The publisher is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at http://dx.doi.org/10.1088/0967-3334/29/11/R01

UWB Characteristics of RF Propagation for Body Mounted and Implanted Sensors

Body Area Network (BAN) technology is related to many applications inside, on and around the human body. The basic configuration of a BAN is a set of sensors, which are wearable or are placed inside the human body, transmitting signals to a terminal situated in a doctor’s office, in order to assess or monitor some aspect of a patient’s physical condition. Additionally, in many BAN applications the information about the sensor location is very important, since without knowing a sensor’s location, the transmitted data may be of limited value. As an example, Wireless Video Capsule Endoscopy (VCE) can benefit greatly from the addition of location information. The capsule transmits an RF signal from inside the human body to another sensor on the body surface or external. From the image data provided by the capsule, taken together with the location information, the doctor can locate the infection or lesion and initiate appropriate medical care. In this way, the treatment can be more effective and accurate. In this thesis we investigate the characteristics of Ultra-Wide Band (UWB) RF propagation for BAN devices placed around and inside the human body. We have made measurements around the human body and around a water-filled phantom using an E8363B Vector Network Analyzer (VNA), specifically measuring the S21 signal, which gives the transfer function. Based on these measurement results, we discuss the channel propagation for cases where the transmitter and the receiver are on the surface of the body and analyze the UWB propagation characteristics for RF localization. Because it is impractical or even impossible to make measurements inside the human body, we chose to apply the measurements using a simulation model of homogenous tissue, which serves as an approximation of the signal propagation environment inside the body. First, by comparing the multipath situation in free space and within a model of homogenous tissue, we are able to analyze the multipath effects inside human body. Then, because of the different characteristics of RF propagation in different bandwidths, we have made measurements at UWB (3GHz to 10GHz), and narrowband (402MHz) frequencies

Propagation characterization of implantable antenna at UWB frequency – a review

A technology of wireless body area network (WBAN) was invented in order to enhance the quality of healthcare management as well as to determine faster disease prevention. However, to obtain the real-time data of images and videos from inside the human body, an implantable device is required. Currently, the Medical Implant Communication System (MICS) is used, but, this system has limited data rate which is a narrow-band of 402 – 405 MHz. Thus, this study on Ultra Wideband (UWB) for implanted device is conducted as UWB offers a wide transmission bandwidth as well as high data rate. Knowledge of radio wave propagation behaviour inside human body is needed to perform the implantation. Past researches related to this topic are limited and those conducted focused only on the human torso. This paper aims to provide a better understanding on the characteristics of radio wave propagation inside the human body by using an implantable device at UWB frequency. It is also hoped that this study could be used as reference for future research on this subject

PROPAGATION CHARACTERIZATION OF IMPLANTABLE ANTENNA AT UWB FREQUENCY – A REVIEW

A technology of wireless body area network (WBAN) was invented in order to enhance the quality of healthcare management as well as to determine faster disease prevention. However, to obtain the real-time data of images and videos from inside the human body, an implantable device is required. Currently, the Medical Implant Communication System (MICS) is used, but, this system has limited data rate which is a narrow-band of 402 – 405 MHz. Thus, this study on Ultra Wideband (UWB) for implanted device is conducted as UWB offers a wide transmission bandwidth as well as high data rate. Knowledge of radio wave propagation behaviour inside human body is needed to perform the implantation. Past researches related to this topic are limited and those conducted focused only on the human torso. This paper aims to provide a better understanding on the characteristics of radio wave propagation inside the human body by using an implantable device at UWB frequency. It is also hoped that this study could be used as reference for future research on this subject

Modelling and characterisation of antennas and propagation for body-centric wireless communication

PhDBody-Centric Wireless Communication (BCWC) is a central point in the development of fourth generation mobile communications. The continuous miniaturisation of sensors, in addition to the advancement in wearable electronics, embedded software, digital signal processing and biomedical technologies, have led to a new concept of usercentric networks, where devices can be carried in the user’s pockets, attached to the user’s body or even implanted. Body-centric wireless networks take their place within the personal area networks, body area networks and body sensor networks which are all emerging technologies that have a broad range of applications such as healthcare and personal entertainment. The major difference between BCWC and conventional wireless systems is the radio channel over which the communication takes place. The human body is a hostile environment from radio propagation perspective and it is therefore important to understand and characterise the effect of the human body on the antenna elements, the radio channel parameters and hence the system performance. This is presented and highlighted in the thesis through a combination of experimental and electromagnetic numerical investigations, with a particular emphasis to the numerical analysis based on the finite-difference time-domain technique. The presented research work encapsulates the characteristics of the narrowband (2.4 GHz) and ultra wide-band (3-10 GHz) on-body radio channels with respect to different digital phantoms, body postures, and antenna types hence highlighting the effect of subject-specific modelling, static and dynamic environments and antenna performance on the overall body-centric network. The investigations covered extend further to include in-body communications where the radio channel for telemetry with medical implants is also analysed by considering the effect of different digital phantoms on the radio channel characteristics. The study supports the significance of developing powerful and reliable numerical modelling to be used in conjunction with measurement campaigns for a comprehensive understanding of the radio channel in body-centric wireless communication. It also emphasises the importance of considering subject-specific electromagnetic modelling to provide a reliable prediction of the network performance

High-performance wireless interface for implant-to-air communications

Nous élaborons une interface cerveau-machine (ICM) entièrement sans fil afin de fournir un système de liaison directe entre le cerveau et les périphériques externes, permettant l’enregistrement et la stimulation du cerveau pour une utilisation permanente. Au cours de cette thèse, nous explorons la modélisation de canal, les antennes implantées et portables en tant que propagateurs appropriés pour cette application, la conception du nouveau système d’un émetteur-récepteur UWB implantable, la conception niveau système du circuit et sa mise en oeuvre par un procédé CMOS TSMC 0.18 um. En plus, en collaboration avec Université McGill, nous avons conçu un réseau de seize antennes pour une détection du cancer du sein à l’aide d’hyperfréquences. Notre première contribution calcule la caractérisation de canal de liaison sans fil UWB d’implant à l’air, l’absorption spécifique moyennée (ASAR), et les lignes directrices de la FCC sur la densité spectrale de puissance UWB transmis. La connaissance du comportement du canal est nécessaire pour déterminer la puissance maximale permise à 1) respecter les lignes directrices ANSI pour éviter des dommages aux tissus et 2) respecter les lignes directrices de la FCC sur les transmissions non autorisées. Nous avons recours à un modèle réaliste du canal biologique afin de concevoir les antennes pour l’émetteur implanté et le récepteur externe. Le placement des antennes est examiné avec deux scénarios contrastés ayant des contraintés de puissance. La performance du système au sein des tissus biologiques est examinée par l’intermédiaire des simulations et des expériences. Notre deuxième contribution est dédiée à la conception des antennes simples et à double polarisation pour les systèmes d’enregistrement neural sans fil à bande ultra-large en utilisant un modèle multicouches inhomogène de la tête humaine. Les antennes fabriquées à partir de matériaux flexibles sont plus facilement adaptées à l’implantation ; nous étudions des matériaux à la fois flexibles et rigides et examinons des compromis de performance. Les antennes proposées sont conçues pour fonctionner dans une plage de fréquence de 2-11 GHz (ayant S11-dessous de -10 dB) couvrant à la fois la bande 2.45 GHz (ISM) et la bande UWB 3.1-10.6 GHz. Des mesures confirment les résultats de simulation et montrent que les antennes flexibles ont peu de dégradation des performances en raison des effets de flexion (en termes de correspondance d’impédance). Finalement, une comparaison est réalisée entre quatre antennes implantables, couvrant la gamme 2-11 GHz : 1) une rigide, à la polarisation simple, 2) une rigide, à double polarisation, 3) une flexible, à simple polarisation et 4) une flexible, à double polarisation. Dans tous les cas une antenne rigide est utilisée à l’extérieur du corps, avec une polarisation appropriée. Plusieurs avantages ont été confirmés pour les antennes à la polarisation double : 1) une taille plus petite, 2) la sensibilité plus faible aux désalignements angulaires, et 3) une plus grande fidélité. Notre troisième contribution fournit la conception niveau système de l’architecture de communication sans fil pour les systèmes implantés qui stimulent simultanément les neurones et enregistrent les réponses de neurones. Cette architecture prend en charge un grand nombre d’électrodes (> 500), fournissant 100 Mb/s pour des signaux de stimulation de liaison descendante, et Gb/s pour les enregistrements de neurones de liaison montante. Nous proposons une architecture d’émetteur-récepteur qui partage une antenne ultra large bande, un émetteur-récepteur simplifié, travaillant en duplex intégral sur les deux bandes, et un nouveau formeur d’impulsions pour la liaison montante du Gb/s soutenant plusieurs formats de modulation. Nous présentons une démonstration expérimentale d’ex vivo de l’architecture en utilisant des composants discrets pour la réalisation les taux Gb/s en liaison montante. Une bonne performance de taux d’erreur de bit sur un canal biologique à 0,5, 1 et 2 Gb/s des débits de données pour la télémétrie de liaison montante (UWB) et 100 Mb/s pour la télémétrie en liaison descendante (bande 2.45 GHz) est atteinte. Notre quatrième contribution présente la conception au niveau du circuit d’un dispositif d’émission en duplex total qui est présentée dans notre troisième contribution. Ce dispositif d’émission en duplex total soutient les applications d’interfaçage neural multimodal et en haute densité (les canaux de stimulant et d’enregistrement) avec des débits de données asymétriques. L’émetteur (TX) et le récepteur (RX) partagent une seule antenne pour réduire la taille de l’implant. Le TX utilise impulse radio ultra-wide band (IR-UWB) basé sur une approche alliant des bords, et le RX utilise un nouveau 2.4 GHz récepteur on-off keying (OOK).Une bonne isolation (> 20 dB) entre le trajet TX et RX est mis en oeuvre 1) par mise en forme des impulsions transmises pour tomber dans le spectre UWB non réglementé (3.1-7 GHz), et 2) par un filtrage espace-efficace du spectre de liaison descendante OOK dans un amplificateur à faible bruit RX. L’émetteur UWB 3.1-7 GHz peut utiliser soit OOK soit la modulation numérique binaire à déplacement de phase (BPSK). Le FDT proposé offre une double bande avec un taux de données de liaison montante de 500 Mbps TX et un taux de données de liaison descendante de 100 Mb/s RX, et il est entièrement en conformité avec les standards TSMC 0.18 um CMOS dans un volume total de 0,8 mm2. Ainsi, la mesure de consommation d’énergie totale en mode full duplex est de 10,4 mW (5 mW à 100 Mb/s pour RX, et de 5,4 mW à 500 Mb/s ou 10,8 PJ / bits pour TX). Notre cinquième contribution est une collaboration avec l’Université McGill dans laquelle nous concevons des antennes simples et à double polarisation pour les systèmes de détection du cancer du sein à l’aide d’hyperfréquences sans fil en utilisant un modèle multi-couche et inhomogène du sein humain. Les antennes fabriquées à partir de matériaux flexibles sont plus facilement adaptées à des applications portables. Les antennes flexibles miniaturisées monopôles et spirales sur un 50 um Kapton polyimide sont conçus, en utilisant high frequency structure simulator (HFSS), à être en contact avec des tissus biologiques du sein. Les antennes proposées sont conçues pour fonctionner dans une gamme de fréquences de 2 à 4 GHz. Les mesures montrent que les antennes flexibles ont une bonne adaptation d’impédance dans les différentes positions sur le sein. De Plus, deux antennes à bande ultralarge flexibles 4 × 4 (simple et à double polarisation), dans un format similaire à celui d’un soutien-gorge, ont été développés pour un système de détection du cancer du sein basé sur le radar.We are working on a fully wireless brain-machine-interface to provide a communication link between the brain and external devices, enabling recording and stimulating the brain for permanent usage. In this thesis we explore channel modeling, implanted and wearable antennas as suitable propagators for this application, system level design of an implantable UWB transceiver, and circuit level design and implementing it by TSMC 0.18 um CMOS process. Also, in a collaboration project with McGill University, we designed a flexible sixteen antenna array for microwave breast cancer detection. Our first contribution calculates channel characteristics of implant-to-air UWB wireless link, average specific absorption rate (ASAR), and FCC guidelines on transmitted UWB power spectral density. Knowledge of channel behavior is required to determine the maximum allowable power to 1) respect ANSI guidelines for avoiding tissue damage and 2) respect FCC guidelines on unlicensed transmissions. We utilize a realistic model of the biological channel to inform the design of antennas for the implanted transmitter and the external receiver. Antennas placement is examined under two scenarios having contrasting power constraints. Performance of the system within the biological tissues is examined via simulations and experiments. Our second contribution deals with designing single and dual-polarization antennas for wireless ultra-wideband neural recording systems using an inhomogeneous multi-layer model of the human head. Antennas made from flexible materials are more easily adapted to implantation; we investigate both flexible and rigid materials and examine performance trade-offs. The proposed antennas are designed to operate in a frequency range of 2–11 GHz (having S11 below -10 dB) covering both the 2.45 GHz (ISM) band and the 3.1–10.6 GHz UWB band. Measurements confirm simulation results showing flexible antennas have little performance degradation due to bending effects (in terms of impedance matching). Finally, a comparison is made of four implantable antennas covering the 2-11 GHz range: 1) rigid, single polarization, 2) rigid, dual polarization, 3) flexible, single polarization and 4) flexible, dual polarization. In all cases a rigid antenna is used outside the body, with an appropriate polarization. Several advantages were confirmed for dual polarization antennas: 1) smaller size, 2) lower sensitivity to angular misalignments, and 3) higher fidelity. Our third contribution provides system level design of wireless communication architecture for implanted systems that simultaneously stimulate neurons and record neural responses. This architecture supports large numbers of electrodes (> 500), providing 100 Mb/s for the downlink of stimulation signals, and Gb/s for the uplink neural recordings. We propose a transceiver architecture that shares one ultra-wideband antenna, a streamlined transceiver working at full-duplex on both bands, and a novel pulse shaper for the Gb/s uplink supporting several modulation formats. We present an ex-vivo experimental demonstration of the architecture using discrete components achieving Gb/s uplink rates. Good bit error rate performance over a biological channel at 0.5, 1, and 2 Gbps data rates for uplink telemetry (UWB) and 100 Mbps for downlink telemetry (2.45 GHz band) is achieved. Our fourth contribution presents circuit level design of the novel full-duplex transceiver (FDT) which is presented in our third contribution. This full-duplex transceiver supports high-density and multimodal neural interfacing applications (high-channel count stimulating and recording) with asymmetric data rates. The transmitter (TX) and receiver (RX) share a single antenna to reduce implant size. The TX uses impulse radio ultra-wide band (IR-UWB) based on an edge combining approach, and the RX uses a novel 2.4-GHz on-off keying (OOK) receiver. Proper isolation (> 20 dB) between the TX and RX path is implemented 1) by shaping the transmitted pulses to fall within the unregulated UWB spectrum (3.1-7 GHz), and 2) by spaceefficient filtering (avoiding a circulator or diplexer) of the downlink OOK spectrum in the RX low-noise amplifier. The UWB 3.1-7 GHz transmitter can use either OOK or binary phase shift keying (BPSK) modulation schemes. The proposed FDT provides dual band 500-Mbps TX uplink data rate and 100 Mbps RX downlink data rate, and it is fully integrated into standard TSMC 0.18 um CMOS within a total size of 0.8 mm2. The total measured power consumption is 10.4 mW in full duplex mode (5 mW at 100 Mbps for RX, and 5.4 mW at 500 Mbps or 10.8 pJ/bit for TX). Our fifth contribution is a collaboration project with McGill University which we design single and dual-polarization antennas for wireless ultra-wideband breast cancer detection systems using an inhomogeneous multi-layer model of the human breast. Antennas made from flexible materials are more easily adapted to wearable applications. Miniaturized flexible monopole and spiral antennas on a 50 um Kapton polyimide are designed, using a high frequency structure simulator (HFSS), to be in contact with biological breast tissues. The proposed antennas are designed to operate in a frequency range of 2–4 GHz (with reflection coefficient (S11) below -10 dB). Measurements show that the flexible antennas have good impedance matching while in different positions with different curvature around the breast. Furthermore, two flexible conformal 4×4 ultra-wideband antenna arrays (single and dual polarization), in a format similar to that of a bra, were developed for a radar-based breast cancer detection system

Bounds on RF cooperative localization for video capsule endoscopy

Wireless video capsule endoscopy has been in use for over a decade and it uses radio frequency (RF) signals to transmit approximately fifty five thousands clear pictures of inside the GI tract to the body-mounted sensor array. However, physician has no clue on the exact location of the capsule inside the GI tract to associate it with the pictures showing abnormalities such as bleeding or tumors. It is desirable to use the same RF signal for localization of the VCE as it passes through the human GI tract. In this thesis, we address the accuracy limits of RF localization techniques for VCE localization applications. We present an assessment of the accuracy of cooperative localization of VCE using radio frequency (RF) signals with particular emphasis on localization inside the small intestine. We derive the Cramer-Rao Lower Bound (CRLB) for cooperative location estimators using the received signal strength(RSS) or the time of arrival (TOA) of the RF signal. Our derivations are based on a three-dimension human body model, an existing model for RSS propagation from implant organs to body surface and a TOA ranging error model for the effects of non-homogenity of the human body on TOA of the RF signals. Using models for RSS and TOA errors, we first calculate the 3D CRLB bounds for cooperative localization of the VCE in three major digestive organs in the path of GI tract: the stomach, the small intestine and the large intestine. Then we analyze the performance of localization techniques on a typical path inside the small intestine. Our analysis includes the effects of number of external sensors, the external sensor array topology, number of VCE in cooperation and the random variations in transmit power from the capsule

Empirical RF Propagation Modeling of Human Body Motions for Activity Classification

Many current and future medical devices are wearable, using the human body as a conduit for wireless communication, which implies that human body serves as a crucial part of the transmission medium in body area networks (BANs). Implantable medical devices such as Pacemaker and Cardiac Defibrillators are designed to provide patients with timely monitoring and treatment. Endoscopy capsules, pH Monitors and blood pressure sensors are used as clinical diagnostic tools to detect physiological abnormalities and replace traditional wired medical devices. Body-mounted sensors need to be investigated for use in providing a ubiquitous monitoring environment. In order to better design these medical devices, it is important to understand the propagation characteristics of channels for in-body and on- body wireless communication in BANs. The IEEE 802.15.6 Task Group 6 is officially working on the standardization of Body Area Network, including the channel modeling and communication protocol design. This thesis is focused on the propagation characteristics of human body movements. Specifically, standing, walking and jogging motions are measured, evaluated and analyzed using an empirical approach. Using a network analyzer, probabilistic models are derived for the communication links in the medical implant communication service band (MICS), the industrial scientific medical band (ISM) and the ultra- wideband (UWB) band. Statistical distributions of the received signal strength and second order statistics are presented to evaluate the link quality and outage performance for on-body to on- body communications at different antenna separations. The Normal distribution, Gamma distribution, Rayleigh distribution, Weibull distribution, Nakagami-m distribution, and Lognormal distribution are considered as potential models to describe the observed variation of received signal strength. Doppler spread in the frequency domain and coherence time in the time domain from temporal variations is analyzed to characterize the stability of the channels induced by human body movements. The shape of the Doppler spread spectrum is also investigated to describe the relationship of the power and frequency in the frequency domain. All these channel characteristics could be used in the design of communication protocols in BANs, as well as providing features to classify different human body activities. Realistic data extracted from built-in sensors in smart devices were used to assist in modeling and classification of human body movements along with the RF sensors. Variance, energy and frequency domain entropy of the data collected from accelerometer and orientation sensors are pre- processed as features to be used in machine learning algorithms. Activity classifiers with Backpropagation Network, Probabilistic Neural Network, k-Nearest Neighbor algorithm and Support Vector Machine are discussed and evaluated as means to discriminate human body motions. The detection accuracy can be improved with both RF and inertial sensors