Robert Foster

Wireless body sensor networks for health-monitoring applications

Current wireless technologies, such as wireless body area networks and wireless personal area networks, provide promising applications in medical monitoring systems to measure specified physiological data and also provide location-based information, if required. With the increasing sophistication of wearable and implantable medical devices and their integration with wireless sensors, an ever-expanding range of therapeutic and diagnostic applications is being pursued by research and commercial organizations. This paper aims to provide a comprehensive review of recent developments in wireless sensor technology for monitoring behaviour related to human physiological responses. It presents background information on the use of wireless technology and sensors to develop a wireless physiological measurement system. A generic miniature platform and other available technologies for wireless sensors have been studied in terms of hardware and software structural requirements for a low-cost, low-power, non-invasive and unobtrusive system.

Detecting Vital Signs with Wearable Wireless Sensors

The emergence of wireless technologies and advancements in on-body sensor design can enable change in the conventional health-care system, replacing it with wearable health-care systems, centred on the individual. Wearable monitoring systems can provide continuous physiological data, as well as better information regarding the general health of individuals. Thus, such vital-sign monitoring systems will reduce health-care costs by disease prevention and enhance the quality of life with disease management. In this paper, recent progress in non-invasive monitoring technologies for chronic disease management is reviewed. In particular, devices and techniques for monitoring blood pressure, blood glucose levels, cardiac activity and respiratory activity are discussed; in addition, on-body propagation issues for multiple sensors are presented.

Antennas and Propagation of Implanted RFIDs for Pervasive Healthcare Applications

Radio-frequency identification (RFID) is a growing technology, with the potential for reducing medical errors and improving the quality of healthcare in hospitals. The benefits include more secure and safe access in the healthcare environment (with the possibility, for example, to track patients, personnel, and equipment), as well as providing the means to easily identify patients and their medications with low risk of error. In this paper, we present an overview of the challenges faced in antenna design, electromagnetic modeling and wave propagation for RFID implants. The performance of ultra-high-frequency (UHF) subcutaneous tag antennas was investigated numerically and validated with measurements. Furthermore, the wave propagation between an off-body reader and an implanted tag was analyzed, in both free space and a scattered indoor environment. Results demonstrated that a passive tag solution allows a very limited communication range, due to the body losses, the electrically small size of the antenna, and nulls in the radiation pattern. In comparison, a maximum communication range of 10 m was predicted as achievable for an active tag operating indoors with a limited power (-20 dBm).

Broadband Tissue Mimicking Phantoms and a Patch Resonator for Evaluating Noninvasive Monitoring of Blood Glucose Levels

Tissue mimicking phantoms (TMPs) replicating the dielectric properties of wet skin, fat, blood, and muscle tissues for the 0.3 to 20 GHz frequency range are presented in this paper. The TMPs reflect the dielectric properties with maximum deviations of 7.7 units and 3.9 S/m for relative dielectric constant and conductivity, respectively, for the whole band. The dielectric properties of the blood mimicking material are further investigated by adding realistic glucose amounts and a Cole-Cole model used to compare the behavior with respect to changing glucose levels. In addition, a patch resonator was fabricated and tested with the four-layered physical phantom developed in house. It was observed that the input impedance of the resonator is sensitive to the changes in the dielectric properties and, hence, to the realistic glucose level changes in the blood layer.

Towards Accurate Dielectric Property Retrieval of Biological Tissues for Blood Glucose Monitoring

An analytical formulation for relative dielectric constant retrieval is reconstructed to establish a relationship between the response of a spiral microstrip resonator and effective relative dielectric constant of a lossy superstrate, such as biological tissue. To do so, an analytical equation is modified by constructing functions for the two unknowns, the filling factor A and effective length leff of the resonator. This is done by simulating the resonator with digital phantoms of varying permittivity. The values of A and leff are determined for each phantom from the resulting S-parameter response, using particle swarm optimization. Multiple nonlinear regression is applied to produce equations for A and leff, expressed as a function of frequency and the phantoms relative dielectric constant. These equations are combined to form a new nonlinear analytical equation, which is then solved using the Newton-Raphson iterative method, for both simulations and measurements of physical phantoms. To verify the reconstructed dielectric constant, the dielectric properties of the physical phantoms are determined with commercial high temperature open-ended coaxial probe. The dielectric properties are reconstructed by the described method, with less than 3.67% error with respect to the measurements.

Exploring Physiological Parameters in Dynamic WBAN Channels

On-body radio propagation in the 2.45-GHz industrial-scientific-medical frequency band (2.40-2.48 GHz) was investigated during three different activities: jogging, rowing and cycling. Four different links were examined, from the waist to the wrist, ankle, chest and back; it was observed that the channel behavior could be related to the repetitive nature of the activities. Furthermore, combinations of the wrist, ankle, and chest channels could potentially be used to identify the activity, while the waist-back channel shows little variation between activities (roughly 2 dB, compared to 6-15 dB for the other links). The results also show that dynamic on-body radio channels contain rich biomechanical information, such as motion pattern, heartbeat, and breathing process. It is demonstrated that physiological and kinetic features can, therefore, be extracted through some known signal-processing techniques. For example, the repetitive nature of the activities introduces harmonics into the signal via fading, which correspond to the speed of motion. In addition, the mechanical motion of the torso during respiration and cardiac activity also introduce harmonics due to changes in the path loss, albeit with low magnitudes. The detection of such signals is discussed.

On-Body Channel Measurement Using Wireless Sensors

The on-body channel was characterised at various points on the human torso in an anechoic chamber using a pair of wireless sensor modules. The performance of wireless IEEE 802.15.4 sensor nodes operating in the 2.45 GHz ISM frequency band (2.40-2.4835 GHz) is presented over each of the 16 different channels. It is shown that the response at individual carrier frequencies is dependent not only on the initial antenna response, as determined by the on-body measurement in isolation, but also on the overall system performance. Measurement results are also compared with those from the conventional technique using a Vector Network Analyzer.

Wearable wireless sensors for healthcare applications

Recent activities at Queen Mary, University of London, relating to wearable wireless sensors research for healthcare applications are reviewed in this paper. The monitoring of blood glucose levels using non-invasive radio-based sensors is discussed. The analysis of on-body radio propagation channels is then presented, with an emphasis on variations related to activity.

Patch resonator for non-invasive detection of dielectric property changes in biological tissues

In this study, a patch resonator with two ports is proposed for retrieving the dielectric properties of biological tissues. The resonator is designed to operate in the 2.45 GHz Industrial, Scientific, and Medical band when placed on the tissue. CST Microwave Studio was used to simulate the structure with five layers of tissue above. Two via pins are used to tune the resonance frequency and to miniaturize the patch resonator. Rogers R03010 is used as a substrate. The configuration of the resonator and the simulation results are given. This paper also presents recipes of tissue-mimicking materials, along with dielectric property measurement results of fabricated physical tissue phantoms.

Active absorption of electromagnetic pulses in a cavity

We show that a pulse of electromagnetic radiation launched into a cavity can be completely absorbed into an infinitesimal region of space, provided one has a high degree of control over the current flowing through this region. We work out explicit examples of this effect in a cubic cavity and a cylindrical one, and experimentally demonstrate the effect in the microwave regime.