A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> In-Body Radio Propagation Model <s> The new standard medical implant communications service (MICS) for communication with medical implants uses the 403-405 MHz band. The influence of a patient's body shape and position on the radiation pattern from an implanted radio transmitter has been simulated. Simulations and comparisons have been made with different body shapes (male, female and child) and different arm positions. It can be concluded from the results that the difference between different body shapes are at least as large as the influence of a patients arm movements. <s> BIB001 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> In-Body Radio Propagation Model <s> Propagation model plays a very important role in designing wireless communication systems. Current advances in semiconductor technology has made it possible to implant a network of bio-sensors inside the human body for health monitoring purposes [C. Furse, H.K. Lai, C. Estes, A. Mahadik, A. Duncan, 1999], [C. Furse, R. Mohan, A. Jakayar, S. Karidehal, B. McCleod, S. Going, 2001], [L. Schwiebert, S.K.S. Gupta, P.S.G. Auner, G. Abrams, R. Lezzi, P. McAlister, 2002]. For wireless communication inside the human body, the tissue medium acts as a channel through which the information is sent as electromagnetic (EM) radio frequency (RF) waves. A propagation model is necessary to determine the losses involved in the form of absorption of EM wave power by the tissue. Absorption of EM waves by the tissue body, which consists of mostly saline water, accounts for a major portion of the propagation loss. In this paper we present a propagation loss model (PMBA) for homogeneous tissue bodies. We have verified the model for the frequency range of our interest (900 MHz to 3 GHz) using a 3D EM simulation software, HFSS/spl trade/, and experimental measurements using saturated salt water. <s> BIB002 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> In-Body Radio Propagation Model <s> A network of biosensors can be implanted in a human body for health monitoring, diagnostics, or as a prosthetic device. Biosensors can be organized into clusters where most of the communication takes place within the clusters, and long range transmissions to the base station are performed by the cluster leader to reduce the energy cost. In some applications, the tissues are sensitive to temperature increase and may be damaged by the heat resulting from normal operations and the recharging of sensor nodes. Our work is the first to consider rotating the cluster leadership to minimize the heating effects on human tissues. We explore the factors that lead to temperature increase, and the process for calculating the specific absorption rate (SAR) and temperature increase of implanted biosensors by using the finite-difference time-domain (FDTD) method. We improve performance by rotating the cluster leader based on the leadership history and the sensor locations. We propose a simplified scheme, temperature increase potential, to efficiently predict the temperature increase in tissues surrounding implanted sensors. Finally, a genetic algorithm is proposed to exploit the search for an optimal temperature increase sequence. <s> BIB003 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> In-Body Radio Propagation Model <s> The medical care day by day and more and more is associated with and reliant upon concepts and advances of electronics and electromagnetics. Numerous medical devices are implanted in the body for medical use. Tissue implanted devices are of great interest for wireless medical applications due to the promising of different clinical usage to promote a patient independence. It can be used in hospitals, health care facilities and home to transmit patient measurement data, such as pulse and respiration rates to a nearby receiver, permitting greater patient mobility and increased comfort. As this service permits remote monitoring of several patients simultaneously it could also potentially decrease health care costs. Advancement in radio frequency communications and miniaturization of bioelectronics are supporting medical implant applications. A central component of wireless implanted device is an antenna and there are several issues to consider when designing an in-body antenna, including power consumption, size, frequency, biocompatibility and the unique RF transmission challenges posed by the human body. The radiation characteristics of such devices are important in terms of both safety and performance. The implanted antenna and human body as a medium for wireless communication are discussed over Medical Implant Communications Service (MICS) band in the frequency range of 402-405MHz. <s> BIB004 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> In-Body Radio Propagation Model <s> This paper presents a numerical investigation of the radiation characteristics of gastric, bladder, and cardiac implants based on the finite-differences time-domain method. Simulations were performed at the medical implanted communication services (MICS) and the industrial, scientific, and medical radio bands, respectively, using three different digital inhomogeneous human phantoms (two male and one female models). The numerical analysis demonstrated that the radiation performances are strongly dependant on the location of wireless implants, as well as the body mass index of the subject. The results highlighted the significance of subject specific modeling when designing wireless implants. A link budget calculation was proposed for the communication between a left-ventricular wireless implant and an off-body base station as an example for MICS applications. It is demonstrated that, due to the presence of human tissues, the antenna radiation from wireless implants tends to be directive, and therefore, the signal-to-noise ratio in communication links is strongly dependent on the orientation of the human subject with respect to the base station. <s> BIB005 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> In-Body Radio Propagation Model <s> A 2.5 times 1.8 cm2 medical implant communication service band antenna is combined with an electrode for body channel communication. The proposed design enables a body sensor network controller to communicate with health-care devices located on and inside a patient's body. The spiral microstrip antenna with its radiating body and ground plane placed side-by-side has the thickness of 2 mm and can be attached to human skin conveniently. The propagation loss of the body channel is measured when the proposed antenna is used as the skin interface for BCC in the 10-70-MHz band, and the results are compared with the cases of Ag/AgCl and circular dry electrodes. The equivalent-circuit model of the antenna as the electrode is also derived from the measured impedance characteristics. The LC resonance structure to drive the on-body antenna with its capacitance increased due to the skin contact reduces the power consumption of the TX buffer by >50%. TheS 11-parameter of the on-body antenna, its radiation pattern, and the signal loss inside the human body are investigated. <s> BIB006
As mentioned in the previous section, communication of medical implantable devices is restricted to the MICS frequency band of 402-405 MHz. In this frequency range, the human body can be considered as an inhomogeneous medium consisting of multiple tissue layers with different electrical characteristics. Therefore, it behaves as a communication channel where losses are mainly due to the power absorption by the different tissue layers. Radio propagation through human tissue has been extensively studied in the literature ( BIB004 BIB005 BIB006 BIB002 BIB003 ) and depends on many parameters, including, among others, sex, age, location of the sensor in the human body and general posture of the body. The derivation of an exact expression for the in-body propagation model is extremely difficult. Instead, the SAR level is employed as a standard measure of how much power is absorbed by the tissue. Compared to the free space propagation, an additional 30-35 dB path loss is noticed at small distances. Measurements in BIB006 BIB002 BIB003 demonstrated that direct communication between implanted nodes suffers from a lower path loss with respect to the link establishment between an implant and a node in body surface. Finally, it has been shown that the shape and the position of the patient's body has a significant impact on the radiation pattern of an implanted radio transmitter BIB001 .