Spatial In-Body Channel Characterization Using an Accurate UWB Phantom

Abstract

Abstract-Ultra-wideband (UWB) systems have emerged as a possible solution for future wireless in-body communications. However, in-body channel characterization is complex. Animal experimentation is usually restricted. Furthermore, software simulations can be expensive and imply a high computational cost. Synthetic chemical solutions, known as phantoms, can be used to solve this issue. However, achieving a reliable UWB phantom can be challenging since UWB systems use a large bandwidth and the relative permittivity of human tissues are frequency dependent. In this paper, a measurement campaign within 3.1-8.5 GHz using a new UWB phantom is performed. Currently, this phantom achieves the best known approximation to the permittivity of human muscle in the whole UWB band. Measurements were performed in different spatial positions, in order to also investigate the diversity of the in-body channel in the spatial domain. Two experimental in-body to in-body (IB2IB) and in-body to on-body (IB2OB) scenarios are considered. From the measurements, new path loss models are obtained. Besides, the correlation in transmission and reception is computed for both scenarios. Our results show a highly uncorrelated channel in transmission for the IB2IB scenario at all locations. Nevertheless, for the IB2OB scenario, the correlation varies depending on the position of the receiver and transmitter.Index Terms-Body area network, in-body communications, path loss, ultra-wideband (UWB) phantom, uncorrelated channel.

Ultrawideband Technology for Medical In-Body Sensor Networks: An Overview of the Human Body as a Propagation Medium, Phantoms, and Approaches for Propagation Analysis

“…Regarding the correlation in transmission -calculated to study the diversity of the UWB in-body channel in several locations of transmitting antennas-it decreases rapidly whatever the distance between transmitter antennas was, as authors concluded in [134], in an IB2IB phantom-based setup. They also concluded that correlation is quite high when transmitting antennas are aligned at the same height and the distance between their centers is below 5 cm for the IB2OB scenario.…”

“…Therefore, more studies to enhance the communication among implanted sensor networks should be conducted. On the other hand, the path loss is fitted by a log-distance model for the IB2OB scenario, as concluded in [134]. Likewise, the shadowing is well-fitted by a normal distribution.…”

“…Furthermore, transmitters and receivers involved in the propagation scenario should be moved accurately to different locations in order to research the radio channel characteristics, knowing the position of the sensors as well as the distance between antenna centers. In [134], authors performed a measurement campaign within UWB (3.1-8.5 GHz) by using a novel experimental setup (see Fig. 10).…”

“…The diversity in reception is assessed by considering different receiving antenna locations. In [134], the study concluded that correlation decreases as the distance between the receiving antennas increases, as in [144]. Besides, the receiving antennas should be separated more than one wavelength in order to increase the diversity in reception, i.e., to obtain uncorrelated signals in reception.…”

Accurate broadband measurement of electromagnetic tissue phantoms using open-ended coaxial systems

“…To this end, it is necessary to develop accurate tissue phantoms, which are materials that imitates the electromagnetic characteristics of human tissues. They are cost-effective and easy to produce, allowing the assessment of different electromagnetic parameters related to transmission [1] and correlation [2] for wireless implanted devices in Body Area Networks (BAN), as well as specific absorption rate [3] and dosimetry in mobile communications scenarios. Electromagnetic tissue phantoms avoid as well the experimentation with animal specimens and humans in in vivo conditions [4] in preliminary stages.…”