Ultra Wideband Signals and Systems in Communication Engineering

In the early ages of implantable devices, radio frequency (RF) technologies were not commonplace due to the challenges stemming from the inherent nature of biological tissue boundaries. As technology improved and our understanding matured, the benefit of RF in biomedical applications surpassed the implementation challenges and is thus becoming more widespread. The fundamental challenge is due to the significant electromagnetic (EM) effects of the body at high frequencies. The EM absorption and impedance boundaries of biological tissue result in significant reduction of power and signal integrity for transcutaneous propagation of RF fields. Furthermore, the dielectric properties of the body tissue surrounding the implant must be accounted for in the design of its RF components, such as antennas and inductors, and the tissue is often heterogeneous and the properties are highly variable. Additional challenges for implantable applications include the need for miniaturization, power minimization, and often accounting for a conductive casing due to biocompatibility and hermeticity requirements [1]?[3]. Today, wireless technologies are essentially a must have in most electrical implants due to the need to communicate with the device and even transfer usable energy to the implant [4], [5]. Low-frequency wireless technologies face fewer challenges in this implantable setting than its higher frequency, or RF, counterpart, but are limited to much lower communication speeds and typically have a very limited operating distance. The benefits of high-speed communication and much greater communication distances in biomedical applications have spawned numerous wireless standards committees, and the U.S. Federal Communications Commission (FCC) has allocated numerous frequency bands for medical telemetry as well as those to specifically target implantable applications. The development of analytical models, advanced EM simulation software, and representative RF human phantom recipes has significantly facilitated design and optimization of RF components for implantable applications.

Implantable RF Medical Devices: The Benefits of High-Speed Communication and Much Greater Communication Distances in Biomedical Applications

We propose a dispersive finite-difference time domain (FDTD) suitable for the electromagnetic analysis of human tissues. The dispersion relation of biological tissues is characterized by a quadratic complex rational function (QCRF) that leads to an accurate FDTD algorithm in 400 MHz-3 GHz. QCRF coefficients are extracted by applying the complex-curve fitting technique, without initial guess. Numerical examples are used to illustrate the computational accuracy and stability of QCRF-based FDTD.

FDTD Dispersive Modeling of Human Tissues Based on Quadratic Complex Rational Function

A compact, printed, capsule-shaped ultrawideband (UWB) antenna for biomedical implants is presented. The 10-dB return loss bandwidth of the proposed antenna is 3.5-4.5 GHz, which covers the recently proposed UWB for biomedical applications. The antenna matching has been optimized using CST Microwave Studio and verified by measurements. An optimized feed mechanism to reduce guided wavelength, as well as integration with other electronics, has been considered in the antenna design. Radiation performance has been evaluated on an impulse-based UWB transmitter/receiver testbed to show that the antenna is usable in biomedical applications, such as capsule endoscopes. The antenna has been tested both in free space and with tissue loading.

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Design and Evaluation of a Compact Antenna for Implant-to-Air UWB Communication

IEEE 802.15 established a new working group, wireless body area networks (WBAN), to develop short range wireless technology in and around human body recently. This paper investigates networking issues in implant communications of WBAN. The object is better understanding of medical implant sensor networks and how to start WBAN's work. We applied IEEE 802.15.4b and 802.15.4a-chirp spread spectrum (CSS) for implant communications. We found two issues: clear channel assessment of implant devices and adjacent-channel interference from free space signals. Both of them can be attributed to the rapid attenuation of electromagnetic wave through tissues. Therefore the carrier sense multiple access mechanism and transmit mask of 802.15.4b cannot be directly adopted. The modulation of 802.15.4a-CSS is a good reference to WBAN. Besides, a simple two-hop protocol which uses a body surface forwarder was presented for long distance wireless implant communications.

/pdf/ieee-body-area-networks-and-medical-implant-communications-ulmrkms7qx.pdf

IEEE body area networks and medical implant communications

The objective of this study is to investigate the feasibility of an ultra wideband (UWB) system for in-body wireless communications of biomedical applications. We first designed an implanted elliptic disc dipole antenna with a UWB frequency band in a human body. We then calculated the channel characteristics for UWB signal propagation from the implanted antenna to the out-of-body using a frequency-dependent finite difference time domain (FD2TD) method. Based on the in-body channel characteristics we optimized the UWB pulse shape. We then proposed a UWB system with bi-phase modulation for the in-body wireless communications, and derived the bit-error rate (BER) of the proposed system under the additive Gaussian noise environment. The results show the feasibility of the UWB system for in-body wireless communications of biomedical applications.

Donglin Su

Papers

Design of an Ultra Wideband System for In-Body Wireless Communications