Jingjing Shi

Channel characterization and diversity feasibility for in-body to on-body communication using low-band UWB signals

This paper aims at the feasibility study of a wireless link for capsule endoscope by using of low-band ultra wideband (UWB) signals. The UWB technique has a potential to provide real-time image transmission from the inside to outside of the body, but it suffers from the large attenuation in the human tissue. We employ the finite difference time domain (FDTD) numerical technique together with an anatomical human body model to derive the channel characteristics such as the path loss and shadow fading. We also investigate the feasibility to use a space diversity technique to improve the communication performance. The results have shown a possibility to use the low-band UWB technique to realize a data rate as high as 80 Mbps for the capsule endoscope application.

Numerical Techniques for SAR Assessment of Small Animals in Reverberation Chamber

Reverberation chamber (RC) has been recently developed and used in bio-electromagnetic (EM) field research for investigation of possible adverse health effect of EM waves to human body. Concerning the use of an RC as an exposure device, accurate dosimetry or quantification of EM energy absorbed in exposed animals inside an RC is actually of importance. However, the dosimetry of animals inside an RC is one of challenging problems due to its size and complex behavior of EM fields inside the chamber. This paper is dedicated to the demonstration of three different numerical techniques developed for dosimetry of small animals exposed to EM fields inside an RC at microwave frequencies. First we briefly review procedures of each numerical method and clarify its advantages, disadvantages, and range of applications. Then we demonstrated their validity by either experiments or cross-verification. Finally we discuss the results obtained from each numerical technique.

A two-step approach for EMI evaluation of a wearable ECG

In this study, we propose a two-step approach to evaluate electromagnetic interference (EMI) with a wearable electrocardiogram (ECG) sensor. The two-step approach combines a quasi-static electromagnetic (EM) field analysis and an electric circuit analysis, and is applied to the EMI analysis at frequencies below 1 MHz for our developed wearable ECG to demonstrate its usefulness. The quasi-static EM field analysis gives the common mode voltage coupled from the incident EM field at the ECG sensing electrodes, and the electric circuit analysis quantifies a differential mode voltage at the differential amplifier output of the ECG detection circuit. The differential mode voltage has been shown to come from a conversion from the common mode voltage due to an unbalance between the contact impedances of the two sensing electrodes. It may achieve nearly 0.6 V at the differential amplifier output under 10-V/m plane-wave incident electric field, and completely mask the ECG signal. It is essential to reduce the unbalance as much as possible to not cause a significant interference voltage in the amplified ECG signal.

Two whole-body exposure systems for biological effect test of RF electromagnetic fields

This paper describes two whole-body exposure systems for biological effect tests of radio frequency (RF) electromagnetic fields. The first exposure system is designed at 2 GHz band to have a feature of circular polarization for simulating a variety of coupling with humans in daily environment. The second exposure system is designed to simulate a multiple-frequency exposure between 800 MHz and 5.5 GHz. In order to get an accurate evaluation on the exposure level for rats in the exposure systems, we developed a statistical analysis tool in our systems. We first took documentary photos of rat activity in the exposure box in a real time. Then we derived the frequency of rats staying in various positions in the exposure box. Using the stay frequency as a weighting factor, we can calculate the whole-body average SAR statistical characteristics during the exposure period. The developed systems and demonstrated performances have shown their high quality and convenience as an exposure system for the above biological effect tests.

Performance analysis of diversity effect for in-body to on-body wireless UWB link

The objective of this study is to perform a quantitative performance analysis of diversity effect for in-body to on-body ultra wideband (UWB) transmission for capsule endoscope. UWB technology has a potential to provide real-time image transmission from inside to outside of human body owing to its inherent features. However, it suffers from large attenuation together with shadowing in human tissues. In view of this distinctive property, a diversity scheme is expected to provide an effective improvement on this wireless link performance. Based on finite-difference time-domain (FDTD) numerically-derived in-body to on-body characteristics, we derive probability density function (PDF) for combined communication channels with two different approximation methods and compare their accuracy at first. Then we calculate average bit error rate (BER) with pulse position modulation (PPM) and on-off keying (OOK) modulation scheme to clarify the possible diversity effect.