Kimihiro Tajima

Proposal of A Novel EMI Diagnostic System using Independent Component Analysis

This paper presents a noise diagnosing system that can separate multiple interfering signals due to crosstalk or common-mode noise problems. In estimating original time-series signals from measured data sets, our system uses the independent component analysis (ICA) scheme, which uses a statistical technique to separate blind source signals from measured data sets. In addition, mutual-correlation coefficients between separated and measured signals are used to obtain a set of measured and estimated signals. Evaluations of transmission lines confirmed that our system is effective for diagnosing multiple electromagnetic interference (EMI) problems, resulting in the mutual-correlation coefficients between the original and estimated signals being more than 0.9 for 1-20 MHz sinusoidal signals.

Theoretical analysis of the sensitivity of electric field sensors using LiNbO3 optical modulator

The electric field sensor using an optical modulator makes possible accurate measurement without disturbing the electromagnetic field to be measured and is expected to have applications in EMC measurement. In this paper, a theoretical analysis of the sensitivity of the electric field sensor using an LiNbO3 modulator and the error factors are described. First, the electric field sensor consisting of a rod, an optical modulator, an optical source, and an optical detector is expressed by an equivalent circuit. Next, of the equivalent circuit parameters, those related to the sensor rod are derived by a numerical analysis using the method of moments. Those related to the optical modulator are derived by the theoretical analysis and measurement. A method is presented for determination by measurement in regard to the optical source and the detector. An electric field sensor is fabricated and its characteristics are evaluated. It is found that the difference between the measured value and the theoretical value of the sensitivity is about 8.2 dB. The causes of the difference are the input capacitance and the insertion loss of the optical modulator. These two parameters are measured beforehand and used in the calculation. Then, the sensitivity of the electric field sensor can be estimated with an accuracy of 1 dB. The analysis method used in this paper is found to be effective for sensitivity analysis of the electric field sensor.

Development of wide-band and highly sensitive electric field sensor using LiNbO/sub 3/ optical modulator

A Mach-Zehnder interferometer whose half-wave voltage is about 4 V and a YAG laser pumped by a laser diode whose output power is 25 mW are used to improve the sensitivity of a LiNbO/sub 3/ electromagnetic field sensor. The resulting frequency response is almost flat from 100 Hz to 300 MHz and the minimum detectable electric field strength is 1 mV/m at 50 MHz and 0.14 mV/m at 750 MHz. The frequency response of the sensor is analyzed using the moment method, and the calculated results agree with the measured results. The improved sensor can measure an electromagnetic impulse whose peak value is larger than 10 V/m and width is wider than 5 ns.<<ETX>>

Measurement of subjective communication quality for optical mobile communication systems by using mean opinion score

Since optical mobile communication systems do not radiate radio waves from the mobile terminals, they are expected to be used in environments containing sensitive electronic equipment. However, the placement and direction of the optical receivers must be suitably determined for mobile communication because light has high directivity. In optical mobile communication systems, the communication quality varies with the direction of the mobile terminal. Therefore, we examined the angle over which communication is possible at various measurement points and defined it as the communication angle. The mean opinion score (MOS) was obtained to assess the communication quality using the communication angle as a parameter. In this paper, two situations, walking and sitting down, were regarded as representing the way optical mobile communication systems are actually used. We found that for walking, when the communication angle was over 180 degrees, the MOS was over 3 and over 50% of users could communicate usefully. When a user was sitting down, the communication quality did not depend on the communication angle, but only on whether or not the user could communicate in the direction he/she was facing. Thus, if the communication angle in the service area is over 180 degrees, it is possible to communicate in practical situations, even while walking.

Propagation characteristics of ESD-induced electromagnetic pulses measured using optical E-field sensor

This paper describes the propagation characteristics of electromagnetic pulses induced by electrostatic discharge (ESD) in the far field. ESD energy spectra measured with an electric field sensor using a Mach-Zehnder interferometer are analyzed for the frequency band DC-1 GHz by short-time Fourier transform (STFT). Analytical results show that ESD energy in high frequency band (100 MHz-1 GHz) decrease more rapidly in proportion to the distance from a source point.

Evaluation of voltage induced at telecommunication line end by a near electromagnetic radiation source

The coupling coefficient between an electric field radiated from close to an overhead cable and the voltage appearing at the cable end is studied experimentally and theoretically. The calculated results closely agree with the experimental results. The voltage induced by a near radiation source is smaller than the voltage induced by a far radiation source for the same electric field strength at the cable.

Calculation of service area for mobile communication system using optical rays

Communication systems using optical rays are expected to be used in environments containing sensitive electronic equipment. This paper studies a method of calculating the service area for an optical mobile communication system. The service area is defined by the communication angle, which is calculated using ray-tracing theory considering reflections from materials in the room. The calculated results are compared with experimentally measured ones, and the difference is less than 12%.