Dongsheng Zhao

A Multistep Approach for Accurate Permittivity Measurements of Liquids Using a Transmission Line Method

High-precision permittivity measurements of liquids are essential for specifying the specific absorption rate (SAR) of radio-frequency power absorbed by the human tissue. At Van Swinden Laboratorium (VSL), a commercial unit is used for these measurements, which uses a combination of transmission and reflection methods. The permittivity of unknown liquids is derived from the measured different scattering parameters of a transverse electromagnetic cell when the cell is empty and when it is filled with liquid. The flat slab structure of the cell makes it convenient for liquid filling and cleaning. The method is an efficient complementary approach for permittivity measurements compared with more complex setups in other national metrology institutes, but for reaching a low uncertainty, some inherent disadvantages need to be overcome. In this paper, a multistep approach is proposed using a combination of curve fitting, nonlinear progressive technique, and improved transmission line models in order to improve the uncertainty of the permittivity measurements. This approach is applicable even without a priori knowledge of the liquid properties. Using this approach, the useful frequency range of the commercial unit is successfully extended from 200 MHz-3 GHz to at least 100 MHz-4 GHz, and the accuracy is significantly improved to the level where it becomes comparable to more primary methods. The results obtained with this new method agree very well with the reference data from the literature.

Performance optimization aspects of common mode chokes

Optimization aspects of common mode chokes are presented. These are based on a behavioural model for common mode chokes and its sensitivity study. Results are used to show the influence of the designable parameters on the final performance of the choke placed in a circuit.

A method for in-situ measurement of grid impedance and load impedance at 2 k–150 kHz

A new approach to measure the grid and load impedance of converters in-situ at frequency range 2k-150 kHz has been developed. It is called three-probe approach. This approach allows impedance measurements of power supplies and electric appliances without interrupting their normal operations. The measurement accuracy is improved by proper Fast Fourier Transform (FFT) process to obtain both amplitude and phase information in the measurement. With the proposed setup, the equivalent model consisting of both resistive and reactive components can be derived to represent the grid and load in this frequency range. Grid impedance at different locations and load impedance of various solid state lamps and a SMPS are measured and the results are shown in the paper.

Design and implementation of conducted emission reference source

To meet the requirement of doing periodic inter-laboratory verification and self assessment, a device so called reference source is crucial. In this paper, an existing conducted emission reference source is reviewed and a new design is proposed. The considerations are explained, preliminary results are presented thereupon, and the benefits of the design are emphasized in the conclusion.