Design Of A Bioimpedance Spectroscopy Measurement System Based On Multisien Excitation And Integer-period Sampling

The traditional single sinusoidal excitation sweep-frequency and time-sharing principle based bioimpedance spectroscopy(BIS)measurement is time-consuming and have difficulty in implementation of the integer-period sampling,which will inevitably cause spectrum leakage when Discrete Fourier Transformation(DFT)is performed,and as a consequence,the accuracy of the measurement result will be influenced.This paper puts forward a Multisine-based integer-periodical synchronization sampling method for the BIS measurement,by which the spectrum leakage will be inhibited fundamentally and the multi-frequency synchronous measurement will be achieved fast and accurately.This article mainly includes the following aspects:1.By introducing the measurement principle and the development history of BIS technology,the strength of choosing Multisine as the excitation signal is explained,meanwhile the shortage of the existing methods for achieving Multisines with low CFs are discussed;2.A Multisine-based integer-periodic synchronization sampling system for the BIS measurement is proposed,and the function of the integer-period sampling method in inhibiting spectrum leakage is theoretically verified by using simulation of the MATLAB software;3.A hardware system for synchronous integer-period BIS measurement is designed,of which a Field Programmable Gate Array(FPGA)is used for Multisine generation with a digital to analog controller(DAC),and for synchronization of integer-period sampling of the excitation and response signal with a analog to digital controller(ADC).In addition,an integer-periodic synchronization sampling and data buffering method which is realized on the control of the ADC with a Nios II based FPGA is detailed introduced;4.An optimization algorithm for low CF Multisine generation is proposed,which is able to synthesize Multisines with any shapes of spectrums such as a flat amplitude&equal frequency distribution,a non-flat amplitude&equal frequency distribution,a flat amplitude&quasi-logarithmic frequency distribution and a non-flat amplitude&quasi-logarithmic frequency distribution.By comparison of the results with former documentary records,it shows that the CFs of the Multisines have reached or nearly reached the best values;5.The low CF Multisines excitation synthesized by the previous algorithm along with three 3-RC phantoms in different parameters are tested for the integer-period BIS measurement hardware system,and up to a thousand frequency points can be accurately measured within a few milliseconds;6.Considering the source of the measurement noises,a BIS measurement model under the noise interference is established and the influence on the measurement results of the current noise and voltage noise are analyzed,in addition,the unbiased estimation of the measured value is calculated for achieving the signal-to-noise ratio(SNR).The achievement of this paper such as synchronous integer-period sampling as well as its realization method,and the improved Multisine synthesizing algorithm will have broad application prospects in the BIS measurement,which has the signification of academic reference and practical application.