Mixing Frequency Bioelectrical Impedance Measuring System

Bioelectrical impedance measuring technology is a developing technology that iscalling the attentions of the researchers, due to its low-cost, wealth of information andnon-invasive. This technology can extract biomedical information relating to humanbody's physiological and pathology status, through the change of electrical characters(impedance, admittance, permittivity etc.) in biological tissue and organ. Using thisinformation, function evaluation of heart, brain, lung and circulation system can beachieved, so it has extensive application perspective.According to R-C three parameter model of bioelectrical impedance andfrequency dispersion theory, a phenomenon can be found that the information ofbioelectrical impedance is difference at differenct frequency. To acquire thebioelectrical impedance information at differenct frequency synchronally, abioelectrical impedance measuring system based on mixing frequency excitationmode (the highest frequency up to 1MHz) is designed and realized, which covers theshortage of the former system. According to the virtual reference point technology,combined with difference amplify and multiplicative demodulation, the system isconstructed. A mixing frequency excitation signal unit is designed in this system,which applies only one oscillator to six direct digital synthesis synthesizers. Thefrequency, amplitude and phase of excitation signal and reference signal produced bythis unit can be adjusted. To demodulate the mixing frequency signal, a multiplicativedemodulation unit with bandpass filters is also designed in this system. The hardwaresystem also includes the main controller unit, signal selection unit, A/D collection unit.Then, the software for DSP and PC, which accomplishes the control of hardware,communication between DSP and PC, calculation and display the acquired data, isdesigned to work with the hardware system.