Abstract
Herein, we propose an impedance spectroscopy method using a mode-switching nonsinusoidal oscillator and apply this method for measuring the impedance of biological tissues and continuous impedance measurement. To obtain impedance spectra over a wide frequency range, we fabricated a novel nonsinusoidal oscillator incorporating binary counters and analog switches. This oscillator could periodically switch oscillation frequency through the mode switching of the feedback resistor. From the oscillation waveform at each oscillation frequency of this circuit (oscillator), we determined the impedance spectrum of a measured object using the discrete-time Fourier transform. Subsequently, we obtained the broad impedance spectrum of the measured object by merging odd-order harmonic spectral components up to the 19th order for each oscillation frequency. From the measured spectrum, the resistive and capacitive components of the circuit simulating bioimpedance were estimated with high accuracy. Moreover, the proposed method was used to measure the impedance of porcine myocardium; changes in the impedance spectrum of the myocardial tissue due to coagulation could be measured. Furthermore, rapid variations in the resistance value of a CdS photocell could be continuously measured using the proposed method.
Highlights
Bioelectrical impedance analysis has become an important technique in the medical and healthcare fields [1,2,3,4,5,6,7,8,9]
CSX = 9.76 nF are connected as Zx in the mode-switching nonsinusoidal oscillator
Switched every two cycles, and the oscillation frequency changed in four modes
Summary
Bioelectrical impedance analysis has become an important technique in the medical and healthcare fields [1,2,3,4,5,6,7,8,9]. Impedance may be measured using a single frequency or a few frequencies. Bioimpedance has frequency characteristics over a wide range of frequencies, which originate from impedance components such as intracellular fluid resistance, extracellular fluid resistance, and the capacitance of cell membranes. If the impedance spectrum over a wide frequency range could be measured rapidly and conveniently, more detailed information about biological tissues could be obtained, which would be useful for diagnosing and treating medical conditions
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