Broadband spectroscopy of a dynamic impedance

Abstract

Impedance spectrum of dynamic systems is time dependent. For example, fast impedance changes take place in high throuput microfluidic devices. Also, the impedance of cardiovascular system is dynamic. Measurements must be as short as possible to avoid significant impedance changes during the spectrum analysis and, at the same time, as long as possible for enlarging the excitation energy. The authors propose to use specific short chirp pulses for excitation. Thanks to unique properties of the chirp function, it is possible to meet the needs for spectrum bandwidth, measurement time, and signal-to-noise ratio so that the most accurate impedance spectrogram is obtained. The chirp wave excitation pulse can include thousands of cycles when the impedance changes slowly, but in the case of very high-speed changes it can be even shorter than a single cycle, preserving the same excitation bandwidth. For example, 100 kHz bandwidth can be covered by the chirp pulse with duration from 10 μs to 1 s, only its excitation energy differs also 105 times. © 2010 IOP Publishing Ltd.