An impedance spectrum of dynamic systems is time dependent. Fast impedance changes take place, for example, in high throughput microfluidic devices and in operating cardiovascular systems. Measurements must be as short as possible to avoid significant impedance changes during the spectrum analysis, and as long as possible for enlarging the excitation energy and obtaining a better signal-to-noise ratio (SNR). The authors propose to use specific short chirp pulses for excitation. Thanks to the specific properties of the chirp function, it is possible to meet the needs for a spectrum bandwidth, measurement time and SNR so that the most accurate impedance spectrogram can be obtained. The chirp wave excitation can include thousands of cycles when the impedance changes slowly, but in the case of very high speed changes it can be shorter than a single cycle, preserving the same excitation bandwidth. For example, a 100 kHz bandwidth can be covered by the chirp pulse with durations from 10 µs to 1 s; only its excitation energy differs also 10(5) times. After discussing theoretical short chirp properties in detail, the authors show how to generate short chirps in the microsecond range with a bandwidth up to a few MHz by using digital synthesis architectures developed inside a low-cost standard field programmable gate array.

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Method of time domain impedance spectroscopy using of rectangular wave chirp excitation is presented in the paper. Effectiveness of the excitation is high -more than 85% of the generated energy lies in the useful excitation bandwidth, which can cover several decades of frequency. Fast measurement and joint time-frequency analysis of dynamic impedances is envisaged. Implementations in impedance spectroscopy for cell detection and characterizing in different lab-on-a-chip type high-throughput microfluidic devices can be one recommended area for the proposed method. This method offers important diagnostic information about the dynamic and structural properties of biological cells, organs like beating heart, and the whole cardiovascular system.

In this paper, certain aspects of choosing excitation waveforms for fast identification of the complex electrical impedance over a wide frequency range are discussed. For this purpose, several chirp-like short-time excitation signals with near to minimal duration are proposed. The results of computer simulation and analysis are promising for implementing such kind of signals as the stimulating ones in the bioimpedance measurement.