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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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This paper presents an adaptive filtering system for separation of two bio-impedance signal components: cardiac and respiratory signals. The proposed filtering system is adaptive to the parameters of the input signal's cardiac component (the reference signal), which is corrupted by the respiratory component and also by additive stochastic disturbances. The adaptation is achieved applying estimation and continuous tracking of the heart rate using a time-optimal Adaptive Phase-Locked Loop (APLL). Technical solutions of the filtering system are oriented on applications in portable and implantable medical devices.

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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.