Ants Ronk

Synchronous Sampling and Demodulation in an Instrument for Multifrequency Bioimpedance Measurement

Direct sampling of known carriers is the preferred digital method for measuring biomodulation of tissue impedance. Due to limited resolution and conversion rate of analog-to-digital converters and limited processing power of available digital processors and/or lack of energy resources, conventional discrete-Fourier-transform-based algorithms are not efficient in small medical devices. Knowing exactly the frequencies of carriers (and excitations), an energy-saving fast signal processing method can be developed and implemented. When sampling synchronously with a carrier, it is possible to minimize the complexity of calculations and to introduce a digital-to-analog feedback for enhancement of resolution by digitizing only the small variations between adjacent samples. The proposed system is qualified on proprietary hardware.

A sampling multichannel bioimpedance analyzer for tissue monitoring

The paper focuses on principles of designing of a multichannel bioimpedance analyzer based on simultaneous multisine measurement. The measurement task arises due to the need to monitor patients during and after heart surgery operation performing MIMO (multiple-input-multiple-output) bioimpedance measurement. Frequencies of the simultaneously applied sinusoidal excitations must be close but simultaneously varied in a larger range (e.g. from 1 kHz up to 10 MHz). The main idea of the proposed approach is that the use of a rather specific signal system (frequencies of sinusoidal excitations are related as integers and sampling frequencies are properly related/adapted to them) makes it possible to separate responses to different excitations from the measured summary signals by means of a quite simple filter and different (under) sampling rates.

Design concepts of instruments for vector parameter identification

The design concepts for phase-sensitive measuring instruments, which are based on two-phase synchronous detection and known as vector analyzers, are proposed. The main idea of the design is to use the advantages of both analog and digital signal processing methods by combining the synchronous detection and averaging procedures with the integrating analog-to-digital and functional digital-to-analog conversion principles. The reference channel of the vector analyzer is built up on the basis of the adaptive third-order phase-locked loop (PLL). >

An Adaptive Filtering System for Separation of Cardiac and Respiratory Components of Bioimpedance Signal

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 signals 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

Simultaneous multi-frequency bio-impedance measurement applying synchronised uniform or non-uniform sampling

The paper presents some possibilities to perform multi-frequency bio-impedance measurement simultaneously for K tissue-channels (MIMO measurement). The multi-sine excitation currents of all the channels have frequency-sets which 1) consist of L frequencies and 2) are different enough for separating the responses of all the K ∙ L frequencies and close enough for comparing the frequency responses of the tissue-channels in (neighbourhoods of) L points. The approach is based on use of such excitation frequencies and the sampling frequency (or sampling frequencies, simultaneous applying of which leads to non-uniform sampling), which all are properly chosen integer multiples of the basis frequency f E ≥ 1 T0 , where T0 is the desired measurement interval.

A Digital Multichannel Bioimpedance Analyser: Signal Processing Task and its Solution

Measurement of electrical bioimpedance enables to characterize a state of tissues/organs, to get diagnostic images, to find hemodynamical parameters, etc. In this paper we consider a digital multichannel bioimpedance analyser developed for monitoring of the state of a working heart. The signal-processing task, which must be solved in this analyser, is described and some proposed alternative algorithmic and hardware solutions of this task are considered and compared

Analysis and reproduction of a signal's periodic components by means of an extended block-adaptive Fourier analyzer

This paper presents some results of developing a signal analyzer for performing spectral analysis and simultaneous reproduction/filtering of the input signals periodic components of different (in general, not harmonically related) frequencies and waveforms/spectra. The proposed analyzer accomplishes this task by applying adaptive recursive Fourier analysis.