Olev Martens

Lock-in measurement of bio-impedance variations

Abstract Electrical impedance measured between suitably placed electrodes can give a reasonable amount of information about the basic physiological parameters of the patient’s body and its organs and vital systems. High noise immunity of the lock-in demodulation technology allows one to obtain, from the bio-impedance variations, the signals corresponding to breathing and heart beating, even using the handles of the veloergometer or other similar equipment as the electrodes. From these signals it is possible to get not only simple physiological parameters like the breathing rate and heart rate, but also to derive more complex parameters like the tidal volume and minute volume of respiration, and stroke volume and cardiac output of the heart. The application specific integrated circuit (ASIC) has been designed for electrical bio-impedance measurements in portable and implantable equipment.

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.

DSP-based Power-Quality Monitoring Device

A prototype for DSP-based power quality monitoring device has been proposed, developed and investigated. Solution is based on 16-bit more than 100 ks/s analog-front-end, modern programmable DSP, and various data saving and communication interfaces. A special software-PLL has been developed, for synchronous measurements with 50 or 60 Hz line frequency. Prototype measures RMS values of voltages and currents in 3-phase power system, and also harmonics, active and reactive powers, and transients, and other features, required by according standards.

Binary signals in impedance spectroscopy

Using of binary waveforms in the fast impedance spectroscopy of biological objects is discussed in the paper. There is shown that the energy of binary waveforms can be concentrated onto selected separate frequencies. We can optimize the binary excitation waveform depending on the shape of frequency response of the impedance under study to maximize the levels of signal components with certain selected frequencies. As a result, we are able to receive maximal amount of information about the properties and behavior of the impedance to be studied. We have designed and prototyped the impedance spectroscopy device operating in the frequency range from 100 mHz to 500 kHz to cover α- and β-regions of the bio-impedance spectrum of time-varying subjects as, for example, fast moving cells in micro-fluidic devices, beating heart and breathing lungs or the whole cardiovascular system.

Cross-correlation-based image matching of coins

Grey-scale multiresolution cross-correlation, combined with Canny edge detection algorithms, has been proposed and investigated for relatively simple and efficient coin recognition and matching algorithm. First experiments and investigations of the proposed solution show promising results. Also an overview of the alternative or complimentary image matching by support vector machines algorithm has been given in the paper. Finally, ideas for further improvement of the efficiency of the proposed solution are discussed.

Adaptively undersampled, circular histogram based image processing for rotation invariant coin detection

As in many real time signal processing application in image processing the computation time and the number of operations is very critical. Correlation as the most known and most widely used algorithm in image matching has a tendency to grow the number of operations rapidly when the range of discretion increases. In this paper adaptively undersampled circular histogram based image processing algorithm for the validation of fast moving and rotating coins has been developed and evaluated. The combination of adaptive undersampling and circular area histogram matching makes the method highly accurate and rotation invariant while significantly reducing the calculations operations needed for the validation of fast moving and rotating coins. This method has been tested on real euro coins and the results show that this method is suitable for accurate rotation invariant coin verification system.

Chirp-based impedance spectroscopy of piezo-sensors

Impedance spectroscopy is widely used in various test& measurement fields and applications. In current paper a novel approach of excitation with chirp signal with simple time-domain analysis of response signal for such task is introduced and described with examples of measurement of the electro-mechanical impedance of piezo-sensors, in the frequency range of several hundred kiloherz. In one approach smoothed separately (by Savitzky-Golay filter) of excitation voltage and (current) response signals in a sliding window are found and their ratio is used for impedance module estimation, at corresponding time and frequency values. Alternative method for vector measurement of impedance spectra in time domain has also tested.

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

Adaptively undersampled image processing for fast multiline laser detection

In many image processing applications one of the main problem is how to create algorithms, which are fast enough to be implemented on embedded (with limited resources) computing platforms, like DM3730 processor based development boards (Beagleboard-XM). One such image processing area is related to laser scanners, which are usually implemented on multi-core high performance personal computers. In this paper an adaptively undersampled image processing method for fast multiline laser detection has been proposed. The combination of adaptive undersampling and multiline laser detection significantly reduces the calculation operations, needed for laser line detections, thus making this method highly suitable for limited embedded platforms. This method has been tested with real multiline laser images on pavement surface, on 4 different computing platforms and the results are presented at the end of the paper.

Simple DSP interface for impedance spectroscopy of piezo-sensors

An interface for impedance spectroscopy measurements of piezo-sensors has been developed, for a digital signal processor of Delfino series of Texas Instruments. DAC of the interface is based on a 16-bit PWM with extra 8-bit part of “high resolution” (of picoseconds), with external simple (3-rd order) analog filter. Internal 12-bit ADC is converting at rates of up to 10 MS/s with 2 simultaneous sample-and-holds. So, with few extra components, high-performance analog interface has been “improvised” (developed and investigated) with a frequency range 10 kHz −400 kHz about 0,1% of the full scale resolution and repeatability of measurements.