Biomedical subjects

I D Schneider

Publications and source records attributed to I D Schneider.

3 recordsLinked to original sources

PubMed2001

Front-end architecture for a multi-frequency electrical impedance tomography system.

This paper provides a critical review of a number of the primary aspects of EIT system hardware presented in the literature. A thorough analysis of injection and measurement errors is presented to provide clarifying extensions to that provided by previous authors. From this basis, it proposes a novel design for a distributed parallel multi-frequency EIT system. The system described is modular, employs active electrodes to maximise CMRR (common mode rejection ratio) and was designed to employ digitally generated current injection and digital demodulation of the acquired signals.

Electric Impedance↗

PubMed2000

Design of an electrical impedance tomography phantom using active elements.

The architecture of a novel phantom for electrical impedance tomography (EIT) is proposed. The design employs active elements, which include multiplying digital to analogue converters (MDAC), so that the impedance distribution in the phantom may be varied dynamically using computer control. The phantom is designed to assist in the validation of an EIT system under test. A number of published layouts for passive phantoms are analysed, and the requirements for an active element are specified for the most applicable of these. The use of active elements throughout a phantom imposes significant costs because of the need for each active element to operate independently. This proposal limits the cost and complexity by employing active elements in a restricted region of the phantom. Currently available technology, principally due to the limited analogue bandwidth of the MDAC, precludes the construction of a fully capable phantom from active elements. However, a design is specified that would enable its future development to cover the frequency range from 10 kHz to 1 MHz.

Electric Impedance↗

PubMed2000

Synthesis of a digitally controlled impedance element.

A practical design for the synthesis of a digitally controlled electrical impedance element is presented. The impedance element comprises a real impedance element in series with a voltage source whose magnitude is determined by the applied voltage multiplied by a factor k. The value of k is shown strongly to affect the circuit's performance. Results are presented which demonstrate the correspondence between circuit models and practical measurements. When negative values for k were employed the circuit element offered a controlled impedance range of 1:1000 and was stable to at least 1.5 MHz, providing that low source impedance values were used. With a positive k, a restricted range of impedance values could be obtained and the value of source impedance was less critical, though the circuit's performance was acceptable only to about 100 kHz. Consideration is given to the specification of a multiplier that would permit the circuit's range of application to be extended to low megahertz frequencies.

Electric Impedance↗