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Biomedical subjects

P T Kolen

Publications and source records attributed to P T Kolen.

4 recordsLinked to original sources
PubMed1999

Transformer miniaturization for transcutaneous current/voltage pulse applications.

A general procedure for the design of a miniaturized step up transformer to be used in the context of surface electrode based current/voltage pulse generation is presented. It has been shown that the optimum secondary current pulse width is 4.5 tau, where tau is the time constant associated with the pulse forming network associated with the transformer/electrode interaction. This criteria has been shown to produce the highest peak to average current ratio for the secondary current pulse. The design procedure allows for the calculation of the optimum turns ratio, primary turns, and secondary turns for a given electrode load/tissue and magnetic core parameters. Two design examples for transformer optimization are presented.

Electric Conductivity↗
PubMed1998

Pulsewidth optimisation for transformer-coupled transcutaneous current pulse generation.

A general theoretical approach for the determination of the optimum pulsewidth used for TENS/EMS/FES is presented. Analysis based on the interaction between a step-up transformer-coupled nerve stimulator and an electrode-tissue load modelled as a simple lossy capacitive load results in excellent agreement between the predicted and measured performance. The analysis shows that, by adjusting the pulsewidth (PW) of a push-pull symmetric square waveform such that PW = 4.5 tau, the total charge delivered to the tissue load can be minimised without impacting the efficiency of the nerve stimulation. Additionally, by minimising the charge exchange supported portion of the current pulse, which is primarily responsible for the pH shift and subsequent tissue burning with long-term use, the latter can be reduced to an acceptable level.

Electric Stimulation Therapy↗
PubMed1993

Absolute angle measurement using the earth-field-referenced hall effect sensors.

A miniaturized absolute angle sensor utilizing Hall generators referenced to the Earth's ambient magnetic field has been developed. The sensor has three-dimensional angular sensitivity which allows the output to be self-normalized resulting in high immunity to both B-field and temperature induced errors. The individual Hall generator elements were operated with a final sensitivity of 4.07 V G-1. The Earth's field, magnitude 0.486 G with a surface declination angle of 58.2 degrees (San Diego, California), was used as the excitation/reference field. Bandwidth limiting, low-noise design, and active/passive thermal compensation techniques were employed resulting in a sensor bandwidth of DC to 100 Hz with a maximum signal-to-noise ratio of 44.5 dB. The maximum angular resolution of the sensor was measured to be +/- 0.27 degrees. Temperature induced error was measured to be less than 2% from 25 degrees C to 40 degrees C. The measurement of shoulder joint rotation was used as the test case application for the sensor with excellent agreement between theoretical and experimental performance.

Biophysics↗