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An Active Circuit for Wireless Broadcast of Sensor Information: Application to Humidity Monitoring

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Abstract:

A wireless, inexpensive, active transmitter circuit is described for broadcast of ambient humidity levels. The radio-frequency transmitter is comprised of a square-wave, inverter-type 68 MHzRC relaxation oscillator circuit the output frequency of which depends on the sensor impedance. A spiral antenna operates at the third harmonic frequency of the oscillator is used to broadcast the sensor information to minimize the physical size of the circuit. Application to humidity monitoring is demonstrated with a nanoporous titania sensor. The oscillator circuit showed a frequency shift of 2.2 MHz when the relative humidity changed from 5% to 70%.

Keywords: FREQUENCY; HARMONIC; HUMIDITY; OSCILLATOR; SENSOR; TITANIA; WIRELESS

Document Type: Research Article

DOI: http://dx.doi.org/10.1166/sl.2004.047

Publication date: September 1, 2004

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  • The growing interest and activity in the field of sensor technologies requires a forum for rapid dissemination of important results: Sensor Letters is that forum. Sensor Letters offers scientists, engineers and medical experts timely, peer-reviewed research on sensor science and technology of the highest quality. Sensor Letters publish original rapid communications, full papers and timely state-of-the-art reviews encompassing the fundamental and applied research on sensor science and technology in all fields of science, engineering, and medicine. Highest priority will be given to short communications reporting important new scientific and technological findings.
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