An Active Circuit for Wireless Broadcast of Sensor Information: Application to Humidity Monitoring
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%.
Document Type: Research Article
Publication date: 2004-09-01
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