A simple 250 degrees celsius frequency modulation transmitter for use in wireless sensor networks

This paper presents a voltage-controlled oscillator (VCO) operating up to 250°C and usable as a simple frequency modulation (FM) transmitter in wireless sensor networks (WSN). The device is a simple LC oscillator which uses the channel depletion capacitance as a variable capacitor controlled by the gate voltage V_G to enable the sustained oscillating behaviour of a tank circuit. The context of operation, failure mechanisms and limitations of electronic components in high temperature environments are studied. The designed component operates successfully in the frequency range from 48 to 62 MHz at room temperature and 56 to 59 MHz at 250°C. Output powers have been measured from -30 dBm to -10 dBm. The proposed circuit enables frequency modulation for wireless communications in the context of ruggedized wireless sensor networks, that is, sensor networks which are designed to operate in very harsh conditions such as fire fighting and industrial applications.