A new thermal conductivity detector based on a lithium niobate surface acoustic wave (SAW) resonator has been fabricated for use in a gas chromatograph. The device exploits the large temperature coefficient of LiNbO3 to detect low concentrations of CO2 in air by sensing the change in the thermal conductivity of a helium camer gas and the CO2 exiting the capillary gas chromatograph column. The LiNb03 resonator is maintained at 150oC and is held in close proximity (0.2-0.3 mm) to the exit of the capillary column which is maintained at 5OOC. Heat loss from the LiNb03 is primarily due to the thermal conductivity of the gas exiting the capillary column such that changes in the constituency of the gas result in temperature changes on the surface of the resonator. The surface temperature change is monitored by recording the resulting frequency change in a 342 MHz SAW resonator controlled oscillator circuit. The entire system is small, battery powered and rugged enough to monitor green house gases in remote field sites throughout the world.
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