A novel gas concentration monitor using a solid state modulator

In this paper, we demonstrate the application of a novel solid state modulator in monitoring the concentration of a test gas. A widespread cost-effective method of gas concentration monitoring currently uses a blackbody source and pyroelectric detector combined with a filter to isolate the required infrared spectral region. Presently the intensity on the detector is modulated by either a mechanical chopper or by electrically-pulsing the source. The device described by this work uses a continuously-driven blackbody source with a novel solid state infrared modulator operating in the 8–14 μm band to generate the required change in intensity on the pyroelectric detector, eliminating the need for moving parts. The modulator may be incorporated into the detector’s optical window in a more-compact future device. The modulator operation is outlined, and the results of determining the concentration of SF6 test gas in a dedicated cell are compared for the solid state modulator and a mechanical chopper.