Purely thermal wave based nonchemical photopyroelectric gas sensor: Application to hydrogen

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Abstract
A commercially available polyvinylidene fluoride (PVDF) pyroelectric film with an optically generated thermal wave field has been introduced as the active device of a new nonchemical photopyroelectric gas sensor. The purely thermal wave based operating mechanism of this gas sensor is in contrast with a similar, surface chemically active Pd‐coated device introduced earlier [A. Mandelis and C. Christofides, J. Appl. Phys. 70, 4496 (1991)]. The sensitivity to a particular gas at low flow rates (−1) is obtained through thermal boundary condition changes introduced by the gas at the film–gas interface, which depend on the thermophysical properties of the gas. The theoretical basis of this device is described. Photopyroelectric voltage amplitude and phase changes due to ambient hydrogen–air mixtures with respect to pure air, obtained through a lock‐in amplifier, are also presented. It is shown that the data are in good agreement with the thermal wave theory. Sensitivity to other common gases used in industry and in environmental studies is also discussed.