Sensitivity of a plate pyroelectric detector to ambient acoustic noise: The significance of the perfectly-clamped mounting condition

The unwanted sensitivity of a plate pyroelectric detector to airborne acoustic noise is depends critically on the mounting conditions for the plate. We consider a plate in an isotropic acoustic pressure field oscillating at angular frequency omega(d). We analyze the situation in terms of a mechanically isotropic material, and show that for one type of boundary conditions, the so-called clamped-boundary conditions, the strain-induced time-varying surface charges caused by the pressure in various regions of the plate, completely cancel out. This suggests that significantly reduced noise sensitivity of a practical free-standing pyroelectric detector can be achieved by paying careful attention to the mounting conditions. We also derive the strains for the case of the trigonal 3m class within the framework developed for the thin-plate approximation, and show that the result is unchanged. This has implications for the design of pyroelectric detectors based on a stiff material such as LiTaO3.