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Modelling of Pyroelectric Detectors Detection by Digital Signal Processing Algorithms
[Thesis]. Manchester, UK: The University of Manchester; 2013.
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Abstract
Pyroelectric Detector (PED) models are developed considering the classical heatbalance equation to simulate the detector’s response under specified radiationconditions. Studies on the behaviour of a PED are presented under the conditions of stepfunction and a pulsed load. Finite Element Methods (FEMs) have been used to obtained3D models of the resulting temperature field in a Lithium Tantalate (LiTaO3)pyroelectric crystal, incorporated in a complete commercial detector, taking intoaccount details of its geometry and thermal connectivity. The novelty is the achievedfacility to predict the response to pulsed radiation, which is valuable for the engineeringof pulsed-source sensor systems requiring detection at room temperature.In this thesis, we present a signal processing (SP) algorithm, which combines theprinciple of Quadrature Synchronous Demodulation (QSD) and Gated Integration (GI),to achieve achieve an improved signal-to-noise ratio (SNR) in pulsed signalmeasurements. As a first step, the pulse is bracketed by a gating window and thesamples outside the window are discarded. The gate duration is calculated to ensure thatthe periodic signal at the output has an “apparent” duty factor close to 0.5. This signalis then fed continuously for QSD to extract the magnitude and phase of its fundamentalcomponent, referenced to a sinusoidal signal with period defined by the gate length. Animproved SNR performance results not only from the increase of the average signalenergy, but also from the noise suppression inherent to the QSD principle. We introducethis method as Gated Quadrature Synchronous Demodulation (GQSD), emphasizing thesynergy between GΙ and QSD.