Abstract
Mini-cameras are one of several emerging types of cat-eye devices using small lenses with insufficient retro-reflection for traditional detection systems to identify. Based on a structural analysis of these devices, this paper provides an accurate theoretical description of the received beam profile. The simulated and experimental results have good similarity in terms of profile shapes and trends with different incident angles and defocus distances. An analysis of the detection conditions and the reflection image features described in this article can thus be applied to hidden camera detection. Mini-cameras can be detected according to these features of the received beam profiles.
Highlights
Active laser reconnaissance technology has undergone great advancements over the past few decades, enabling most conventional cat-eye devices to be detected based on the chatoyancy effect
Different types of retro-reflection of a mini-camera are systematically analyzed based on the angular spectrum method (ASM) and combined aperture method
We divided the retro-reflection of the mini-camera into three components: front-lens reflection (FLR), diffracted cat-eye reflection (DCR), and arrayed cat-eye reflection (ACR)
Summary
Active laser reconnaissance technology has undergone great advancements over the past few decades, enabling most conventional cat-eye devices to be detected based on the chatoyancy effect. Unlike most ordinary cat-eye devices, mini-cameras are usually undetectable using conventional methods because of the sizes of their lenses and small overall dimensions. For normal-sized cat-eye devices, the models or systems performed well, but when applied to mini-cameras, the results and systems did not work adequately because of the diffraction phenomenon. Zhao and Sun [4] simulated diffracted beam profiles at different distances and incident angles. Analyzed the periodicity of the detection distance in the beam propagation [5] Their works have successfully described the special profiles in cat-eye reflection images to some extent. The spectral characteristics of the reflection images were studied in combination with the characteristics of diffraction and the arrayed spots. We can obtain the conditions to detect a mini-camera, which can help us design a mini-camera detection system
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