Analysis of Mini-Camera's Cat-Eye Retro-Reflection for Characterization of Diffraction Rings and Arrayed Spots

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.

Design of an Active Laser Mini-Camera Detection System Using CNN

“…The limitations of the proposed system is the range of detection distances and angles of incidence, because the reflection intensity of a mini-camera is greatly reduced with the degradation of these two conditions. The dependence of a traditional cat-eye target reflection on incident angle has been studied in [19], [20], while the mini-camera's distant or oblique-incidence reflection has been analyzed in [5], [8]. However, the actual upper limits of the distance and incident angle vary greatly depending on the working conditions and target characteristics of each system.…”

“…These characteristics explain the previously mentioned limitations when detecting mini-cameras using traditional laser active detection systems. Additionally, the reflection characteristics of mini-cameras under laser irradiation have been described and analyzed in detail by Liu et al in reference [8].…”

“…The reflection images of targets are divided into four main types; diffraction, array, traditional cat-eye, and mixed [8] as shown in Fig. 8.…”

“…Long et al [5] analyzed the diffraction phenomenon of the retro-reflection, whereas Change et al [6] and Gong et al [7] described the arrayed spots in reflected image profiles. Liu et al [8] performed systematic analysis of mini-camera reflection, proposed an optical model, and implemented a reflection simulation. Based on these studies, this paper proposes an innovative method for building an anti-mini-camera system with a monostatic optical design and a convolutional neural network (CNN)-based classification algorithm.…”

Mechanisms of active detection on micro-cameras based on cat-eye effect with different incident angles

“…By analyzing the detailed structure of the micro-camera and different reflection lights, researchers form the light intensity formula after the light passes a micro-camera and falls on a CCD camera. Throughout four types of reflection lights, it is found that arrayed cateye reflection (ACR) has the best reflecting light intensity and could be applied to micro-camera detections [10].…”