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.
The growing popularity of the mini-camera is posing a serious threat to privacy and personal security. Disguised as common tools in rooms, these devices can become undetectable. Moreover, conventional active laser detection systems often fail to recognize them owing to their small lens size, weak reflectivity, and the influence of interference targets. In this paper, a method for building a laser active detection system for minicameras is proposed. Using a monostatic optical system and a deep learning classification algorithm, this anti-camera system can detect mini-cameras accurately in real time. This article describes the system components including its optical design, core components and image processing algorithm. The capability of the system for detecting mini-cameras and identifying interference is also experimentally demonstrated. This work successfully overcomes the limit of mini-camera detection using deep learning methods in active laser detection systems.
Wireless laser power transmission is a promising technique in the far-field wireless power supply with the advantages of high-power density, and small transmitter and receiver sizes. This article proposes a high-efficiency pulse width modulation-based wireless laser power transmission step-down system based on an 808 nm laser diode and gallium arsenide photovoltaic cells. The output voltage of the proposed system is controlled with the use of pulse width modulation of the laser diode in the transmitter without switch tubes and rectifier diodes in the receiver. The model of the proposed system is built, and characteristics of the system is analyzed based on the state-space averaging method. Additionally, the steady and dynamic operations, as well as the efficiency analyses, are investigated and evaluated experimentally. With the use of the propounded system, when the load is 3 ohms and the output voltage is 1.5 V, a converter efficiency of 96.6% is obtained that is ∼10% and ∼5% higher than those of continuous wireless power transmission constant voltage systems with asynchronous and synchronous buck converters, respectively.
<p>In the pursuit of sustainable development and the mitigation of climate change, shallow geothermal energy has been widely recognized as a type of clean energy with great potential. Accurate estimation of thermal ground properties is needed to optimally apply shallow geothermal energy technologies, which are of growing importance for the heating and cooling sector. A special challenge is posed by the often significant heterogeneity and variability of the geological media at a site.</p><p>As an innovative investigation method, we focus on the actively heated fiber optics-based thermal response test (ATRT) and its application in a borehole in Changzhou, China. A copper mesh heated optical cable (CMHC), which both serves as a heating source and a temperature sensing cable, was applied in the borehole. By inducing the electric current to the cable at a relatively low power of 26 W/m, the in-situ heating process was recorded at high depth resolution. This information serves to infer the thermal conductivity distribution along the borehole. The presented field experience reveals that the temperature rise in the early phase of the test should not be used due to initial heat accumulation caused by the outer jacket of the CMHC. The comparison of these results with those of a conventional thermal response test (TRT) and a distributed thermal response test (DTRT) in the same borehole confirmed that the ATRT result is reliable (with a difference less than 5% and 1%, respectively). Most importantly, this novel method affords much less energy and testing time.</p><p>Additionally, to estimate the uncertainty and limits associated with the method, a 2D axisymmetric numerical model based on&#160;COMSOL Multiphysics&#174; has been developed. The results indicate that an accurate calculated thermal conductivity requires heating duration to be in the range of 90~400 min considering test efficiency and cost. Our study promotes ATRT as an advanced geothermal field investigation method and it also extends the applicability of the thermal response test as a downhole tool for measurement of soil hydraulic properties.</p>
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