A flexible acoustic pressure sensor was developed based on the change in electrical resistance of three-dimensional (3D) graphene change under the acoustic waves action. The sensor was constructed by 3D graphene foam (GF) wrapped in flexible polydimethylsiloxane (PDMS). Tuning forks and human physiological tests indicated that the acoustic pressure sensor can sensitively detect the deformation and the acoustic pressure in real time. The results are of significance to the development of graphene-based applications in the field of health monitoring, in vitro diagnostics, advanced therapies, and transient pressure detection.

The parameters of In_0.3Ga_0.7As PV cell applied in laser wireless power transmission (LWPT) system dependence on temperature was investigated at a temperature range of 5-90°C under 100mW/cm² laser intensity with 1070nm wavelength. The pollination algorithm method was used to extract parameters, viz., photocurrent, series and shunt resistance, reverse saturation current, and ideality factor from the I-V curves at each temperature point. The results show that the short circuit current decrease exponentially with temperature increasing, which is obviously different from the condition with solar irradiation. As temperature increases, the conversion efficiency and the open circuit voltage decreases linearly at the rate of 0.095%/°C and 1.89mV/°C, respectively. In addition, the dependence of series and shunt resistance, ideality factor, and fill factor on temperature was also analyzed. This research gives us a new understanding of PV cells under laser irradiation condition, also provides a direction for manufacturing the cells used in LWPT system.

In IoT applications, energy supply, especially wireless power transfer (WPT), has attracted the most attention in the relevant literature. In this paper, we present a new approach to laser irradiance solar cell panels and predicting energy transfer efficiency. From the previous experimental datasets, it has been discovered that in the laser charging (LC) process, temperature has a great impact on the efficiency, which is highly correlated with the laser intensity. Then, based on artificial neural network (ANN), we set the above temperature and laser intensity as inputs, and the efficiency as output through back propagation (BP) algorithm, and use neural network and BP to train and modify the network parameters to approach the real efficiency value. We also propose the genetic algorithm (GA) to optimize the learning rate of the BP, which achieved slightly superior results. The results of the experiment indicate that the prediction method reaches a high accuracy of about 99.4%. The research results in this paper provide an improved solution for the LC application, particularly the energy supply of IoT devices or small electronic devices through WPT.

The traditional optical detection method has a limitation in detecting closed cracks in optical elements. In this Letter, a novel, to the best of our knowledge, method has been developed for the detection of closed cracks in transparent samples. Firstly, behaviors of closed cracks under ultrasonic waves loading are demonstrated through the finite-element method (FEM). Simulation results show that the crack can be opened by the laser ultrasonic shear wave (S-wave). Then, a Mach–Zehnder interferometer system is experimentally established to detect closed cracks under ultrasonic waves loading in the sample. It is demonstrated that closed cracks which cannot be detected by interferometry become visible in interferogram images under ultrasonic waves loading. The width of the opened crack can also be quantitatively estimated. Thus the method would be a promising approach to detect initially closed cracks in optical elements.

Three-dimensional and time-dependent thermal lens distribution was measured in K9 glass by a Mach-Zehnder interferometer in this paper. The thermal lens was introduced by focusing a millisecond pulse laser into the glass, and the phase information was extracted by Fourier analysis. The specific internal three-dimensional refractive index variation (RIV) was then deduced from phase maps by an inverse Abel algorithm. It is demonstrated that the stress-induced birefringence would lead to negative RIV, which is contrary to results of temperature increment. The method proposed herein would provide a novel idea for measurement of thermal lenses. (C) 2019 Optical Society of America