Most Cited
2023, 72 (22): 224206.
doi: 10.7498/aps.72.20230579
Abstract +
The lock-in amplifier can perform high-precision measurement in both time and amplitude dimensions, so that it becomes a key component of instrumental system for precision measurement and control. This article overviews the concept, technology, and application of phase-locked amplifiers as a guide. It first explains the development and evolution of phase-locked amplifiers of analog, digital, and virtual phase-locked amplifiers, demonstrating their relationship and differences. Then, it classifies phase-locked amplifiers from a mathematical perspective based on the order and type of phase-locked loops. Subsequently, the testing process and metrological calibration progress of the main performance of phase-locked amplifiers, such as amplitude, frequency, and phase noise, are introduced. The conversion relationship between key indicators such as phase noise, time-domain jitter, Allan variance, and the coupling relationship with amplitude noise are discussed. Finally, the application forms and effects of phase-locked amplifiers in the fields of spectral enhancement, impedance analysis, magnetic measurement, microscopic imaging, and space exploration are listed. Through some new applications, the prospects of their transition from scientific instruments to industrial and even civilian products through intelligent computing, precise IoT, and other means are briefly given.
2023, 72 (1): 018401.
doi: 10.7498/aps.72.20222012
Abstract +
Dielectric capacitors have been widely used in crucial energy storage systems of electronic power systems because of their advantages such as fast charge discharge rates, long cycle lifetimes, low losses, and flexible and convenient processingc. However, the dielectric capacitors have lower energy storage densities than electrochemical energy storage devices, which makes them difficult to meet higher application requirements for electrical engineering at the present stage. Polyvinylidene fluoride (PVDF) based polymers show great potential in achieving improved energy storage properties, which is attributed to their high dielectric constants and high breakdown strengths. This work systematically reviews PVDF-based nanocomposites for energy storage applications. Dielectric constant, breakdown strength and charge discharge efficiency are three main parameters related to energy storage properties, which are proposed to discuss their mechanisms of action and optimization strategies. Finally, the key scientific problems of PVDF-based high energy storage composites are summarized and considered, and the future development trend of dielectric capacitors is also prospected.
2023, 72 (22): 224203.
doi: 10.7498/aps.72.20231035
Abstract +
2023, 72 (23): 237201.
doi: 10.7498/aps.72.20231786
Abstract +
The bulk photovoltaic effect is a second-order nonlinear photoelectric response, which refers to a phenomenon that non-centrosymmetric structural material generates a steady-state photocurrent under uniform light irradiation. The bulk photovoltaic effect has attracted widespread attention due to its open-circuit voltage is not limited by the semiconductor bandgap and power conversion efficiency breaks through the Shockley-Queisser limit. In addition, the bulk photovoltaic effect is closely related to the quantum geometric properties (such as Berry curvature and quantum metric) of solids, thus making it an effective means to study crystal polarization, orbital magnetization, and quantum Hall effects. Two-dimensional (2D) materials are rich in electrical, optical, magnetic, topological properties and their interactions, which can effectively improve the performances of bulk photovoltaic devices (such as expanding response range of bulk photovoltaic effect) and have important research value for exploring basic physical problems. This paper reviews the development process of bulk photovoltaic effect and its physical mechanism. The research progress of bulk photovoltaic effect in 2D materials is discussed in detail, including single component 2D materials, 2D material stacking engineering (such as 2D material homojunctions and heterojunctions), and other factors (such as magnetic field, strain engineering) to generate or regulate the bulk photovoltaic effect response. Finally, the development prospect of two-dimensional bulk photovoltaic effect is prospected.
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