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Highly sensitive atomic magnetometers (AMs) have been wildly used to form magnetocardiography (MCG) or magnetoencephalography (MEG) devices recently. However, signal detection noise, including light noise due to pump light fluctuations and electrical noise introduced by the detection circuit, will inevitably affect the sensitivity of the AM. Therefore, this article proposes a novel method to suppress signal detection noise and improve the sensitivity of AM. We first propose a low-noise preamplifier circuit to suppress the electrical noise of the signal detection part. Then, based on the equivalent magnetic noise amplitude, a method to optimize the pump light intensity is proposed. The experimental setup has been established. Both the analysis and experimental results can be evaluated that the magnetometer sensitivity can always be maintained at a relatively high-sensitivity level (around 24 fT/Hz $^{1/2}$) over a wide range of light intensities. We hope that the method proposed in this article can contribute to the improvement of sensor sensitivity in array AM systems. [ABSTRACT FROM AUTHOR]

We propose a design method for liquid crystal lens with positive-negative tunable focal length and rectangular aperture. The designed electrodes produce a parabolic profile of voltage difference over the lens aperture. Parabolic phase profile is then obtained by controlling the voltage difference within the linear response range of liquid crystal materials, and high-quality performance liquid crystal lens can be realized. The principle of the design is described and the lens is demonstrated experimentally. [ABSTRACT FROM AUTHOR]

Recently, black-box domain adaptation attracts a lot of attention. It is a new concept to realize domain adaptation of instance image classification with only a cloud API service, reflecting the focus on development of cloud services and concerns about data security. However, the existing black-box domain adaptation methods always only use high-confidence image samples which limits their classification performance. We propose a self-alignment approach to realize black-box domain adaptation. First, an initial model is constructed for target domain. Then, we put target data into source model API to obtain the pseudo-labels and divide the target data into high-confidence and low-confidence parts according to their pseudo-label confidences. By matching the data distributions between these two parts and self-supervised learning on high-confidence part, the classification performance of initial model on both parts samples can be boosted respectively. Information maximization is also applied to further improve classification performance. Experiment results confirm that our method achieves the state-of-the-art performance on image classification. [ABSTRACT FROM AUTHOR]

Atomic magnetometers are widely acknowledged as one of the most sensitive devices for magnetic field measurement. Our study presents a novel method that enables bandwidth expansion of single-beam magnetometers in the spin-exchange relaxation-free regime. This method bases on increasing the modulation amplitude of magnetic field combining with negative feedback with proportional gain. Through our method, the magnetometer’s total relaxation rate is moderately increased by elevating modulation amplitude and frequency, and correspondingly, the detection bandwidth experiences dramatic improvement from 230 Hz to 1380 Hz. The application of negative feedback with proportional gain further increases this bandwidth to higher than 4 kHz, which is over 17 times of its original value. The sensitivity of the magnetometer under this condition is measured as 25 fT/ $\text {Hz}^{\text {1/2}}$ for open-loop scheme and 35 fT/ $\text {Hz}^{\text {1/2}}$ for closed-loop scheme. Comparatively, the sensitivity measured on conventional conditions in our experiment is 12 fT/ $\text {Hz}^{\text {1/2}}$. This approach offers a profitable trade-off that extraordinary expansion of detection bandwidth can be acquired with the price of a little sensitivity loss. Our method is advantageous for miniaturization of atomic magnetometers as no extra hardware is added, which is of special interest for applications including biomagnetic measurement where large detection bandwidth is sometimes in need. [ABSTRACT FROM AUTHOR]

Traditional practice of suppressing low-frequency noise in atomic magnetometers is mainly through the application of magnetic field modulation, while magnetic fields of this kind introduce extra transverse relaxation, which results in a decrease of sensitivity. In this study, a novel method of measuring relaxation rate induced by spin-destruction, wall collisions and modulation magnetic fields is proposed. The optical pumping model is studied both in optical-thin and optical-thick vapor cell through the analysis of total relaxation, thus the optical pumping rate can be separated from total relaxation by analyzing the optical depth. Furthermore, based on the analysis of optical pumping rate and relaxation rate, the polarization of the electron ensemble was evaluated. A compact magnetometer with single-beam configuration is developed for the proof of concept, and the experimental results show good agreements with theoretical calculation. Our method provides a simple and feasible approach to in-situ measurement of transverse relaxation rate and optical pumping rate with physical structure of the device untouched, which is especially advantageous for designing and optimizing compact atomic magnetometers. [ABSTRACT FROM AUTHOR]

In recent years, significant developments have occurred in the field of optically pumped magnetometers (OPMs), which are widely used in biomagnetic measurements. In this study, we propose a temperature optimization model for a single-beam miniaturized atomic magnetometer. Based on this model, we find that there is an optimal operating temperature for each individual vapor cell, under which the OPM achieves optimal performance. We construct a single-beam zero-field modulation OPM to prove this model. The sensitivity of the magnetometer reaches 18 fT/Hz1/2 (close to the theoretical sensitivity) when we adjust the temperature of the vapor cell through our model, and a detection bandwidth of more than 160 Hz is achieved. It is also discovered that the system bandwidth is reduced when the temperature is increased, whereas the sensitivity of the system does not show notable variation during this process. Our model enables a quick definition of the best working temperature for each individual magnetometer, ensuring the best performance at the lowest operating temperature. This model is especially advantageous for miniaturized OPMs and can also be further applied to arrayed integration for biomagnetic measurement in the future work. [ABSTRACT FROM AUTHOR]

With the successful application of deformable convolution in aligning different video frames, it has also been used in video compression artifact reduction. The existing methods based on deformable convolution only apply 2D convolutional layers to generate the features for predicting alignment offsets, which is inaccurate due to limited receptive field. In this letter, we propose a new end-to-end network called Coarse-to-Fine Spatio-Temporal Information Fusion (CF-STIF) for compressed video quality enhancement by predicting better offsets with a larger receptive field. Specifically, several 3D convolutional layers are first to roughly fuse the spatio-temporal information in the video sequence, and then a Multi-level Residual Fusion Module (MLRF) is developed to generate global and local fused fine features from different levels for predicting deformable offsets. Thanks to the inherent advantages of 3D convolution and multi-scale strategy, the receptive field is greatly increased in both spatial and temporal dimensions, so that information from neighboring frames can be efficiently aggregated. In the end, the enhanced frame is derived by the proposed reconstruction module (REModule). Both qualitative and quantitative experimental results show that the proposed CF-STIF performs better than the state-of-the-art approaches. [ABSTRACT FROM AUTHOR]

Planar optical device with continuous phase shifting (CPS) has raised widespread interest recently. Formed by subwavelength micro/nano structures, planar optics are able to control wavefront in multi aspects including phase and polarization. Most phase shifters for CPS devices are individual structures such as cylinders or cuboids. In this study, we specifically discuss grating based continuous phase shifting lenses comparing with aforementioned counterparts, in terms of differences of design mechanism and polarization responses. In addition we found that grating based metalens has outstanding potential in generating emerging artificial focus pattern. A grating based CPS lens with ‘U’ shaped focus was fabricated and characterized for prove of concept. Planar optics with artificial focus pattern has great potential for future applications including micro beam shaping and maskless nano lithography. [ABSTRACT FROM AUTHOR]

This article presents investigation of 3-D electrical capacitance tomography (ECT) sensors with different excitation strategies, including dual-electrode excitation in the same plane, in adjacent plane, in planes separated by one plane or two planes, and in the adjacent position or opposite position in the same or different planes. The results show that a 3-D ECT sensor with dual-electrode excitation in the opposite position provides higher mean capacitance and lower standard deviation than in the adjacent position. Dual-electrode excitation in different planes can increase the capacitance signal and decrease the dynamic range of capacitance measurements, and thus, decrease random errors and improve the quality of 3-D reconstructed images. A 3-D ECT sensor with dual-electrode excitation in planes separated by one plane and opposite position can provide small measurement uncertainty and high image quality. [ABSTRACT FROM AUTHOR]

A conventional electrical capacitance tomography (ECT) sensor consists of multiple rectangular electrodes in a single plane. To generate 3-D images, some researchers use an ECT sensor with multiplane rectangular electrodes and in-line arrangement of different electrode planes and measure the capacitance between the electrode pairs not only within the same plane but also between different planes. Because those electrode pairs in different planes are far away from each other, the measured capacitance signals between them are weak and, hence, are easily affected by noise, resulting in the obvious disturbance on the measured signals and, hence, low image quality. To address those problems, the 3-D ECT sensors with different arrangements and different shapes of electrodes are studied to investigate the effect of different arrangements and different shapes of electrodes on the measured capacitance signals and the image quality. Four 3-D ECT sensors are made with different arrangements or shapes of electrodes: rectangular electrodes are in line arrangement, whereas diamond, circular, and hexagon electrodes are staggered arrangement. The performance of the four 3-D ECT sensors is compared. The results show that 3-D ECT sensors with staggered electrodes can decrease the disturbance on the measured signals and improve the image quality of static models compared with that with conventional rectangular electrodes. Among the three 3-D ECT sensors with staggered electrodes, the 3-D ECT sensor with hexagonal electrodes has superior performance to the other two 3-D ECT sensors with diamond and circular electrodes. It was used to measure moving objects and a fluidized bed. [ABSTRACT FROM AUTHOR]

In this brief, a 32-channel analog front end circuit featured with high gain, high bandwidth, and low noise characteristics is designed. The proposed three-stage analog front end (TS-AFE) includes a variable gain transimpedance amplifier, a differential voltage amplifier, and an analog equalizer. The first stage adopts the shunt-feedback topology to optimize the overall noise, the second stage helps to enlarge the input dynamic range further, and the last stage boosts the channel bandwidth. Furthermore, a 6-bit current digital-to-analog converter (DAC) is integrated in the equalizer to produce a built-in threshold voltage. The 32-channel TS-AFE chip is fabricated with 0.18- ${\mu }\text{m}$ CMOS technology. The measurement results show that with the highest gain configuration, the circuit realizes 101.6 dB transimpedance gain, 190 MHz bandwidth, and 2.6 pA/sqrt(Hz) input noise current spectral density, respectively. The minimum detectable current achieves 0.4 ${\mu }\text{A}$ with SNR = 10. The maximum output voltage swing is greater than 1000 mV, and the linear dynamic range reaches 64 dB. The power consumption per channel is as low as 37 mW from a single 3.3 V supply. [ABSTRACT FROM AUTHOR]

Image reconstruction plays a key role in the application of electrical capacitance tomography (ECT). Although many different algorithms have been developed in the past, it is often difficult to obtain satisfactory images in all imaging regions by the use of a single algorithm due to the soft-field nature of ECT. This motivated us to develop a novel ECT image reconstruction strategy, in which a high-quality image can be obtained by combining the images reconstructed by two different algorithms via a graph cut method. By doing so, it is possible to retain the advantage of each algorithm for specified imaging regions and improve the quality of the whole image. This strategy was verified both numerically and experimentally for two widely used ECT reconstruction algorithms, i.e., linear backprojection and Tikhonov regularization. The results for stationary objects as well as gas–solid fluidized beds demonstrated that this graph-cut-based combination strategy presents a promising approach for ECT image reconstruction. [ABSTRACT FROM AUTHOR]

Metalens as one of the most popular applications of emerging optical metasurfaces has raised widespread interest recently. With nano structures fully controlling phase, polarization and transmission, metalens has achieved comparable performance of commercial objective lenses. While recent studies seeking for the accomplishment of traditional focusing behaviors through metalens are successful, in this work, we have discovered that instead of focusing light to a point, metasurface further enables shaping the focus into flexibly designed patterns, with more promises and potentials. New mechanism and generalizations of conventional point-focused metalens guiding principles have been proposed with metalens concentrating light to artificial focus pattern. As proving examples, the metalens with ‘M’ shaped focus are fabricated and characterized. It is fabricated with a single layer of silicon-based material through CMOS compatible nano fabrication process. The mechanism to generate artificial focus pattern can be applied to a plethora of future on-chip optical devices with applications ranging from beam engineering to next generation nano lithography. [ABSTRACT FROM AUTHOR]

This brief presents a low-complexity hybrid readout architecture that can extract both timing and amplitude information of the return pulse concurrently for a light detection and ranging radar (Lidar) receiver. To reconstruct the short return pulse, the core circuit of one sampling and storage array with an embedded time-to-digital converter (SSA-TDC) is proposed. Instead of relying on the conventional power-hungry high-speed ADC, it selectively samples the interested return pulse with high speed and stores the voltages for later quantization in the long idle interval. In the preceding stage of the SSA-TDC, the analog front-end circuit cascaded of a narrow-bandwidth transimpedance amplifier, a voltage amplifier, and an equalizer circuit is included. The prototype chip of the eight readout channels is designed and fabricated with the 0.18- $\mu \text{m}$ CMOS process. The active circuit occupies an area of $1200\,\,\mu \text{m}\,\,\times 2100\,\,\mu \text{m}$ , and the power consumption of one single channel is 45 mW with 3.3-V supply. The proposed SSA-TDC has achieved a dynamic error of 180 ps in the experimental study. [ABSTRACT FROM AUTHOR]

Sensitivity improvement and measurable pressure limit extension of Pirani vacuum gauge are urgent needed for meeting the rapid growing requirements in ultra-low and wide-range pressure applications. However, the adjustable range of measureable pressure of the Pirani vacuum gauge is limited to only several orders of magnitude of vacuum range. In this work, a fusion method was proposed to improve the sensitivity and extend the measurable pressure limit of the wafer-level packaged Pirani gauge for meeting the wider applications. An analytical temperature model was presented for estimating the electrothermal behavior of the suspended micro-heater with multi heat dissipation paths. The results calculated by the model are validated by the test results of Pirani gauges with both three and four heat sinks. The results indicate that the model for Pirani gauge with one heat sink structure will no longer make sense for devices with multi heat sinks. The electrical fusion of the Pirani gauges with these structure parameters extends dynamic range from 1 ~ 104 Pa to that of $6 \times 10^{-2} \sim 10^{4}$ Pa, which generates one more sensitivity peak compared to one single device. The sensitivity peaks are $5.7 \times 10^{3}$ K/W/decade and $3.4 \times 10^{3}$ K/W/decade around the upper and lower limits, respectively. [2019-0201] [ABSTRACT FROM AUTHOR]