Performance of aluminum nitride-based piezoelectric micromachined ultrasonic transducers under different readout configurations

In this paper, a low noise amplification circuit is designed for aluminum nitride (AlN)-based piezoelectric micromachined ultrasonic transducers (PMUTs) with three diffenent sensing configurations. The acoustic pressure sensitivity and noise resolution of PMUTs corresponding to different readout configurations are analyzed and characterized. With the differential readout configuration, the acoustic pressure sensitivity of the PMUTs is improved by 5.76 dB (re: 1 V/μPa) on average, and the noise resolution is reduced by about 8 dB at 500 Hz (re: 1 μPa/√Hz). Compared to the conventional readout configuration, both theoretical analysis and measurement results show that the output voltage of PMUTs is doubled with the differential readout configuration and thus the acoustic pressure sensitivity is improved. Moreover, the noise resolution of PMUTs is reduced and thus the signal-to-noise (SNR) is improved. This work offers new insight on improving the receiving performance of PMUTs.

Low illumination image enhancement based on multi-scale CycleGAN with deep residual shrinkage

Low-illumination image restoration has been widely used in many fields. Aiming at the problem of low resolution and noise amplification in low light environment, this paper applies style transfer of CycleGAN(Cycle-Consistent Generative Adversarial Networks) to low illumination image enhancement. In the design network structure, different convolution kernels are used to extract the features from three paths, and the deep residual shrinkage network is designed to suppress the noise after convolution. The color deviation of the image can be resolved by the identity loss of CycleGAN. In the discriminator, different convolution kernels are used to extract image features from two paths. Compared with the training and testing results of Deep-Retinex network, GLAD network, KinD and other network methods on LOL-dataset and Brightening dataset, CycleGAN based on multi-scale depth residuals contraction proposed in this experiment on LOL-dataset results image quality evaluation indicators PSNR = 24.62, NIQE = 4.9856, SSIM = 0.8628, PSNR = 27.85, NIQE = 4.7652, SSIM = 0.8753. From the visual effect and objective index, it is proved that CycleGAN based on multi-scale depth residual shrinkage has excellent performance in low illumination enhancement, detail recovery and denoising.

Enhancement of digitized X-ray films using Contrast-Limited Adaptive Histogram Equalization (CLAHE)

Background: Rural clinics still have X-ray facilities that produce physical films, which are sent to the nearest hospital for evaluation. Purchasing digitalization facilities is costly, thus, sending digitized films to the radiologist may be a solution. This can be achieved via digital photo capture. However, there can be different output resolutions that may not be optimized for online diagnosis. This paper investigates if digitized X-ray films can be enhanced using image processing techniques of Contrast-Limited Adaptive Histogram Equalization (CLAHE), Normalized-CLAHE (N-CLAHE) and Min-Max Normalized-CLAHE (MMCLAHE). Methods: We collected and digitized 21 X-ray films with low, medium, and high resolutions and implemented the CLAHE, N-CLAHE and MMCLAHE image enhancement. These methods introduced a limit to clip the histogram of image intensities so as to reduce any noise amplification before file compression with the Fast Fourier Transform (FFT) and Discrete Cosine Transform (DCT). Quantitative metrics of the Peak Signal-to-Noise Ratio (PSNR) and Mean-Squared Error (MSE) were used to compare the accuracies between digitized and processed X-ray films. A qualitative evaluation was performed by a medical practitioner to validate the accuracy of enhanced digitized X-ray. Results: It had been found that both CLAHE and MMCLAHE provided good average PSNR values of 31dB - 32dB and produced low MSE values compared to N-CLAHE. The results of qualitative evaluation attained 89.9% correct diagnosis on nine randomly selected images. Generally, the evaluation indicated that the results fulfill the acceptable criteria for further evaluation and there seemed to be no pathological differences observed. Conclusion: This paper presented a proof of concept on an implementation of the CLAHE technique and its variations on digitized X-ray films. This paper had shown potential improvements with the proposed enhancement methods that may contribute to an increase efficiency in healthcare processes at rural clinics.

Feedforward of Measurable Disturbances to Improve Multi-Input Feedback Control

The availability of multiple inputs (plants) can improve output performance by conveniently allocating the control bandwidth among them. Beyond that, the intervention of only the useful plants at each frequency implies the minimum control action at each input. Secondly, in single input control, the addition of feedforward loops from measurable external inputs has been demonstrated to reduce the amount of feedback and, subsequently, palliate its sideband effects of noise amplification. Thus, one part of the action calculated by feedback is now provided by feedforward. This paper takes advantage of both facts for the problem of robust rejection of measurable disturbances by employing a set of control inputs; a previous work did the same for the case of robust reference tracking. Then, a control architecture is provided that includes feedforward elements from the measurable disturbance to each control input and feedback control elements that link the output error to each control input. A methodology is developed for the robust design of the named control elements that distribute the control bandwidth among the cheapest inputs and simultaneously assures the prescribed output performance to correct the disturbed output for a set of possible plant cases (model uncertainty). The minimum necessary feedback gains are used to fight plant uncertainties at the control bandwidth, while feedforward gains achieve the nominal output response. Quantitative feedback theory (QFT) principles are employed. An example illustrates the method and its benefits versus a control architecture with only feedback control elements, which have much more gain beyond the control bandwidth than when feedforward is employed.

Influence of the liner-type treatment on the trailing-edge noise generated by a flat plate

Several liner-type treatments (three different rectangular grooves covered by three different low porosity wire-mesh screens) on the trailing edge of a flat plate have been investigated in the anechoic wind-tunnel of Université de Sherbrooke. Far-field acoustic directivity measurements have been achieved at Reynolds numbers based on the plate length from [Formula: see text] to [Formula: see text], yielding radiation maps of all possible liner combinations that are then compared to the reference solid flat plate and to the plate with inserts alone. Noise from the flat plate corresponds to dipolar trailing-edge scattering with an extra shallow hump attributed to the unsteady flow recirculation behind the thick plate. When grooves are added, the latter contribution is amplified and additional cavity noise is observed with several tones and humps. The tones are shown to be resonance between high order modified Rossiter modes and cavity depthwise modes. The hump is a combination of drag dipoles and cavity monopoles from the groove row. The addition of screens always reduces the amplification of the dipolar edge scattering but exhibits very different non-linear responses for the cavity noise. The combination screen with the smallest cells and the insert with the shallowest cavities (corresponding to the same type of treatment applied previously on the Controlled-Diffusion airfoil) yields the lowest levels overall, while the screen with intermediate cell size almost always triggers noise amplification and the screen with a coarse mesh has an intermediate behavior. At high frequencies, the previously reported roughness noise is also observed.

Target Design For Lida-Based ICP Pose Estimation For Space Vision Tasks

The goal of this thesis is to develop a methodology for designing 3D target shapes for accurate LIDAR pose estimation. Scanned from a range of views, this shape can be attached to the surface of a spacecraft and deliver accurate pose scanned. It would act as an LIDAR- based analogue to fiducial markers placed on the surface and viewed by CCD camera(s). Continuum Shape Constraint Analysis (CSCA) which assesses shapes for pose estimation and measures the performance of the Iterative Closest Point (ICP) Algorithm is used as a shape design tool. CSCA directly assesses the sensitivity of pose error to variation in viewing direction. Three of the CSCA measures, Noise Amplification Index, Minimal Eigen-value and Expectivity Index, were compared, and Expectivity Index was shown to be the best index to use as shape design tool. Using CSCA and numerical simulations, a Cuboctahedron was shown to be an optimal shape which delivers an accurate pose when viewed from all angles and the nitial pose guess is close to the true poses. Separate from Constraint Analysis, the problem of shape ambiguity was addressed using numerical tools. The Cuboctahedron was modified in order to resolve shape ambiguity - the tendency of the ICP algorithm to converge with low registration error on a pose configuration geometrically identical, but actually different from a “true pose”. The numerical characteristics of geometrical ambiguity were studied, and a heuristic design methodology to reduce shape ambiguity was developed and is presented in this thesis. A Reduced Ambiguity Cuboctahedron is the resultant shape that delivers an accurate pose from all views and does not suffer from shape ambiguity. The shapes were subjected to simulation and experimental validation. They were manufactured using 3D Rapid Prototyper, and a NEPTEC Design Group TriDAR Scanner was used to obtain experimental data for three shapes: the Tetrahedron, Cuboctahedron, and reduced Ambiguity Cuboctahedron. The Tetrahedron, which has poorly constrained views, was included in the testing process as a comparison shape. The simulation and experimental results were congruent, and validated the design methodology and the designed shapes.

Target Design For Lida-Based ICP Pose Estimation For Space Vision Tasks

The goal of this thesis is to develop a methodology for designing 3D target shapes for accurate LIDAR pose estimation. Scanned from a range of views, this shape can be attached to the surface of a spacecraft and deliver accurate pose scanned. It would act as an LIDAR- based analogue to fiducial markers placed on the surface and viewed by CCD camera(s). Continuum Shape Constraint Analysis (CSCA) which assesses shapes for pose estimation and measures the performance of the Iterative Closest Point (ICP) Algorithm is used as a shape design tool. CSCA directly assesses the sensitivity of pose error to variation in viewing direction. Three of the CSCA measures, Noise Amplification Index, Minimal Eigen-value and Expectivity Index, were compared, and Expectivity Index was shown to be the best index to use as shape design tool. Using CSCA and numerical simulations, a Cuboctahedron was shown to be an optimal shape which delivers an accurate pose when viewed from all angles and the nitial pose guess is close to the true poses. Separate from Constraint Analysis, the problem of shape ambiguity was addressed using numerical tools. The Cuboctahedron was modified in order to resolve shape ambiguity - the tendency of the ICP algorithm to converge with low registration error on a pose configuration geometrically identical, but actually different from a “true pose”. The numerical characteristics of geometrical ambiguity were studied, and a heuristic design methodology to reduce shape ambiguity was developed and is presented in this thesis. A Reduced Ambiguity Cuboctahedron is the resultant shape that delivers an accurate pose from all views and does not suffer from shape ambiguity. The shapes were subjected to simulation and experimental validation. They were manufactured using 3D Rapid Prototyper, and a NEPTEC Design Group TriDAR Scanner was used to obtain experimental data for three shapes: the Tetrahedron, Cuboctahedron, and reduced Ambiguity Cuboctahedron. The Tetrahedron, which has poorly constrained views, was included in the testing process as a comparison shape. The simulation and experimental results were congruent, and validated the design methodology and the designed shapes.

Investigation of β-Ga2O3-based HEMT for Low Noise Amplification and RF Application

Here we demonstrate a two-dimensional β-gallium oxide-based high electron mobility transistor (HEMT) comprising of a finite gap—access region gap (L_ARG ) in Ohmic-contact access regions with record transconductance linearity. Apart from limiting two-dimensional electron gas (2DEG) density n_s dependency on gate voltage, higher saturation current is estimated for the proposed design. Since the access regions length directly affects the Capacitance of the device and resultant switching applications. In this work, the effect of the gate-source and gate-drain length on device linearity is performed using Atlas-2D simulations. C-V characteristics of the proposed device are explained based on the physical explanation and validated using appropriate models. The higher values of transconductance g_m and current gain cut-off frequency f_T on a large span of operating voltages ensure improved transistor performance for low-noise amplification and RF application and are reported for the first time.<br>