An Improved 2-D DOA Estimation with L-shaped Arrays Based on PM

In this paper, an improved two-dimensional (2-D) direction of arrival (DOA) estimation method is proposed for narrow signals impinging on an L-shaped arrays. Based on the propagator method (PM), the computational loads of the proposed method can be significantly smaller since the PM does not require any eigenvalue decomposition of the received data. With a propagator matrix, the proposed method constructs a new extended matrix to estimate the elevation angle, which improves the DOA estimation performance in low SNR. By exploiting the covariance matrix of the received data, another propagator matrix is achieved, then pair matching and peak searching are used to achieve the corresponding 2-D azimuth angles, which reduces the occurrence of estimation failure and errors. In the case of DOA estimation for two signals, at RMSE = 0.2, the proposed method results in a gain improvement of about 5dB over the joint singular value decomposition (SVD) method and 9.5 dB over the PM method

Compact meta-differentiator for achieving isotropically high-contrast ultrasonic imaging

Abstract Ultrasonic imaging is crucial in the fields of biomedical engineering for its deep penetration capabilities and non-ionizing nature. However, traditional techniques heavily rely on impedance differences within objects, resulting in poor contrast when imaging acoustically transparent targets. Here, we propose a compact spatial differentiator for underwater isotropic edge-enhanced imaging, which enhances the imaging contrast without the need for contrast agents or external physical fields. This design incorporates an amplitude meta-grating for linear transmission along the radial direction, combined with a phase meta-grating that utilizes focus and spiral phases with a first-order topological charge. Through theoretical analysis, numerical simulations, and experimental validation, we substantiate the effectiveness of our technique in distinguishing amplitude objects with isotropic edge enhancements. Importantly, this method also enables the accurate detection of both phase objects and artificial biological models. This breakthrough creates new opportunities for applications in medical diagnosis and nondestructive testing