Presence Of Near Field Scatterers Research Articles

Adaptive beamforming with unknown scattering coefficients of near‐field scatterers

Conventionally, near-field scattering effect was considered in antenna measurement, which requires a great amount of measuring efforts and re-measurement if the operational platform has changed. In this study, the authors consider the near-field scattering problem in the framework of adaptive array beamforming theory, which avoids re-measurement and can be adaptive to the arbitrary scenario. Generally, the near-field scattering can result in severe performance degradation in adaptive beamforming applications. They propose a robust adaptive beamforming approach that can maintain the performance in the presence of near-field scatterers with unknown scattering coefficients. In the authors’ approach, the near-field scatterering signal component is incorporated into the presumed steering vector. Thus, it is treated as useful information in this study instead of nuisance interference in the literature. In particular, the properties of the far-field direct-path signal and near-field signal are explored and the large uncertainty set is divided into two small ones describing the far-field and near-field steering vectors, respectively. Simulation examples are provided to show the performance improvement by making use of the near-field scattering signals.

Adaptive processing using a single snapshot for a nonuniformly spaced array in the presence of mutual coupling and near-field scatterers

This paper presents an adaptive technique to extract the signal of interest (SOI) arriving from a known direction in the presence of strong interferers using a single snapshot of data. The antenna elements in this method can be nonuniformly spaced and there can be mutual coupling between them. In addition, near-field scatterers can also be present. First, the voltages induced in the antenna elements of the array due to interferers, mutual coupling between the elements, and near-field scatterers is preprocessed by applying a transformation matrix to these voltages through a rigorous electromagnetic analysis tool. This electromagnetic preprocessing technique transforms the voltages that are induced in a nonuniformly spaced array containing real antenna elements to a set of voltages that will be produced in a uniform linear virtual array (ULVA) containing omnidirectional isotropic point radiators. In the transformation matrix we would like to include various electromagnetic effects like mutual coupling between the antenna elements, presence of near-field scatterers and the platform effects on which the antenna array is mounted. This transformation matrix when applied to the actual measured voltages yields an equivalent set of voltages that will be induced in the ULVA. A direct data domain least squares adaptive algorithm is then applied to the processed voltages to extract the SOI in the presence of interferers. Limited numerical examples are presented to illustrate the novelty of the proposed method.

Electrically steered acoustic lens

This invention is a composite acoustic lens that can be steered internally through electrical control. It can collect and direct acoustic energy from a plane wave to focus it on a transducer. It can also take the nearly omnidirectional output from a standard acoustic transducer and direct its energy in a plane wave. In the receive role the lens increases the effective signal-to-noise ratio of the array; in the transmit role it reduces the output energy that is responsible for reverberation. The lens is steerable by virtue of its material: it is electrorheological. Its bulk modulus, and the resulting speed of sound, can be changed electrically. Controlling the gradient of the index of refraction allows the steering to be adjusted precisely, continuously, and quickly. It is held by a container of plastic material that matches the acoustic impedance of water and minimizes the presence of near-field scatterers. A system based on the proposed lens can improve the effectiveness of both active and passive sonars, reduce the detectability of active transmissions and reduce the inboard footprint. Medical applications exist for both imaging and lithotriptic devices.