Phased-array Source Research Articles

A novel phased-array transmitting source in controlled-source audio-frequency magnetotellurics

Abstract In traditional controlled-source audio-frequency magnetotellurics (CSAMT), the orthogonal magnetic and electric field components in the far-field region are recorded to calculate the apparent resistivity. However, as the distance between the receiver and the transmitter increases, the electromagnetic signal weakens considerably. Moreover, as the location of the transmitter is fixed, the location of the far-field region also is fixed, which limits the exploration range. In this study, a novel phased-array transmitting source was proposed to overcome this limitation. In traditional CSAMT, a grounded single-dipole long-line source is used to transmit the electromagnetic wave. This source has a low gain and no directionality, resulting in a low signal-to-noise ratio (SNR) in the area of interest (AoI). Conversely, by using a phased-array source, beam control and stable directional radiation will be achieved so that the electromagnetic energy should be capable of effectively focusing within the AoI. Without increasing the transmitting power, the SNR should be conveniently enhanced and the size of the AoI can be greatly increased. In this paper, the characteristics of the radiation field of a single-dipole long-line source and its application in traditional CSAMT are analyzed. The design principle and the method of implementation of a novel phased-array source are provided. The feasibility and effectiveness of the proposed source are verified by simulations and experiments, and a prototype is realized.

Compressed sensing in the far-field of the spatial light modulator in high noise conditions

Single-pixel imaging techniques as an alternative to focal-plane detector arrays are being widely investigated. The interest in these single-pixel techniques is partly their compatibility with compressed sensing but also their applicability to spectral regions where focal planes arrays are simply not obtainable. Here, we show how a phased-array modulator source can be used to create Hadamard intensity patterns in the far-field, thereby enabling single-pixel imaging. Further, we successfully illustrate an implementation of compressed sensing for image reconstruction in conditions of high noise. In combination, this robust technique could be applied to any spectral region where spatial light phase modulators or phased-array sources are available.

Mach-number scaling of individual azimuthal modes of subsonic co-flowing jets

The Mach-number scaling of the individual azimuthal modes of jet mixing noise was studied for jets in flight conditions, i.e. with co-flow. The data were obtained via a series of direct numerical simulations (DNS), performed of fully turbulent jets with a target Reynolds number, based on nozzle diameter, of $Re_{jet}=8000$. The DNS included a pipe 25 diameters in length in order to ensure that the flow developed to a fully turbulent state before exiting into a laminar co-flow, and to account for all possible noise generation mechanisms. To allow for a detailed study of the jet mixing noise component of the combined pipe–jet configuration, acoustic liner boundary conditions on the inside of the pipe and a modification to the synthetic turbulent inlet boundary condition of the pipe were applied to minimize internal noise in the pipe. Despite these measures, the use of a phased-array source breakdown technique was essential in order to isolate the sources associated with jet noise mechanisms from additional noise sources that could be attributed to internal noise or unsteady flow past the nozzle lip, in particular for the axisymmetric mode. Decomposing the sound radiation from the pipe–jet configuration into its azimuthal Fourier modes, and accounting for the co-flow effects, it was found that at $90^{\circ }$ the individual azimuthal Fourier modes of far-field pressure for the jet mixing noise component exhibit the same $M^{8}$ scaling with the centreline jet Mach number as that experimentally documented for the overall noise field. Applying the phased-array source breakdown code to the DNS data at smaller angles to the jet axis, an increase of the velocity exponent of the jet noise source was found, approaching 10 at $30^{\circ }$. At this smaller angle the higher azimuthal modes again showed the same behaviour as the axisymmetric mode.

ARRAY-FED BEAM-SCANNING PARTIALLY REFLECTIVE SURFACE (PRS) ANTENNA

A beam-scanning partially reflective surface (PRS) antenna is presented in this paper. By employing a reconfigurable feed network to a two-element phased array source, the PRS antenna can realize beam steering between −10◦ and 10◦ with respect to the broadside direction across an overlapped frequency range from 5.35GHz to 5.76GHz. Good agreement between the simulated and measured results is achieved, which validates its capability to be a good candidate for the modern communication systems.

Phased array compaction cell for measurement of the transversely isotropic elastic properties of compacting sediments

Sediments undergoing compaction typically exhibit transversely isotropic (TI) elastic properties. We present a new experimental apparatus, the phased array compaction cell, for measuring the TI elastic properties of clay-rich sediments during compaction. This apparatus uses matched sets of P- and S-wave ultrasonic transducers located along the sides of the sample and an ultrasonic P-wave phased array source, together with a miniature P-wave receiver on the top and bottom ends of the sample. The phased array measurements are used to form plane P-waves that provide estimates of the phase velocities over a range of angles. From these measurements, the five TI elastic constants can be recovered as the sediment is compacted, without the need for sample unloading, recoring, or reorienting. This paper provides descriptions of the apparatus, the data processing, and an application demonstrating recovery of the evolving TI properties of a compacting marine sediment sample.

Laboratory measurements of stress-induced velocity anisotropy in unconsolidated sands

An experimental device for measuring the transverse isotropic (TI) elastic properties of sediments under uniaxial strain conditions has been developed. The phased array compaction cell utilizes matched sets of P- and S-wave ultrasonic transducers located along the sides of the sample and an ultrasonic P-wave phased array source with pinducer receiver on the ends of the sample. The phased array provides plane P-waves that are used to measure phase velocities over a range of angles. From these measurements, the five elastic constants for TI media can be recovered as the sediment is compacted, without the need for sample unloading or reorienting. Descriptions of the apparatus and data processing and an application to an unconsolidated sand sample are provided in this paper. P-wave anisotropy of 20% has been observed in dry sand under an axial stress of 5 MPa.

Boosting Signal to Noise Ratio of Seismic Signals Using the Phased-Array Vibrator System

When noise in the field is very strong, we can not get data with proper signal to noise ratio (SNR) even if combination vibroseis is used. To solve this problem we proposed to apply a phased-array vibrator, which can form a directional seismic wave. We have made numerical simulation of multi-track seismograms and computed reflected waves’ SNR for combination and phased-array sources on a given horizontal stratified model. The result shows that the average SNR of reflected waves increases by 1.54_9.90dB with respect to the combination source when 4,8,15 and 20-unit phased-array vibrators are used. We conclude that phased-array source is competent to improve seismic signal SNR. Moreover, the phased-array source can boost SNR obviously when more vibrators are applied but there is no similar result for the combination source.