Abstract
This paper addresses the challenging problem of ultrasonic non-destructive evaluation (NDE) imaging with adaptive transducer arrays. In NDE applications, most materials like concrete, stainless steel and carbon-reinforced composites used extensively in industries and civil engineering exhibit heterogeneous internal structure. When inspected using ultrasound, the signals from defects are significantly corrupted by the echoes form randomly distributed scatterers, even defects that are much larger than these random reflectors are difficult to detect with the conventional delay-and-sum operation. We propose to apply adaptive beamforming to the received data samples to reduce the interference and clutter noise. Beamforming is to manipulate the array beam pattern by appropriately weighting the per-element delayed data samples prior to summing them. The adaptive weights are computed from the statistical analysis of the data samples. This delay-weight-and-sum process can be explained as applying a lateral spatial filter to the signals across the probe aperture. Simulations show that the clutter noise is reduced by more than 30 dB and the lateral resolution is enhanced simultaneously when adaptive beamforming is applied. In experiments inspecting a steel block with side-drilled holes, good quantitative agreement with simulation results is demonstrated.
Highlights
Quantitative characterizations of materials and structures by non-invasive means are essential in a wide range of applications like flaw detection, structure health monitoring, materials characterization, and etc. [1]
The applications of transducer array systems to ultrasound non-destructive evaluation (NDE) have increased dramatically in recent years, due to the great advantages of enhanced coverage, sensitivity and flexibility, where multiple inspections can be performed without the need for reconfiguration [2]
If the complete set of time domain data from all combinations of transmitter and receiver elements is acquired with full matrix capture (FMC), the total focusing method (TFM) [3] can be used as an offline imaging technique
Summary
Quantitative characterizations of materials and structures by non-invasive means are essential in a wide range of applications like flaw detection, structure health monitoring, materials characterization, and etc. [1]. In recent works, advanced beamforming has been investigated for medical ultrasound imaging, where the received per-element delayed data samples are weighted with a data-dependent or spatially variant apodization vector prior to summation. This delay-weight-and-sum operation can be considered as applying an adaptive spatial filter to the received signals across the probe aperture to remove the interference and noise. The Capon adaptive beamformer was applied to compute the data-dependent weight vector by several authors, and demonstrated improved imaging contrast and resolution for simulated and phantom data [7,8,9,10].
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