The evaluation of search units used for ultrasonic reference block calibrations

Abstract

The effects of using different (nominally identical) quartz search units in the evaluation of ASTM-type standard reference blocks are determined. Various characteristics of the search units are measured and correlated with the amplitude of the ultrasonic response from reference blocks to determine which characteristics must be specified if reproducible results are to be obtained. It is shown by a series of experiments that the exact shape of the distance-amplitude curve in water (axial profile) is a primary characteristic that must be considered. When operational corrections for differences in axial profiles are made, the variability in ultrasonic responses from reference blocks, measured with different search units, is reduced from about 25 percent to 4 percent.

An assessment of ultrasonic reference block calibration methodology

“…Furthermore, its physical structure or housing can have a significant effect on its performance via the damping effects on the piezoelectric crystal. [11]. An encouraging aspect to that study, however, was the ability to compensate for the respective transducers' beam pattern differences by means of a farfield echo normalization procedure.…”

“…A continuous profile scan of the back-surface echo amplitude from A) the anomalous block material, and B) the normal block material. Substantial research has been undertaken to elucidate the causes [9][10][11][12][13].…”

Transducer Radiation Modeling for Ultrasonic Inspection Purposes

“…In taking t(rT) to be real-valued, it is assumed that the phase remains constant across the transmitting plane. If the transducer operates as a linear device, then we can define a transmitting response function (2) so that the velocity profile can be written as (3) where the terms inside the bracket characterize the transmitting transducer.…”

“…However, one of the important conditions for the accuracy of the deconvolution process is the proper modeling of the individual transducer diffraction characteristic. There is evidence [2,3) based upon on-axis pressure studies and C-scan profiles that considerable discrepancies can occur between individual transducers of the same diameter and nominal frequency. The main purpose of this paper is to study the acoustic characteristics of a set of three unfocused, immersion, piezoelectric, pulse-echo transducers.…”

Recent improvements to the ASTM-type ultrasonic reference block system

“…Posakony [6] has been studying the effects of transducer design and excitation waveform on the output of quartz transducers. At NBS, we completed a study* intended to quantify the extent of the difference in reference block response when measured with different but very similar transducers, and to identify what characteristics of the transducers contributed to these differences [7], A critical parameter, seldom specified explicitly or exactly, was the shape of the far-field on-axis pressure amplitude. Among six nominally identical, *partially supported by this project 2 5-MHz, 0.375-in (9.52-mm) quartz transducers, readings from the same reference blocks, taken in accordance with the procedures and equipment specified in ASTI!…”