Analysis of Two Methods for Calibrating a Wedge-Mounted Ultrasonic Antenna Array

The image quality of reflectors reconstructed using digital focusing antenna technology or a phased array antenna depends on the accuracy of determining such wedge parameters as X-value, path, longitudinal wave speed, and angle of probe. These parameters do not always correspond to their rated values both due to the imprecision of manufacturing wedges and placing antenna array elements in the housing and due to the wear of wedges during operation. The present paper discusses two types of calibration of a wedge-mounted antenna array, viz., variational and simplified. The principle of variational calibration is to minimize the objective function that describes the difference between the echo signals measured by the antenna array from side drilled holes, for example, in  an ISO 19675 PAUT (phased array ultrasonic testing) calibration block, and the calculated echo signals. Simplified calibration is based on analyzing the arrival time of echo signals from the wedge base; this makes it possible to estimate the path and angle of the wedge knowing the velocity of a longitudinal wave in it. The operation of variational calibration is tested on echo signals calculated in CIVA software to demonstrate the multiravine structure of the objective function. An assessment is made of the required accuracy in determining all four wedge parameters. The results of calibrating an antenna array on four wedges are presented and the results of variational and simplified calibrations are verified. The accuracy of determining wedge parameters using variational calibration is more than twice as good as the results obtained with simplified calibration. However, the time required to carry out calculations for variational calibration is more than three orders of magnitude longer than for simplified calibration.