Quantifying the Injected Disturbance for Susceptibility Testing in Ultrasonic Imaging: Objective Physical Parameters and Correlation With the Subjective Image Degradation

The statement of the tolerable level of dis-turbance produced by interfering signals in susceptibil-ity tests requires the subjective evaluation of the dis-turbance threshold above which the useful information is deemed to have become irreparably corrupted. This evaluation is in all cases on the responsibility of the end user. Objective physical parameters correlated to the amount of corruption are highly desirable in test-ing, design, prototyping, activities. An analysis is here offered based on statistical evaluations of the image signal plus the superimposed disturbance. The specific application here considered is in the field ultrasonic scanning devices but the principles and the method are applicable to all situations where the deterioration of an image is to be quantitatively described. The basic quantity here adopted is the mean-square deviation between the natural and the disturbed images. The evo-lution of this and other objective parameters is studied theoretically and experimentally and the results are compared to subjective evaluation, showing a reliable correlation which suggests a potential for industrial applications. To corroborate the method, the distur-bance current levels (injected according to standard testing) are both measured and calculated using an elementary transmission line model which shows a very good predictability, hence reliability, of the ex-perimental method.