Air-coupled ultrasonic investigation of stacked cylindrical rods

Measurement of the periodicities of diffraction gratings composed of stacked cylindrical rods is explored using an air-coupled ultrasonic technique. Acoustic Bragg scattering from three periodic structures is investigated by means of a polar scan. Consequently, Bragg angles and corresponding frequencies are obtained from angular spectrograms, using two different data acquisition approaches. According to the principle of Bragg scattering, the periodicities of the three periodic structures, which are equal to the diameter of the cylindrical rods, are determined. In order to evaluate the reliability of the technique and its accuracy, the obtained diameters are compared with those directly measured with a digital caliber. To show the robustness of the technique measurements are done with transducers of different quality.