The current standard used for the characterization of ultrasonic transducers is the hydrophonic technique able to measure the acoustic pressure profile. This technique allows a quantitative analysis, though marred by several problems. The scan of the region of interest appears to be a very costly operation in terms of time, especially when we want to measure a long acoustic beam. Furthermore, a hydrophone placed near the radiating surface is certainly a nuisance to the free propagation of the field. Off-axis measurements can be inaccurate because of the angular response of the hydrophone. These problems together with the costs have encouraged the search for a complementary, quick, and inexpensive test system. The well known Schlieren technique allows a real time visualization of the whole pressure range of the transducers, but to display the entire beam emitted by the transducers it is necessary to use very large-diameter lenses, with focal lengths of several meters. Such systems are very cumbersome, and make their usage very difficult. The system developed in this paper allows the image of an acoustic beam up to 200 mm in length, but the system is compact, being only about 1 meter long and 0.30 meter wide. A similar system based on a classic Schlieren effect would size several meters, with lenses of 200 mm in diameter. Finally, the system can reconstruct the section of the beam at any height, using an acoustic tomography technique, and can also implement a quantitative analysis. Since it uses only commercial components, the developed ultrasonic beam analyzer fabricated is a very low-cost imaging system. This work is aimed at creating a compact, low cost system based on this technique to test a wide range of ultrasonic transducers up to 40 MHz, and above.
Caliano, G., Savoia, A.S., Iula, A. (2012). An Automatic Compact Schlieren Imaging System for Ultrasound Transducers Testing. IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL, 59(9), 2102-2110 [10.1109/TUFFC.2012.2431].