A 5 MHz, 16-element phased array concave ultrasonic probe for non-destructive testing has been designed,
fabricated and tested. To improve the probes performance its curvature, as opposed to present solutions, was
not obtained by adding a corresponding delay wedge, but rather by manufacturing the functional elements (i.e.
active material, matching layer) with a curvature. The piezoelectric material used here was a 1-3 composite
material made of PZT. The finished probe was tested on a steel half circle with the corresponding radius
(100 mm) and on the Olympus PAUT test piece. Good results could be obtained. Three transverse holes with
a diameter of 1 mm and a distance of 5 mm to one another could be detected and resolved.
Aluminum nitride is a promising material for the use as a piezoelectric sensor material for resonance frequencies higher
than 50 MHz and contains the potential for high frequency phased array application in the future. This work represents
the fundamental research on piezoelectric aluminum nitride films with a thickness of up to 10 μm based on a double ring
magnetron sputtering process.
The deposition process of the aluminum nitride thin film layers on silicon substrates was investigated and optimized
regarding their piezoelectric behavior. Therefore a specific test setup and a measuring station were created to
characterize the sensors. Large single element transducers were deposited on silicon substrates with aluminum
electrodes, using different parameters for the magnetron sputter process, like pressure and bias voltage. Afterwards
acoustical measurements were carried out in pulse echo mode up to 500 MHz and the piezoelectric charge constants (d<sub>33</sub>)
were determined. As a result, two parameter sets were found for the sputtering process to obtain an excellent
piezoelectric charge constant of about 7.2 pC/N maximum.