FAQ: : If our converter ceramic has cracks, is it possible see this problem using a TRZ® Analyzer? I know the documentation shows the analyzer is able to test the ceramic alone for the detection of cracks, but can it do it when the ceramic is mounted in a converter. Does the TRZ® Analyzer have enough resolution to see cracks?
Comparison of a cracked and intact ultrasonic horn curve, the crack decreases the frequency and Qm.
If your converter has any cracked part (ceramic, frontal mass, back mass or bolt), the mechanical quality factor (Qm) will be drastically reduced (Qm is the last parameter listed on TRZ® Software Results box and should be higher than 250 for a converter alone). Other changes that may happen in the impedance scan include Zr increase, Za decrease and frequencies decrease, but the Qm is the most sensitive one. Because of the prestress, the curve graphical pattern may not change much, large cracks may induce the occurrence of additional resonances.
Qm is a parameter proportional to the device under test efficiency in vibrating, and inversely proportional to its damping or internal losses. For power applications, the higher the Qm, the better the device. You can think of the Qm as being approximately the number of times the element oscillates at no-load condition after excitation ceases. For a car, Qm would be roughly equal to the distance it is able to move on a flat road after fuel is over.
Everything that interferes with the device efficiency in vibrating will affect the Qm, not only cracks. For example, joints condition, mechanical parallelism, alloy, piezoceramics quality and frequency matching between the acoustic stack elements. Cracks in piezoelectric ceramics or metallic masses sharply reduce Qm, which allows using this parameter to identify these faults.
The knowledge of Qm is highly useful for maintenance and quality control of power ultrasonics because it is an absolute parameter and does not depend on device under test frequency or power.
Learn more about testing converters and acoustic stacks.