Beam Profile Characterization for Thickness Mode Transducers versus Radial Modes

In this work, previous work performed in our team that established the viability of using radial clamping on piezoelectric discs operating on their radial mode resonant frequencies to produce a collimated, yet low-frequency ultrasonic beam is expanded to test commercial viability by comparing against high quality, commercially available thickness mode transducers. A concern that is brought against the competitiveness of using the radially clamped transducer for collimated, low-frequency operation is that a higher quality substitute is available in the form of a thickness mode transducer with a piston mode frequency matching that of the radially clamped radial mode transducer. This work aims to show the advantages of radially clamped radial mode transducers versus thickness mode transducers of the same frequency. In particular, it was found that although the thickness mode transducers generated larger main lobe energies at close distances, they suffered from larger dispersion at longer distances. The radial mode transducers were capable of maintaining a very narrow beam throughout the entire measurement range (one meter), demonstrating superior performance for long range applications. Both transducers, however, performed far better than a free boundary radial mode transducer, which shows that if radial mode operation is to be used, radial clamping is a necessity.