Focal power efficiencies achieved with aluminum Fresnel and fraxicon low-profile lenses

• Published in: The Journal of the Acoustical Society of America 2019-03, Vol.145 (3), p.1863-1863
• Main Authors: Lirette, Robert L., Mobley, Joel
• Format: Article
• Language: English
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.5101730

Fresnel and fraxicon phase plate lenses modify incident acoustic radiation by a series of phasing steps. A Fresnel lens is designed to approximate a spherical lens, and a fraxicon is designed to approximate an axicon generating a non-diffracting Bessel beam out to a depth of focus. For this study, two lenses were manufactured out of aluminum, a Fresnel with a focal point of 5 cm and a fraxicon with a DOF of 10 cm. Each lens was bonded to a 1.2-MHz piezoelectric driver with epoxy and the assemblies mounted in PVC housings for use under water. The field from each was measured by a hydrophone scanned in the transverse planes. Using an acoustic force balance, the electromechanical conversion efficiency was measured to be roughly 50% for each. The focal power fraction, defined as the ratio of the power within the -6 dB boundary of the focus to the total emitted power, was determined for both transducers. The results are compared to numerical simulations and previously published results.