Abstract
The purpose of this study was to employ new state-of-the-art micromachining techniques to fabricate acoustical lenses of identical geometric configuration for high frequency ultrasound applications. High frequency (20 MHz) piezoelectric crystals were placed in a holding jig and covered with one of two lens materials, PMMA or Epoxy. After curing, the holding jig was placed in a custom-made ultra-high precision micromilling machine. Each material was machined to yield lenses with focal lengths of 3 mm, 4 mm or 5 mm. A total of 18 lenses were machined and evaluated for compliance with the design specifications using a Roughness/Step Tester. In addition, performance characteristics of each lens were evaluated using a Schlieren Acoustic Visualization System. Overall, the radii of curvatures were within ± 14% and ± 8% of the design for PMMA and Epoxy, respectively. The focal lengths were found to be within ± 25% and ± 19% of the design, respectively. Finally, the lenses caused the acoustic beam to converge, which resulted in a reduction in the lateral dimension of the beam and an increase in the signal intensity within the near field.
