Planar Lens For Ghz Fourier Ultrasonics

The Fourier transform is a widely used mathematical algorithm that decomposes a time-domain function into its component frequencies. A highly efficient ultraSonic Fast Fourier Transform (SFFT) [1] hardware accelerator will drastically improve the computational speed needed in real-time image recognition and signal processing. The planar GHz frequency compatible ultrasonic lens presented in this paper is necessary to realize a compact (<1cc) SFFT system [2]. The wavefronts generated from an array of piezoelectric transducers are focused by the lens to meet the requirement of wavefront FFT computing. This paper presents a planar GHz ultrasonic lens consisting of SiO2 posts embedded into a silicon substrate, fabricated using DRIE processing of silicon wafers. The spatial density of the posts generates a varying phase shift for waves passing through the lens, as shown by FEM simulations. The FEM simulations and the devices provide a pathway to verify lens operation experimentally.