Broadband Aperiodic Air Coupled Ultrasonic Lens (Preprint).

摘要

This paper demonstrates the possibility of subwavelength, defined as less than the incident wavelength, broadband focusing in an aperiodic air coupled ultrasonic lens. A near field probe is used to detect well defined resonances from 75 to 125 kHz. The spatial resolution at each of the resonant frequencies is determined and demonstrated to be smaller than the wavelength of the ultrasonic waves. The strongest resonance is observed at 82.9 kHz with a focal spot size of 3.12 mm. The subwavelength spatial resolution of the lens structures at the resonances is attributed to the near field scattering of the acoustic waves.