Achromatic transmitted acoustic lens arrayed by cascaded Helmholtz resonators

By utilizing an array of cascaded Helmholtz resonators (HRs) with high transmittance and linear phase response, a broadband achromatic acoustic lens (AAL) is realized and verified in numerical simulations as well as experimental measurements. The focal length is independent of the incident frequencies from 2000 to 4500 Hz owing to the phase compensation provided by HR arrays. The FWHM of the focal point could remain approximately half of the wavelength within the operating band, showing an excellent performance of the lens. This work enriches the design of AAL, which may have potential applications in biomedical imaging and acoustic detection.