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High efficiency acoustic Fresnel lens

We present a water-immersed ultrasound high-efficiency Fresnel lens based on the theory of extraordinary acoustic transmission of plate-wave resonance. We studied, experimentally and numerically, the acoustic pressure gain of the Fresnel lens with and without gratings on the back. We found that the transmission coefficient of the incident acoustic waves through the lens with gratings on the back was much higher than that of the lens without gratings, thus increasing the acoustic pressure gain at the focal point of an impedance-mismatched Fresnel lens by 14.1 dB. We then optimized the grating width in the structure, thereby increasing the acoustic pressure gain by 16.3 dB. This lens has potential applications in acoustic imaging and medical diagnosis.