Mechanically tunable ultrasonic metamaterial lens with a subwavelength resolution at long working distances for bioimaging

In this study, a novel acoustic doublet meta-material lens has been designed and tested to demonstrate both a far-field focal point and ultra-long collimation characteristics past the Fresnel zone. The switching of the two behaviors can be adjusted by a simple linear mechanical translation of one of the lens units. The doublet lens can focus the sound wave beyond 38 λ away from the experiment’s lens, which is farther than any existing ultrasonic transducer or meta-lenses lenses. In terms of collimating behavior, the doublet lens is a unique metamaterial lens that experimentally demonstrates a long and narrow collimating beam over 70 λ . Besides the design and characterization, the meta-lens have been used to detect real objects, including inorganic and organic matter. A subwavelength spatial resolution has been demonstrated. The detection limit was 0.26 λ in the monostatic setup and 0.62 λ in a bistatic experimental setup. This lens demonstrates super-resolution detection capabilities at distances of 42 λ and can enable ultrasonic diagnostics deep within a material or a biological tissue. The experimental performance of the doublet meta-material lens illustrated its potential to apply acoustic metamaterial elements in a practical imaging application, including the detection of biological tissues