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 38λ 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 70λ. 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 0.26λ in the monostatic setup and 0.62λ in a bistatic experimental setup. This lens demonstrates super-resolution detection capabilities at distances of 42λ 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 (paper)