Acoustic Magnifying Lens for Far-Field High Resolution Imaging Based on Transformation Acoustics

Based on transformation acoustics and effective medium theory, a magnifying lens is proposed at sound frequencies, which is employed to realize the far-field high resolution imaging with matched impedance to free space. Different from the acoustic superlens that creates images with sub-wavelength features in narrow frequency band, the proposed acoustic magnifying lens enables high-resolution imaging over broadband that can be captured directly by normal microphone in the far field. Since the acoustic lens is made of inhomogeneous but nearly isotropic sub-wavelength structures, the design will be greatly simplified without considering the influence of anisotropic mass density or bulk modulus exhibited by most meta-atoms. The high-resolution imaging effect is demonstrated both numerically and experimentally, showing promise for a variety of potential applications such as medical imaging, biomedical sensors, as well as focused ultrasound surgery.