Acoustic meta-stethoscope for cardiac auscultation

Straight cylindrical stethoscopes serve as an important alternative to conventional stethoscopes, whose application in the treatment of infectious diseases might be limited by the use of protective clothing. Yet their miniaturization is challenging due to the long wavelength of low-frequency cardiac sounds. Here, we present and experimentally demonstrate an acoustic meta-stethoscope with subwavelength size, simple fabrication, and easy assembly for high-sensitivity cardiac auscultation, which simply comprises multilayered perforated round plate units and a cylindrical shell. We elucidate our proposed mechanism by analytically deducing the frequency response equation and the effective material properties of the meta-stethoscope, which proves that the equivalent acoustic propagation path is substantially increased by the metamaterial with a high refractive index, enabling downscaling the device to a subwavelength footprint. The auscultation performance of the meta-stethoscope is experimentally characterized by detecting the cardiac sound signal from the human heart through different clothing, showing an expected sensitivity enhancement exceeding 10 dB within the predicted working frequency regardless of the type of clothing. Our portable, detachable, yet effective meta-stethoscope opens a route to the metamaterial-based stethoscope research paradigm, with potential applications in diverse scenarios such as medical diagnosis and acoustic sensing.