A group of students/postdocs in our acoustics lab have succeeded in achieving a very high ratio of acoustic impedance modulation, enabling meaningful alteration of sound frequency from audible to inaudible ranges, paving a new way of wave manipulation and noise control. The paper was recently published in Communications Physics (2021) 4:220 (article short link: https://rdcu.be/cyEMc ) Full DOI: 10.1038/s42005-021-00721-1
Towards altering sound frequency at will by a linear meta-layer with time-varying and quantized properties
By Yumin Zhang, Keming Wu, Chunqi Wang & Lixi Huang
Wave frequency is a critical parameter for applications ranging from human hearing, acoustic
non-reciprocity, medical imaging to quantum of energy in matter. Frequency alteration holds
the promise of breaking limits imposed by the physics laws such as Rayleigh’s criterion and
Planck–Einstein relation. We introduce a linear mechanism to convert the wave frequency to
any value at will by creating a digitally pre-defined, time-varying material property. The device
is based on an electromagnetic diaphragm with a MOSFET-controlled shunt circuit. The
measured ratio of acoustic impedance modulation is up to 45, much higher than nonlinearity-
based techniques. A significant portion of the incoming source frequency is scattered to
sidebands. We demonstrate the conversion of audible sounds to infrasound and ultrasound,
respectively, and a monochromatic tone to white noise by a randomized MOSFET time
sequence, raising the prospect of applications such as super-resolution imaging, deep sub-
wavelength energy flow control, and encrypted underwater communication.
