Abstract
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.
Highlights
Wave frequency is a critical parameter for applications ranging from human hearing, acoustic non-reciprocity, medical imaging to quantum of energy in matter
A linear temporal modulation device called acoustic meta-layer (AML) is introduced, which converts the color, or rather the frequency in acoustics, of a monochromatic sound wave to another color with two orders of magnitude higher efficiency when compared to the existing nonlinearity-based devices[7]
The metal-oxide-semiconductor field-effect transistor (MOSFET) state is described by the function of gðtÞ 1⁄4 HðVgðtÞ À V0Þ, where H is the Heaviside step function
Summary
Wave frequency is a critical parameter for applications ranging from human hearing, acoustic non-reciprocity, medical imaging to quantum of energy in matter. 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 subwavelength energy flow control, and encrypted underwater communication. Conventional materials, including spatial modulation metamaterials, such as photonic and sonic crystals[1,2,3,4], have time-invariant physical properties, which may be called static materials They shape the wave front and change wavenumbers, but the wave frequency is unaffected. A linear temporal modulation device called acoustic meta-layer (AML) is introduced, which converts the color, or rather the frequency in acoustics, of a monochromatic sound wave to another color with two orders of magnitude higher efficiency when compared to the existing nonlinearity-based devices[7]. Clinical trials show that random noise (white or pink) promotes sleep for the neonates[43], patients in intensive care unit[44], and coronary care unit[45]
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