10/4/2023 0 Comments Sound diffraction materials![]() ![]() However, these extra benefits of active control often come with the extra cost of a sensor or extra complication of having to deal with system instability. Recently, active nonlinear metamaterials greatly lower the requirement for excitation 21. Alternatively, active metamaterials with sensors offer more possibilities such as tuning the effective material parameters 19 and shaping the frequency spectra of sound waves 20. However, such desirable nonlinear effects require a high level of excitation not readily available in daily life. Nonlinearity produces higher harmonics of signals, and offers super-resolution in optical 8, 9 and ultrasonic 7, 10, 11 imaging, rectification and reciprocity breaking 12, 13, 14, 15, 16, and directional radiation 16, 17, 18. Pursuit of dynamic materials 5 normally begins with material nonlinearity, such as nonlinear optical crystal 6 and ultrasound contrast agent 7. Time-variant materials, or dynamic materials, however, can enable the control of wave in terms of time-base, which offers more possibilities for wave manipulation. They shape the wave front and change wavenumbers, but the wave frequency is unaffected. 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. Altering frequency can break the limits currently imposed by laws of physics for a given frequency condition, such as imaging resolution limits, energy capacity, and propagation behavior of a wave. Most laws on wave propagation, wave–matter interaction, such as Rayleigh’s criterion, Planck–Einstein’s energy–frequency relation, diffraction law, mass-density law, are frequency-dependent. 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.įrequency, the reciprocal of wavelength, is one of the fundamental parameters governing wave behaviors and its interaction with matters. A significant portion of the incoming source frequency is scattered to sidebands. The measured ratio of acoustic impedance modulation is up to 45, much higher than nonlinearity-based techniques. The device is based on an electromagnetic diaphragm with a MOSFET-controlled shunt circuit. ![]() 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. Frequency alteration holds the promise of breaking limits imposed by the physics laws such as Rayleigh’s criterion and Planck–Einstein relation. Wave frequency is a critical parameter for applications ranging from human hearing, acoustic non-reciprocity, medical imaging to quantum of energy in matter. ![]()
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