学术文献库

Wave is crucial to acquiring information from the world and its interaction with matter is determined by the wavelength, or frequency. Search for the ability to shift frequency often points to material nonlinearity, which is significant only when the excitation level is very high. Temporal modulated material is expected to shift sound frequency in a linear manner, but is so far not effectively realized due to inadequate modulation ratio. This study introduces a new class of temporal modulation material with a giant modulation ratio. When the modulation is given in a random time sequence, a monochromatic sound wave is converted to a white noise of a continuous frequency band. The demonstrated device is called a randomized acoustic meta-layer, consisting of a suspended diaphragm shunted by an analog circuit. The circuit alters the acoustic impedance of the layer which operates in two quantized states when the shunt is connected and disconnected by a MOSFET with a pseudo-random time sequence. The device has unprecedented potential applications such as converting annoying tones to white-noise-like hum to improve psychoacoustic quality, allowing encrypted underwater communication, and super-resolution imaging.