Acoustic interferometer

About: Acoustic interferometer is a research topic. Over the lifetime, 1493 publications have been published within this topic receiving 19355 citations.

P0-11 Experimental Study of Complete Band Gaps and Waveguiding Inside Phononic Crystal Slabs

Abstract: The propagation of elastic waves in inhomogeneous media has attracted much attention over the last years. Media with periodically varying elastic coefficients are called phononic crystals. Phononic crystals can be the siege of complete acoustic band gaps. For frequencies within a complete band gap, there can be no vibration and no propagation of acoustic waves, whatever the polarization and the wave vector. In such a situation, a phononic crystal behaves like a perfect mirror and can be further modified to gain control over acoustic waves. This principle can be used to obtain acoustic cavities, acoustic filters, or very efficient waveguides by adding certain defects to the lattice. All these functions can be achieved in a very tight space of the order of the acoustic wavelength. The purpose of this paper is to demonstrate a complete band gap in a phononic crystal slab and to investigate the propagation of acoustic waves within it. The system we have chosen is a finite thickness, solid/solid and two face free phononic crystal slab. This system lends itself to numerical simulation by a finite element method developed previously. Furthermore, by using a combination of ultrasonic electrical transduction and optical detection by a laser interferometer, we can obtain a map of the propagation of waves at any monochromatic frequency. This experimental set-up is used to quantify the attenuation on propagation and the confinement of acoustic energy within a line-defect waveguide. A complete band gap was identified by measuring the transmission spectrum along the two most symmetric directions of the Brillouin zone by laser interferometry. The measured transmission spectra and the theoretical band structure obtained by a finite element method are in agreement and show that the complete band gap ranges from 255 kHz to 340 kHz. The dependence of the attenuation on the propagation distance was studied. Little attenuation is observed below the complete band gap and a clear exponential decay is observed within it. Unexpectedly, a pronounced unexpected decay is observed for frequencies above the complete band gap, unlike observations for bulk acoustic waves. Finally, a defect line waveguide was formed. The transmission through the waveguide was measured and the wave field was imaged. The observations show that the waveguide confine the acoustic energy within the complete band gap.

Experimentally study of a sharp bending wave-guide constructed in a sonic-crystal slab of an array of short aluminum rods in air

Abstract: We have made a sonic-crystal slab (SCS) of a square-array of 16/spl times/12 short Al rods between a pair of parallel Al plates in air, as an alternative of a 2D sonic crystal. The observed full band-gap was between 15.1-18.8 kHz below -20dB, although the lower and higher boundaries were not sharp enough as 2D sonic crystals. An acoustic wave-guide was constructed in the SCS with a sharp bend. We have measured the intensities of the sound waves traveled along the wave-guide and the leaky waves which propagated straight, without turning the bend. Especially at the center of the full band-gap of the SCS, about 17 kHz, the sound waves were well guided and the ratio of the guided waves to the leaky waves was 22 dB. We have reported here the first experimentally measured characteristics of a pair of acoustic coupled waveguides constructed in an SCS. The coupling between the sound waves travelling along the waveguides was almost uniform inside of the full band-gap of the SCS. They functioned as a 3/spl sim/4 dB unidirectional acoustic coupler.