We show that a sonic crystal made of periodic distributions of rigid cylinders in air acts as a new material which allows the construction of refractive acoustic devices for airborne sound. It is demonstrated that, in the long-wave regime, the crystal has low impedance and the sound is transmitted at subsonic velocities. Here, the fabrication and characterization of a convergent lens are presented. Also, an example of a Fabry-Perot interferometer based on this crystal is analyzed. It is concluded that refractive devices based on sonic crystals behave in a manner similar to that of optical systems.
We report extraordinary effects in the transmission of sound through periodically perforated plates, supported by both measurements and theory. In agreement with recent observations in slit arrays [M. H. Lu et al. Phys. Rev. Lett. 99, 174301 (2007)], nearly full transmission is observed at certain resonant frequencies, pointing out at similarities of the acoustic phenomena and their optical counterpart. However, acoustic screening well beyond that predicted by the mass law is achieved over a wide range of wavelengths in the vicinity of the period of the array, resulting in fundamentally unique behavior of the sound as compared to light. The randomness of the hole distribution and the impedance contrast between the fluid and the solid plate are found to play a crucial role.PACS numbers: 43.35.+d, 42.79.Dj, 43.20.Fn Wave phenomena manifest themselves through different physical realizations [1], ranging from the mechanical nature of sound to the electromagnetic origin of light. In particular, the enhanced optical transmission observed in metallic membranes pierced by subwavelength hole arrays [2] has prompted interest in areas as diverse as quantum optics [3] and negative refraction [4]. In the case of acoustic waves, full transmission through subwavelength hole arrays was firstly predicted in [5] and confirmed experimentally for 1D case in [6]. Similar to light transmission through holes, which is boosted when they are arranged periodically [2], plates can be made nearly transparent to sound at certain frequencies if they are pierced by a periodic array of apertures. Like in its optical counterpart, this extraordinary acoustic phenomenon occurs for openings much narrower than the wavelength. But in contrast to light, (a) small holes drilled in hard materials can support at least one guided mode, regardless how narrow they are (provided the hole radius remains larger than the viscous skin depth of the fluid), and (b) sound penetrates into the solid depending on the impedance contrast between fluid and plate, making sound unique and giving rise to colorful behavior of perforated plates. We have measured sound transmission in perforated plates immersed in water at ultrasonic frequencies using a transducer to generate a pulse that is normally incident on a plate, transmitted through the sample plate, and detected by another transducer on the far side of the sample. We use a couple of transmitter/receiver ultrasonic Imasonic immersion transducers with 32 mm in active diameter, -6 dB bandwidth between 169-330 kHz (corresponding to wavelengths between 4.5 mm and 8.8 mm in water), and with a far-field distance of 42 mm. A pulser/receiver generator (Panametrics model 5077PR) produces a pulse which is applied to the emitter transducer to launch the signal through the inspected plate. The signal is detected by the receiving transducer, acquired by the pulser/receiver, post amplified, and finally digitized by a digital PC oscilloscope (Picoscope model 3324). Each measure consist in the average over 256 pulses to increase t...
It is well known that certain periodic structures built by repetition of elements produce sound attenuation effects as a consequence of the destructive interference of the scattered waves by these elements. The sound attenuation results that we got from transmission experiments with these kind of structures, so-called sonic crystals (SCs), led us to think that SCs could be used as an acoustic barrier. Until now, most of the transmission experiments with these periodic arrays of scatterers have been performed under controlled conditions, so how they would behave outdoors is still not well known. In this letter we present outdoor-experimental results for two-dimensional SCs and from these it can be concluded that periodic arrays of scatterers are a suitable device to reduce noise in free-field conditions.
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