Extraordinary Sound Screening in Perforated Plates

Abstract

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...

Influence of lattice symmetry on ultrasound transmission through plates with subwavelength aperture arrays

“…This discrepancy originates in the effect of finite impedance ratio between the plate and the fluid. 18,19 The transmission spectrum for t = 5 mm follows quite closely the prediction of the hard-solid model.Differences between square and triangular lattices can be clearly seen by comparing their respective spectra. The positions of the Wood anomaly ͑vertical arrows in Fig.…”

“…The transmission is dipped right at the Wood anomalies. 19 Comparison between results obtained for both lattices leads to the following conclusions:…”

“…10,11,16,17 Also, sound can be extraordinarily shielded near the onset of diffraction. 18 Furthermore, intrinsic acoustic modes ͑Lamb and Scholte-Stoneley waves͒ are conspicuous in thin plates, quite different from optics. 19 Finally, we have recently shown 18 that perforated plates are highly transparent to sound for both periodic and random distributions of holes.…”

“…In order to perform ultrasonic transmission measurements, we use the well-known ultrasonic immersion technique. 18 The angle of incidence is varied by rotating the plate sample from 0°to 60°in steps of 1°. Moreover, we calculate transmission intensities by rigorously solving the sound wave equation within a hard-solid model, 18 in which infinite impedance mismatch between the fluid and the plate is assumed.…”

A comprehensive discrete-time computer modeling of acoustic Transmission Line loudspeakers

“…Estrada et al [16] reported that periodically perforated aluminium plates immersed in water can achieve lower ultrasonic transmission values than homogeneous plates. The influence of the filling fraction of holes and the lattice geometry in the transmission properties has also been studied [17,18].…”