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...

We study the angle and frequency dependence of sound transmission through water-immersed perforated aluminum plates. Three types of resonances are found to govern the acoustic properties of the plates: lattice resonances in periodic arrays, Fabry-Perot modes of the hole cavities, and elastic Lamb modes. The last two of them are still present in random arrays and have no parallel in optical transmission through holes. These modes are identified by comparing experiment with various levels of theoretical analysis, including full solution of the elasto-acoustic wave equations. We observe strong mixture of different transmission mechanisms, giving rise to unique acoustic behavior and opening new perspectives for exotic wave phenomena.

In this paper, we propose the use of local regression techniques to analyse experimental data in the graduate physics laboratory. These techniques allow a better understanding of the system dynamics, based on the estimation of both the system response and its derivatives, by using an adaptive weight function. This method provides a comprehensive analysis of the governing differential equation. Local polynomial fitting presents several advantages over conventional adjustment methods, such as a better sensitivity to small model deviations and the possibility of analysing local aspects. Moreover, phase space representation is employed for analysing the system dynamical behaviour. Additionally, the students are confronted with an alternative point of view, very useful in experimental data exploration and result interpretation. The proposed methodology is demonstrated with the analysis of electric oscillations in an RLC circuit.

Tunable time-reversal cavity for high-pressure ultrasonic pulses generation: A tradeoff between transmission and time compression Appl. Phys. Lett. 101, 064104 (2012) Producing an intense collimated beam of sound via a nonlinear ultrasonic array J. Appl. Phys. 111, 124910 (2012) Formation of collimated sound beams by three-dimensional sonic crystals J. Appl. Phys. 111, 104910 (2012) Contribution of dislocation dipole structures to the acoustic nonlinearity

In recent years, natural materials are becoming a valid alternative to traditional sound absorbers due to reduced production costs and environmental protection. This paper reports the acoustical characterization of sheep wool. Measurements on normal incidence and diffuse-incidence sound absorption coefficients of different samples are reported. The airflow resistance has also been measured. The results prove that sheep wool has a comparable sound absorption performance to that of mineral wool or recycled polyurethane foam. An empirical model is used to calculate the sound absorption of sheep wool samples. A reasonable agreement on the acoustic absorption of all sheep wool samples is obtained.