Deaf Bands Research Articles

Acoustic imaging and collimating by slabs of sonic crystalsmade from arrays of rigid cylinders in air

We show some properties of the acoustic propagation in two-dimensional sonic crystals, formed by parallel rigid cylinders placed in air. The transmission through slabs of sonic crystals and the associated band structures are considered. It is shown that within partial band gaps, the waves tend to be collimated or guided into the direction in which the propagation is allowed. Such a feature also prevails in the situations in which deaf bands appear. We show that within the partial band gaps, a stable imaging effect can be obtained for flat sonic crystal slabs, in analogy to the cases with photonic crystals.

Experimental determination of acoustic bands in two-dimensional sonic band gap crystals

The dispersion relation of acoustic bands in sonic band gap crystals built up with periodic arrays of rigid cylinders in air have been characterized both experimentally and theoretically. A technique based on the analysis of the phase-shift experienced by the sound is used to construct the experimental acoustic dispersion relation. Measurements have been performed in square, triangular, and honeycomb lattices for different filling fractions. The experimental setup also allows to detect the so-called ‘‘deaf bands’’ [J. V. Sánchez-Pérez et al., Phys. Rev. Lett. 80, 3080–3083 (1998)]. A variational method is employed to calculate the corresponding acoustic bands. The good agreement between theory and experiment supports the experimental technique here described as an important characterization tool for these systems. [Work supported by CyCIT of Spain and Generalitat of Valencia.]

The existence of full gaps and deaf bands in two-dimensional sonic crystals

Theoretical and experimental determination of sonic band structures of two-dimensional (2-D) arrays of rigid cylinders in air is reported. We present measurements for square and triangular lattices. A variational method is employed to calculate the acoustic dispersion relation. Experimentally, a transmission technique and the analysis of the phase delay between the incident and scattered waves by the structure are used to construct the acoustic bands. The comparison between theory and experiments allows to fully characterize the band gaps and it has also demonstrated the existence of deaf bands; i.e., bands which cannot be excited due to symmetry reasons. For the case of square lattice we show that the structure with a filling fraction of 0.41 has a full acoustic gap.

Sound attenuation by a two dimensional array of cylinders

Here, it is shown, for the first time, a systematic analysis (experiment and theory) of the acoustic transmission of a two-dimensional periodic array of rigid cylinders with two different configurations: square and triangular. The influence of the filling fractions, ranging from 0.06 up to 0.41, on the appearance of the pseudogaps and full band gaps is studied. Above a certain filling fraction, an overlap is observed between the attenuation peaks measured along the two high symmetry directions of the Brillouin zone. This effect is considered as the fingerprint of the existence of a full acoustic gap. Nevertheless, the comparison with our calculation of band structures shows that the lattice has band states in that frequency range. These bands are called deaf bands (i.e., they cannot be excited by experiments of sound transmission) [Sanchez-Perez et al., Phys. Rev. Lett. (to be published)].

Sound Attenuation by a Two-Dimensional Array of Rigid Cylinders

In this Letter we present an experimental analysis of the acoustic transmission of a two-dimensional periodic array of rigid cylinders in air with two different geometrical configurations: square and triangular. In both configurations, and above a certain filling fraction, we observe an overlap, in the range of the audible frequencies, between the attenuation peaks measured along the two high-symmetry directions of the Brillouin zone. This effect is considered as the fingerprint of the existence of a full acoustic gap. Nevertheless, the comparison with our calculation of band structures shows that the triangular lattice has band states in that frequency range. We call them deaf bands. This contradictory result is explained by looking at the symmetry of the deaf bands; they cannot be excited by experiments of sound transmission.

The Illinois School for the Deaf Band: A Historical Perspective

From 1923 until 1942, the Illinois School for the Deaf included in its offerings for its resident boys the opportunity to participate in a brass band. The band was supported by state and private funds throughout its nearly twenty-year existence. It gave students a musical outlet, provided functional music and entertainment for the other resident students as well as community members, and became a symbol of strength and ability among members of the deaf community. Historical reports recount the outstanding quality of the music performed by the boys. While the band received a fair amount of criticism along with a vast amount of praise, it has been lauded as a most successful and meaningful endeavor. Even though the band has been defunct for more than fifty years, some music classes and activities at the Illinois School for the Deaf are still offered to students.