Topical Issue - CFA 2022
Open Access
Review

Table 1

Characteristics and performance of the devices investigated in literature when experiments have been presented in the paper. The devices are sorted as a function of the kh product, and the λ/h and natural frequencies are added for reference.

Ref. kh λ/h Target freq. or freq. range Description Performance Exp. values (when available)
[58] 0.15 43 700 Hz Local resonance slab with steel plate backing. Absorption coefficients (α) of the sample with the steel plate of different thickness. α≈0.98 at 700 Hz.
[36] 0.17 37.5 1 kHz Viscoelastic rubber matrix, conical cavity, cylindrical oscillator and steel backing. Acoustic absorption. α≈0.67 around 800 Hz.
[45] 0.2 31 800 Hz Array of multi-resonant steel scatterers in a silicone rubber cylinder, inside a viscoelastic polymer matrix with steel backing. Significant acoustic absorption on a large bandwidth (300–2000 Hz). α≈0.9 under low hydrostatic pressure.
[13] 0.21 30 5 kHz Viscoelastic materials with micro-spheres (fluid-filled or elastic cavities). Transmission loss (TL) increases with frequency in a wide band (up to 100 kHz). TL around 3 and 13 dB at 5 and 100 kHz, respectively.
[59] 0.23 27.3 1 kHz Two types of local resonance units in the metamaterial slab. Steel spheres embedded in a viscoelastic polymer matrix. Design deduced from optimization. Acoustic absorption. α≈1 at 1 kHz.
[23] 0.29 21.4 1.75 kHz Periodic array of air cylindrical cavities in silicone. Transmission (T) measurement. T≈−31 dB at 2 kHz.
[62] 0.32–1.58 20–4 4–20 kHz Composite rods placed on a stepped stainless-steel base. Measured transmittance, reflectance and absorption. Broad band performance. α around 0.9 in the band.
[37] 0.6–2.51 10.4–2.5 2.4–10 kHz Gradient cavity shaped polyurethane composite array supported by carbon fiber honeycomb with steel backing. Acoustic absorption on a large bandwidth under hydrostatic pressure (3 MPa). α>0.9 in the band.
[19] 0.71 8.8 170 kHz Macro-porous silicone rubber microbeads embedded in a water-based gel matrix. Layer with negative index (n). n≈−0.8.
[63] 1–2.51 6.2–2.5 12–30 kHz Phononic glass: interpenetrating network structure is introduced into a locally resonant phononic crystal. Impedance matching with water. Acoustic absorption. α>0.9 in the band.
[26] 1.35–2.79 4.7–2.2 1.4–2.9 MHz Air inclusions in PDMS. Several layers. Acoustic absorption. α>0.95 in the band.
[64] 2.28–6.45 2.8–1 14.3–40.5 kHz Square holes drilled into a steel plate. Scattering cross section reduction. Below −10 dB in the band.

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