Acoustic transmission line metamaterial with negative/zero/positive refractive index

Abstract

A one-dimensional acoustic negative refractive index metamaterial based on the transmission line approach is presented. This structure implements the dual transmission line concept extensively investigated in microwave engineering. It consists of an acoustic waveguide periodically loaded with membranes realizing the function of series "capacitances" and transversally connected open channels realizing shunt "inductances." Transmission line based metamaterials can exhibit a negative refractive index without relying on resonance phenomena, which results in a bandwidth of operation much broader than that observed in resonant devices. In the present case, the negative refractive index band extends over almost one octave, from 0.6 to 1 kHz. The developed structure also exhibits a seamless transition between the negative and positive refractive index bands with a zero index at the transition frequency of 1 kHz. At this frequency, the unit cell is only one tenth of the wavelength. Simple acoustic circuit models are introduced, which allow efficient designs both in terms of dispersion and impedance, while accurately describing all the physical phenomena. Using this approach, a good matching at the structure terminations is achieved. Full-wave simulations, made for a 10-cell-long structure, confirm the good performances in terms of dispersion diagram, Bloch impedance, and reflection and transmission coefficients.

Elastic metamaterials and dynamic homogenization: a review

“…Negative modulus could be achieved through a periodic array of Helmholtz resonators [31,32], and the negative density could be achieved through an array of thin membranes [33]. The combination of these two structures was shown to exhibit LHM properties [34,35] Since then, researchers have proposed more complicated acoustic/elastic LHM architectures. These include multiply resonant microstructures that lead to density and some components of the modulus tensor simultaneously becoming negative [36], periodic array of curled perforations [37,38], tunable piezoelectric resonator arrays [39], anisotropic LHMs by arranging layers of perforated plates [40], etc.…”

Anisotropic Complementary Acoustic Metamaterial for Canceling out Aberrating Layers

“…It has been demonstrated that for the 1D membranebased metamaterial shown in Fig. 2(b), the effective density depends on the properties of the membranes [25,[27][28][29]. The side branches are assumed to have a negligible effect on the effective density [25].…”

“…CMMs are also expected to be useful for the design of acoustic cloaking [32] and all-angle antireflection materials [33,34]. To extend the current design to 3D, the branch openings can be replaced by slits, which also yield a negative compressibility or bulk modulus [27]. The major challenge in realizing the proposed CMM is that the thicknesses of the membranes should be reasonably accurate, as they determine the effective density of the metamaterial.…”

“…The effective density with clamped membranes can be derived by using the lumped model. Figure 2(c) shows the equivalent acoustic circuit of the 1D membrane-based metamaterial, where m a is the effective acoustic mass of the tube, C a is the acoustic capacitance of the waveguide, and Z am is the acoustic impedance of the membrane, which can be approximated by an inductor and capacitor in series in the low-frequency region [27].…”

Zero phase delay induced by wavefront modulation in photonic crystals

“…The zero phase delay propagation, independent of the propagating distance, is attributed to an invariable wavefront modulation of photonic crystal in the direction of wave propagation, where the phase velocity is perpendicular to the group velocity with parallel wavefronts (or phasefronts) extending along the direction of energy flow. This effect can be extended to the three-dimensional cases or other artificially engineered materials, and may open a new route to obtain perfect zero-phase-delay propagation for electromagnetic wave instead of using zero-index or zero-averaged-index materials and have significant potential in many applications.Recently, great efforts have been made to construct materials with zero or near-zero-n with quasi-uniform phase and infinite wavelength [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. Zero-n materials have a series of exciting potential applications, such as wavefront reshaping [10], beam self-collimation [5,13], extremely convergent lenses [17], etc.…”