Predicting double negativity using transmitted phase in space coiling metamaterials

Abstract

Metamaterials are engineered materials that offer the flexibility to manipulate the incident waves leading to exotic applications such as cloaking, extraordinary transmission, sub-wavelength imaging and negative refraction. These concepts have largely been explored in the context of electromagnetic waves. Acoustic metamaterials, similar to their optical counterparts, demonstrate anomalous effective elastic properties. Recent developments have shown that coiling up the propagation path of acoustic wave results in effective elastic response of the metamaterial beyond the natural response of its constituent materials. The effective response of metamaterials is generally evaluated using the ‘S’ parameter retrieval method based on amplitude of the waves. The phase of acoustic waves contains information of wave pressure and particle velocity. Here, we show using finite-element methods that phase reversal of transmitted waves may be used to predict extreme acoustic properties in space coiling metamaterials. This change is the difference in the phase of the transmitted wave with respect to the incident wave. This method is simpler when compared with the more rigorous ‘S’ parameter retrieval method. The inferences drawn using this method have been verified experimentally for labyrinthine metamaterials by showing negative refraction for the predicted band of frequencies.

Multi-Order Asymmetric Acoustic Metamaterials with Broad Bandgaps at Subwavelength Scales

“…The reason for this phenomenon is that due to the increased geometric asymmetry, high-order AAMs generate stronger resonance at lower frequencies driven by the Mie scattering mechanism [34], thereby broadening the bandgap at lower frequencies. In addition, the proposed AAMs have a broad bandgap and a larger proportion of omnidirectional bandgaps in the subwavelength range compared with the reported fractal-type acoustic metamaterials [16,35] and zigzag-type acoustic metamaterials [36,37]. This shows that we can use AAMs with a structure size that is much smaller than the wavelength in the required frequency range to achieve subwavelength broadband sound isolation.…”

Additive manufacturing of metamaterials: A review

“…With the correct design, such metamaterials can exhibit a negative refractive index, leading to possibilities such as high-resolution imaging. If local resonances are avoided, space coiling can create doubly-negative structures using features that are sub-wavelength in dimensions, as demonstrated by Maurya et al [215] using FDM fabrication with ABS polymer at frequencies of up to 4 kHz in the air. Phase gradients were also created by Xie et al [216,217] to demonstrate extraordinary beam steering and negative refraction at similar frequencies, using FDM fabrication methods.…”

Low Frequency Band Gap and Wave Propagation Properties of a Novel Fractal Hybrid Metamaterial

“…In the low frequency range, the material can have unusual acoustic parameters, such as high refractive index, negative equivalent mass density and negative equivalent bulk modulus. [ 31,32 ] In recent years, the mixing of materials and the change of structural shape have provided a variety of methods to study metamaterials, and the concept of fractal has gradually been introduced into the creation of spatially curled fractal acoustic metamaterials (FAMS), such as Hilbert FAMS, [ 33,34 ] Menger FAMS [ 35,36 ] and Wunderlich FAMS. [ 37 ] Compared with the traditional spatial crimp AMS, the core of FAMS is the mathematical model, which has the characteristics of self similarity, multi‐scale and high spatial utilization, which makes it possible to realize broadband and lightweight AMS.…”