Sound beyond the speed of light: Measurement of negative group velocity in an acoustic loop filter

Robertson, W. M.; Pappafotis, J.; Flannigan, P.; Cathey, J. L.; Cathey, Brandon; Klaus, Colin

doi:10.1063/1.2423240

Cited by 46 publications

(36 citation statements)

References 17 publications

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“…18 The slope of the phase versus frequency is opposite to that of the phase change through resonance, thus, according to Equation (6), transmission of a narrow pulse would experience a group delay that was advanced compared to a directly transmitted pulse an example of a fast wave effect. 19 Finally, we examined a pair of Helmholtz resonators in parallel with frequency transmission bands that were well separated. The dimensions of neck opening diameter, neck length, and volume for the lower frequency resonator were 1.91 cm, 6.5 cm, and 96 cm 3 .…”

Section: Transmission Through Helmholtz Resonators In Parallelmentioning

confidence: 99%

Experimental realization of extraordinary acoustic transmission using Helmholtz resonators

et al. 2015

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The phenomenon of extraordinary acoustic transmission through a solid barrier with an embedded Helmholtz resonator (HR) is demonstrated. The Helmholtz resonator consists of an embedded cavity and two necks that protrude, one on each side of the barrier. Extraordinary transmission occurs for a narrow spectral range encompassing the resonant frequency of the Helmholtz resonator. We show that an amplitude transmission of 97.5% is achieved through a resonator whose neck creates an open area of 6.25% of the total barrier area. In addition to the enhanced transmission, we show that there is a smooth, continuous phase transition in the transmitted sound as a function of frequency. The frequency dependent phase transition is used to experimentally realize slow wave propagation for a narrow-band Gaussian wave packet centered at the maximum transmission frequency. The use of parallel pairs of Helmholtz resonators tuned to different resonant frequencies is experimentally explored as a means of increasing the transmission bandwidth. These experiments show that because of the phase transition, there is always a frequency between the two Helmholtz resonant frequencies at which destructive interference occurs whether the resonances are close or far apart. Finally, we explain how the phase transition associated with Helmholtz-resonator-mediated extraordinary acoustic transmission can be exploited to produce diffractive acoustic components including sub-wavelength thickness acoustic lenses.

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Section: Transmission Through Helmholtz Resonators In Parallelmentioning

confidence: 99%

Experimental realization of extraordinary acoustic transmission using Helmholtz resonators

et al. 2015

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“…The segments with different lengths between every pair of adjacent nodes form an asymmetric loop similar to an acoustic loop filter device. 18 The band structure of a SMCN with d 2 =2d 1 is plotted in Fig. 3͑a͒, where a large gap with a width of c / d 1 can be seen.…”

Section: Band Structures and Attenuation Of Square Multiconnectementioning

confidence: 99%

Strong attenuation within the photonic band gaps of multiconnected networks

Wang

Yang

2007

Phys. Rev. B

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We study the photonic band structures and the attenuation behavior of waves in configuration-periodic square networks where nearest-neighbor nodes are connected by more than one segment. It is shown that even though the period of the unit cell of a square network cannot be defined by the lengths of the segments and the nodes may not be arranged periodically in space, one can still use the Floquet-Bloch theorem in this network system if the theorem is modified. We find that the attenuation can be extremely large even though there is no absorption in the networks and its strength does not have a quasiparabolic profile as a function of wave frequency inside a gap. Large gaps and narrow passbands created by resonances and antiresonances are found.

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“…Among them, it is worth citing the investigations carried out in optical- [1][2][3][4][5], electronic- [6][7][8], and even acousticdomains [9,10]. These experiments evidenced that the occurrence of this counterintuitive phenomenon does not contradict the causality principle.…”

Section: Introductionmentioning

confidence: 95%

Synthesis of frequency-independent phase shifters using negative group delay active circuit

Ravelo

Pérennec

Roy

2010

Int J RF and Microwave Comp Aid Eng

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This article describes a synthesis method dedicated to the design of frequency-independent phase shifters (PSs). This innovative PS structure consists in a transmission line cascaded with a negative group delay (NGD) active circuit so that the absolute constant group delays generated by both of them are identical but of opposite signs. So, in principle, it exhibits a constant overall phase and a group delay close to zero. Broadband linear positive phase slopes are obtained through use of an NGD active circuit whose characteristics are recalled prior to the extraction of the PS synthesis relations. The design and simulations of a PS of compact size are reported. The experimental results confirm the expected frequency-independent transmission-phase value of 145 6 10 with an insertion gain of 2 6 2 dB over a 160% relative frequency band. At last, future prospects allowed by the specific properties of this PS are presented.

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Sound beyond the speed of light: Measurement of negative group velocity in an acoustic loop filter

Cited by 46 publications

References 17 publications

Experimental realization of extraordinary acoustic transmission using Helmholtz resonators

Experimental realization of extraordinary acoustic transmission using Helmholtz resonators

Strong attenuation within the photonic band gaps of multiconnected networks

Synthesis of frequency-independent phase shifters using negative group delay active circuit

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