A highly attenuating and frequency tailorable annular hole phononic crystal for surface acoustic waves

This is the final version of the article. Available from Springer Nature via the DOI in this record.Surface acoustic wave (SAW) devices are widely used for signal processing, sensing and increasingly for lab-on-a-chip applications. Phononic crystals can control the propagation of SAW, analogous to photonic crystals, enabling components such as waveguides and cavities. Here we present an approach for the realisation of robust, tailorable SAW phononic crystals, based on annular holes patterned in a SAW substrate. Using simulations and experiments, we show that this geometry supports local resonances which create highly attenuating phononic bandgaps at frequencies with negligible coupling of SAWs into other modes, even for relatively shallow features. The enormous bandgap attenuation is up to an order-of-magnitude larger than that achieved with a pillar phononic crystal of the same size, enabling effective phononic crystals to be made up of smaller numbers of elements. This work transforms the ability to exploit phononic crystals for developing novel SAW device concepts, mirroring contemporary progress in photonic crystals.The control and manipulation of propagating sound waves on a surface has applications in on-chip signal processing and sensing. Here, Ash et al. deviate from standard designs and fabricate frequency tailorable phononic crystals with an order-of-magnitude increase in attenuation.B.J.A. acknowledges funding from the EPSRC Centre for Doctoral Training in Metamaterials, grant number EP/L015331/1

Sonic and Photonic Crystals

Sonic/phononic crystals termed acoustic/sonic band gap media are elastic analogues of photonic crystals and have also recently received renewed attention in many acoustic applications. Photonic crystals have a periodic dielectric modulation with a spatial scale on the order of the optical wavelength. The design and optimization of photonic crystals can be utilized in many applications by combining factors related to the combinations of intermixing materials, lattice symmetry, lattice constant, filling factor, shape of the scattering object, and thickness of a structural layer. Through the publications and discussions of the research on sonic/phononic crystals, researchers can obtain effective and valuable results and improve their future development in related fields. Devices based on these crystals can be utilized in mechanical and physical applications and can also be designed for novel applications as based on the investigations in this Special Issue

Ultrasonic transmission through periodically perforated plates

Las estructuras periódicas macroscópicas han sido objeto de una intensa investigación durante las dos últimas décadas debido a su capacidad de imitar fenómenos ondulatorios que son inherentes a la escala atómica. Aunque las placas perforadas son estructuras muy comunes en acústica, éstas parecen guardar propiedades de transmisión de sonido inexploradas, cuyo estudio ha sido impulsado por el descubrimiento de la Transmisión Óptica Extraordinaria en láminas de metal perforadas con agujeros distribuidos periódicamente cuando interactúan con la luz. En el presente trabajo se muestra que las placas perforadas no sólo presentan máximos de transmisión total resonante y mínimos de la anomalía de Wood cuando los agujeros están distribuidos de forma periódica, sino también apantallamiento acústico extraordinario debido al cortocircuito hidrodinámico producido por el acoplamiento entre la placa y el fluido. También se detalla el rol de los parámetros geométricos de las placas perforadas en las características de transmisión, ilustrando diferentes estrategias para moldear el espectro de transmisión. La transmisión acústica a través de placas de aluminio con perforaciones regulares sumergidas en agua presenta una alta complejidad tanto a incidencia normal como cuando se varía el ángulo de incidencia del sonido. Aparecen ondas de superficie radiantes provenientes de la vibración de la placa, lo cual es demostrado usando un nuevo modelo teórico que incluye el acoplamiento elastoacústico completo. Gracias al estudio complementario de la transmisión y la propagación en placa de una placa fonónica sólido-sólido se retrata una perspectiva completa del efecto del acoplamiento. Como consecuencia directa, se observan fenómenos de plegamiento y bandas de propagación prohibida en modos tipo Scholte-Stoneley sin necesidad de corrugaciones o de agujeros. Finalmente, se comparan las propiedades de transmisión de agujeros individuales y redes de agujeros para luz, electrones y sonido analizando y comentando sus diferencias. Se ha encontrado que, aunque para la luz la red de agujeros en sí misma lleva a transmisiones del 100% y modos atrapados a la superficie, esto no se produce ni para electrones ni para sonido. En consecuencia, las resonancias del agujero constituyen el mecanismo clave que posibilita la existencia de fenómenos exóticos en sonido. Los resultados principales aquí mencionados son explicados de manera detallada y comentados sobre la base de datos teóricos y experimentales. El objetivo general de esta tesis es dilucidar por medios teóricos y experimentales los fenómenos físicos que se hayan involucrados en la transmisión acústica a través de placas perforadas. En este estudio se usa esencialmente el método de transmisión de ultrasonidos bajo el agua. Los modelos teóricos desarrollados tienen en cuenta la configuración experimental para poder establecer comparaciones precisas entre las medidas y los cálculos. Se toman en cuenta diversos factores que pueden modificar la transmisión de sonido a través de placas perforadas tales como: - La orientación de la onda incidente con respecto a la placa. .- Los parámetros geométricos que definen la placa, es decir, la distancia entre agujeros, el diámetro de los mismos y el espesor de la placa. .- Los parámetros elásticos relacionados con el contraste de impedancia entre el sólido y el fluido. .- El material contenido en los agujeros, de modo que se estudian no sólo placas fonónicas constituidas por un fluido y un sólido sino también aquellas formadas por dos sólidos distintos. Para el caso particular de una placa fonónica constituida por dos sólidos se emplea además una técnica para medir las vibraciones de la placa directamente en su superficie con el fin de complementar las medidas de transmisión de ultrasonidos. Desde una perspectiva teórica, el problema ha sido abordado para estructuras infinitas partiendo de diversas hipótesis.Estrada Beltrán, HA. (2011). Ultrasonic transmission through periodically perforated plates [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/14119Palanci

Study of Abnormal Group Velocities in Flexural Metamaterials

Generally, it has been known that the optical branch of a simple one-dimensional periodic structure has a negative group velocity at the first Brillouin zone due to the band-folding effect. However, the optical branch of the flexural wave in one-dimensional periodic structure doesn't always have negative group velocity. The problem is that the condition whether the group velocity of the flexural optical branch is negative, positive or positive-negative has not been studied yet. In consequence, who try to achieve negative group velocity has suffered from trial-error process without an analytic guideline. In this paper, the analytic investigation for this abnormal behavior is carried out. In particular, we discovered that the group velocity of the optical branch in flexural metamaterials is determined by a simple condition expressed in terms of a stiffness ratio and inertia ratio of the metamaterial. To derive the analytic condition, an extended mass-spring system is used to calculate the wave dispersion relationship in flexural metamaterials. For the validation, various numerical simulations are carried out, including a dispersion curve calculation and three-dimensional wave simulation. The results studied in this paper are expected to provide new guidelines in designing flexural metamaterials to have desired wave dispersion curves

Review of foundational concepts and emerging directions in metamaterial research: Design, phenomena, and applications

In the past two decades, artificial structures known as metamaterials have been found to exhibit extraordinary material properties that enable the unprecedented manipulation of electromagnetic waves, elastic waves, molecules, and particles. Phenomena such as negative refraction, bandgaps, near perfect wave absorption, wave focusing, negative Poissons ratio, negative thermal conductivity, etc., all are possible with these materials. Metamaterials were originally theorized and fabricated in electrodynamics, but research into their applications has expanded into acoustics, thermodynamics, seismology, classical mechanics, and mass transport. In this Research Update we summarize the history, current state of progress, and emerging directions of metamaterials by field, focusing the unifying principles at the foundation of each discipline. We discuss the different designs and mechanisms behind metamaterials as well as the governing equations and effective material parameters for each field. Also, current and potential applications for metamaterials are discussed. Finally, we provide an outlook on future progress in the emerging field of metamaterials.Comment: 22 pages, 3 figures, 1 tabl