Acoustic Grating Research Articles

Experimental validation of anomalous acoustic wave refraction using Double layered acoustic gratings

Acoustic metasurfaces (AMSs) have garnered increasing attention over the past decade due to their remarkable capability for wave manipulation. AMSs have been widely applied in diverse domains, including anomalous refraction and extraordinary sound absorption/isolation, among others. However, typical AMS designs, such as Helmholtz resonator-like or labyrinthine structures, are often geometrically complex, limiting their practical usability. In this paper, we introduce an ultracompact Double Layered Acoustic Grating (DLAG) to achieve anomalous acoustic wave refraction. The DLAG comprises double-layered rigid panels with multiple perforated subwavelength slits. By optimizing the positions of these slits on the rigid panels, the acoustic energy of an obliquely incident plane wave can be concentrated within a predetermined region in an arbitrary direction. The paper will first review the theoretical background to predict the wave propagation controlled by DLAGs based on the surface coupling approach. Subsequently, the underlying principle to achieve anomalous refraction using DLAGs will be discussed. A 3D-printed DLAG with the optimized slit positions is used for demonstration. In the experiment, the acoustic energy of a plane wave with an incident angle of 36 degrees was successfully collimated within a predetermined focusing region with a negative refracted angle of -36 degrees.

Performance and influencing factors of acoustic grating based on signal enhancement

Performance and influencing factors of acoustic grating based on signal enhancement

Anomalous refraction of acoustic waves using double layered acoustic grating

The paper proposes a double layered acoustic grating for fulfilling acoustic focusing in an anomalous direction. The acoustic grating consists of two layers of rigid panels with periodically perforated slits. By optimizing the positions of the slits on the two layers, both positive and negative refractive indices can be achieved with the phase shift tailored within [-π/2, π/2]. This allows acoustic energy of an obliquely incident plane wave to converge in a predefined focusing region in any direction. The paper predicts the wave propagation manipulated by the acoustic grating based on the surface coupling approach. Then, it discusses how to optimize the slits' positions to collimate the acoustic energy of an obliquely incident plane wave in a specific direction. Such acoustic grating has various potential applications, such as deflecting outdoor noise away from sensitive areas in building acoustics, enhancing acoustic energy in a target audience area in auditorium design, collimating acoustic surface waves, etc.

Rapid Estimation of Ethanol Concentration using Acousto‐Optic Diffraction

AbstractFast and accurate determination of ethanol concentration is important in alcohol industries for testing the purity and quality of their products. Here, we demonstrate a quick, robust, and accurate technique to estimate the concentration of ethanol in aqueous solutions. Our method utilizes the principle of diffraction of light in the presence of high frequency ultrasound waves that create diffraction grating in solution. A monochromatic light interacts with this acoustic grating and produces an intensity distribution pattern, which was used to determine the ethanol concentration. We measured ethanol concentrations in various alcoholic solutions and beverages at room temperature with very high accuracy down to 2 % over a concentration range of 30–100 %. The experimental results have been supported with analytical calculations and simulations. We believe that our method will benefit alcohol production industries and lead to the development of portable, inexpensive, and reliable ethanol concentration measurement devices.

Measurement of transparent liquid concentration based on ultrasonic grating method

In this experiment, ultrasonic grating method is used to measure the concentration of transparent liquid. The principle is that the liquid forms standing waves, namely ultrasonic grating, by using a signal generator. The monochromatic parallel light diffracted after entering the ultrasonic grating, and the sound velocity could be obtained by the spacing of diffraction fringes. The experimental equipment includes three parts: light source system, ultrasonic generation system and digital observation system. The experimental test shows that the experimental device can be used to measure the concentration of sugar water, salt water and other transparent liquid, with simple operation and high measurement accuracy.

Acoustic focusing by a double layered acoustic grating

Acoustic focusing has wide applications in many domains including non-destructive evaluation, medical diagnosis and particle manipulation. In the past decades, due to their outstanding capacity of wave manipulation, acoustic metasurfaces (AMSs) based on various structures, such as coiling-up space structures, Helmholtz-resonator-like structures and membrane-type structures, have been proposed to achieve different functionalities including acoustic focusing. However, given their complex geometries and narrow channels, these structures inevitably cause fabrication difficulties and limit energy transmission efficiency due to the thermoviscous loss. To overcome these drawbacks, a double layered acoustic grating (DLAG) is proposed in the paper to focus acoustic waves with high energy transmission efficiency. The DLAG consists of two layers of rigid panels with periodically perforated subwavelength slits on each layer. The surface coupling approach (SCA) which was proposed to predict the sound radiation in multiple connected spaces is employed to predict acoustic field through the DLAG. The widths of the slits and the cavity between the two layers of the DLAG can be optimized to converge the acoustic energy of an incident plane wave into a predefined focusing region, while the slits’ spacing and the thickness of the DLAG are set to be a fraction of wavelength. Using a 3D printed DLAG with the optimized geometrical size, the acoustic focusing was validated experimentally, which show very good agreements with the prediction from the SCA.

Experimental investigation of multiple-particle pattern based on one-dimensional grating resonance field

Manipulation of particles by ultrasonic waves is a primary technique in the fields of precision manufacturing, materials engineering, and in vitro diagnosis, since it can control the motion of objects in the sound field in a contactless and noninvasive manner. In general, the free sound field, such as the focused field and the plane wave generated by a single transducer can only manipulate a single particle. While the complex field generated by a transducer array should be actuated by a complex electric control system, which makes the manipulation device expensive and cumbersome. Thus, modulated acoustic field for particle manipulation is still needed. Here, we experimental realize a one-dimensional acoustic grating to tune sound fields for the parallel pattern of multiple particles. The physical mechanism is that due to the resonance coupling between the periodic diffraction wave on the surface of the acoustic grating and the Fabry-Perot resonant sound field in the acoustic grating slit, a periodical gradient sound field on the surface of the acoustic grating is induced. Then, particles in the periodical gradient sound field can be trapped in two stable positions in one period of the grating. These concepts and realizations of particle patterns in the acoustic grating pave the way for implementing the parallel manipulation of particles in acoustic manipulation technologies.

Impact of finite bandwidth on PRBS-modulated optical spectra.

Applying a pseudo-random binary sequence (PRBS) to phase modulators is a recent development in the broadening of optical spectra of laser sources to defeat stimulated Brillouin scattering (SBS). The theoretical underpinning of this method relies on alternating the phase of the optical signal between its native value and an out-of-phase value (i.e., imposing a binary phase shift of 0 or π in a pseudo random manner) to prevent coherent buildup of the SBS acoustic grating. In real physical systems, realizing such a binary shift is impossible due to the finite response times of the electronics and electro-optic components. The influence of these effects is investigated in this work, specifically the finite bandwidth of the electronic PRBS generator and the frequency-dependent response of the phase modulator, on the resultant temporal waveforms of the PRBS signal and its RF optical spectra. It is found that the optimal SBS suppression in real systems is achieved when the phase modulator is driven at a voltage beyond V π, even though driving at V π has been deemed as ideal. Moreover, both the SBS suppression and spectral broadening are always weaker than what is predicted by analytical results since any degradation of the sharp edges of the PRBS signal result in loss of high-frequency content in the RF spectrum of the PRBS signal. Lastly, it is noticed that the typical ways of measuring spectral width are not relevant when applied to the complex PRBS RF optical spectrum. An 'equivalent spectral width' is defined to accurately quantify the correlation between spectral width an SBS suppression.

Acoustic wonders of Crane Mountain reproduced in backyard

The chirping echo after a handclap in front of the stairs found in Crane Mountain and elsewhere in the world are caused by periodic structures of the stairs acting as acoustic gratings. The sound notes of specific frequencies are enhanced due to interference effect. We reproduced the fantastic acoustic phenomena found in Crane Mountain (‘chirping sound of echoing crane’ and ‘dripping on celestial staircases’) with a ‘do it yourself’ model comprising an array of wooden boards. The ‘chirping echo’ and ‘dripping’ effects are clearly audible to human ears and can be used for demonstration in schools or public performance. With this device, we also verified that the grating equation in optics can be approximately applied to predict the chirping frequencies when incident angle and diffraction angel are small.

Tunable asymmetric acoustic transmission device based on acoustic grating and sonic crystal with point defect

A numerical demonstration is given of the feasibility of a newly designed tunable asymmetric acoustic transmission device, for which the acoustic transmission coefficients for perpendicularly incident left- and right-running waves are different at a particular single frequency within a forbidden zone. The proposed device consists of a hybrid, sonic-crystal-based resonant structure with horizontal periodicity and a one-dimensional periodic rectangular acoustic grating with vertical periodicity. The former structure exhibits a wide bandgap through which only waves with particular combinations of their frequency and propagation direction can tunnel. The direction dependence of the acoustic transmission is based on the geometrical asymmetry of the placement of the grating, and on the narrowband correspondence between the diffraction angle of the grating and the allowed transmission direction through the sonic-crystal-based structure. Angular and spectral tuning are possible by changing the grating and/or the sonic crystal periodicity. The device has potential applications in underwater acoustics for asymmetric transmission systems and secure communication systems.

Inhomogeneous acoustic grating model for stimulated Brillouin scattering

Stimulated Brillouin scattering (SBS) is well recognized as being useful in quantum information processing, optical fiber sensing, and LIDAR remote sensing. Here an inhomogeneous acoustic grating model based on coupled wave and dielectric grating theories is established to analyze the SBS process in water. The acoustic grating modulation process was theoretically analyzed based on the proposed model. The results show that variations of the Stokes peak intensity, frequency shift, and linewidth of SBS in water depend on the cosinusoidal refractive index modulation and periodic modulation of the acoustic grating. To verify the theoretical simulation results, an experimental system was designed to measure the SBS process in seawater with different temperatures and salinities. Theoretical results show coincidence with experimental values in the variation trend, and the numerical difference is about 10 MHz per degree Celsius or one thousandth of salinity. This work is essential to future applications of SBS in quantum communication, fiber sensing, and LIDAR technology.

Broadband and Deep Subwavelength Acoustic Antenna Based on Fabry-Perot-Like Acoustic Grating Resonators

Broadband and Deep Subwavelength Acoustic Antenna Based on Fabry-Perot-Like Acoustic Grating Resonators

Enhanced broadband monopole emission and acoustic energy harvesting via a dual anisotropic metamaterial

Broadband sound energy enhancement is essential in practical scenarios, such as acoustic positioning and acoustic communication. In this paper, a dual anisotropic metamaterial composed of an inner Mie resonator and an outer acoustic grating is proposed, aiming to achieve enhanced broadband monopole emission and acoustic energy harvesting (AEH) via the coupling of the first and second monopole resonances. Considering thermo-viscous dissipation, numerical simulations and experimental results demonstrate that the dual anisotropic metamaterial can realize omnidirectional enhanced broadband monopole emission at 795 Hz–1511 Hz, the maximum sound pressure level (SPL) gain is 16.4 dB and the SPL gain fluctuation is 3 dB. Furthermore, simulation results reveal that the broadband AEH can be achieved by the dual anisotropic metamaterial, the fluctuation of the SPL gain at 794 Hz–1537 Hz is 3 dB and the maximum is 14.7 dB. Based on the results, the dual anisotropic metamaterial is expected to show significant potentials in acoustic positioning and acoustic communication.

Multifunctional Waterborne Acoustic Metagratings: From Extraordinary Transmission to Total and Abnormal Reflection

Wavelength-thick multifunctional metagratings for waterborne sound are highly desirable in various application scenarios, such as human health monitoring and ocean exploration. In this article, we present a class of metagratings with which distinct and switchable wave manipulation functionalities, such as extraordinary transmission, total reflection, and abnormal reflection can be achieved through a single acoustic grating. Simultaneous and high-efficiency control over both reflected and transmitted waves is achieved through a systematic design approach in which wave diffraction theory, effective medium theory, and intelligent optimization algorithms are concurrently utilized. Switching between different functionalities can be achieved simply by changing the operation frequency, or by changing the incident angles. Robust and perfect wave-front manipulation effects are obtained over a wide range of incident angles and operation frequencies. Our work not only provides a design paradigm of planar acoustic devices for multiple manipulation purposes, but also presents a feasible solution for the development of integrated acoustic devices for distinct underwater applications.

Broadband monopole emission enhancement using a dual acoustic grating

The enhanced broadband emission of monopole source is achieved by a dual acoustic grating with anisotropic mass density. The exact expressions among the enhanced efficiency and all the structural parameters of the dual acoustic grating are obtained through rigorous analytical model based on the radiation impedance theory. The results show that the enhanced broadband monopole emission can be realized in the dual acoustic grating through the coupling of the first and the second resonance modes. Considering the thermo-viscous dissipation, the broadband monopole emission can be enhanced through parameter optimization and the sound pressure level (SPL) gain is above 11 dB. Its bandwidth is 1060-1920 Hz and the fluctuation of the SPL gain in the frequency band is 3 dB. The sample is further fabricated and the enhanced broadband emission of monopole sources by the dual acoustic grating is experimentally verified. The study of this letter could have potential application for loudspeaker design and acoustic communication.

Behavior of the Fused Quartz Suspended Core Acoustic Waveguide Sensor in Gamma Radiation

Previously, a fused-quartz acoustic waveguide named the suspended core waveguide with tight-field confinement in a small diameter was developed and its sensing potential in harsh environment was demonstrated with the fabricated periodic acoustic fiber Bragg grating. In this paper, the acoustic sensor was exposed to around 70 Gy/h gamma radiation at room temperature for 3550 h at Oak Ridge National Laboratory. For comparisons, a thermocouple and two optical fiber Bragg gratings were tested under the same conditions. The central frequency reading of the acoustic sensor was found to encounter a relatively fast decrease of 0.5 kHz in the first 800 hours. The reading then became stable, centering at 478.5 kHz with a fluctuation of ±0.2 kHz, and responded to small environmental temperature variations less than 1.2 °C. The major effect to the fluctuation was concluded to be radiation-induced material compaction and expansion. For optical fiber Bragg gratings, the same one-directional fast change of readings in the first 500 hours were observed as well. Although the optical gratings were able to track temperature changes, they also showed continuous drifts. The survivability and consistency of the acoustic sensor under long-term gamma radiation could lead to new sensing methods in nuclear applications.

An Acoustic Waveguide With Tight Field Confinement for High Temperature Sensing

A fused quartz acoustic waveguide structure was reported as the suspended core waveguide. The waveguide featured good acoustic wave confinement within the core and a relatively small diameter. Consistent high-temperature sensing was also demonstrated with the waveguide after a temperature sensor was fabricated inside. The waveguide was fabricated by suspending its core rod in the middle of the hollow cladding tube by discrete thin supporting disks. It was found that the characteristics of acoustic propagation in the waveguide was similar to that in a bare core rod and that the waveguide was largely insensitive to lossy surface perturbations. The diameter of the waveguide was relatively small, little more than the bulk longitudinal acoustic wavelength. For sensing, the periodic structure, the acoustic fiber Bragg grating, was fabricated on the core of the suspended core waveguide. A temperature test up to 1000 °C was performed. The central frequency of the reflected acoustic wave was found to change unidirectionally and consistently with changes in temperature. With its good field confinement and consistent sensing capabilities, the suspended core waveguide could find vast potential in many applications.

Acoustic enhancement and weak signal detection based on the space-coiling gradient acoustic grating

Weak signal detection plays an important role in industrial production. We propose the space-coiling gradient acoustic grating to control the sound wave transmission and realize acoustic enhancement. The numerical results show that the acoustic pressure amplitude can be amplified more than 240 times, and the corresponding frequency can be reduced to 500 Hz. Besides, we optimize properties of the space-coiling acoustic grating and apply it into the field of weak signal detection. For periodic impulse signals, the amplitude of the characteristic frequency is effectively enlarged, which makes the detection of the characteristic frequency much easier.

Diffraction control in a non-Hermitian acoustic grating

Losses in media have become fresh elements in the designing of asymmetric acoustic transmission and reflection without the nonlinear effect. In this paper, we demonstrate the diffraction control by equipping fine-tuned losses in a non-Hermitian acoustic grating. Compared to the Hermitian grating without losses, the positive first order diffracted wave with negative incidence will be suppressed perfectly, but the negative first order diffracted wave with positive incidence will be enhanced counterintuitively in the lossy diffraction grating. The physical mechanism is that losses can modulate the magnitudes of Bloch wave vectors through the interplay with the real modulation of the refractive index. Absorption is demonstrated as a powerful way to control the acoustic diffraction.

Experimental Demonstration of an Acoustic Asymmetric Diffraction Grating Based on Passive Parity-Time-Symmetric Medium

Passive parity-time-symmetric medium provides a feasible scheme to investigate non-Hermitian systems experimentally. Here, we design a passive PT-symmetric acoustic grating with a period equal to exact PT-symmetric medium. This treatment enhances the diffraction ability of a passive PT-symmetric grating with more compact modulation. Above all, it eliminates the first-order disturbance of previous design in diffraction grating. Additional cavities and small leaked holes on top plate in a 2D waveguide are used to construct a parity-time-symmetric potential. The combining between additional cavities and leaked holes makes it possible to modulate the real and imaginary parts of refractive index simultaneously. When the real and imaginary parts of refractive index are balanced in modulation, asymmetric diffraction can be observed between a pair of oblique incident waves. This demonstration provides a feasible way to construct passive parity-time-symmetric acoustic medium. It opens new possibilities for further investigation of acoustic wave control in non-Hermitian systems.