Acoustic Phased Array Research Articles

The design method and test of a Dual-Focused ultrasound transducer toward small and adjustable F-numbers

An ultrasound transducer with a F-number less than 1.0 has been used in many fields such as non-destructive testing, medical treatment, particle manipulation, and so on. Traditional focusing technologies such as self-focusing structure and lens sets suffer from undesired surface cavitation due to large cavity depth, difficulties in fabrication, and most of designs have a fixed focal depth. This paper presents a small F-number ultrasound transducer design using a combination of acoustic lens and phased array, its fabrication process is not complicated, and focal depth is adjustable when applying different time delays. The design methods, including analytical expression, empirical equation and numerical results, are elaborated in this paper, followed by fabrication and tests. Simulations and experimental results prove that this dual-focused transducer can reach a changeable F-number as small as 0.72. The cavity depth of the transducer is relatively small (1.1 λ) compared to existing focusing transducers (4 ∼ 10 λ), which is not prone to unexpected surface cavitation. Moreover, the array in transducer has no grating lobes with an expanded pitch of 1.43 λ, which not only increase the fill factor and effective area but also further reduces the fabrication difficulty, especially in high frequency applications.

Tunable acoustic passive phased array based on double-opening resonant rings

The special structural design of acoustic metamaterials further extends acoustic properties of the materials. We design a tunable acoustic passive phased array based on double-opening resonant rings, which modulates the acoustic waves only by the rotational angle, making up for the defect of the fixed structure of ordinary metamaterials. The rotation angle is selected based on the generalized Snell’s law, which not only enables focusing in a large frequency band range but also meets the focusing demand of acoustic waves incident at different angles and controls the position of the focal point.

Full-duplex underwater acoustic communications via self-interference cancellation in space

Traditionally, underwater acoustic communications are half-duplex (HD), i.e., the hydrophones and transducers operate in non-overlapping time-slots/frequency-bands in one direction. To double the spectral efficiency into the full-duplex (FD) mode, which transmit and receive signals simultaneously, a self-interference cancellation (SIC) technique in space is introduced and deployed. Specifically, a novel underwater acoustic system is proposed to perform FD-SIC efficiently via an integrated design combining underwater acoustic vector sensor (AVS) and phased array transducer (PAT) to realize the spatial SIC. The energy focusing function of the beamformer (BF) helps PAT avoid self and mutual spatial interference. The AVS keeps updating the direction of arrival information to let BF adjust the steering angle via an adaptive protocol. The field-programmable gate array (FPGA) Direction of Arrival Estimation (DOA) estimation is done by a 12-element AVS, run-time is 1.22×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−4</sup> s by MUSIC method, which is promising for real-time applications. In this work, phase-shift keying (PSK) and PSK-based orthogonal frequency-division multiplexing (OFDM) are deployed as the FD transmission modulation methods in the spacial SIC. The proposal is evaluated and verified via both simulations and emulations in real underwater acoustic channels collected in the Gulf of La Spezia, Italy, and it is able to achieve 59 dB SIC while modulating with binary phase-shift keying (BPSK) with carrier wave frequency 80 kHz and AVS steering angle −5°. Moreover, it has at least 37 dB SIC within the steering angle region.

Coding Piezoelectric Metasurfaces

AbstractThe manipulation of acoustic waves plays an important role in a wide range of applications. Currently, acoustic wave manipulation typically relies on either acoustic metasurfaces or phased array transducers. The elements of traditional metasurfaces are usually designed with complex artificial structures and limited by the additive manufacturing capability, which are difficult to apply in MHz frequency underwater acoustic wave control. Phased array transducers, suffering from high‐cost and complex control circuits, are usually limited by the array size and the filling ratio of the control units. Coding piezoelectric metasurfaces are reported; three wave functionalities, including beam steering, beam focusing, and vortex beam focusing are demonstrated; and acoustic tweezers and ultrasound imaging are eventually realized. The information coded on the piezoelectric metasurfaces herein is frequency independent and originates from the polarization directions, pointing either up or down, of the piezoelectric materials. Such a piezoelectric metasurface is driven by a single electrode and acts as a controllable active sound source, which combines the advantages of acoustic metasurfaces and phased array transducers while keeping the devices structurally simple and compact. The coding piezoelectric metasurfaces lead to potential technological innovations in underwater acoustic wave modulation, acoustic tweezers, biomedical imaging, industrial nondestructive testing, and neural regulation.

Multichannel frequency-selective beaming in time-modulated electroacoustic phased arrays

Acoustic phased arrays have been a cornerstone of non-destructive evaluation, sonar communications, and medical imaging for years. Conventional arrays work by imparting a static phase gradient across a set of acoustic transceivers to steer a self-created wavefront in a desired direction. In a reception mode, they abide by basic reciprocity principles and exhibit the strongest gain for waves incident from the same direction to which they transmit. This talk sheds light on a class of dynamic phased arrays which is capable of (a) generating multiple scattered harmonics of a single-frequency voltage input which simultaneously propagate in different directional lanes and (b) exhibiting non-identical TX/RX patterns. We will show that such lanes emerge in the form of artificially-synthesized directional channels each with a distinct frequency signature that can be predicted a priori. To achieve this, we devise a class of phase shifters, which augment the array elements with a dynamic phase modulation using an array of piezo-wafer discs bonded to an elastic medium. The scattered beams propagate simultaneously in the transmitted wave field but can be visualized using an FFT of the time-transient measurements via laser Doppler vibrometry. The experimental realization illustrates the array’s ability to guide incident waves within tunable frequency channels that are commensurate with the modulation rate and along the intended directions.

Practical considerations for ray casting shear layer corrections

Aircraft noise reduction technology development has been aided by the use of acoustic phased arrays to identify component-level locations of noise sources. Acoustic phased arrays are commonly used in both closed-wall and open-jet wind tunnels, thus requiring accurate acoustic propagation models to focus the array. In particular, open-jet wind tunnels have complex flow fields including a free shear layer that the acoustic waves must propagate through. A method using ray tracing is reviewed and an enhancement proposed to reduce the computational time for cases requiring a large number of rays. The proposed reduced ray casting method uses ray tracing to the extreme edges of the region of interest and limits all casted acoustic rays to within that region. The results showed that a hemispherical spiral discretization had lower error in the estimated acoustic propagation time than uniform angular discretization. The proposed reduced ray casting method showed similar accuracy as the original ray casting method but with improvement in the computational times when the number of cast rays was greater than 3200 as needed for modeling acoustic propagation in larger industrial sized open-jet wind tunnels.

Origami inspired phononic structure with metamaterial inclusions for tunable angular wave steering

The ability to create directional sound beams is fundamental to acoustic sensing. Traditionally, acoustic beams are most commonly produced by phased arrays, which increase the cost and complexity of the systems in which they are implemented. Phononic structures have theoretically been shown to possess Dirac cones that can be manipulated to produce angular collimated beams. Dirac cones are usually encountered in phononic crystals with inclusions significantly more compressible than the surrounding media, e.g., rubber inclusions in a water medium, a characteristic not easily realized in air. In addition, there are no effective and practical means to tune phononic structures that can achieve a broad range of Dirac point manipulation, which is essential to changing the direction and focus of acoustic beams. To advance the state of the art, this research proposes a novel approach to produce steerable collimated beams in air by harnessing reconfigurable origami phononic structures with adjustable metamaterial inclusions. The proposed structure is shown to produce dramatic lattice reconfiguration and control of Dirac points in a broad range, and thus achieve collimated beams with on-demand tunable frequency and angle. These advancements provide a simple, cost-effective alternative to acoustic phased arrays, greatly expanding the potential of acoustic sensing.

Acoustic emission monitoring and phased array ultrasonic testing for the steel bifurcated pipe of 800MPa grade strength in hydraulic test

The paper analyzes and studies the acoustic emission monitoring and phased array ultrasonic testing of steel bifurcated pipe of 800MPa grade strength in hydraulic test. The comprehensive grade of AE location source is assessed, and the structure health is evaluated, the AE characteristic parameters of an important hazardous area corresponding to the load elevated stage and load holding stages are analyzed and compared, and Kaiser effect is verified. PAUT is used to examine the area of great activity located by AE, and the position of welding defects found by PAUT is basically consistent with the AE location map, then the location error of AE is illustrated in the region of irregular shape. The AE and PAUT are of great advantage in hydraulic test of the steel bifurcated pipe.

Modeling of physical processes of interaction of ultrasonic wave with metal structures for detection of defects

In the article the features of the physical processes modeling of the ultrasonic wave interaction to the metal structures are considered. The mathematical model for calculating the acoustic field of a single element of a 32-element electromagnetic acoustic phased array of SV-waves is developed. The computer simulation of the process of reflection of the ultrasonic beam from a defect is carried out. The developed model allows to study the influence of the shape, size, location of defects in the plate, as well as the geometric parameters of the plate, on the formation of the reflected signal.

Frequency selective wave beaming in nonreciprocal acoustic phased arrays

Acoustic phased arrays are capable of steering and focusing a beam of sound via selective coordination of the spatial distribution of phase angles between multiple sound emitters. Constrained by the principle of reciprocity, conventional phased arrays exhibit identical transmission and reception patterns which limit the scope of their operation. This work presents a controllable space–time acoustic phased array which breaks time-reversal symmetry, and enables phononic transition in both momentum and energy spaces. By leveraging a dynamic phase modulation, the proposed linear phased array is no longer bound by the acoustic reciprocity, and supports asymmetric transmission and reception patterns that can be tuned independently at multiple channels. A foundational framework is developed to characterize and interpret the emergent nonreciprocal phenomena and is later validated against benchmark numerical experiments. The new phased array selectively alters the directional and frequency content of the incident signal and imparts a frequency conversion between different wave fields, which is further analyzed as a function of the imposed modulation. The space–time acoustic phased array enables unprecedented control over sound waves in a variety of applications ranging from ultrasonic imaging to non-destructive testing and underwater SONAR telecommunication.

Modeling of physical processes during the propagation of ultrasonic waves in metallic media

The paper deals with the features of modeling physical processes during the propagation of ultrasonic waves in metallic media. A mathematical model for the propagation of shear vertical (SV) ultrasonic waves generated by a single element of a 32-element electromagnetic acoustic phased array has been developed. The calculation of the acoustic field of the 32-element SV electromagnetic acoustic transducer (EMAT) phased array was made. The total displacements for models with defects and without them were calculated. A computer simulation of the process of reflection of the ultrasonic beam from a defect was made. The developed model allows one to study the influence of shape, size, location of defects in the plate as well as the plate geometric parameters on the formation of the reflected signal.

Geometry-independent attenuation and randomness of ultrasound wave propagation in concrete measured by embedded PZT transducers

Ultrasound is widely used in nondestructive testing (NDT). It is the basis of many NDT techniques, such as acoustic emission, phased array and synthetic aperture focusing technique. The attenuation of ultrasound is a key factor that ensures the feasibility of these techniques. Conventional studies of attenuation are mostly conducted in specimens that have dimensions smaller than ultrasound wavelengths. In this type of study, reflections from media boundaries interfere with the wave, resulting in a geometry-dependent attenuation that cannot be applied in another specimen with a different geometry, even if the material is identical. Another factor that impacts on the viability of ultrasound NDT techniques is the spatial uniformity of waves in the concrete sample. To serve as a reference in testing defects, the degree of randomness caused by the material’s heterogeneity should be estimated in conditions free of defects. In this study, a large concrete specimen was fabricated to suppress boundary reflections of the wave, creating an environment less dependent on geometry. Twenty-two PZT (lead zirconate-titanate ceramics) transducers were arranged in a three-by-seven array to transmit and receive ultrasound waves. This experiment sought to measure attenuation over distance and by frequency, as well as analyzing attenuation factors such as geometrical spreading and material absorption. A quadratic trend with good consistency between attenuation and frequency was found, indicating minimal local attenuation. The degree of randomness in the wave was measured by three indices: amplitude, group velocity and the frequency spectrum cross-correlation factor. Frequency dispersion was also described using group velocity. The findings of this study can serve as a reference for other NDT research, disclosing geometry-independent attenuation and the variability of wave characteristics in concrete.

Мощные акустические антенные решетки для атмосферных приложений

Мощные акустические антенные решетки для атмосферных приложений

Broadband acoustic phased array with subwavelength active tube array

Acoustic metasurfaces provide a way to manipulate wavefronts at anomalous reflection or refraction angles through subwavelength structures. Here, based on the generalized Snell's refraction law for acoustic metasurfaces and the classical acoustic phased array (PA) theory, a broadband acoustic PA with a subwavelength active tube array has been proposed to form a special acoustic beam and to determine the directivity characteristics of the acoustic source. Theoretical analysis shows that the dispersionless wavefront manipulation can be realized by the gradient model of the active tube array, and a wide working frequency band can be obtained in practical applications from the simulated and experimental results. The numerical results of forming a special acoustic beam and establishing an acoustic focus model with an arbitrary focal position are consistent with the theoretical predictions. The experimental results agree well with the simulated results in the model of forming the acoustic beam of 45°. By combining acoustic metamaterials and conventional acoustic PA, the model of the active tube array paves a way to design a composite acoustic PA with high radiation efficiency and system robustness without the need for any complex circuit control system. This design concept is expected to be used in the design of ultrasonic therapy devices and high-efficiency transducers.

Experimental Research on Noise Source Spectrogram of a High-speed Train’s Pantograph

Using acoustic phased array technique to take an experiment research on noise source spectrogram of a high-speed train’s Pantograph. The post-processing algorithm Non Negative Least Squares method (NNLS) is applied to deal with the initial source image obtained by traditional beamforming algorithm Day-and-Sum (DAS), and the number of iterations is chosen as 300 steps. The results of experiment show that noise of the pantograph raised is obviously larger than noise of the pantograph dropped, and the SIL of the pantograph “knuckle” facing backward is greater about 1dBA than the SIL of pantograph “knuckle” faced forward. Last, the noise source spectrogram of the pantograph raised is fitted by quadratic polynomial. According to the spectral fitting, the peak frequency is around 1.4kHz which is greater than the spectrogram of experiment. Therefore the sound energy of pantograph is mainly concentrated in the high frequency region.

Chip-Scale Near-Field Resonant Power Transfer via Elastic Waves

This paper reports on the proof-of-concept demonstration of an approach for the synthesis of a through package charging and authenticating communication link enabled by GHz-range aluminum nitride (AlN) piezoelectric transducers. The acoustic link is formed by two thickness-mode acoustic transducers placed on the two sides of a packaging substrate. The link leverages the enhancement of energy transfer that occurs at resonance; 1- $\mu \text{m}$ -thick (2.7 GHz) and 6- $\mu \text{m}$ -thick (500 MHz) AlN acoustic links are demonstrated showing substantial enhancement of power transfer efficiencies (PTE) when using thicker AlN substrates. PTEs of −8 dB at 2.7 GHz and −2 dB at 500 MHz are measured for transducers’ size of $1\times 100\times 100~\mu \text{m}^{3}$ and $6\times 100\times 100~\mu \text{m}^{3}$ through 700- and 500- $\mu \text{m}$ -thick silicon substrates, respectively. The experimental values are in very close agreement with the analytical model of the acoustic link. The potential misalignment between the two transducers is the main limitation of this approach. To overcome this challenge, acoustic phased arrays are devised to enable steering of the transmitted beam. Preliminary results on the steering capability demonstrate about 8 dB of improvement in PTE via a two-element array when dealing with a 100- $\mu \text{m}$ misalignment. This paper is the first step toward the development of next-generation high-efficiency and micro-scale power transfer units that could energize chips through packages. [2017-0010]

On Using an Acoustic Antenna Array for Testing Thermal Damages in Austenitic Steel by the Spectral Method

Results of testing a technique for evaluating damages on the inner surface of austenitic-steel pipe samples by the spectral acoustic method with the use of an acoustic phased antenna array are provided. It is shown that accumulated damages can be revealed in the surface layer at a level of 10% of exhausting the resource of an article made of 12Kh18N10T steel.

Photoacoustic ultrasound sources from diffusion-limited aggregates

Metallic diffusion-limited aggregate (DLA) films are well-known to exhibit near-perfect broadband optical absorption. We demonstrate that such films also manifest a substantial and relatively material-independent photoacoustic response, as a consequence of their random nanostructure. We theoretically and experimentally analyze the photoacoustic phenomena in DLA films and show that they can be used to create broadband air-coupled acoustic sources. These sources are inexpensive and simple to fabricate and work into the ultrasonic regime. We illustrate the device possibilities by building and testing an optically addressed acoustic phased array capable of producing virtually arbitrary acoustic intensity patterns in air.

Vortex shedding noise from a beveled trailing edge

Coherent vortex shedding from blunt and beveled trailing edges generates tonal noise, which is usually undesired. To obtain a better understanding of the noise generation under such conditions, the flow field around a beveled trailing edge was characterized for Reynolds numbers based on the bluntness ranging from 2.5 × 104 to 5.1 × 104. Flow field statistics were obtained by means of planar high-speed two-component and stereoscopic particle image velocimetry measurements. The development of the shear layers and vortex roll-up is described in the present study. Related length scales, the vortex formation length, and wake thickness parameter were derived from the measurements. Noise emission due to vortex shedding was predicted from an analytic solution, derived from diffraction theory and the reversed Sears’ problem, and compared to acoustic phased array measurements. This approach has previously been shown to provide accurate results for sharply truncated edges, but questions with regard to the applicability with different trailing edge geometries remained open. The prediction required the auto-spectral density, correlation length, and convective velocity of the upwash velocity component in the vortex formation region. Direct application with data obtained from particle image velocimetry measurements showed an overestimation of about 20 dB when compared to the acoustic measurements. The results thus showed that the prediction of vortex shedding noise based on the simplified wake model and diffraction theory is not generally applicable.

Numerical and experimental investigation of a beveled trailing-edge flow field and noise emission

Efficient tools and methodology for the prediction of trailing-edge noise experience substantial interest within the wind turbine industry. In recent years, the Lattice Boltzmann Method has received increased attention for providing such an efficient alternative for the numerical solution of complex flow problems. Based on the fully explicit, transient, compressible solution of the Lattice Boltzmann Equation in combination with a Ffowcs-Williams and Hawking aeroacoustic analogy, an estimation of the acoustic radiation in the far field is obtained. To validate this methodology for the prediction of trailing-edge noise, the flow around a flat plate with an asymmetric 25° beveled trailing edge and obtuse corner in a low Mach number flow is analyzed. Flow field dynamics are compared to data obtained experimentally from Particle Image Velocimetry and Hot Wire Anemometry, and compare favorably in terms of mean velocity field and turbulent fluctuations. Moreover, the characteristics of the unsteady surface pressure, which are closely related to the acoustic emission, show good agreement between simulation and experiment. Finally, the prediction of the radiated sound is compared to the results obtained from acoustic phased array measurements in combination with a beamforming methodology. Vortex shedding results in a strong narrowband component centered at a constant Strouhal number in the acoustic spectrum. At higher frequency, a good agreement between simulation and experiment for the broadband noise component is obtained and a typical cardioid-like directivity is recovered.