Directivity and Excitability of Ultrasonic Shear Waves Using Piezoceramic Transducers-Numerical Modeling and Experimental Investigations.

In this paper, piezoceramic-based excitation of shear horizontal waves is investigated. A thickness-shear d15 piezoceramic transducer is modeled using the finite-element method. The major focus is on the directivity and excitability of the shear horizontal fundamental mode with respect to the maximization of excited shear and minimization of Lamb wave modes. The results show that the geometry of the transducer has more effect on the directivity than on the excitability of the analyzed actuator. Numerically simulated results are validated experimentally. The experimental results show that transducer bonding significantly affects the directivity and amplitude of the excited modes. In conclusion, when the selected actuator is used for shear excitation, the best solution is to tailor the transducer in such a way that at the resonant frequency the desired directivity is achieved.

Sensors Layout Optimization Design of Rocket Sled Test System.

The rocket sled, as a ground dynamic test system, combines the characteristics of the wind tunnel test and the flight test. However, some practical factors, such as shock wave interference, ground effect, and high-intensity aerodynamic noise will cause serious interference and even failure of the uniformly distributed sensors during horizontal sliding in a wide speed range. The AGARD HB-2 standard model is employed as the payload to simulate the aerodynamic and aeroacoustic characteristics during the variable acceleration period, aiming to optimize the test sensors layout. It is observed that in the high Mach number flow fields, strong coupling behaviors among complex waves will occur. The peak of wake vortex strength will appear at 1.5 s and gradually diminish over time. In addition, when the vortex between the load and the booster is monitored, its position shifts forward in the subsonic stage, then gradually moves backward and expands in the supersonic stage. Acoustic directivity is pronounced at subsonic and transonic speeds, pointing towards 75° and 135° relative to the sliding speed, respectively. These results can provide technical support for sensor layout and high-precision testing in rocket sled tests.

Vectorized facial skin tightening: A study on the Thermal Thread Technique™ utilizing high-intensity, high-frequency, parallel ultrasound beam.

BACKGROUND: Facial skin tightening with wrinkle/fine line reduction is a highly demanded procedure in the aesthetic field. Although there are studies focused on the types of energy sources, the total amount of thermal energy, and the affected depth, there have been no reports examining the relationship between the shape of thermal energy and the directivity of skin tightening. We have developed a specific method to apply thermal energy to the dermis in continuous parallel lines, resembling a thread, perpendicular to the Relaxed Skin Tension Lines (RSTL) for vectorized collagen contraction using synchronous ultrasound parallel beam technology. OBJECTIVE: To evaluate the safety, tightening capability, and directivity of the Thermal Thread Technique™ utilizing a high-intensity, high-frequency, parallel ultrasound beam. MATERIALS AND METHODS: A total of 34 cases, both males and females aged between 30 and 70 years with Fitzpatrick skin types 2-4, exhibiting mild to moderate skin laxity, participated. All subjects received one treatment using the Thermal Thread Technique™ utilizing high-intensity, high-frequency parallel ultrasound beam to cover the full face and submental area. 3D clinical images were captured before, 8 weeks, and 24 weeks after the treatment. A quantitative image analysis of captured 3D images was performed to objectively measure the direction and distance of contraction. RESULTS: The average contraction distance from baseline (0 mm) to 8 weeks and 24 weeks posttreatment were 1.91 ± 0.61 mm (p < 0.001) and 1.96 ± 0.67 mm (p < 0.001) respectively. Regarding the contraction direction at 24 weeks posttreatment, the angle formed between the contraction direction and the base axis, which is perpendicular to the RSTL, was + 9.85° ± 32.94°. Out of 34 cases, 28 met the criteria with the angle within ±22.5° of the base axis (p < 0.001). The average pain score on a 0-5 scale (0 being no pain, and 5 being maximum pain) was 2.63 ± 0.78. No side effects were reported during the treatment or observation period. CONCLUSION: The Thermal Thread Technique™ utilizing a high-intensity, high-frequency, parallel ultrasound beam was proven to be clinically safe and effective for vectorized facial skin tightening.

Reconstruction and validation of ground motions across dip-slip faults: an application to response analysis of a long-span suspension bridge.

Recent seismic events have unequivocally highlighted the susceptibility of fault-crossing bridges to the synergistic effects of ground surface vibrations on either side of the fault plane and the tectonic dislocations arising from fault-induced surface ruptures. This study delineates both seismic and parametric response analyses of fault-crossing suspension bridges, employing a straightforward yet efficacious method for simulating desired ground motions near fault-rupture zones. Herein, we introduce a user-friendly method to incorporate predicted fault-induced displacements, accounting for both fling-step and directivity effects, into processed ground motion chronologies, enabling the generation of dip-slip fault ground motions. The accuracy and efficacy of the proposed method are affirmed by juxtaposing the generated ground motions with the observed ones (MGM). An exhaustive parametric analysis, addressing factors like fault-crossing location, fault-crossing angle, and frequency components of fault-crossing ground motions, of a suspension bridge over a rupture fault, is executed using the fashionable ANSYS software. This study provides clear and specific guidelines for the seismic design of suspension bridges traversing rupture faults.

Finite element modelling strategy for determining directivity of thermoelastically generated laser ultrasound.

Laser ultrasound (LU) is a contactless and couplant-free remote non-destructive (NDE) technique, which uses lasers for ultrasonic generation and detection rather than conventional piezoelectric transducers. For a transducer, an important characteristic is the directivity, the angle-dependent amplitude of the ultrasonic waves generated in the material. In the non-destructive thermoelastic regime, LU source has been widely modelled as a surface force dipole. However, the directivity of LU in more complex material, where there is an increasing demand for NDE, such as carbon fibre reinforced plastic (CFRP), is yet to be understood. In the current paper, a finite element (FE) modelling methodology to obtain the directivity of LU in complex material is presented. The method is applied to a conductive isotropic material (aluminium, Al) for validation against an existing analytical solution and then applied to a heterogeneous anisotropic material (carbon-fibre reinforced plastic, CFRP). To get the directivity of a specific wave mode, the signal for that mode needs to be resolved in time from other modes at all angles. This is challenging for shear (S) waves in a small model domain due to the head wave, so a technique for suppressing the head wave is shown. The multi-physics model solves for thermal expansion, which models the laser source as a surface heat flux for the Al case, and a buried heat source for the CFRP case, according to where the energy is deposited in the material. The same ultrasound generation pattern can be obtained by using a suitable pure elastodynamic loading, which is shown to be a surface force dipole as per the validation case for Al, and a buried quadrupole for the CFRP case. The modelled directivities are scaled and fitted to experimental measurements using maximum likelihood, and the goodness of fit is discussed. For the Al case, the S wave is preferred over the longitudinal (L) wave for inspection due to greater signal amplitude. For the CFRP case, the quasi-longitudinal (qL) wave in CFRP shows a maximum amplitude directly below the source, and has a greater amplitude than the quasi-shear (qS) wave, suggesting a better choice for inspection.

Shape-Configurable MXene-Based Thermoacoustic Loudspeakers with Tunable Sound Directivity.

Film-type shape-configurable speakers with tunable sound directivity are in high demand for wearable electronics. Flexible, thin thermoacoustic (TA) loudspeakers-which are free from bulky vibrating diaphragms-show promise in this regard. However, configuring thin TA loudspeakers into arbitrary shapes is challenging because of their low sound pressure level (SPL) under mechanical deformations and low conformability to other surfaces. By carefully controlling the heat capacity per unit area and thermal effusivity of an MXene conductor and substrates, respectively, it fabricates an ultrathin MXene-based TA loudspeaker exhibiting high SPL output (74.5 dB at 15 kHz) and stable sound performance for 14 days. Loudspeakers with the parylene substrate, whose thickness is less than the thermal penetration depth, generated bidirectional and deformation-independent sound in bent, twisted, cylindrical, and stretched-kirigami configurations. Furthermore, it constructs parabolic and spherical versions of ultrathin, large-area (20 cm × 20 cm) MXene-based TA loudspeakers, which display sound-focusing and 3D omnidirectional-sound-generating attributes, respectively.

Development of Split Ring Resonator Shaped Six Element 2 × 3 Multiple Input Multiple Output Antenna for the C/X/Ku/K Band Applications.

In this manuscript, we have numerically investigated and experimentally verified the six-element split ring resonator and circular patch-shaped multiple input, multiple output antenna operating in the 1-25 GHz band. MIMO antennas are analyzed in terms of several physical parameters, such as reflectance, gain, directivity, VSWR, and electric field distribution. The parameters of the MIMO antenna, for instance, the envelope correlation coefficient (ECC), channel capacity loss (CCL), the total active reflection coefficient (TARC), directivity gain (DG), and mean effective gain (MEG), are also investigated for identification of a suitable range of these parameters for multichannel transmission capacity. Ultrawideband operation at 10.83 GHz is possible for the theoretically designed and practically executed antenna with the return loss and gain values of -19 dB and -28 dBi, respectively. Overall, the antenna offers minimum return loss values of -32.74 dB for the operating band of 1.92 to 9.81 GHz with a bandwidth of 6.89 GHz. The antennas are also investigated in terms of a continuous ground patch and a scattered rectangular patch. The proposed results are highly applicable for the ultrawideband operating MIMO antenna application in satellite communication with C/X/Ku/K bands.

Directivity of quasi-SH0 modes in cubic anisotropic media.

We studied the zeroth order shear horizontal modes (SH0 modes) and the quasi-SH0 modes in cubic-anisotropic plates and proposed a formula to describe the scattering directivity of these guided wave modes in arbitrary directions. The quasi-SH0 waves has many unique advantages. However, their velocity and amplitude are influenced by the material anisotropy and change with incidence orientation. In our finding, when the guided wave incidence orientation coincides with the material symmetry plane, the quasi-SH0 modes' amplitudes generated by a uniform force are approximately equal. Otherwise, the amplitudes are significantly smaller. The formula derived by reciprocity consideration explains this phenomenon. We applied the formula to monocrystalline silicon. The results also show that the quasi-SH0 mode is both velocity non-dispersive and directivity non-dispersive in low-fd (frequency thickness product) state. We established an experimental system based on EMATs and verified the theoretical predictions. This paper completes the theoretical basis for damage reconstruction and acoustic imaging by guided waves in complex structures with cubic anisotropy.

Ultrasound computed tomography based on full waveform inversion with source directivity calibration.

Ultrasound computed tomography based on full waveform inversion has the potential to provide high-resolution images of human tissues in a quantitative manner. A successful ultrasound computed tomography system requires the decent knowledge of acquisition array, including the spatial position and the directivity of each transducer, to meet the high-level demand of clinical applications. The conventional full waveform inversion algorithm assumes a point source with the omni-directional emission. Such assumption does not hold when the directivity of emitting transducer is not negligible. For a practical implementation, an efficient and accurate self-checking evaluation of directivity is crucial prior to the reconstruction of images. We propose to measure the directivity of each emitting transducer using the full-matrix captured data obtained with a water-immersed and target-free experiment. We introduce the weighted virtual point-source array to act as the proxy of emitting transducer during the numerical simulation. The weights of different points in the virtual array can be calculated from the observed data using the gradient-based local optimization method. Although the full waveform imaging method relies on the finite-difference solver of wave equation, such directivity estimation benefits from the introduction of analytical solver. The trick significantly reduces the numerical cost, enabling an automatic directivity self-check at boot. We verify the feasibility, efficiency, and accuracy of the virtual array method through simulated and experimental tests. For the experimental test, we also illustrate that full waveform inversion with directivity calibration can reduce the artifacts introduced by the conventional point source assumption, improving the quality of reconstructed images..

Design and Fabrication of Compact, Multiband, High Gain, High Isolation, Metamaterial-Based MIMO Antennas for Wireless Communication Systems.

We proposed a novel approach based on a complementary split-ring resonator metamaterial in a two-port MIMO antenna, giving high gain, multiband results with miniature size. We have also analyzed a circular disk metasurface design. The designs are also defected using ground structure by reducing the width of the ground plane to 8 mm and etching all other parts of the ground plane. The electric length of the proposed design is 0.5λ × 0.35λ × 0.02λ. The design results are also investigated for a different variation of complementary split-ring resonator ring sizes. The inner and outer ring diameters are varied to find the optimized solution for enhanced output performance parameters. Good isolation is also achieved for both bands. The gain and directivity results are also presented. The results are compared for isolation, gain, structure size, and the number of ports. The compact, multiband, high gain and high isolation design can apply to WiMAX, WLAN, and satellite communication applications.

Design and Fabrication of a Low-Cost, Multiband and High Gain Square Tooth-Enabled Metamaterial Superstrate Microstrip Patch Antenna.

The manuscript represents a novel square tooth-enabled superstrate metamaterial loaded microstrip patch antenna for the multiple frequency band operation. The proposed tooth-based metamaterial antenna provides better gain and directivity. Four antenna structures are numerically investigated for the different geometry of the patch and tooth. These proposed structures are simulated, fabricated, measured, and compared for the frequency range of 3 GHz to 9 GHz. The electrical equivalent model of the split-ring resonator is also analyzed in the manuscript. The comparative analysis of all of the proposed structures has been carried out, in terms of several bands, reflectance response, VSWR, gain and bandwidth. The results are compared with previously published works. The effects are simulated using a high-frequency structure simulator tool with the finite element method. The measured and fabricated results are compared for verification purposes. The proposed structure provides seven bands of operation and 8.57 dB of gain. It is observed that the proposed design offers the multiple frequency band operation with a good gain. The proposed tooth-based metamaterial antenna suits applications, such as the surveillance radar, satellite communication, weather monitoring and many other wireless devices.

Automated identification and assessment of environmental noise sources.

Noise pollution is one of the major health risks in urban life. The approach to measurement and identification of noise sources needs to be improved and enhanced to reduce high costs. Long measurement times and the need for expensive equipment and trained personnel must be automated. Simplifying the identification of main noise sources and excluding residual and background noise allows more effective measures. By spatially filtering the acoustic scene and combining unsupervised learning with psychoacoustic features, this paper presents a prototype system capable of automated calculation of the contribution of individual noise sources to the total noise level. Pilot measurements were performed at three different locations in the city of Ljubljana, Slovenia. Equivalent sound pressure levels obtained with the device were compared to the results obtained by manually marking individual parts of each of the three measurements. The proposed approach correctly identified the main noise sources in the vicinity of the measurement points.

Stepped-Tube Backside Cavity Piezoelectric Ultrasound Transducer Based on Sc0.2AI0.8N Thin Films.

This paper presents a novel piezoelectric micromachined ultrasonic transducer (PMUT) with theoretical simulation, fabrication, and testing. Conventional methods using a PCB or an external horn to adjust the PMUT acoustic field angle are limited by the need for transducer size. To address this limitation, the stepped-tube (expanded tube) backside cavity PMUT has been proposed. The stepped-tube PMUT and the tube PMUT devices have the same membrane structure, and the acoustic impedance matching of the PMUT is optimized by modifying the boundary conditions of the back cavity structure. The acoustic comparison experiments show that the average output sound pressure of the stepped-tube backside cavity PMUT has increased by 17%, the half-power-beam-width (θ-3db) has been reduced from 55° to 30° with a reduction of 45%, and the side lobe level signal is reduced from 147 mV to 66 mV. In addition, this work is fabricated on an eight-inch wafer. The process is compatible with standard complementary metal oxide semiconductor (CMOS), conditions are stable, and the cost is controllable, plus it facilitates the batch process. These conclusions suggest that the stepped-tube backside cavity PMUT will bring new, effective, and reliable solutions to ranging applications.

Design of Longitudinal-Torsional Transducer and Directivity Analysis during Ultrasonic Vibration-Assisted Milling of Honeycomb Aramid Material.

This paper presents a longitudinal-torsional transducer for use during the ultrasonic vibration-assisted milling (UVAM) of honeycomb aramid material. The mechanism of longitudinal-torsional conversion was analyzed to guide the design of a vibration transducer. The transducer features five spiral grooves around the front cover plate, which function under the excitation of a group of longitudinal piezoelectric ceramics. A portion of the longitudinal vibration was successfully converted into torsional vibration. The resonant frequency, longitudinal vibration displacement and torsional amplitude at the top of the disk milling cutter were 24,609 Hz, 19 µm and 9 µm, respectively. In addition, the directivity of the longitudinal-torsional transducer was theoretically analyzed. Compared with conventional milling, UVAM with the longitudinal-torsional could significantly reduce the cutting force (40-50%) and improve the machining stability.

A High Gain Embedded Helix and Dielectric Rod Antenna with Low Side Lobe Levels for IoT Applications.

In this paper, a novel embedded helix dielectric rod antenna is presented for high gain radiation with circular polarization (CP) and low side lobe levels for IoT Applications. Different from the conventional dielectric rod antennas, this proposed antenna is an integrated structure that combines the advantages of the helix and dielectric rod antennas. The presented antenna mainly consists of three parts: a tapered helix as primary feeding for CP, a dielectric rod with printed loops embedded for higher directivity, and a dielectric rod end for improving the gain further. After studying and analyzing the working principles of each part, an optimum design operating at 8-9.7 GHz is carried out as an example. A prototype is also fabricated and tested. The measured results show that the prototype can provide 18.41 dB maximum gain within the length of 7.7 λ. The side lobe level is below -20 dB, and the axial ratio is better than 1.14 dB in the whole frequency band. Compared with the traditional helix antenna and dielectric rod antenna with the same electric length, the presented antenna has a higher gain with a lower side lobe level and with good polarization purity.

Directivity Dependence of a Distributed Fiber Optic Hydrophone on Array Structure.

A distributed fiber optic hydrophone (DFOH) is a new type of fiber optic hydrophone (FOH) with adjustable structure. The dependence of the directivity of a DFOH on array structure is theoretically and experimentally studied. The directivity function of a sensing channel and that of a DFOH are derived. Based on the directivity function, the simulations are performed. Finally, the theoretical analysis is demonstrated by the experiments performed on Qingyang lake, and the results reveal that the longer sensing channel length guarantees the lower first-order side lobe and the narrower main lobe. As the channel length increased from 1 to 3, the main lobe width and first-order side lobe height decreased by 4.9° and 6 dB, respectively. In addition, channel spacing is irrelevant to directivity as the spacing is shorter than the wavelength. As the channel spacing increased from 0 to 1, the variations of the main lobe width and first-order side lobe height are lower than 0.5° and 0.94 dB, respectively. This study would provide guidance for the structure design of a distributed fiber optic hydrophone in signal processing.

Analysis of the directivity of longitudinal waves based on double-fold coil phased EMAT.

Longitudinal critically refracted (LCR) waves have already been widely applied for residual stress characterization. Such waves are usually generated using mode-conversion at the first critical angle of the incident longitudinal wave, which gives waves that then propagate at a dip-angle, and this places energy close to the surface of the specimen. The dip-angle needs to be minimized to improve both velocity measurement and residual stress characterization sensitivity. This paper reports a novel double-fold coil phased EMAT that can decrease the dip-angle. The performance of this new EMAT was investigated using both a COMSOL model and experiments. Initial model validation was provided through a comparison with experimental data. The EMAT design also enables scanning of samples, and operation in harsh environments where use of a PZT based transducer and couplants can complicate and limit inspection. The use of the EMAT has the potential to give more accurate time of flight (TOF) data and enhances the reliability and accuracy for residual stress measurement.

Carbon emission efficiency network formation mechanism and spatial correlation complexity analysis: Taking the Yangtze River Economic Belt as an example.

The spatial correlation of carbon emissions poses new challenges to constructing ecological civilisation and sustainable development in the Yangtze River Economic Belt. This study explains the formation mechanism of the carbon emission efficiency network and attempts to explore its structural complexity and spatial directivity. It focuses on the carbon emission efficiency network's structural entropy, node efficiency, hierarchy, connection symmetry, and transmission characteristics. The main conclusions are as follows: (1) The carbon emission efficiency of the Yangtze River Economic Belt has significantly improved, and the gap between cities is narrowing, but there is gradient differentiation on the provincial spatial scale that exhibits a strong Matthew effect; (2) There is an imbalance in carbon emission efficiency, which is primarily reflected in spatial distribution and hierarchical structure. Low-efficiency cities have played an important role in promoting the spatial evolution of carbon emission efficiency in the Yangtze River Economic Belt, but they have not completely changed the imbalance in carbon emission efficiency; (3) Supporting sub-networks and basic sub-networks have emerged as critical groups in promoting the complexity of carbon emission efficiency network structures, and have formed distinctive network structures in different basins of the Yangtze River; (4) The overall convergence of the carbon emission efficiency network has improved, and it exhibits preference attachment characteristics. The connection symmetry has been reduced from 5 to 7 times to 1 to 3 times, and the situation of unilateral unequal connection has been alleviated. Finally, this study puts forward some policy suggestions to improve carbon emission efficiency from the aspects of low-carbon technology research and development and carbon emission rights market construction.

On the selection of the number of beamformers in beamforming-based binaural reproduction.

In recent years, spatial audio reproduction has been widely researched with many studies focusing on headphone-based spatial reproduction. A popular format for spatial audio is higher order Ambisonics (HOA), where a spherical microphone array is typically used to obtain the HOA signals. When a spherical array is not available, beamforming-based binaural reproduction (BFBR) can be used, where signals are captured with arrays of a general configuration. While shown to be useful, no comprehensive studies of BFBR have been presented and so its limitations and other design aspects are not well understood. This paper takes an initial step towards developing a theory for BFBR and develops guidelines for selecting the number of beamformers. In particular, the average directivity factor of the microphone array is proposed as a measure for supporting this selection. The effect of head-related transfer function (HRTF) order truncation that occurs when using too many beamformer directions is presented and studied. In addition, the relation between HOA-based binaural reproduction and BFBR is discussed through analysis based on a spherical array. A simulation study is then presented, based on both a spherical and a planar array, demonstrating the proposed guidelines. A listening test verifies the perceptual attributes of the methods presented in this study. These results can be used for more informed beamformer design for BFBR.

Optimizing Radiation Patterns of Thinned Arrays with Deep Nulls Fixed through Their Representation in the Schelkunoff Unit Circle and a Simulated Annealing Algorithm.

The present work develops an innovative methodology for fixing deep nulls in radiation patterns of symmetrical thinned arrays while maintaining a low side lobe level (SLL) and a high directivity, implementing an optimization strategy based on the simulated annealing algorithm (SA). This procedure optimizes a cost function that has a term for each characteristic of the desired radiation pattern and can distinguish between the deep nulls and the filled ones depending on whether they are on the Schelkunoff unit circle or not. Then, a direct extension of the methodology for planar arrays based on the separable distribution procedure is addressed. Consequently, some examples with half-wavelength spacing are presented, where the fixing of one, two, or three deep nulls in arrays of 40, 60, and 80 elements are illustrated as well as an extension to a 40 × 40-element planar array with rectangular grid and rectangular boundary, with two deep nulls fixed on each one of its main axes. Additionally, a comparison of the obtained results with a genetic algorithm (GA) alternative is performed. The main advantage of the proposed method is its ability to fix deep nulls in the radiation patterns, while maintaining an easy feeding network implementation.