Rectangular Transducer Research Articles

Guided elastic wave propagation in elastic metamaterial plate with periodic array of interfacial crack-like voids

Abstract A special kind of elastic metamaterials with periodic unit-cells composed of two layers with internal crack-like voids situated at the interfaces between two neighboring sub-layers is studied. To investigate experimentally guided waves propagation in EMMs with arrays of voids, several specimens with periodic arrays of crack-like voids have been manufactured using additive manufacturing techniques. The elastic waves have been excited by a rectangular piezoelectric transducer bonded at the surface of the specimen, while the wave-fields on the surface of the EMM specimen are measured by a laser Doppler vibrometer. The dispersion characteristics are investigated using the matrix pencil method and band-gaps are observed experimentally.

The Acoustic Field Distribution Inside the Ultrasonic Ring Array

This paper presents and analyses the results of a simulation of the acoustic field distribution in sectors of a 1024-element ring array, intended for the diagnosis of female breast tissue with the use of ultrasonic tomography. The array was tested for the possibility to equip an ultrasonic tomograph with an additional modality - conventional ultrasonic imaging with the use of individual fragments (sections) of the ring array. To determine the acoustic field for sectors of the ring array with a varying number of activated ultrasonic transducers, a combined sum of all acoustic fields created by each elementary transducer was calculated. By the use of MATLAB software, a unique algorithm was developed, for a numerical determination of the distribution of pressure of an ultrasonic wave on any surface or area of the medium generated by the concave curvilinear structure of rectangular ultrasound transducers with a geometric focus of the beam. The analysis of the obtained results of the acoustic field distribution inside the ultrasonic ring array used in tomography allows to conclude that the optimal number of transducers in a sector enabling to obtain ultrasound images using linear echographic scanning is 32 ≤ $n$ ≤ 128, taking into account that due to an increased temporal resolution of ultrasonic imaging, this number should be as low as possible.

A Correction Method for the Measurement of Frequency-Dependent Attenuation Coefficient With Curved Surface Specimens Using Normal Contact Transducer

The ultrasonic pulse-echo technique has been widely employed for the measurement of the frequency-dependent attenuation coefficient in polycrystalline metals. However, the nonuniform thickness of the coupling layer between the transducer piston and the curved surface is inevitable for curved specimens, resulting in a significant overestimation. In addition, the curved surface also affects the diffraction loss caused by the divergence and convergence of ultrasonic beams during the propagation path. In this study, a correction method is proposed for the experimental calculation of the frequency-dependent attenuation with the curved surface components using a contact transducer. First, with the analysis of the nonuniform coupling layer created by the curved surface and transducer piston, the integral over the effective cross-sectional area is introduced to determine the reflection coefficient. Second, an equivalent rectangular transducer sound field model is proposed to calculate the diffraction loss for different curvatures and propagation distances based on the multi-Gaussian beam (MGB) theory. Then, a correction model is established to compensate for the deviation caused by the curved surfaces. To verify the feasibility of the proposed method, two cylindrical bars and five blanks with different curvatures were designed. The experimental results show that the proposed correction method can effectively eliminate the deviation caused by the curved surface and improve the stability of measurement. With the correction, the variation of the attenuation spectrum for the curved specimens is reduced by approximately 5%. This facilitates researchers to better develop and use frequency-dependent attenuation coefficients of materials for further applications.

Design and Manufacturing of the Multi-Layered Metamaterial Plate with Interfacial Crack-like Voids and Experimental-Theoretical Study of the Guided Wave Propagation

A novel kind of acoustic metamaterials (AMMs) with unit cells composed of two layers made of dissimilar materials with a crack-like void situated at the interface between bars is considered. Recently, the authors showed numerically that this novel kind of AMMs can provide unidirectional propagation of guided waves. Several AMM specimens (the finite stack of periodic elastic layers with and without voids) have been manufactured using additive manufacturing techniques and regular gluing. The details of the manufacturing process are discussed. In the experiment, the elastic waves have been excited by a rectangular piezoelectric wafer active transducer bonded at the surface of the specimen. Vibrations of the opposite side of the AMM specimen are measured via a piezoelectric sensor. The band gaps are observed in the experiment and values of their width and location correlate with numerically predicted ones.

Research on the sensing performance calibration of omni-directional broadband interdigital transducer based on PVDF substrate

Structural health monitoring (SHM) is of vital importance to the detection of damage in large structures. Ultrasonic transducers used to excite and receive signals have become an important part of SHM. For the traditional PZT ultrasonic transducer, there are some shortcomings such as poor flexibility and designability. Due to the limitation of structure shape, the rectangular interdigital transducers, which are widely used in structural health monitoring, have difficulty in receiving signals in all directions and the frequency bandwidth is narrow and the detection efficiency is low. On this basis, it is proposed to use the flexible piezoelectric material PVDF as the substrate. Combined with the dispersion theory of aluminium plate and the design principle of IDT, an omni-directional flexible annular PVDF Interdigital Transducer (PVDF-IDT) is designed. The device is produced by 3D printing technology. The sensitivity, frequency response, orientation and other performances of the flexible annular PVDF-IDT are calibrated, which lays the foundation for its application in structural inspection.

Investigating atherosclerotic plaque phantoms for ultrasound therapy.

The aim of the proposed study was to conduct a feasibility study using a flat rectangular (2 × 10 mm2) transducer operating at 4.0MHz for creating thermal lesions in an arterial atherosclerotic plaque phantom. The proposed method can be used in the future for treating atherosclerotic plaques in human arteries. The flat rectangular transducer was firstly assessed in agar/silica evaporated milk phantom, polyacrylamide phantom and freshly excised turkeytissue phantom. Then, the same transducer was assessed in an arterial atherosclerotic plaque phantom which was created in the laboratory with a very low cost. The recipe of the atherosclerotic plaque phantom was 4% w/v agar, 1% w/v gypsum, 2% w/v butter and 93% water. The amount of plaque removal was evaluated visually and using an X-Ray system. It was shown that the flat rectangular transducer can create thermal lesions on the agar/silica evaporated milk phantom, polyacrylamide phantom and in excised tissue. The size of the lesions matches the geometry of the transducer. Moreover, this transducer destroyed 27.1% of the atherosclerotic plaque phantom with 8W acoustical power and 30s duration. This feasibility study demonstrated that atherosclerotic plaque can be destroyed using a very small flat rectangular (2 × 10 mm2) transducer in a very small time interval of 30s. In future clinical trials the transducer will be incorporated in a catheter which will be inserted intravascular (1-3mm) wide and can be used to treat atherosclerotic plaques in the coronary arteries.

Evaluating elongated grains with diffuse ultrasonic double scattering and rectangular transducers.

Diffuse scattering of ultrasound by the microstructure of polycrystal specimens can be used to evaluate grain size and grain elongation. The existing diffuse scattering models mostly dealt with circular transducers whose symmetrical sound field is insensitive to the asymmetric elongated grain. The sound field of a rectangular transducer provides a new perspective for acquiring additional information. First, the existing single scattering response (SSR) and double scattering response (DSR) models are modified for a rectangular transducer, where the sound field of a rectangular transducer is equivalent to that of an elliptical transducer in the far-field. Therefore, an equivalent single Gaussian beam model is derived using amplitude-equivalent and beamwidth-equivalent coefficients. Then, the spatial correlation function of elongated grains is transformed into the wavenumber domain, giving rise to the SSR and DSR of a rectangular transducer that reveals the interaction effect of an asymmetric sound field and elongated grains on ultrasonic backscattering. The experimental results show that the sizes of elongated grains in a cold-rolled aluminum are evaluated as 1086 ± 8, 90 ± 4, and 10 ± 1 μm in the x, y, and z directions, where the exact values are 1184.2 ± 11.9, 80.7 ± 5.2, and 8.3 ± 0.5 μm according to metallographic measurements.

A wideband tonpilz transducer with a transverse through-hole in the radiating head.

We propose a rectangular transverse through-hole wideband tonpilz transducer using multimode coupling. To excite a vibration mode that can be coupled with the longitudinal vibration for broadening the frequency band, a rectangular through-hole is opened at a certain distance from the front head of the conventional longitudinal vibration tonpilz transducer. To achieve the best bandwidth, the finite element method was used to optimize the length and width of the through-hole and the distance between the front end of the hole and the end surface of the front head. In addition, to obtain the best hole position and size, a prototype tonpilz transducer was developed. The test results show that the transducer has three main operating modes within 12-32.5 kHz, and the latter two modes contribute to the widening of operating bandwidth. A longitudinal vibration tonpilz transducer of the same size with no hole has a 3 dB bandwidth of only 3 kHz, whereas the holed transducer has a bandwidth of 10.5 kHz. Effectively expanding the working bandwidth shows that the theoretical calculations and experimental results are in good agreement.

Study on the bending vibration of bimorph rectangular transducer based on type 2-2 piezoelectric composites

In order to improve the acoustic radiation capability of piezoelectric ultrasonic transducer in gas, a bimorph rectangular transducer based on type 2-2 piezoelectric composites is proposed in this paper, which is composed of two piezoelectric composite rectangular slices with thickness polarization. First, the bending vibration of the rectangular transducer is divided into two bending vibrations of the thin rods in the x and y directions using the equivalent elastic method. When the mechanical coupling coefficient is introduced and combined with the anisotropic piezoelectric equations, the resonance frequency equations of the thickness-polarized transducer are derived with simply supported boundary conditions. Then the bending vibration of the transducer is numerically simulated. The results show that the resonance frequency obtained by the analytical method is in good agreement with the numerical simulation results. Finally, the influence of geometrical size and two-phase volume ratio on the bending vibration performance of the transducer is analyzed. Compared with the piezoelectric bimorph transducer, the piezoelectric composite bimorph transducer has a larger bending vibration displacement amplitude, a larger transmitting voltage response, a lower resonant frequency and better acoustic radiation capability.

Lamb Wave Scattering Analysis for Interface Damage Detection between a Surface-Mounted Block and Elastic Plate.

Since stringers are often applied in engineering constructions to improve thin-walled structures’ strength, methods for damage detection at the joints between the stringer and the thin-walled structure are necessary. A 2D mathematical model was employed to simulate Lamb wave excitation and sensing via rectangular piezoelectric-wafer active transducers mounted on the surface of an elastic plate with rectangular surface-bonded obstacles (stiffeners) with interface defects. The results of a 2D simulation using the finite element method and the semi-analytical hybrid approach were validated experimentally using laser Doppler vibrometry for fully bonded and semi-debonded rectangular obstacles. A numerical analysis of fundamental Lamb wave scattering via rectangular stiffeners in different bonding states is presented. Two kinds of interfacial defects between the stiffener and the plate are considered: the partial degradation of the adhesive at the interface and an open crack. Damage indices calculated using the data obtained from a sensor are analyzed numerically. The choice of an input impulse function applied at the piezoelectric actuator is discussed from the perspective of the development of guided-wave-based structural health monitoring techniques for damage detection.

Fast 3-D Opto-Acoustic Simulation for Linear Array With Rectangular Elements.

Simulation involves predicting the responses of a physical system. In this article, we simulate opto-acoustic signals generated in a 3-D volume due to the absorption of an optical pulse. A separable computational model is developed, which splits processing into two steps, permitting an order-of-magnitude improvement in computational efficiency over a nonseparable model. The simulated signals represent acoustic waves, measured by a probe with a linear transducer array, in a rotated and translated coordinate frame. Light is delivered by an optical source that moves with the probe's frame. Spatiotemporal impulse response for rectangular-element transducer geometry is derived using Green's function solution to the acoustic wave equation. The approach permits fast and accurate simulation for a probe with an arbitrary trajectory, which is useful for modeling freehand acquisitions. For a 3-D volume of n3 voxels, computation is accelerated by a factor of n . This may potentially have application in opto-acoustic imaging, where clinicians visualize structural and functional features of biological tissue for assessment of cancer and other diseases.

Rod drive type ultrasonic linear motor with quadruped stator

Piezoelectric motors exhibit advantages such as high force density and linear motion with simple and compact configuration compared to electromagnetic motors. Among them, an inchworm mechanism provides high holding force and thrust, and high positioning accuracy. However, the drawback is its complicated structure combining multiple transducers. On the other hand, an ultrasonic linear motor with quadruped stator can achieve the inchworm movement by using a single rectangular plate transducer, which is advantageous for miniaturization. In this study, we propose a novel ultrasonic linear motor that drives a slider rod inside the quadruped stator to realize a compact linear motion system. A prototype was fabricated and an excitation of each vibration mode and a bidirectional drive was confirmed via experiments. Maximum no-load speed of 258 mm s−1 and maximum thrust of 490 mN were obtained with total length of the stator transducer of 20 mm and its weight of 4.9 g.

Theoretical and experimental investigation of Lamb waves excited by partially debonded rectangular piezoelectric transducers

The paper proposes a new hybrid approach technique to simulate acousto-ultrasonic wave excitation and propagation due to operation of the partially debonded piezoelectric transducer attached to a plate-like structure. The semi-analytical boundary integral equation method is applied to calculate guided waves propagation in the unbounded structures and to separate different guided waves in the piezo-induced wave-fields. The obtained model is verified experimentally using the scanning laser Doppler vibrometry. Eigenfrequencies are calculated and analysed for various sizes of the transducer and for different bonding conditions between the transducer and the waveguide. The impact of the transducer’s height, size and debonding area on symmetric and antisymmetric Lamb waves excitation is analysed. The paper demonstrates that one-sided debonding of the transducer exerts intense influence on the distribution of the wave energy among the excited Lamb wave modes, while center debonding has a sizable impact only at relatively high frequencies.

Rectangular Array Electric Current Transducer with Integrated Fluxgate Sensors.

Novel rectangular yokeless current transducer with the range 400 A using 16 microfluxgate sensors around the busbar conductor is presented in this paper. Compared to yokeless transducers utilizing the differential pair of magnetic sensors, our solution has much better suppression of the external currents (lower crosstalk). Compared to industrial transducers with yoke, the new transducer has 15-times lower noise, 7-times better temperature stability, and same crosstalk. Sensor design and design of current monitoring system is presented together with the results of long-term field tests. Crosstalk error is examined in dependence on the number of the operating sensors and external current position.

Dielectric and piezoelectric properties of Pb[(Mg1/3Nb2/3)0.52(Yb1/2Nb1/2)0.15Ti0.33]O3 single-crystal rectangular plate and beam mode transducers poled by alternate current poling

The dielectric, piezoelectric and physical properties of the [001]-oriented rectangular plate and beam mode of Pb[(Mg1/3Nb2/3)0.52(Yb1/2Nb1/2)0.15Ti0.33]O3 (PMN-PYbN-PT) ternary single crystals (SC) poled by alternate current poling (ACP) were investigated. The dielectric permittivity and average piezoelectric coefficient d33 were 6800 and 2490 pC/N, respectively, for the rectangular plate sample after ACP, which were 31% and 41% larger than those of the same sample after conventional direct current poling. The highest value of d33 reached 2750 pC N−1. The dielectric loss was reduced by 31%; nevertheless, the d33 improved after ACP. The beam mode electromechanical coupling factor () was 91% by using ACP, showing the highest value among all relaxor-PT SC systems reported so far. The regular periodic stripe domains were observed in ACP samples, showing high domain wall density and uniform domain size. This work demonstrates that the high performance after ACP is an effective method of improving the relaxor-PT SC transducers.

In Vitro Superharmonic Contrast Imaging Using a Hybrid Dual-Frequency Probe

Superharmonic imaging is an ultrasound contrast imaging technique that differentiates microbubble echoes from tissue through detection of higher-order bubble harmonics in a broad frequency range well above the excitation frequency. Application of superharmonic imaging in three dimensions allows specific visualization of the tissue microvasculature with high resolution and contrast, a technique referred to as acoustic angiography. Because of the need to transmit and receive across a bandwidth that spans up to the fifth harmonic of the fundamental and higher, this imaging approach requires imaging probes comprising dedicated transducers for transmit and receive. In this work, we report on a new dual-frequency probe including two 1.7-MHz rectangular transducers positioned one on each side of a 20-MHz 256-element array. Finite element modeling-based design, fabrication processes and assembly of the transducer are described, as is integration with a high-frequency ultrasound imaging platform. Dual-frequency single-plane-wave imaging was performed with a microbubble contrast agent in flow phantoms and compared with conventional high-frequency B-mode imaging, and resolution and contrast-to-tissue ratio were quantified. This work represents an intermediate but informative step toward the development of dual-frequency imaging probes based on array technology, specifically designed for clinical applications of acoustic angiography.

Simulation and Experimental Verification for a 52 GHz Wideband Trapped Surface Wave Propagation System

Trapped surface wave (TSW) provides a flexible 2-D wireless solution when compared to existing wired and free space communications systems. This work aims to provide the theoretical guidance, supported by simulation techniques and experimental verifications, for 1) designing the wideband and highly efficient rectangular aperture TSW transducers and 2) selecting the best reactive surface impedance for high efficiency. First, a method for computing the TSW excitation efficiency is proposed for the first time and it can be applied to different kinds of reactive surface geometries and transducer apertures. Then, the relation between the TSW excitation efficiency, surface reactance, and aperture height is derived. Then, the maximum excitation efficiency, the corresponding optimal surface reactance, and aperture height are presented. Furthermore, the relation between the TSW angular coverage and aperture width is determined. These studies show that the aperture height mainly determines the TSW excitation efficiencies, while the aperture width controls the TSW angular coverage; hence, the two aperture parameters of a transducer can be independently determined. Finally, an experiment setup, based on the provided guidelines, has been built to demonstrate a 52 GHz wide 3 dB-transmission-bandwidth for high-performance communications systems.

Energy harvesting from low-frequency vibration using a shear-mode rectangular cymbal transducer with a piezoelectric array

Energy harvesting from ambient environment has become a hot topic in recent years. In this paper, a shear-mode cymbal transducer is proposed to convert vibration energy into electric energy. The harvester is composed of a piezoelectric array, two brass caps, added mass, and an aluminum plate. Shear stress is induced on the piezoelectric array under vibration due to the interaction of the caps and the aluminum plate. The harvester then produces electric power. A prototype is fabricated. The prototype exhibits a flat response at low frequency of 20 Hz -38 Hz. Under an acceleration of 1.0 g, the shear-mode device can generate a load power of 0.88×10-9 W with an optimal load resistance of 0.5 MΩ.

MRI-guided frameless biopsy robotic system with the inclusion of unfocused ultrasound transducer for brain cancer ablation.

A magnetic resonance image (MRI) guided robotic system dedicated for brain biopsy was developed. The robotic system carries a biopsy needle and a small rectangular unfocused, single element, planar ultrasonic transducer which can be potentially utilized to ablate small and localized brain cancer. The robotic device includes six computer-controlled axes. An agar-based phantom was developed which included an olive that mimics brain target. A rectangular ultrasonic transducer operated at 4MHz was used. The functionality of the robotic system was assessed by means of ultrasound imaging, MRI imaging, and MR thermometry, demonstrating effective targeting. The heating capabilities of the ultrasonic transducer were also evaluated. A functional MRI-guided robotic system was produced which can perform frameless brain biopsy. In the future, if a tumour is proven malignant, the needle can be pulled-out and a small ultrasonic transducer can be inserted to ablate the tumour.

Monitoring of Pulse Pressure and Arterial Pressure Waveform Changes during the Valsalva Maneuver by a Portable Ultrasound System.

This work presents non-invasive evaluation of the arterial blood pressure (ABP) waveform during the Valsalva maneuver. Ultrasound scanning is conducted to acquire blood flow and arterial distension signals. Motion-tolerant ultrasound measurement schemes are employed by using two wide rectangular transducers. Pulse pressure (PP) estimated at the common carotid artery is compared to that of a finger waveform measured by a volume clamping device. The changes of PP are correlated between the two measurements. A more depressed dicrotic notch during the Valsalva strain is observed, and beat-to-beat variations of PP and a pulse rate caused by respiration and baroreflex is observed during the control. This validation suggests novel opportunities to investigate the pathophysiology of cardiovascular diseases through the noninvasive ABP waveform monitoring during the stress test.