Annular Transducer Research Articles

Control of myotube orientation using ultrasonication

This study investigated a technique for controlling the orientation of C2C12-derived myotube cells using ultrasonication for future clinical applications of cultured skeletal muscle tissues. An ultrasonicating cell culture dish, comprising a plastic-bottomed culture dish and a circular glass plate (diameter, 35 mm; thickness, 1.1 mm) attached to an annular piezoelectric ultrasonic transducer (inner diameter, 10 mm; outer diameter, 20 mm; thickness, 1 mm), was constructed. A concentric resonant vibrational mode at 89 kHz was generated on the bottom of the dish, and the orientations of myotube cells were quantitatively evaluated using two-dimensional Fourier transform analysis of phase contrast microscopy images captured over a 14 × 10 mm2 area at the center of the dish. Unsonicated myotube cells grew in random directions, but ultrasonication aligned them circumferentially in the culture dish. The timing of treatment was important, with ultrasonication for 48 h before differentiation having a greater impact on myotube orientation than ultrasonication after differentiation. A larger ultrasonic vibration, with an amplitude of over 20 Vpp, resulted in significantly smaller angles of deviation in the circumferential direction than the control. Ultrasonication enhanced the expression of differentiation-related genes and the formation of aligned myotubes, suggesting that it promotes differentiation of C2C12 cells into myotubes.

An 8 mm endoscopic histotripsy array with integrated high-resolution ultrasound imaging

An 8 mm diameter, image-guided, annular array histotripsy transducer was fabricated and characterized. The array was laser etched on a 5 MHz, 1–3 dice and fill, PZT-5H/epoxy composite with a 45 % volume fraction. Flexible PCBs were used to electrically connect to the array elements using wirebonds. The array was backed with a low acoustic impedance epoxy mixture. A 3.6 by 3.8 mm, 64-element, 30 MHz phased array imaging probe was positioned in the center hole, to co-align the imaging plane with the bubble cloud produced by the therapy array. A custom 16-channel high voltage pulse generator was used to test the annular array for focal lengths ranging from 3- to 8-mm. An aluminum lens-focussed transducer with a 7 mm focal length was fabricated using the same piezocomposite and backing material and tested along with the histotripsy array. Simulated results from COMSOL FEM models were compared to measured results for low voltage characterization of the array and lens-focussed transducer. The measured transmit sensitivity of the array ranged from 0.113 to 0.167 MPa/V, while the lens-focussed transducer was 0.192 MPa/V. Simulated values were 0.160 to 0.174 MPa/V and 0.169 MPa/V, respectively. The measured acoustic fields showed a significantly increased depth-of-field compared the lens-focussed transducer, while the beamwidths of the array focus were comparable to the lens. The measured cavitation voltage in water was between 254 V and 498 V depending on the focal length, and 336 V for the lens-focussed transducer. The array had a lower cavitation voltage than the lens-focussed transducer for a comparable operating depth. The histotripsy array was tested in a tissue phantom and an in vivo rat brain. It was used to produce an elongated lesion in the brain by electronically steering the focal length from 3- to 8-mm axially. Real time ultrasound imaging with a Doppler overlay was used to target the tissue and monitor ablation progress, and histology confirmed the targeted tissue was fully homogenized.

A general structural design method, dynamics modeling and application study for built-in sandwich annular traveling wave piezoelectric transducers

This study first summarized a piezoelectric excitation source arrangement guideline for sandwich annular traveling wave transducers, which can excite ideal traveling waves for driving while ensuring consistent circumferential stiffness of the annular transducer. Consequently, a general structural design method was proposed for annular sandwich traveling wave piezoelectric transducers operating with out-of-plane traveling waves based on the above-mentioned arrangement guideline. Moreover, to study the vibration characteristics of the designed transducer based on the proposed method, an electromechanical coupled dynamics model was developed using the dynamic substructure method combined with the Lagrange equation. This model is universal and has guiding significance for the design and optimization of the same type of annular traveling wave piezoelectric transducers. Thereafter, the feasibility of the transducer structure design method and the correctness of the developed dynamics model were verified through appropriate vibration measurement experiments on the transducer prototype. The measured ideal mode shape and regular elliptical motion verified the feasibility of the transducer design method, and the comparison between the vibration measurement and theoretical model calculation results confirmed the correctness of the developed dynamic model. Finally, an application study of the proposed built-in sandwich traveling wave transducer was conducted to investigate its driving characteristics. The proposed transducer was used to drive a rotor to build a traveling wave piezoelectric motor. In addition, output performance experiments of the motor prototype were conducted. The experimental results indicated that under the driving conditions of 300 N pre-pressure, 500 Vpp voltage, and 19 kHz exciting frequency, the no-load speed of the motor was 19.04 RPM, its stall torque was 1.2 N·m, the maximum output power of the entire machine reached 0.6453 W, and its maximum output efficiency was 15.87%. Moreover, the normal operation of the rotating motor further verified the feasibility of the transducer structure design approach and the reliability of the drive application. The structural design method and the corresponding dynamic model proposed in this study are expected to have important guiding significance for the design and optimization of sandwich-type annular traveling wave transducers. Furthermore, the application investigation in this study provides a typical example for the traveling wave transducer.

Arbitrary variable thickness annular piezoelectric ultrasonic transducer based on transfer matrix method

The variable thickness annular radial piezoelectric ultrasonic transducer can realize impedance transformation and energy concentration, has the advantages of large radiation area and full directivity, and is widely used in power ultrasound, underwater acoustic and other fields. Because solving complex variable thickness metal ring radial vibration wave equation is more difficult, in this paper, the radial vibration of metal rings with variable thickness is transformed into the superposition of the radial vibrations of N metal rings with equal thickness by using the transfer matrix method. The equivalent circuit diagram, the resonance frequency equation and the expression of the displacement amplification coefficient of the radial vibration of the metal thin ring with arbitrary thickness are obtained. The relationship between the displacement amplification coefficient and the geometric size of the cone, power function, exponential and catenary metal rings is analyzed. On this basis, the equivalent circuit and resonance frequency equation of radial vibration of piezoelectric ultrasonic transducer which is composed of a metal ring with variable thickness and a piezoelectric ring with equal thickness are derived. In order to verify the correctness of the theoretical results, the finite element software is used in simulation, and the numerical solutions of the first and second order resonance frequency and displacement amplification coefficients are in good agreement with the theoretical solutions. In this paper, the universal solution of radial vibration of metal ring with arbitrary variable thickness is given, which provides theoretical guidance for designing and optimizing the radial piezoelectric ultrasonic transducers.

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.

Recursive algorithm for solving the axial acoustic radiation force exerted on rigid spheres at the focus of acoustic vortex beams

The trapping capability of focused acoustic vortex (FAV) beams along the radial and axial directions has significant potential in biomedical applications. However, analyses based on the acoustic gradient force are only applicable to tiny particles when acoustic scattering is neglected, and the ideal Bessel beams are still difficult to implement in experiments. In the present work, the axial acoustic radiation force (A-ARF) exerted on objects at the focus for FAV beams is calculated based on an annular spherical transducer with a continuous phase spiral. Through a partial wave series expansion, a recursive algorithm based on acoustic scattering is proposed to calculate the acoustic field for FAV beams with arbitrary order. The A-ARF distributions exerted on rigid spheres with respect to k0a (the product of the wave number and the sphere radius) are simulated. The results demonstrate that the A-ARF created by on-axis acoustic reflection is mainly manifested as a pushing force for FAV beams of all orders. The pulling force produced by off-axis scattering is more likely to be exerted on spheres with a smaller k0a in higher-order FAV beams constructed by narrower transducers. The A-ARF generated by a ring-array of sectorial transducers with more than 16 sources can be estimated from the equivalent result produced by the continuous model. The favorable results demonstrate the validity of the recursive algorithm for solving the A-ARF of FAV beams and the feasibility of experimental ring-arrays of spherical sources, suggesting the potential for the application of dual-directional object manipulation in biomedical fields.

Multielement Ring Array Based on Minute Size PMUTs for High Acoustic Pressure and Tunable Focus Depth.

This paper presents a multielement annular ring ultrasound transducer formed by individual high-frequency PMUTs (17.5 MHz in air and 8.7 MHz in liquid) intended for high-precision axial focalization and high-performance ultrasound imaging. The prototype has five independent multielement rings fabricated by a monolithic process over CMOS, allowing for a very compact and robust design. Crosstalk between rings is under 56 dB, which guarantees an efficient beam focusing on a range between 1.4 mm and 67 µm. The presented PMUT-on-CMOS annular array with an overall diameter down to 669 µm achieves an output pressure in liquid of 4.84 kPa/V/mm2 at 1.5 mm away from the array when the five channels are excited together, which is the largest reported for PMUTs. Pulse-echo experiments towards high-resolution imaging are demonstrated using the central ring as a receiver. With an equivalent diameter of 149 µm, this central ring provides high receiving sensitivity, 441.6 nV/Pa, higher than that of commercial hydrophones with equivalent size. A 1D ultrasound image using two channels is demonstrated, with maximum received signals of 7 mVpp when a nonintegrated amplifier is used, demonstrating the ultrasound imaging capabilities.

Varifocal optical lens using ultrasonic vibration and thixotropic gel.

A variable focus optical lens using a thixotropic gel and ultrasonic vibration is discussed. The surface profile of the gel could be deformed via acoustic radiation force generated by ultrasound. A thixotropic gel in which the viscosity was changed by shear stress was employed as a transparent lens material. The thixotropic gel allowed the lens to maintain shape deformation in the absence of continuous ultrasound excitation. The lens had a simple structure with no mechanical moving parts and included an annular piezoelectric transducer, a glass disk, and the thixotropic gel film. The axisymmetric concentric flexural vibration mode was generated on the lens at 71 kHz, which resulted in static surface deformation of the gel via the acoustic radiation force. The preservation rate was investigated after switching off the ultrasonic excitation. There was a trade-off between the preservation rate of the lens deformation and the response time for focusing. The focal length could be controlled via the input voltage to the lens, and a variable-focus convex lens could be realized; the change in the focal length with 4.0 Vpp was 0.54 mm. The optical transmittance of the lens was measured and the transmittance ranged 70%-80% in the visible spectral region.

Optimal Design of Annular Phased Array Transducers for Material Nonlinearity Determination in Pulse–Echo Ultrasonic Testing

Nonlinear ultrasound has been proven to be a useful nondestructive testing tool for micro-damage inspection of materials and structures operating in harsh environment. When measuring the nonlinear second harmonic wave in a solid specimen in the pulse–echo (PE) testing mode, the stress-free boundary characteristics brings the received second harmonic component close to zero. Therefore, the PE method has never been employed to measure the so-called “nonlinear parameter (β)”, which is used to quantify the degree of micro-damage. When there are stress-free boundaries, a focused beam is known to improve the PE reception of the second harmonic wave, so phased-array (PA) transducers can be used to generate the focused beam. For the practical application of PE nonlinear ultrasonic testing, however, it is necessary to develop a new type of PA transducer that is completely different from conventional ones. In this paper, we propose a new annular PA transducer capable of measuring β with improved second harmonic reception in the PE mode. Basically, the annular PA transducer (APAT) consists of four external ring transmitters and an internal disk receiver at the center. The focused beam properties of the transducers are analyzed using a nonlinear sound beam model which incorporates the effects of beam diffraction, material attenuation, and boundary reflection. The optimal design of the APAT is performed in terms of the maximum second harmonic reception and the total correction close to one, and the results are presented in detail.

Pulling force of acoustic-vortex beams on centered elastic spheres based on the annular transducer model**Project supported by the National Natural Science Foundation of China (Grant Nos. 11934009, 11974187, and 11604156).

To solve the difficulty of generating an ideal Bessel beam, an simplified annular transducer model is proposed to study the axial acoustic radiation force (ARF) and the corresponding negative ARF (pulling force) exerted on centered elastic spheres for acoustic-vortex (AV) beams of arbitrary orders. Based on the theory of acoustic scattering, the axial distributions of the velocity potential and the ARF for AV beams of different orders generated by the annular transducers with different physical sizes are simulated. It is proved that the pulling force can be generated by AV beams of arbitrary orders with multiple axial regions. The pulling force is more likely to exert on the sphere with a smaller k0a (product of the wave number and the radius) for the AV beam with a bigger topological charge due to the strengthened off-axis acoustic scattering. The pulling force decreases with the increase of the axial distance for the sphere with a bigger k0a. More pulling force areas with wider axial regions can be formed by AV beams using a bigger-sized annular transducer. The theoretical results demonstrate the feasibility of generating the pulling force along the axes of AV beams using the experimentally applicable circular array of planar transducers, and suggest application potentials for multi-position stable object manipulations in biomedical engineering.

Coupling of electroelastic dynamics and direct contact ultrasonic drying formulation for annular piezoelectric bimorph transducers

A newly developed technique for drying clothes without thermal energy has been developed through the utilization of ultrasonic vibrations from piezoelectric transducers. The novel technique incorporates the actuation of a thin stainless steel disk in contact with wet fabric via annular piezoelectric rings, where water in the liquid form is atomized, transported through microchannels in the disk, and ejected as a mist. In such a system, resonance matching between the actuation portion of the transducer and the portion contacting fabric must be realized, with theoretical results from the developed electromechanical model showing a reduction in energy consumption by 50% when resonance matching is achieved. The electrically coupled distributed parameter model for an annular bimorph piezoelectric transducer is developed for optimization of ultrasonic drying technology. The thickness mode vibrations are shown to dominate the behavior of the system, where the analytically developed model can be optimized to increase the output acceleration of the transducer, thus increasing drying performance. The electromechanical equation developed will be connected to the drying rates of fabrics in contact with said vibrations, where the novelty of the coupled equations and its description of the physics of ultrasonic drying will be discussed.

Corrosion monitoring of the reinforced concrete by using the embedded annular piezoelectric transducer

It is an important issue to ensure the long-term reliable service of the reinforced concrete structures by developing effective online monitoring techniques. In this paper, three different accelerated corrosion experiments were conducted by using the electrochemical method, and the ultrasonic pitch-catch and the electrochemical impedance spectroscopy methods were employed to discuss the corrosion phenomena by using the embedded annular piezoelectric ultrasonic transducer. The results show that the capacitance arc length in the high frequency zone of the electrochemical impedance spectra increases gradually with increasing the corrosion rate. When the corrosion rate is larger than 3%, obvious corrosion products can be found on surface of the reinforced concrete, and there exist two capacitance arcs in the corresponding electrochemical impedance spectra. The ultrasonic analysis results show that there is an obvious longitudinal mode wave packet in the time domain spectra, and the peak-peak value shows a linear decreasing trend with increasing the corrosion time. The dominant frequency peak value also decreases with increasing the corrosion time accompanying with the appearances of the new peaks in the low frequency zone. The wavelet transform method was also employed for the ultrasonic time-frequency domain analysis. Based on variations of the acoustic energy and dominant frequency components of the ultrasonic wave, the corrosion extent of the reinforced concrete can be qualitatively evaluated.

Phased array ultrasonic testing of micro-flaws in additive manufactured titanium block

While titanium components manufactured by additive manufacturing have been widely used in direct molding of complex components, their performance is strongly affected by existing internal flaws generated in the unique manufacturing process. Thus, how to efficiently and accurately characterize geometrical characteristics of internal flaws is critical for enhancing applications of additive manufactured titanium components. In the present work, an effective non-destructive method by using phased array ultrasonic testing is proposed to characterize sub-millimeter artificial deep bottom holes in additive manufactured TC18 titanium block. Specifically, a phased array ultrasonic testing platform integrated with total focusing method-based post-processing algorithm is established. Flat bottom holes with a diameter of 0.8 mm and a depth of 5.0 mm in 55 mm-sized cube titanium block are detected using both linear and annular array transducers. Experimental results show that pre-existing holes can be characterized by both linear and annular transducers, in despite of accompanied high acoustic attenuation. Furthermore, the annular phased array ultrasonic testing has higher detection accuracy and resolution than the linear phased array one, for its stronger capability of sound field focusing. More importantly, the annular phased array ultrasonic testing shows similar high testing accuracy in different relative orientations between forming orientation of the titanium component and sound wave propagation direction. These findings provide an effective strategy for the non-destructive ultrasonic testing of titanium components by additive manufacturing.

Investigation of novel embedded piezoelectric ultrasonic transducers on crack and corrosion monitoring of steel bar

A novel embedded piezoelectric ultrasonic transducers suitable for damage monitoring of steel bar were developed, and the crack and corrosion damages of the steel bar were investigated based on the ultrasonic pitch-catch technique. The experimental results of crack damages show that there exist series of wave packets in the ultrasonic time domain spectra, and some characteristic wave packets can be determined based on relationship of the length of the steel bar, crack location and acoustic velocity. With increasing the crack depth, the ultrasonic amplitudes in time domain spectra decrease gradually, and some individual peaks couple together. The location of crack on the steel bar can be calculated based on propagation time and acoustic velocity of the longitudinal mode wave. Different corrosion experiments were carried out to verify the corrosion monitoring ability of the proposed ultrasonic transducer, and the local corrosion monitoring results show that the head wave amplitude and the peak to peak value decrease with increasing the corrosion time, and a new wave packet related to corrosion damage appears in the spectra. The peak amplitude in the frequency domain spectra decreases with increasing the corrosion rate accompanying with disappearance of some frequency components. The proposed annular piezoelectric ultrasonic transducer was experimentally proved to be efficient in different damage monitoring of the steel bar.

Investigation on novel embedded piezoelectric ultrasonic transducers for corrosion monitoring of reinforced concrete

The corrosion monitoring of reinforced concrete is important for the structural safety. A kind of embedded annular piezoelectric ultrasonic transducers suitable for corrosion monitoring of the reinforced concrete were proposed and fabricated, and the electrical impedance spectra and ultrasonic pitch-catch characteristic of the transducers in the steel rebar were discussed. The results show that after the annular piezoceramic disk was encapsulated, the resonance of the piezoelectric ceramic under effects of electric excitation was restricted due to the damping effect of the packaging layer. Comparing with the annular piezoelectric ceramic disk, the wall thickness extensional resonance frequency of the annular ultrasonic transduces decreases, however, the corresponding frequency bandwidth increases. The ultrasonic pitch-catch experimental results indicate that the annular full-electrode transducer has the largest wave duration time and the minimum head wave amplitude than others, but the annular serial transducer has the largest head wave amplitude and peak to peak value. When the excitation frequency of the signal is in the range of 100–160 kHz, the annular serial transducer has the best ability to receive the ultrasonic wave. A good distinguishability of the longitudinal and flexural wave can be obtained in the reception waveform when the distance between the emission and reception transducers is larger than 600 mm in a long round steel rebar.

Asymmetric Dynamics of the Native Aortic Annulus Evaluated by Force Transducer and Sonomicrometry in a Porcine Model

PurposeWith new repair techniques of the aortic root and valve emerging, a detailed understanding of the dynamics of the aortic annulus and valve is required for optimal results. The objective of this study was to characterize geometrical changes and force distribution of the native porcine aortic annulus throughout the cardiac cycle.MethodsMeasurements were performed in an acute 80 kg porcine model (n = 7) using sonomicrometry crystals in the aortic annulus for evaluation of geometry and dynamics, annular force transducer evaluating force distribution, and pressure measurements and echocardiography evaluating valve performance.ResultsOverall, segmental force distribution and geometrical changes differed between different segments of the aortic annulus. The highest force development was found at the left/right interleaflet triangle (2.87 ± 2.1 N) and the largest segmental expansion was observed at the right-coronary and left-coronary sinus. The aortic annulus changed configuration throughout the cardiac cycle and became more oval in systole.ConclusionsThis study is the first to describe detailed segmental dynamics and force distribution of the native aortic annulus in a porcine model in vivo. The heterogenous behavior of the aortic annulus suggests that different segments demand different support for repair of the aortic root and valve.

Design and fabrication of an annular array high intensity focused ultrasound transducer with an optimal electrode pattern

In this study, an annular high intensity focused ultrasound (HIFU) array transducer was developed to suppress the level of sidelobes below a given requirement with a minimum number of channels. The electrode patterns analyzed for the transducer were equal electrode area pattern and variable electrode width pattern. In finite element analysis of the transducer performance, the variable electrode width pattern transducer was proven to be able to suppress the level of sidelobes below −12 dB with 9 channels, while the equal electrode area pattern transducer required at least 10 channels to suppress the level of sidelobes by the same amount. Hence, the variable electrode width pattern was preferred for the annular array HIFU transducer. The validity of the comparison was verified by fabricating and characterizing prototypes of the transducer of each electrode pattern. The variable electrode width pattern annular array HIFU transducer is expected to be an effective tool for various therapeutic ultrasound applications.

Concentrated vertical jetting mechanism for isotropically focused Zno/Si surface acoustic waves

This paper investigates vertical droplet jetting using circular surface acoustic wave (CSAW) devices with annular interdigitated transducers (AIDTs) fabricated on ZnO film coated silicon substrate. The surface vibration on the CSAW devices was simulated using finite element analysis and characterised using laser vibrometry. Results showed that focused wave patterns and compact nodal distributions of vibration were formed at the centre of ZnO/Si CSAW device, which is contrast to an anisotropic wave distribution patterns generated by the same pattern of AIDTs fabricated on 128° Y-cut LiNbO3. Simulation of liquid jetting induced by the isotropically focused CSAW was performed using coupled Volume of Fluid and Level-Set method. Results showed that a sharp and cylindrical liquid column was generated from the ZnO/Si CSAW device induced by acoustic energy coming from all directions within the plane due to the in-plane isotropic nature of the ZnO thin films. The simulation enabled us to capture the different streaming/jetting processes induced by the anisotropic distributions of acoustic pressure generated by the AIDTs on the 128° Y-cut LiNbO3 CSAW device. The concentrated vertical droplet jetting behaviour from the ZnO/Si CSAW devices was investigated experimentally and supported the simulated results.

Piezoelectric particle sizer for measuring bed load using a combination of resonance vibration modes

To predict environmental changes and prevent disasters in rivers it is important to track how the size distributions of sand and stones in the riverbed change over time. In this paper, we used a passive piezoelectric sensor to measure the particle distribution of a simulated bed load. The sensor had a simple, robust structure consisting of a circular aluminum plate and an annular piezoelectric transducer. The detection characteristics were evaluated by measuring the impact of alumina spheres with diameters of 3–8mm in air. When particles hit the sensor, the impact excited a flexural vibration in the circular plate, generating electric power through the piezoelectric effect. The electric output signal exhibited two main frequency peaks, at 16.3 and 66.7kHz, whose amplitude ratio depended on particle size. These two frequencies correspond to the fundamental and third resonance vibration modes. When particles hit the sensor surface sequentially, we could determine their particle sizes from short-term frequency analysis of the observed voltage waveform.

Focus control in the radial direction using an ultrasound liquid crystal lens

Nematic liquid crystal is widely used in optical devices such as liquid crystal displays and controlled by electric fields through the liquid crystal layer. Our group has proposed a control technique of liquid crystal molecular orientation using ultrasound vibration without indium tin oxide electrodes [1]. In this study, using ultrasound and nematic liquid crystal, we realized a variable focus liquid crystal lens. The liquid crystal lens has no transparent electrodes and consists of a simple structure; a nematic liquid crystal layer with a thickness of 50 μm is formed between two circular grass plates. An annular PZT ultrasonic transducer was bonded on the glass plate. By exciting the transducer at the resonance frequencies (28 kHz), the flexural vibration modes were generated. The acoustic radiation force from the vibration changed the molecular orientation of the liquid crystals, which induced the distribution of the execution refractive indices. The liquid crystal layer then worked as a lens. The focal points could be controlled by the radiation force and moved in the radial direction. [1] S. Taniguchi, D. Koyama, Y. Shimizu, A. Emoto, K. Nakamura, and M. Matsukawa, Appl. Phys. Lett. 108(2016), 101103.