Piezoceramic Disk Research Articles

A dual-mode hemispherical sparse array for 3D passive acoustic mapping and skull localization within a clinical MRI guided focused ultrasound device

Previous work has demonstrated that passive acoustic imaging may be used alongside MRI for monitoring of focused ultrasound therapy. However, past implementations have generally made use of either linear arrays originally designed for diagnostic imaging or custom narrowband arrays specific to in-house therapeutic transducer designs, neither of which is fully compatible with clinical MR-guided focused ultrasound (MRgFUS) devices. Here we have designed an array which is suitable for use within an FDA-approved MR-guided transcranial focused ultrasound device, within the bore of a 3 Tesla clinical MRI scanner. The array is constructed from 5 × 0.4 mm piezoceramic disc elements arranged in pseudorandom fashion on a low-profile laser-cut acrylic frame designed to fit between the therapeutic elements of a 230 kHz InSightec ExAblate 4000 transducer. By exploiting thickness and radial resonance modes of the piezo discs the array is capable of both B-mode imaging at 5 MHz for skull localization, as well as passive reception at the second harmonic of the therapy array for detection of cavitation and 3D passive acoustic imaging. In active mode, the array was able to perform B-mode imaging of a human skull, showing the outer skull surface with good qualitative agreement with MR imaging. Extension to 3D showed the array was able to locate the skull within ±2 mm/2° of reference points derived from MRI, which could potentially allow registration of a patient to the therapy system without the expense of real-time MRI. In passive mode, the array was able to resolve a point source in 3D within a ±10 mm region about each axis from the focus, detect cavitation (SNR ~ 12 dB) at burst lengths from 10 cycles to continuous wave, and produce 3D acoustic maps in a flow phantom. Finally, the array was used to detect and map cavitation associated with microbubble activity in the brain in nonhuman primates.

A study on the performance of piezoelectric composite materials for designing embedded transducers for concrete assessment

Ultrasonic measurements of concrete can provide crucial information about its state of health. The most common practice in the construction industry consists in using external probes which strongly limits the use of the method since large parts of the in-service structures are difficult to access. It is also possible to assess in real time the setting process of the concrete using ultrasonic measurements. In practice, the field measurement of the concrete hardening is limited by the formworks. As an alternative, some research teams have studied the possibility to directly embed the transducers into the concrete structures. The current embedded ultrasonic transducers are of two categories: bulk piezoelectric elements surrounded by several coating and matching layers and composites piezoelectric elements. Both technologies aim at optimizing the wave energy transmitted to the tested medium. The performances of the transducers of the first kind have been studied in a previous study. A fair amount of recent research has been focused on the development of novel cement-based piezoelectric composites. In this study, we first compare the effective properties of such cement-based materials with more widespread composites made with matrices of epoxy resins or polyurethane. The study only concerns the 1–3 fiber arrangement composites. The effective properties are computed using both an analytical mixing rule method and a finite element based homogenization method using representative volume elements (RVEs) which allows for considering more realistic fiber arrangements, leading yet to very similar results. The effective piezoelectric properties of cement-based composites appear to be very low compared to composites made of epoxy or polyurethane. This result is underlined by looking at the acoustic response and the electric input impedance of different piezoelectric disks where we compare performances of such transducers with a low-cost bulk piezoelectric disc element. The first radial mode of the latter is responsible for an acoustic response of the same order of magnitude as those for the piezo-composites. This result confirms that the design of efficient low-cost embedded ultrasonic transducers can be done with such piezoceramic disks.

Simulation Study of Lead Ball Contact with Piezoceramic Disc Type Actuators

Simulation Study of Lead Ball Contact with Piezoceramic Disc Type Actuators

Methodology to evaluate variations in piezoelectric constants after aging process

ABSTRACTPiezoelectric ceramic properties change with time. Detected aging effects for PZT ceramics are; the difference in the value of the dielectric constants diminishes, whereas dielectric losses and elastic stiffness increases. In this work, an optimisation technique based on adjusting a finite element model to reproduce the complex impedance curves of a resonant piezoceramic disk is analysed aiming to detect changes due to aging. This technique allows estimating all material parameters, both their real and imaginary parts. The optimisation uses the constitutive equations of the piezoelectric effect in the linear regime. The evolution of elastic, piezoelectric and dielectric constants is evaluated after 5 years of aging. To compute the ten complex parameters, the piezoelectric model is adjusted to minimise the difference between finite element simulations and the experimental data. Results presented here, show that the proposed technique is sensitive enough to detect changes in the individual parameters due to aging process.

Three-dimensional ultrasonic trapping of micro-particles in water with a simple and compact two-element transducer

We report a simple and compact piezoelectric transducer capable of stably trapping single and multiple micro-particles in water. A 3D-printed Fresnel lens is bonded to a two-element kerfless piezoceramic disk and actuated in a split-piston mode to produce an acoustic radiation force trap that is stable in three-dimensions. Polystyrene micro-particles in the Rayleigh regime (radius λ/14 to λ/7) are trapped at the focus of the lens (F# = 0.4) and manipulated in two-dimensions on an acoustically transparent membrane with a peak trap stiffness of 0.43 mN/m. Clusters of Rayleigh particles are also trapped and manipulated in three-dimensions, suspended in water against gravity. This transducer represents a significant simplification over previous acoustic devices used for micro-particle manipulation in liquids as it operates at relatively low frequency (688 kHz) and only requires a single electrical drive signal. This simplified device has potential for widespread use in applications such as micro-scale manufacturing and handling of cells or drug capsules in biomedical assays.

Novel genetically optimised high-displacement piezoelectric actuator with efficient use of active material

This paper introduces a new type of piezoelectric actuator, Mikbal. The Mikbal was developed from a Cymbal by adding steel structures around the steel cap to increase displacement and reduce the amount of piezoelectric material used. Here the parameters of the steel cap of Mikbal and Cymbal actuators were optimised by using genetic algorithms in combination with Comsol Multiphysics FEM modelling software. The blocking force of the actuator was maximised for different values of displacement by optimising the height and the top diameter of the end cap profile so that their effect on displacement, blocking force and stresses could be analysed. The optimisation process was done for five Mikbal- and two Cymbal-type actuators with different diameters varying between 15 and 40 mm. A Mikbal with a Ø 25 mm piezoceramic disc and a Ø 40 mm steel end cap was produced and the performances of unclamped measured and modelled cases were found to correspond within 2.8% accuracy. With a piezoelectric disc of Ø 25 mm, the Mikbal created 72% greater displacement while blocking force was decreased 57% compared with a Cymbal with the same size disc. Even with a Ø 20 mm piezoelectric disc, the Mikbal was able to generate ∼10% higher displacement than a Ø 25 mm Cymbal. Thus, the introduced Mikbal structure presents a way to extend the displacement capabilities of a conventional Cymbal actuator for low-to-moderate force applications.

A dual mode hemispherical sparse array for B-mode skull localization and passive acoustic mapping within a clinical MRI guided focused ultrasound platform

Previous work has demonstrated that passive acoustic imaging may be used alongside MRI for monitoring of focused ultrasound therapy. However, current implementations have generally made use of either linear arrays originally designed for diagnostic imaging or custom narrowband arrays specific to in-house therapeutic transducer designs, neither of which is fully compatible with clinical MR-guided focused ultrasound devices. Here we have designed an array which is suitable for use within an FDA-approved MR-guided transcranial focused ultrasound device, within the bore of a 3 Tesla clinical MRI scanner. The array is constructed from 5 × 0.4mm piezoceramic disc elements arranged in pseudorandom fashion on a low profile laser-cut acrylic frame designed to fit between the therapeutic elements of a 230 kHz InSightec ExAblate 4000 transducer. By exploiting thickness and radial resonance modes of the piezo discs the array is capable of both B-mode imaging at 5 MHz for skull localization, as well as passive reception at the second harmonic of the therapy array for mapping of acoustic sources such as emissions from cavitation. The strengths and limitations of the system for passive acoustic imaging during in vivo experiments will be discussed, utilizing robust and conventional time and frequency domain beamforming methods.

FORCED ELECTRO-ELASTIC VIBRATIONS OF THE PIEZOCERAMIC PLATES AND RODS WITH DIVIDED ELECTRODES. PART I: ANALYTICAL RELATIONS FOR COUPLING COEFFICIENTS AND ADMITTANCE’S COMPONENTS

This article analyses the forced vibrations of the non-uniform loaded piezoceramic transducers, such as plates-rods with thickness polarization and one or two bilateral electrode coating divisions, thin disks and circular rings with full or concentric and diameter divided electrodes, as well as partly electroded plates. The analytical relations for thin piezoceramic discs’ with partial electrodes radial vibrations and for rods’ with no uniform electric loading longitudinal vibrations are represented in a first part. The experimental data for rods with divided or partial electrodes are represented in a second part.Ref. 74, fig. 1.

Influence of Electric Loading Conditions on the Vibrations of Piezoceramic Resonators

Experimental data for the fundamental radial mode of a thin piezoceramic disk are analyzed. It is established that the voltage drops and instantaneous powers are very sensitive to the loading conditions, while admittances, impedances, and phase shifts do not depend on them. If the current is set constant, the instantaneous power decreases as the resonance is approached and increases as the antiresonance is approached. If the voltage is set constant, the instantaneous power increases as the resonance is approached and decreases as the antiresonance is approached

Design of transmission-mode measurements for estimating ultrasound attenuation and nonlinearity in liver

Previously, it has been shown that ultrasound measurements of sound speed and nonlinearity can be used to quantify the fatty and non-fatty components of liver tissue. In addition, it has been proposed that ultrasound attenuation measurements can be used to distinguish fatty components comprising either sub-micron lipid droplets (microsteatosis) or much larger cell-sized droplets (macrosteatosis). To perform all of these measurements, a caliper device is being developed based on a transmission-mode approach. Design challenges are posed by competing requirements: sub-megahertz frequencies for optimal detection of microsteatosis and nonlinearity estimation based on waveform distortion over relatively short distances. To meet these challenges, a design is proposed in which ultrasound at 667 kHz is generated by a 50 mm piezoceramic disk and all measurements are made in the plane-wave regime. Given geometrical and physical constraints, all analysis was performed in the time domain. The nonlinearity coefficient ...

Tailoring the efficiency of ultrasonic transducers for physiotherapy

ABSTRACTPhysiotherapy ultrasonic transducers are mainly composed by a piezoelectric ceramic bonded to a metallic thin membrane. These transducers vibrate at the thickness fundamental mode. The acoustic efficiency depends on the vibration pattern of the transducer face in contact with the human skin. Radial modes excited by the piezoceramic disc introduce a distribution of amplitude and phase that penalizes both the efficiency and the acoustic field distribution.In this work, different designs have been studied to decrease the influence of the radial modes on the vibration pattern. For this end, both the metallic membrane and the piezoceramic have been modified in shape.

Piezoelectric energy harvester for public roadway: On-site installation and evaluation

This paper presents the development of a novel piezoelectric energy harvester (PEH) to harness the great amount of energy wasted by the vehicles on public roadways was described. The PEH is designed to convert the deformation energy induced by moving vehicle from pavement into electrical energy. The prototype harvester consists of PZT piezoceramic disks sealed in a protective package is developed. Six prototype PEHs were fabricated and installed in real pavement to evaluate the feasibility of this application. The electric productivity of the installed harvesters was evaluated by measuring the output voltage and current generated under real traffic. Instant and average power outputs are calculated from the measured waveforms of output voltage and current. The analysis of the testing results shows that the electrical productivity of the energy harvesters are highly relevant to the axle configuration and magnitude of passing vehicles.

Dynamics Characterisation of Cymbal Transducers for Power Ultrasonics Applications

A class V cymbal flextensional transducer is composed of a piezoceramic disc sandwiched between two cymbal-shaped shell end-caps. Depending on the type of piezoceramic, there exists a maximum voltage that can be reached without depolarisation, but also, at higher voltage levels, amplitude saturation can occur. In addition, there is a restriction imposed by the mechanical strength of the bonding agent. The effects of input voltage level on the vibration response of two cymbal transducers are studied. The first cymbal transducer has a standard configuration of end-caps bonded to a piezoceramic disc, whereas the second cymbal transducer is a modified design which includes a metal ring to improve the mechanical coupling with the end-caps, to enable the transducer to operate at higher voltages, thereby generating higher displacement amplitudes. This would allow the transducer to be suitable for power ultrasonics applications. Furthermore, the input voltages to each transducer are increased incrementally to determine the linearity in the dynamic responses. Through a combination of numerical modelling and experiments, it is shown how the improved mechanical coupling in the modified cymbal transducer allows higher vibration amplitudes to be reached.

Optimisation of a Cymbal Transducer for Its Use in a High-power Ultrasonic Cutting Device for Bone Surgery

The class V cymbal is a flextensional transducer commonly used in low-power ultrasonic applications. The resonance frequency of the transducer can be tailored by the choice of end-cap and driver materials, and the dimensions of the end-caps. The cymbal transducer has one significant limitation which restricts the operational vibration amplitude of the device. This is the limit imposed by the mechanical strength of the bonding agent between the metal end-cap and the piezoceramic driver. Therefore, when there is an increase in the input power or displacement, the stresses in the bonding layer can lead to debonding, thereby rendering the cymbal transducer ineffective for high-power ultrasonic applications. In this paper, several experimental analyses have been performed, complemented by the use of Abaqus/CAE finite element analysis, in order to develop a high-power ultrasonic cutting device for bone surgery using a new configuration of cymbal transducer, which is optimised for operation at high displacement and high input power. This new transducer uses a combination of a piezoceramic disc with a metal ring as the driver, thereby improving the mechanical coupling with the metal end-cap.

Comparison of analytical and numerical approaches for CT-based aberration correction in transcranial passive acoustic imaging

Computed tomography (CT)-based aberration corrections are employed in transcranial ultrasound both for therapy and imaging. In this study, analytical and numerical approaches for calculating aberration corrections based on CT data were compared, with a particular focus on their application to transcranial passive imaging. Two models were investigated: a three-dimensional full-wave numerical model (Connor and Hynynen 2004 IEEE Trans. Biomed. Eng. 51 1693–706) based on the Westervelt equation, and an analytical method (Clement and Hynynen 2002 Ultrasound Med. Biol. 28 617–24) similar to that currently employed by commercial brain therapy systems. Trans-skull time delay corrections calculated from each model were applied to data acquired by a sparse hemispherical (30 cm diameter) receiver array (128 piezoceramic discs: 2.5 mm diameter, 612 kHz center frequency) passively listening through ex vivo human skullcaps (n = 4) to emissions from a narrow-band, fixed source emitter (1 mm diameter, 516 kHz center frequency). Measurements were taken at various locations within the cranial cavity by moving the source around the field using a three-axis positioning system. Images generated through passive beamforming using CT-based skull corrections were compared with those obtained through an invasive source-based approach, as well as images formed without skull corrections, using the main lobe volume, positional shift, peak sidelobe ratio, and image signal-to-noise ratio as metrics for image quality. For each CT-based model, corrections achieved by allowing for heterogeneous skull acoustical parameters in simulation outperformed the corresponding case where homogeneous parameters were assumed. Of the CT-based methods investigated, the full-wave model provided the best imaging results at the cost of computational complexity. These results highlight the importance of accurately modeling trans-skull propagation when calculating CT-based aberration corrections. Although presented in an imaging context, our results may also be applicable to the problem of transmit focusing through the skull.

A digital measurement system based on laser displacement sensor for piezoelectric ceramic discs vibration characterization

This study describes the innovative design of a digital measurement system based on a laser displacement sensor (LDS) as a vibrometer which is capable to measure a dynamic displacement response dependence on a stimulated vibration. The frequency response of a piezoelectric ceramic disc is obtained by processing the input/output signals obtained from the function generator and digital oscilloscope (digitizer) cards driven by a personal computer. Resonant frequencies of vibration are achieved utilizing the swept-sine signal excitation following the peak values in the signal response measured by LDS. The analogue signal from LDS controller represents directly a mechanical vibration of a piezoceramic disc. The test measurement results indicate that the system can distinguish resonance frequencies of piezoelectric ceramic discs up to 40kHz with the resolution 1Hz. Piezoelectric coefficient d33 and its linearity along the excited voltage amplitudes have been calculated by the applied methods as a demonstration of a successful system concept. The results achieved are in compliance with the reference value declared by the manufacturer of the piezoceramic disc.

Experimental demonstration of passive acoustic imaging in the human skull cavity using CT-based aberration corrections.

Experimentally verify a previously described technique for performing passive acoustic imaging through an intact human skull using noninvasive, computed tomography (CT)-based aberration corrections Jones et al. [Phys. Med. Biol. 58, 4981-5005 (2013)]. A sparse hemispherical receiver array (30 cm diameter) consisting of 128 piezoceramic discs (2.5 mm diameter, 612 kHz center frequency) was used to passively listen through ex vivo human skullcaps (n = 4) to acoustic emissions from a narrow-band fixed source (1 mm diameter, 516 kHz center frequency) and from ultrasound-stimulated (5 cycle bursts, 1 Hz pulse repetition frequency, estimated in situ peak negative pressure 0.11-0.33 MPa, 306 kHz driving frequency) Definity™ microbubbles flowing through a thin-walled tube phantom. Initial in vivo feasibility testing of the method was performed. The performance of the method was assessed through comparisons to images generated without skull corrections, with invasive source-based corrections, and with water-path control images. For source locations at least 25 mm from the inner skull surface, the modified reconstruction algorithm successfully restored a single focus within the skull cavity at a location within 1.25 mm from the true position of the narrow-band source. The results obtained from imaging single bubbles are in good agreement with numerical simulations of point source emitters and the authors' previous experimental measurements using source-based skull corrections O'Reilly et al. [IEEE Trans. Biomed. Eng. 61, 1285-1294 (2014)]. In a rat model, microbubble activity was mapped through an intact human skull at pressure levels below and above the threshold for focused ultrasound-induced blood-brain barrier opening. During bursts that led to coherent bubble activity, the location of maximum intensity in images generated with CT-based skull corrections was found to deviate by less than 1 mm, on average, from the position obtained using source-based corrections. Taken together, these results demonstrate the feasibility of using the method to guide bubble-mediated ultrasound therapies in the brain. The technique may also have application in ultrasound-based cerebral angiography.

In-plane torsion of discal piezoelectric actuators with spiral interdigitated electrodes

Piezoceramic disks with spiral interdigitated electrodes (SIDEs) on their surfaces are proposed to produce in-plane torsion. With constant electrode spiral angle (Type I) and constant pitch between adjacent electrodes (Type II), two typical types of the SIDEs are developed and studied. Working principles of the discal piezoelectric actuators are explained and their static in-plane torsional deformations are formulated. Finite element simulations are used to investigate the static and dynamic properties of the actuators. Non-ideal distributions of electric fields appear serious suppressions on the actuating abilities, even worse for Type I actuator. Due to unsymmetric piezoelectric strains in the thickness direction, bending deformations of the disks are inevitable. Prototype actuators with fixed boundary at the radius of 12mm are fabricated and tested. With a driving voltage of 400 Vp-p at 1Hz, the maximum quasi-static in-plane torsional angles are 0.00458° for Type I actuator and 0.00605° for Type II actuator at the radius of 6mm. With a driving voltage of 10 Vp-p, the vibration amplitudes at the radius of 6mm are 0.00105° at 86.0kHz for Type I actuator and 0.00149° at 84.4kHz for Type II actuator at the first in-plane torsional vibration modes.

Ultrasonic Cutting Device for Bone Surgery Based on a Cymbal Transducer

In this study, we introduce a new prototype ultrasonic cutting device for bone surgery based on a class V flextensional cymbal transducer, configured for use in power ultrasonics applications, which removes many of the geometrical restrictions on the cutting tip of Langevin-based transducers. The benefit of incorporating a cymbal transducer is that since the cutting blade itself does not have to be tuned, blade design can focus more closely on delivering the best interaction with bone to provide a highly accurate cut. Small variations to the geometry of the blade do not affect the final resonance frequency. Also the ultrasonic device can be miniaturised to allow the design of devices for delicate orthopaedic procedures involving minimal-access surgery. The results show how the cymbal transducer, driven by a single piezoceramic disc, can excite sufficiently high vibration displacement amplitudes at lower driving voltages. This is achieved by adapting the configuration of the cymbal to remove the problem of epoxy layer debonding, and by optimising the cymbal end-cap and geometry through finite element modelling supported with experimental vibration characterisation. Preliminary characterisations of the resulting prototype ultrasonic bone cutting device, which operates at around 25kHz, illustrate the success of this novel device design.

ACUPAD: A track-pad device based on a piezoelectric bimorph

A track-pad is a pointing device, featuring a tactile sensor, able to translate the motion and position of a user's finger, or a stylus, to a relative position on a screen. In this paper a piezoelectric tactile sensor for track-pad applications is proposed; the active element of the device is a cheap piezoceramic bimorph disk, widely used in buzzers and telephone receivers, clamped all around its border. The device operating principle is the following: when a stylus is positioned on the bimorph surface, the displacement field of the contact point is modified, with a consequent variation of the device electrical input impedance; the stylus position can be therefore related to the impedance variation. The system was analyzed by FEM, obtaining a clear dependence of the device characteristic frequencies on the stylus radial position, while by moving the stylus along the angle, a clear variation of impedance values is obtained. A device prototype was realized and FEM results were experimentally confirmed, validating the proposed device performance.