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Piezoelectric single crystals (piezocrystals) of lead magnesium niobate-lead titante (PMN-PT) and lead zinc niobate-lead titanate (PZN-PT) have extremely large electromechanical coupling coefficients and exhibit strains of over one percent. The technical significance of these properties to devices is enormous and includes a doubling of bandwidth, decreased package size, and increased resolution. The...
Coupling between surface acoustic waves (SAW) and arrays of mechanical resonators has appeared early in SAW history as a potential means to slow down wave propagation through mass-loading, in particular by creating corrugations on the substrate surface. This concept has been revisited over the past few years in the context of locally-resonant phononic crystals where pillars deposited on a homogeneous...
Suppression of the SH-SAW response is mandatory to design TC SAW devices on θ degree rotated Y-cut LiNbO3. However, it is not easy because K2 for SH SAW changes rapidly with θ, and its optimal value in terms of the SH-SAW suppression is dependent on electrode and SiO2 thicknesses. The authors found that the optimal θ always locates close to θ where difference in velocities of two SAWs is minimum....
Lithium niobate (LN) based thin film piezoelectrics have being extensively explored [1-3] for the making of high coupling and high performance resonators. The most important bottleneck for the use of LN film is related to fabrication process and it is particularly challenging when a bottom electrode is included in the stack to increase the film capacitance per unit area. We have explored Y-cut LN...
For evaluation of aged concrete structure, it is expected to apply ultrasonic nondestructive measurement. Special coupling media with high viscosity made scanning difficult and the application to huge structure was not practical. Our group prototyped a couplant-free probe realizing strong acoustic coupling using high pressure due to Hertzian contact and found a potential to excite longitudinal wave...
ScAlN films are well-researched for GHz acoustic wave devices. Large-area growth techniques of ScAlN films are necessary for the practical application. A single sputtering source with a ScAl alloy metal target is suitable for the film growth from the point of view of the composition stability. However, it is difficult to alloy Al with Sc in the large-size target. Therefore, a mosaic target of Sc and...
Electro-mechanical devices for sensing, actuation, and communication are necessary ingredients for the ongoing 4th industrial revolution. Piezoelectricity plays an important role in electromechanical conversion, and is e.g. used in ultrasonic imaging and mobile phone communication. The drive for miniaturization will result in a strong demand for piezoelectric thin films, with improved, optimized properties...
Water continues to be the most commonly used fluid when coupling the energy emanating from a therapeutic ultrasound transducer to its target tissue. In many therapeutic ultrasound systems, this coupling fluid performs additional functions, such as transducer cooling, target tissue temperature management, and transducer/target tissue separation management, and is typically degassed to prevent the formation...
Polyvinylidene fluoride (PVDF) and its copolymer (PVDF-TrFE) are known to yield lower electromechanical coupling than ceramic transducers. It is possible to increase transducer efficiency by using two or more PVDF layers with embedded electrodes by configuring the transducer layers in different ways such as folded, barker coded and switchable barker coded [Zhang et al., 1997]. A multi-layer transducer...
Recent literature has focused on improving piezoelectric coupling coefficients by alloying aluminum nitride (AlN) with scandium (Sc). Akiyama et al. showed the highest d_33 piezoelectric coefficient increase of >4x at a 41% Sc substitution for Al. Thus far, studies mainly focus on material measurements such as x-ray diffraction or piezoelectric constants to assess the material quality. Although...
The piston mode operation (PMO) is quite effective for realization of spurious-free and low-loss SAW resonators. The scalar potential (SP) analysis indicates that “phase shifters” are necessary for PMO at edges of the acoustic aperture. Nakamura, et al., pointed out that for SAW resonators using SiO2/LiNbO3 structure, PMO is possible by simply removing SiO2 in the dummy electrode region [1]. This...
Conventional acoustic wave correlators are known for their small size (nearly 105 times smaller than an analogous electromagnetic correlator), zero DC power consumption, and linearity. Reconfigurable orthogonally coded correlators could be used at the front-end of a RF transmit and receive chain to provide cross-correlation properties that can aide in simultaneous transmit and receive (STAR) systems...
Ultrasound shear wave imaging has been extensively studied in thin tissues, such as the artery and cornea. The dispersion analysis of the guided wave propagating in such layered structures based on a modified Lamb wave model for homogeneous and isotropic thin soft media in water has been shown to yield accurate elasticity estimates. Nonetheless, thin soft tissues are often bounded with other tissue...
Phononic crystals have attracted intensive research interest for decades since the early 1990s. They exhibit a spatially periodic feature regarding the distribution of physical properties, geometry, boundary conditions, or/and external stimuli, making their wave spectrum quite different from the conventional continuous one, usually with frequency band gaps where waves cannot propagate through them...
Air-coupled ultrasonic testing is required for inspection of materials where liquid acoustic coupling media cannot be applied, but transmission efficiency is a problem. Our group prototyped an ultrasonic probe fabricated using an array of piezoelectric ceramics rods by dicing a thickness-mode vibrator and the usefulness was found. However, a dicing method without rod broken was not established and...
The propagation of the S0 Lamb mode in AlN membrane combined with continuous and structured SiO2 thin films is theoretically studied with respect of the materials geometrical parameters and electrical boundaries conditions. A comparison is made in terms of the phase velocity, electromechanical coupling coefficient and temperature coefficients of frequency (TCF) between the studied structures. The...
A piezoelectric plate, poled along its thickness, that supports on its top surface a periodic grating of electrodes is considered. If wave propagation is assumed along the length of the plate, one demonstrates that an electrical Bragg band gap can be observed, depending on the electrical boundary conditions applied on the electrodes. This gap is associated with a discontinuity of the electric field...
Acoustic wave characteristics are numerically investigated and compared in AlN/ZnO/diamond and Al2O3/GaN/sapphire with Pt electrodes. These structures have been previously reported as candidates for application in packageless sensors. They include a low-velocity guiding piezoelectric layer sandwiched between two high-velocity materials. The anisotropy of the combined materials, their symmetry and...
The most important bottleneck for the use of lithium niobate (LN) films for making MEMS resonators is related to the fabrication process and it is particularly challenging when a bottom electrode needs to be included in the film stack to increase the resonator's capacitance per unit area. In this work, we propose to access the bottom electrode by using capacitive coupling rather than a direct resistive...
Despite the progress of focused ultrasound (FUS)-mediated blood-brain barrier (BBB) disruption, neuro-inflammatory responses and the high variability of the FUS transmission through the human skull make the control of the acoustic parameters challenging. In this study, we developed a high-field (7-T) magnetic resonance (MR)-guided FUS system with a feedback control based on passive cavitation detection...
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