Tao Han

Effect of acoustic parameters on the cavitation behavior of SonoVue microbubbles induced by pulsed ultrasound.

SonoVue microbubbles could serve as artificial nuclei for ultrasound-triggered stable and inertial cavitation, resulting in beneficial biological effects for future therapeutic applications. To optimize and control the use of the cavitation of SonoVue bubbles in therapy while ensuring safety, it is important to comprehensively understand the relationship between the acoustic parameters and the cavitation behavior of the SonoVue bubbles. An agarose-gel tissue phantom was fabricated to hold the SonoVue bubble suspension. 1-MHz transmitting transducer calibrated by a hydrophone was used to trigger the cavitation of SonoVue bubbles under different ultrasonic parameters (i.e., peak rarefactional pressure (PRP), pulse repetition frequency (PRF), and pulse duration (PD)). Another 7.5-MHz focused transducer was employed to passively receive acoustic signals from the exposed bubbles. The ultraharmonics and broadband intensities in the acoustic emission spectra were measured to quantify the extent of stable and inertial cavitation of SonoVue bubbles, respectively. We found that the onset of both stable and inertial cavitation exhibited a strong dependence on the PRP and PD and a relatively weak dependence on the PRF. Approximate 0.25MPa PRP with more than 20μs PD was considered to be necessary for ultraharmonics emission of SonoVue bubbles, and obvious broadband signals started to appear when the PRP exceeded 0.40MPa. Moreover, the doses of stable and inertial cavitation varied with the PRP. The stable cavitation dose initially increased with increasing PRP, and then decreased rapidly after 0.5MPa. By contrast, the inertial cavitation dose continuously increased with increasing PRP. Finally, the doses of both stable and inertial cavitation were positively correlated with PRF and PD. These results could provide instructive information for optimizing future therapeutic applications of SonoVue bubbles.

SAW Characteristics of AlN/SiO 2 /3C-SiC Layered Structure With Embedded Electrodes

A layered structure of aluminum nitride (AlN)/ silicon dioxide (SiO2)/cubic silicon carbide with embedded electrodes, which enables the growth of high-quality AlN thin films, is proposed and studied. The phase velocity, coupling factor, and temperature coefficient of frequency (TCF) of surface acoustic waves in the proposed structure have been investigated using the finite-element method. The simulation results show that a high velocity of 5485 m/s and a large effective coupling factor (K2 ) of 1.45% can be simultaneously obtained for the first mode. The dramatic enhanced K2 of 10.5% is also obtainable on the proposed structure employing Sc0.4Al0.6N thin film. Besides, the excellent zero TCF is also achieved without deteriorating the coupling factor by adding an amorphous SiO2 overlay.

A wireless pressure sensor based on surface transverse wave

The surface acoustic wave (SAW) pressure sensor is usually composed of a clamped circular quartz membrane, where a one-port Rayleigh wave mode resonator is fabricated. In order to improve the reliability and the accuracy of the wireless pressure sensor, a wireless pressure sensor based on surface transverse wave (STW) is studied. Combined with the perturbation theory proposed by Tiersten and the Greens function simulator, the pressure-induced frequency shifts for STW on quartz are calculated. The calculated results demonstrate that the cut orientation in vicinity of BT cut membrane has simultaneously both high pressure sensitivity and delay temperature stability of STW. The pressure sensitivity is over three times that of the ST-cut quartz for SAW. In order to further improve the sensitivity of the sensor, a novel cantilever package is proposed. The geometry of the sensor is determined by using FEM software. The experimental data show that the pressure sensitivity is sufficiently high and the relative frequency shift varies linearly.

Enhancement of effective electromechanical coupling factor by mass loading in layered surface acoustic wave device structures

This paper describes a drastic enhancement of the effective coupling factor by mass loading in layered surface acoustic wave (SAW) device structures such as the ScAlN film/Si substrate structure. This phenomenon occurs when the piezoelectric layer exhibits a high acoustic wave velocity. The mass loading decreases the SAW velocity and causes SAW energy confinement close to the top surface where an interdigital transducer is placed. It is shown that this phenomenon is obvious even when an amorphous SiO2 film is deposited on the top surface for temperature compensation. This enhancement was also found in various combinations of electrode, piezoelectric layer, and/or substrate materials. The existence of this phenomenon was verified experimentally using the ScAlN film/Si substrate structure.

Theoretical analysis of surface acoustic wave propagating properties of Y-cut nano lithium niobate film on silicon dioxide

The surface acoustic wave (SAW) propagating characteristics of Y-cut nano LiNbO3 (LN) film on SiO2/LN substrate have been theoretically calculated. The simulated results showed a shear horizontal (SH) SAW with enhanced electromechanical coupling factor K2 owing to a dimensional effect of the nanoscale LN film. However, a Rayleigh SAW and two other resonances related to thickness vibrations caused spurious responses for wideband SAW devices. These spurious waves could be fully suppressed by properly controlling structural parameters including the electrode layer height, thickness, and the Euler angle (θ) of the LN thin film. Finally, a pure SH SAW was obtained with a wide θ range, from 0° to 5° and 165° to 180°. The largest K2 achieved for the pure SH SAW was about 35.1%. The calculated results demonstrate the promising application of nano LN film to the realization of ultra-wideband SAW devices.

Design of temperature sensor array in smart electric grid based on SAW resonators

The sensor array with six sensors working at the frequency range of 429-436 MHz is designed and fabricated. The temperature sensitivity can be accurately controlled by the metallization thickness of the resonator on quartz substrate to keep the temperature-induced frequency shifts of each sensor within a limited bandwidth over a wide operating temperature ranging from -40°C to +150°C. The thermal parameters of sensor encapsulation are optimized according to the high voltage switchgear application. In order to meet the real-time requirement of sensor array measurement, discrete Hartley Transform (DHT) and the method of fast searching center frequency of sensors by comparison of I/Q and interrogation signals are used to reduce the query time, greatly improving the efficiency of polling of the sensor array. The measurement uncertainty of the practical SAW temperature sensor is less than 1°C, and the sensitivity of sensor is up to 4 KHz/°C.

Mechanistic understanding the bioeffects of ultrasound-driven microbubbles to enhance macromolecule delivery

ABSTRACT Ultrasound‐driven microbubbles can trigger reversible membrane perforation (sonoporation), open interendothelial junctions and stimulate endocytosis, thereby providing a temporary and reversible time‐window for the delivery of macromolecules across biological membranes and endothelial barriers. This time‐window is related not only to cavitation events, but also to biological regulatory mechanisms. Mechanistic understanding of the interaction between cavitation events and cells and tissues, as well as the subsequent cellular and molecular responses will lead to new design strategies with improved efficacy and minimized side effects. Recent important progress on the spatiotemporal characteristics of sonoporation, cavitation‐induced interendothelial gap and endocytosis, and the spatiotemporal bioeffects and the preliminary biological mechanisms in cavitation‐enhanced permeability, has been made. On the basis of the summary of this research progress, this Review outlines the underlying bioeffects and the related biological regulatory mechanisms involved in cavitation‐enhanced permeability; provides a critical commentary on the future tasks and directions in this field, including developing a standardized methodology to reveal mechanism‐based bioeffects in depth, and designing biology‐based treatment strategies to improve efficacy and safety. Such mechanistic understanding the bioeffects that contribute to cavitation‐enhanced delivery will accelerate the translation of this approach to the clinic. Graphical abstract Figure. No Caption available.

A new modular semi-parallel EIT system for medical application

Abstract A modular semi-parallel EIT data acquisition system (SJTU Mk-1) for medical application is newly developed. It consists of one control module and an expandable number of independent frontend modules. The control module generates stimulating signals, intermediates the communication between remote PC and frontends, and synchronize frontends during parallel data acquisition. All frontend modules are closely and symmetrically connected to electrode sensing array, so the length of signal traces can be minimized for better measurement accuracy at higher frequencies. The system can spectrum impedance from 1xa0kHz to 1xa0MHz which covers the majority frequency range of medical impedance investigations. The amplitudes of stimulating currents are limited to 0.4xa0mA with built-in alarm of abnormal current on each frontend module for extra safety protection. Transformers and optoelectronic couplers are used to isolate the human body under test from mains power supply and geological ground. The developed EIT Data Acquisition System (DAS) is natively safe and suitable for medical applications. To maximize number of independent measurement for better spatial resolution of reconstructed image, the sensing array is implemented with compound electrodes. System performance tests at excitation current less than 0.5xa0mA show that, the Signal-to-Noise Ratio (SNR) of transfer impedance is higher than 70xa0dB, the amplitude and phase measurement repeatability are better than 0.6% and 1° respectively. Initial phantom experiments further demonstrate the imaging capability of the developed EIT DAS for medical application.

Influence of coupling with shear horizontal surface acoustic wave on lateral propagation of Rayleigh surface acoustic wave on 128°YX-LiNbO3

In this paper, we investigate the impact of the coupling with shear horizontal (SH) surface acoustic wave (SAW) on the propagation of Rayleigh SAW in periodic grating structures on 128°YX-LiNbO3. First, the frequency dispersion behavior with longitudinal and lateral wavenumbers of Rayleigh SAW is calculated using the finite element method (FEM) software COMSOL. It is shown that the coupling causes (1) the satellite stopband and (2) variation of the anisotropy factor. It is also shown these phenomena remain even when the electromechanical coupling factor of SH SAW is zero. Then, the extended thin plate model which can take coupling between two SAWs into account, is applied to simulate the result of FEM. Good agreement between these results indicated that the mechanical coupling is responsible for these two phenomena. Finally, including electrical excitation and detection, the model is applied to the infinitely long interdigital transducer (IDT) structure and the calculated result is compared with that obtained by the three-dimensional FEM. The excellent agreement of both results confirms the effectiveness of the extended thin plate model.

Recent research results on wireless passive acoustic sensors for smart grids application

The use of wireless SAW sensors for temperature monitoring of electric equipments has become a more favored choice than its counterparts because of the unique characteristics. This paper introduces some research results in SAW wireless temperature sensors. The sensor designs using double resonating elements and a new dual-frequency reading system where the double sensing elements are interrogated simultaneously are implemented. A new encapsulation of the sensors is designed to be in facility clamped on surface of the breaker contacts and the outlet cable joints. An effective error correction method for continuous frequency readout errors is also presented.