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ABSTRACT: The influences of the surface conductivity on the velocity of an acoustic wave (AW) in a multilayered material are studied theoretically with the transfer matrix method and the conductivity sensitivity of the AW sensor is presented. It is found that the velocity of the AW increases with decreasing surface conductivity and vice versa. The result is used to explain the abnormal response of AW sensors, in which the central frequencies of AW sensors increase after they sorb the detected gases. Meanwhile, the conductivity sensitivity is found to be related to the dielectric constants of the multilayered material and the electromechanical coupling coefficient of the sensor. Finally, the sensitivities of AW sensors based on multilayered structures are optimized by considering the influences of the surface conductivities of the sensors with different initial conductivities and thicknesses of the sensitive layers.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 03/2011; · 1.69 Impact Factor
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ABSTRACT: A vibration model of Besocke-style scanners is given based on Timoshenko beam theory. The model is applied to investigate the flexural vibration characteristics of piezotubes in the scanners, in which the effects of affiliated components of the piezo-tubes are considered. The calculated results show that several factors in addition to the piezo-tubes themselves influence the flexural vibration frequencies of the scanners. An example is the balls which support the piezo-tubes. These play important roles in influencing the flexural vibration characteristics of the scanners and can result in high-flexural resonance frequencies. The local resonance of the scanner disk can also influence the flexural vibration characteristics of the piezo-tubes. Finally, we show that the effects of the local resonance on the vibration characteristics of the scanners can be decreased or eliminated by improving the rigidity of connection between the scanner disk and the piezo-tube.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control 05/2010; 57(5):1140-5. · 1.80 Impact Factor
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ABSTRACT: Experimental study of Love-mode immunosensors based on structures of ZnO/36 degrees YX-LiTaO3 is presented, in which the ZnO films with c-axis (002) orientation have been successfully grown on the 36 degrees YX-LiTaO3 substrates by RF magnetron sputtering technique. Then the Love-mode immunosensors based on the ZnO/36 degrees YX-LiTaO3 structures and monitoring antibody-antigen immunoreactions in aqueous solutions in real time are fabricated. The experimental results show that the optimal thickness of ZnO layers is about 1.20 microm in the structures deposited on 36 degrees YX-LiTaO3 substrates, which is much less than that of SiO2 overlayers about 6 microm. The antibody-antigen immunoreaction experiments also show that the frequency shifts of the sensors with 1.33 microm ZnO films are proportional to the concentration of antigen in solution as the concentration range less than 100 microg/ml.
Ultrasonics 10/2009; 50(3):411-5. · 1.84 Impact Factor
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ABSTRACT: Based on the Rayleigh energy theory combining with Timoshenko beam model, the flexural vibration characteristics of piezoelectric tubes in ultrasonic micro-actuators are investigated. Additionally, the simplified formulae are derived to study the fundamental flexural resonance frequencies of the piezoelectric tubes with free-free ends and cantilevers. By changing the sizes of the tubes and the mass loads at the free ends, the variations of the flexural resonance frequencies of the piezoelectric tubes and cantilevers are calculated theoretically. To verify accuracy of the simplified formulae, by changing the lengths of the tubes and the mass loads the flexural resonance frequencies of the piezoelectric tube with free-free ends are measured experimentally. The theoretical results agree well with the experimental measurements, which demonstrate that the simplified formulae are accurate and effective for analyzing the flexural vibration characteristics of the piezoelectric tubes in the ultrasonic micro-actuators.
Ultrasonics 09/2009; 50(3):397-402. · 1.84 Impact Factor
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ABSTRACT: A nonlinear model of electrodynamic loudspeakers excited by voltages is used to study the influences of nonlinearities of loudspeakers on performances of thermoacoustic refrigerators. The theoretical simulated results demonstrate that the nonlinearities of the magnetic fields and vibration components of the loudspeakers change electroacoustic transfer efficiencies and acoustic output powers of the loudspeakers, and the nonlinearities of the vibration components also shift the resonance frequencies of the loudspeakers. In the voltage-excited systems, the product of the magnetic induction intensity and the length of the coil play an important part in the performances of the acoustic source because of the influence of the motional electromotive force exerted on the coil when it is moving in the magnetic field.
Journal of Applied Physics 01/2009; · 2.17 Impact Factor
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ABSTRACT: Anomalous subharmonics named as quasisubharmonics (QSHs) in plates excited by intensive ultrasonic pulses are first observed, in which the QSH frequencies are incommensurable with the fundamental frequency. The experimental results show that the low (such as 1/3) order subharmonics appear in the transient process of the ultrasonic excitation, and then several QSHs successively appear as the ultrasonic power increases and approaches steady state, in which the first QSH appears near the system eigenfrequency. A phenomenological model is presented and the theoretical simulations indicate that the QSHs are produced by the intermittent contacts between the transducer horn and the plate.
Applied Physics Letters 06/2008; 92(22):221902-221902-3. · 3.84 Impact Factor
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ABSTRACT: The dispersive characteristics of higher order mode Lamb waves (HOMLW) excited by interdigital transducers (IDT) are measured and analyzed, which are necessary for designing micro-sensor in ultrahigh frequency (UHF). A measurement system is set up, in which dispersive characteristics of HOMLW are obtained by the method of transform between frequency and time domains. The characteristics of amplitude-frequency and phase-frequency of Lamb wave are auto-measured by the system. By IFFT, the pulse response of the IDT device was obtained. Different modes were separated in time domain and dispersive curve of each mode is calculated by FFT. The best mode is chosen to design the micro-sensor in UHF. The phase velocity of HOMLW is greater than the surface wave (SAW) velocity and an oscillator in higher frequency can be made, so the absolute sensitivity of micro-sensor can be increased. In this paper, the dispersive characteristics of HOMLW excited by an IDT in a 127.86 degrees rotated Y-cut, X propagating lithium niobate plate is analyzed. An oscillator using a(13) mode is made, the phase velocity of which is measured about 19,652 m/s when h/lambda=0.94 (h=plate thickness, lambda=wavelength).
Ultrasonics 01/2007; 44 Suppl 1:e911-5. · 1.84 Impact Factor
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ABSTRACT: Subharmonics are often observed in ultrasonic infrared thermography (UIR) system as samples are excited by ultrasonic transducers, and it is testified that, as the subharmonics appear, the detectability of cracks or defects in the sample is greatly enhanced in the UIR system. A dynamical model to explore the generation mechanism of the subharmonics and simulate the sample motion excited by an ultrasonic transducer in the UIR system is presented in this paper. In the model, the sample is continuously impacted by the transducer as the transducer is pushed to the sample by a constant force, in which the sample is simplified as a damped oscillator and the transducer is simplified as an active oscillator with constant frequency and amplitude. The impact process is also taken into account, in which the acting force is assumed to vary linearly during the impact process. A stable waveform of subharmonics in the sample can be obtained in appropriate conditions.
Ultrasonics 01/2007; 44 Suppl 1:e1343-7. · 1.84 Impact Factor
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ABSTRACT: Two methods have been always used to calculate the electromechanical coupling coefficient of a Lamb wave in a multilayered plate: one is an approximate method using the acoustic velocity difference under different electric boundary conditions and the other is the Green's function method. The Green's function method is more accurate but more complicated, because an 8N-order matrix is used for calculating the electromechanical coupling coefficient of the Lamb wave in an N-layered plate, which induces great computation loads and some calculation deviations. In this paper, a transfer matrix method is used for calculating the electromechanical coupling coefficient of Lamb waves in a multilayered plate, in which only an 8-order matrix is needed regardless of the number of layers of the plate. The results show that the transfer matrix method can obtain the same accuracy as those by the Green's function method, but the computation load and deviation are greatly decreased by avoiding the use of a high order matrix used in the Green's function method.
Ultrasonics 01/2007; 44 Suppl 1:e849-52. · 1.84 Impact Factor
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ABSTRACT: The acoustic characteristics of plate-mode sensors with bi-layered structures composed of a piezoelectric film and a non-piezoelectric substrate are studied by numerical calculations using the transfer matrix method. Performances of the sensors can be evaluated based on the theoretical calculations of the dispersion curves, electromechanical coupling coefficients and sensitivities of the plate-mode sensors with a bi-layered structure. In order to obtain the optimized operating conditions of the sensors, the operating mode, frequency and the ratios of thickness of piezoelectric film to that of the substrate are evaluated when the sensors are applied in gas and/or liquid conditions.
Ultrasonics 01/2007; 44 Suppl 1:e917-21. · 1.84 Impact Factor
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ABSTRACT: At the present moment, the smallest piezoelectric ultrasonic micro-motors utilizing miniature PZT piezoelectric ceramic tubes were developed. The motor consists of a PZT-metal composite tube stator, two steel rotors and a thin shaft that keeps the two rotors pressing on both ends of the stator elastically. The dimensions of the PZT tube are 1.0 mm in outer diameter, 0.6 mm in inner diameter and 5.0 mm in length. The diameter and total length of the assembled micro-motor is 1.0 mm and 8 mm (including an adjusting spring), respectively. The tube-type micro-motor is driven by two pairs of alternative voltages with phase shift 90 degrees between the adjacent electrodes and operated in the first circular-bending vibration mode of the stator with the resonance frequency about 58 kHz. The experimental results show that the tube-type micro-motors have perfect performances: (i) high rotation frequency over 3000 rpm and (ii) large starting torque over 7.8 microN m under the conditions of the input voltage of 110 V(p-p) and the resonance frequency. The micro-motor is well suitable for operating in micro-spaces, such as in intravascular, micro-robots and micro-craft applications.
Ultrasonics 01/2007; 44 Suppl 1:e603-6. · 1.84 Impact Factor
