Zhao-jiang Chen

High piezoelectricity of Pb(Zr,Ti)O3-based ternary compound thin films on silicon substrates

Pb(Zr,Ti)O3 (PZT)-based ternary compound thin films, 0.06PMnN-0.94PZT(50/50) (PMnN-PZT), are deposited on Si-based heterostructures by rf magnetron sputtering system. The intrinsic PZT(50/50) thin films are also deposited on the same kind of substrates for comparison. The PMnN-PZT thin films show the similar polycrystalline structures as those of PZT with highly (111) oriented perovskite phase. The PMnN-PZT thin films show excellent piezoelectricity and ferroelectricity which are distinctly better than those of PZT thin films prepared with the same deposition conditions. Besides, the cantilevers of PMnN-PZT thin films on the heterostructure substrates also exhibit higher sensitivities than the PZT thin film cantilevers.

Anomalous subharmonics excited by intensive ultrasonic pulses with a single frequency

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.

Characterisation of thermal property of materials by infrared thermography

An infrared thermography is used for non-contact characterisations of thermal properties of materials. In the experiment, a pulsed laser is used to excite a transient thermal source in the material, and an infrared camera system is used to record the infrared thermal images of the subsequent heat diffusion and heat loss processes. In the theory, by a solving heat conduction equation, a two-dimensional thermal distribution function produced by the pulsed laser excitation can be obtained. Then, based on the relations between both the two-dimensional thermal distribution functions extracted at any two times, the thermal diffusivities and heat loss rates of the materials can be obtained by fitting the theoretical calculations to the infrared images recorded at different times. The results indicate that this method is useful to determine the thermal diffusivity and thermal loss for industrial non-metallic materials with rough surfaces and/or inhomogeneous microstructures.

Quasisubharmonic vibrations in metal plates excited by high-power ultrasonic pulses

Strongly nonlinear vibration phenomena in metal plates excited by high-power ultrasonic pulses in different conditions are studied experimentally and theoretically. The experimental conditions for generating quasisubharmonics and subharmonics are found and discussed. The plate vibrations are characterized by waveforms, frequency spectra, pseudostate portraits, and Poincare maps. Then, a three-degree-of-freedom vibroimpact-dynamic model is presented to explore the generation mechanisms of the quasisubharmonic and subharmonic vibrations in the plates. According to the model, the intermittent contact-impact forces caused by the interactions between the transducer horn tip and the plate are considered as the main source for generating the complex nonlinear vibration in the plate. The numerical calculation results can explain reasonably the observed experimental phenomena.

Nonlinear vibrations and heating phenomena of cracks in metal plates excited by intensive ultrasonic pulses.

When thin metal plates are excited by intensive ultrasonic pulses, nonlinear vibration phenomena are observed in experiments. As the plates contain cracks, the frictional heating of both faces of the crack appears under the excitation of the ultrasonic pulses. Based on the experimental conditions, a finite element modeling is established and transient dynamic analyzes are performed to explore the generation mechanism of the nonlinear vibrations including superharmonics, subharmonics, and chaotics, as well as the heating phenomena of the cracks. A piezoelectric‐thermal analogy method is used to simulate the high‐power ultrasonic transducer excitation, and a contact‐impact algorithm is used to simulate the dynamical interaction between the ultrasonic horn and plate as well as between both sides of the cracks. By analyzing the vibration velocity waveforms, vibration frequency spectra, and contact force waveform, it can be found that the waveform distortion of the intermittent contact forces between the horn ...

Finite element simulation of the frictional heating of cracks under excitation of intensive ultrasonic waves

A thermo-mechanical coupling finite element (FEM) model is built to simulate frictional heating phenomenon of a crack when the plate containing the crack is excited by intensive ultrasonic waves. In the explicit FEM model, a high-power ultrasonic transducer is included for simulating the phenomena of acoustic chaos, and piezoelectric excitation of the transducer is realized by using a piezoelectric thermal-analogy method. Moreover, the dynamical interaction between both crack faces is modelled by using contact-impact algorithm. In the simulation, Dynamical contact force and relative motion of the crack faces, temperature-rise distribution around the crack, and temperature-rise versus time curves of the crack faces, are quantitatively calculated and analyzed when the plate undergoing chaotic excitation.

Vibration characteristics of besocke-style scanning systems

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.

Subharmonic vibrations in plates excited by high-intensive ultrasonic pulses

In this paper, the experimental and theoretical studies on the excitations of the subharmonic vibration in metal plates by the intensive ultrasonic pulses injected via an ultrasonic horn are presented. A series of experiments is performed to study the subharmonic vibration behaviors of rectangular stainless steel plates. The experimental results show that the excitations of the subharmonics change remarkably with different materials, sizes and fix (boundary) conditions of the plates, as well as the preload forces between the horn and plate. Meanwhile, a vibro-impact dynamical model is put forward to explore the generation mechanism of the subharmonics in the plates. According to the model, the intermittent contact between horn and plates is the reason for the generation of subharmonic vibration in plates. The numerical results are in agreement with the subharmonic phenomena observed in the experiments.