Yoke-Rung Wong

Improved measurement of resistance and calculation of arc power in fusion welding

Abstract We reported a new method based on the input electrical impedance of a welding system to measure the resistance of the welding system for the arc power calculation in fusion welding. This impedance can be obtained by dividing the measured voltage to current in their analytic form. Two time recorded waveforms, namely, resistance and reactance of impedance, are therefore calculated. Theoretically, the resistance used for arc power calculation is obtained by dividing measured voltage to current directly without considering the influence of inductance. Through experimental studies, we confirm that the error of arc power calculation incurred by the influence of inductance can range from 2 to 10% depending on the welding voltage and current setting. Since the proposed method can obtain the resistance of the welding system without the influence of inductance, it is a better approach as compared with the current method to obtain the accurate resistance and then arc power.

Design, fabrication and characterization of a zinc oxide thin-film piezoelectric accelerometer

Conventionally manufactured accelerometers based on piezoelectric lead zirconate titanate (PZT) have been used for decades, but integration issues hinder their application in micro-electro-mechanical systems (MEMS). Compared to PZT, zinc oxide (ZnO) has lower piezoelectricity and is not an attractive material for use in traditional bulky accelerometers due to its low sensitivity. However, ZnO has excellent compatibility with MEMS processing techniques, and furthermore, sensitivity can be enhanced by MEMS miniaturization. In this paper, we report the development of a micromachined ZnO piezoelectric thin-film accelerometer that demonstrates the feasibility of both easy integration and high sensitivity.

Analytical solutions to flexural vibration of slender piezoelectric multilayer cantilevers

The modeling of vibration of piezoelectric cantilevers has often been based on passive cantilevers of a homogeneous material. Although piezoelectric cantilevers and passive cantilevers share certain characteristics, this method has caused confusion in incorporating the piezoelectric moment into the differential equation of motion. The extended Hamiltons principle is a fundamental approach to modeling flexural vibration of multilayer piezoelectric cantilevers. Previous works demonstrated derivation of the differential equation of motion using this approach; however, proper analytical solutions were not reported. This was partly due to the fact that the differential equation derived by the extended Hamiltons principle is a boundary-value problem with nonhomogeneous boundary conditions which cannot be solved by modal analysis. In the present study, an analytical solution to the boundary-value problem was obtained by transforming it into a new problem with homogeneous boundary conditions. After the transformation, modal analysis was used to solve the new boundary-value problem. The analytical solutions for unimorphs and bimorphs were verified with three-dimensional finite element analysis (FEA). Deflection profiles and frequency response functions under voltage, uniform pressure and tip force were compared. Discrepancies between the analytical results and FEA results were within 3.5%. Following model validation, parametric studies were conducted to investigate the effects of thickness of electrodes and piezoelectric layers, and the piezoelectric coupling coefficient d 31 on the performance of piezoelectric cantilever actuators.

Novel classification method of metal transfer modes in gas metal arc welding by real time input electrical impedance

Abstract This paper presents an online, accurate and easy to use method for metal transfer mode classification using the input electrical impedance of arc welding as the signature. The records of the input electrical impedance are obtained by processing the welding voltage and current signals picked up at the output terminal of a welding machine. Similar to a typical linear electrical circuit consisting of a resistor, an inductor and a capacitor connected in series, the real and imaginary part of the input electrical impedance represents the combination of these electrical elements in the arc welding. Their variations directly reflect the switching among the metal transfer modes. A few experiments were conducted to confirm the above working principle and correlations between the input electrical impedance of arc welding and metal transfer. The results were then used to develop a method for online classification of metal transfer modes.

Micro- and nano-force evaluation of bioengineered muscle cells: a non-contact two-dimensional biosensing using surface acoustic wave devices

A high degree of cell-generated force measurement is required to evaluate the biomechanical performance of bioengineered muscle tissues. However, the conventional cantilever types of direct force measurement methods have limitations in developing a non-contact two-dimensional force sensing device for a single muscle cell. In this paper, a method is proposed and discussed by using focused surface acoustic wave and magneto-optic Kerr measurements. To depict the capability of the proposed method, a conceptual design of such a sensory device is demonstrated for non-contact two-dimensional force measurement of a single muscle cell.