Hyun-Woo Joo

Analysis of temperature rise for piezoelectric transformer using finite-element method

Analysis of heat problem and temperature field of a piezoelectric transformer, operated at steady-state conditions, is described. The resonance frequency of the transformer is calculated from impedance and electrical gain analysis using a finite-element method. Mechanical displacement and electric potential of the transformer at the calculated resonance frequency are used to calculate the loss distribution of the transformer. Temperature distribution using discretized heat transfer equation is calculated from the obtained losses of the transformer. Properties of the piezoelectric material, dependent on the temperature field, are measured to recalculate the losses, temperature distribution, and new resonance characteristics of the transformer. Iterative method is adopted to recalculate the losses and resonance frequency due to the changes of the material constants from temperature increase. Computed temperature distributions and new resonance characteristics of the transformer at steady-state temperature are verified by comparison with experimental results

Design and characteristic analysis of L1B4 ultrasonic motor considering contact mechanism

Up to the present time, the analysis and design of ultrasonic motors (USMs) have been performed using rough analytic methods or commercial analysis tools without considering the complex contact mechanisms. As a result, it was impossible to achieve an exact analysis and design of a USM. In order to address the problem, we proposed the analysis and design methodology of an L1B4 USM using a three-dimensional finite element method combined with an analytic method that considers complex contact mechanisms in linear operation. This methodology is applicable to many other kinds of USMs which use resonance modes and contact mechanisms. Also, we designed and prototyped the mechanical system and driving circuit of the L1B4 USM, and finally validated the proposed analysis and design methodology by comparing their outcomes with experimental data.

Identification of material constants for piezoelectric transformers by three-dimensional, finite-element method and a design-sensitivity method

In this paper, an inversion scheme for piezoelectric constants of piezoelectric transformers is proposed. The impedance of piezoelectric transducers is calculated using a three-dimensional finite element method. The validity of this is confirmed experimentally. The effects of material coefficients on piezoelectric transformers are investigated numerically. Six material coefficient variables for piezoelectric transformers were selected, and a design sensitivity method was adopted as an inversion scheme. The validity of the proposed method was confirmed by step-up ratio calculations. The proposed method is applied to the analysis of a sample piezoelectric transformer, and its resonance characteristics are obtained by numerically combined equivalent circuit method.

Analysis of piezoelectric transformer by using finite element method and equivalent-circuit considering load variation

The three-dimensional finite element analysis for piezoelectric transformers is presented. Numerically combined equivalent-circuit method for consideration of load variation, is proposed. The three-dimensional finite element routine in this paper is confirmed experimentally by analyzing piezoelectric transducer. Using results from finite element analysis of piezoelectric transformer, equivalent-circuit parameters of piezoelectric transformer are obtained. The method to calculate loss parameter of piezoelectric transformer is proposed. Characteristics of piezoelectric transformer due to load variation are analyzed. The validity of the proposed method is confirmed by loss calculations.

Analysis of ultrasonic linear motor by using finite element method and equivalent circuit

In this paper, the three-dimensional finite element method and construction of an equivalent-circuit for the linear ultrasonic motor, is presented. The validity of the three-dimensional finite element routine in this paper is experimentally confirmed by analyzing the impedance of a piezoelectric transducer. Using this confirmed finite element routine, the impedance and vibration mode of a linear ultrasonic motor are calculated. Elliptical motion of the contact point between vibrator and rail of a linear ultrasonic motor is shown for determination of the contact point. Using the finite element method and analytic equations, characteristics of linear ultrasonic motor, such as thrust force, speed, losses, power and efficiency, are calculated. And the results are confirmed by experiment. Finally, equivalent circuit parameters of the linear ultrasonic motor are obtained by three-dimensional finite element method and analytic equations.

Inversion of piezoelectric material coefficients by using finite element method with Asymptotic Waveform Evaluation

In this paper, a fast inversion scheme for piezoelectric constants of piezoelectric transformer is proposed. The effects of material coefficients on piezoelectric transformers are investigated by using three-dimensional finite element method (FEM) which is confirmed experimentally. A design sensitivity method adopted as an inversion scheme and Asymptotic Waveform Evaluation (AWE) is used for fast frequency sweep.