Mikio Umeda

Analysis of the Transformation of Mechanical Impact Energy to Electric Energy Using Piezoelectric Vibrator

We propose a new mechanism of electric power generation in which mechanical impact energy is transformed to electric energy by a piezoelectric transducer. To clarify the relationship between the input mechanical impact energy and the output electric energy in this method, we measured the electric output of a piezoelectric vibrator stimulated by an impact with a steel ball. An electrical equivalent model of the phenomenon is proposed to analyze the transformation efficiency as functions of the electromechanical coupling coefficient, the mechanical loss and the dielectric loss of the vibrator.

Energy storage characteristics of a piezo-generator using impact induced vibration

This paper presents theoretical and experimental considerations of the energy storage characteristics of a piezoelectric generator developed previously by the authors. In this paper, the oscillating output voltage induced by mechanical impact via the piezoelectric effect is rectified, and the electrical energy is stored in a capacitor. The effect of the capacitance of the capacitor and the initial voltage is investigated using an equivalent circuit model. A maximum efficiency over 35% has been achieved with a prototype generator.

Effects of Vibration Stress and Temperature on the Characteristics of Piezoelectric Ceramics under High Vibration Amplitude Levels Measured by Electrical Transient Responses

This paper presents a characteristic evaluation of piezoelectric ceramics at high vibration amplitude levels of resonance, based on the electrical transient response technique. Low-Q and high-Q materials are measured, and the effect of vibration stress is obtained without affecting temperature. It is revealed that for low-Q materials an increase of loss is caused mainly by the vibration stress, while for high-Q materials, it is caused by both the vibration stress and the temperature increase. The results show that in some high-Q materials, it is meaningless to evaluate the piezoelectric materials at low vibration level, since the characteristics change variously at high vibration levels. The force factor is changed mainly by the temperature, although its behavior is different, depending on material composition.

An Analysis of Jumping and Dropping Phenomena of Piezoelectric Transducers using the Electrical Equivalent Circuit Constants at High Vibration Amplitude Levels

This paper presents an analysis of the jumping and dropping phenomena of piezoelectric transducers, using the electrical equivalent circuit constants at high vibration amplitude levels of resonance based on the electrical transient response technique. The calculated frequency characteristics well simulated the measured ones driven by a constant voltage source. It is clarified from the results that the jumping and dropping phenomena are caused mainly by the nonlinear behavior of the elastic constant at high vibration amplitude levels. The effects of the loss, the voltage and the driving method are also discussed.

High-Power Characteristics of Multilayer Piezoelectric Ceramic Transducers

In this report, the behavior of the mechanical quality factor Qm for multilayer piezoelectric transducers which operate at a low to high vibratory velocity is described. It has long been known that the Qm of multilayer piezoelectric devices, such as transformers and actuators, decreases when the number of ceramic layers in the devices is increased. In such devices, the output power converges to a saturated value with heat generation much lower than that which the value of Qm measured at low vibration velocity would suggest. This fact implies that the Qm strongly depends not only on the number of ceramic layers, but also on vibratory velocity and temperature. It appears that high-power and vibratory velocity characteristics of the Qm for multilayer piezoelectric transducers have not been studied sufficiently. Taking the temperature factor into consideration, we used the electrical transient response method and equivalent circuit analysis to investigate the vibratory velocity characteristics of the Qm for multilayer piezoelectric transducers.

Effects of a Series Capacitor on the Energy Consumption in Piezoelectric Transducers at High Vibration Amplitude Level

In this paper, a driving method for low-loss generation in piezoelectric transducers at a high vibration amplitude level is presented. First, we analyze the power consumption of several loss mechanisms of piezoelectric transducers using an electrical equivalent circuit model. In this model, loss due to piezoelectric effect is explicitly represented by a series resistor, and pure dielectric loss is separately denoted by a parallel resistor. Mechanical loss is represented by a series resistor in the mechanical arm. The reason for the high efficiency at the anti resonance frequency is explained by this analysis. Next, the effect of an external series capacitor is discussed by comparing the experiment with the calculation, based on the equivalent circuit model for the high vibration amplitude level. By using the external series capacitor, the loss generated at the high vibration amplitude was significantly reduced without a large increase in electrical impedance.

DC bias field dependence on high-power characteristics of PbTiO3 -Pb (Mg1/3Nb2/3)O3 electrostrictive ceramics

The mechanical quality factor Qm of a normal ferroelectric ceramic vibrator decreases and heat is given off when the vibrator is continuously driven at a high level of vibration stress under a resonant mode. The irreversible motions of ferroelectric non-180° domain walls in the ferroelectric ceramic vibrator cause this unfavorable behavior. The effect of ferroelectric domain structure under the vibration stress on electromechanical characteristics was studied using relaxor ferroelectric electrostrictive (1-x)PbTiO3–xPb(Mg1/3Nb2/3)O3 (x=1.00, 0.95, 0.90) ceramics. The Qm of the paraelectric Pb(Mg1/3Nb2/3)O3 ceramics was consistently higher than 5000 at a high stress level under a dc bias field. This Qm is much larger than that of typical hard lead zirconate titanate (PZT) ceramics. The Pb(Mg1/3Nb2/3)O3 ceramics show a considerably large piezoelectric d31 constant which is comparable to that of hard PZT ceramics. The electrostrictive ceramics are therefore superior electromechanical vibrator materials for high-power devices.

Vibration-stress dependence of electromechanical characteristics for electrostrictive Pb(Mg1/3Nb2/3)O3-based ceramics

The mechanical quality factor Qm of a normal ferroelectric, piezoelectric ceramic vibrator decreases and heat is given off, when the vibrator is continuously driven at a high level of vibration-stress under a resonant mode. It has been thought that irreversible motions of ferroelectric non-180° domain walls cause this behavior. The effect of ferroelectric domain structure on the vibration-stress dependence of electromechanical characteristics was studied using relaxor ferroelectric electrostrictive (1-x)PbTiO3-xPb(Mg1/3Nb2/3)O3 (x=1.00, 0.95, 0.90) ceramics. The Qm for the paraelectric crystal phase composition at room temperature is about five times higher than that for hard lead zirconate titanate (PZT) and the decrease of Qm with vibration-stress is suppressed at high stress levels. The piezoelectric d31 constant is almost the same as that of hard PZT. Electrostrictive ceramics are therefore superior electromechanical vibrator materials for high power applications.

DUMBBELL-SHAPED SMALL-SIZED HYBRID ULTRASONIC MOTOR

A dumbbel-shaped torsional vibrator is studied in the construction of a small hybrid transducer type ultrasonic motor whose stator consists of a Langevin type torsional vibrator and a longitudinal piezoelectric actuator. Two kinds of stators 20 mm in diameter are designed by FEM for this construction. These motors proved to operate successfully as expected and maximum torque of 1kgfcm.