Seiji Hirose

Vibration-Level Characteristics of Lead-Zirconate-Titanate Ceramics

Vibration-level characteristics of lead-zirconate-titanate ceramics were studied using the constant current driving method. It was found that resonant frequency and mechanical Q markedly decreased with increasing vibration level, accompanying heat generation. The heat generation was assumed to be caused by vibration loss. The vibration loss was reduced by doping Fe atoms to the ceramics. On the contrary, the vibration loss was increased by doping Nb atoms.

High Power Characterization of Piezoelectric Materials

Three techniques for measuring high voltage/power piezoelectric properties, which have been developed recently, are compared: a voltage-constant piezoelectric resonance method, a current-constant piezoelectric resonance method, and a pulse drive method. The conventional resonance method with a constant voltage circuit exhibits significant distortion (or a hysteresis) in the resonance frequency spectrum under a high vibration level due to large elastic non-linearity, which limits precise determination of the electromechanical coupling parameters. To the contrary, the resonance method with a constant current circuit (i.e., constant velocity) can determine the coupling parameters more precisely from a perfectly-symmetrical resonance spectrum. The general problem in both resonance methods is heat generation in the sample during the measurement. In order to separate the temperature characteristic from the non-linearity, it is recommended that the pulse method be used in parallel, even though the accuracy is not very high.

Miniature Cantilever-Type Ultrasonic Motor Using Pb-Free Multilayer Piezoelectric Ceramics

A Miniature cantilever-type ultrasonic motor was fabricated using multilayer piezoelectric ceramics (MLPC) made of (Sr,Ca)2NaNb5O15 (SCNN), a Pb-free piezoelectric material, and the electrical driving properties were investigated. The displacement of SCNN-MLPC was 177 nm at 100 V, which was 10-fold the voltage of MLPC made of Pb(Zr,Ti)O3–Pb(Ni,Nb)O3–Pb(Zn,Nb)O3 (PZT). The ultrasonic motor using SCNN-MLPC started to rotate at 3.8 Vp–p, and showed the following characteristics: a revolution speed of Ω0=517 rpm, a torque of T0=1.4 µN m, and an efficiency of η=7% at 13.4 Vp–p. The power consumption, in this case, was 0.3 mW, which is not so high. On the other hand, an ultrasonic motor of the same form made of PZT-MLPC showed Ω0=610 rpm, T0=1.6 µN m, and η=9% at 1.9 Vp–p, and the same power consumption as the SCNN motor. That is, it was found that the SCNN motor was not so different from the PZT motor in terms of their characteristics; however, the SCNN motor needed 10 times as high a voltage as the PZT motor in electrical driving. In conclusion, it can be said that we succeeded in realizing a miniature cantilever-type ultrasonic motor using Pb-free MLPC.

Loss mechanisms and high power piezoelectrics

Heat generation is one of the significant problems in piezoelectrics for high power density applications. In this paper, we review the loss mechanisms in piezoelectrics first, followed by the heat generation processes for various drive conditions. Heat generation at off-resonance is caused mainly by dielectric loss tan δ′ (i.e., P-E hysteresis loss), not by mechanical loss, while the heat generation at resonance is mainly attributed to mechanical loss tan ′. Then, practical high power materials developed at Penn State is introduced, which exhibit the vibration velocity more than 1 m/s, leading to the power density capability 10 times of the commercially available “hard” PZTs. We propose a internal bias field model to explain the low loss and high power origin of these materials. Finally, using a low temperature sinterable “hard” PZT, we demonstrated a high power multilayer piezoelectric transformers

Stability of PbZrO3-PbTiO3-Pb(Mn1/3Sb2/3)O3 Piezoelectric Ceramics under Vibration-Level Change.

Vibration-level characteristics of electromechanical properties in the pseudo-ternary solid solution system PbZrO3-PbTiO3-Pb(Mn1/3Sb2/3)O3 ceramics were studied using a constant current control method. Stability under a vibration-level change was determined from the measurements of Youngs modulus Y0 E and mechanical dissipation factor Q m-1. Durability degree for a high vibration-level excitation was estimated by a heat generation phenomenon. The durability was found to be dependent on the stability. As the stability increased, the durability also increased. The durability degree for a high vibration-level excitation was improved in the pseudo-ternary solid solution system PbZrO3-PbTiO3-Pb(Mn1/3Sb2/3)O3 ceramics over the binary solid solution system PbZrO3-PbTiO3 ceramics.

Vibration-Level Characteristics for Iron-Doped Lead-Zirconate-Titanate Ceramic

Vibration-level characteristics for Fe-doped lead-zirconate-titanate ceramic were studied using the constant current driving method. It was found that mechanical Q was markedly decreased with increasing vibration level, accompanying a lot of heat generation. The other electromechanical characteristics were slightly changed. The heat generation was found to decrease with increasing Fe doping concentration up to ~2 at.%, and was found to show a minimum for lead-zirconate-titanate with the basic composition close to the morphotrophic phase boundary. It was assumed that the heat generation was mainly caused by ferroelectric domain wall hysteresis loss.

High power characteristics at antiresonance frequency of piezoelectric transducers

First in this paper, the loss in piezoelectric ceramics is described. Antiresonance is the vibration under constant D (electric displacement) driving, and therefore electro-mechanical loss becomes almost zero: resonance is the vibration under constant E (electric field) driving, and then there exists large electro-mechanical loss. The relations between antiresonance and the constant D driving are explained. Next, a method of measuring the high-power characteristics is described for antiresonance frequency. Experimental results for the quality factor and temperature rise and other equivalent constants are then shown as high-power characteristics obtained at the antiresonance frequency. Finally, some considerations for the stable-state driving of the high-power piezoelectric devices are described.

Piezoelectric Ceramic Transformer Using Piezoelectric Lateral Effect on Input and on Output.

Recently, the authors have investigated the characteristics of many piezoelectric ceramic materials for high-power use. As a result, some advanced materials suitable for high-power ultrasonic devices have been identified. Using these materials, new piezoelectric transformer designs different from Rosens design can be utilized for high-voltage supply. In this paper, a piezoelectric transformer using piezoelectric lateral coupling on Input and on output is presented and simulated transformer characteristics are shown.

Double-Mode Miniature Cantilever-Type Ultrasonic Motor Using Lead-Free Array-Type Multilayer Piezoelectric Ceramics

We studied the following to improve the characteristics of the lead-free ultrasonic micromotor. A double-mode miniature cantilever-type ultrasonic motor was fabricated using array-type multilayer piezoelectric ceramics (A-MLPC) of (Sr,Ca)2NaNb5O15 (SCNN) such as lead-free piezoelectric materials, and the electrical driving properties were investigated. The A-MLPC integrated multilayer piezoelectric ceramics (MLPC) arrayed in a 2 ×2 matrix. By using A-MLPC, double-mode bending vibration of the stator vibrator can be realized easily, and the quality factor of the vibrator increased. Furthermore, with the improvement of the piezoelectric properties of the SCNN, the electromechanical coupling coefficient of the vibrator increased. As a result, we succeeded in improving the driving properties of the motor. In particular, the driving voltage of SCNN motor decreased to 1/10 of the previous study, and this motor is similar to Pb(Zr,Ti)O3–Pb(Ni,Nb)O3–Pb(Zn,Nb)O3 (PZT) one in terms of properties by applying 3 times higher voltage than that required for the PZT one. The SCNN motor started to rotate at 0.3 Vp–p and showed such characteristics as revolution speed of 730 rpm, torque of 0.7 µN m, and efficiency of 3.5% at 1.6 Vp–p. It appeared that the SCNN motor was able to rotate by a lithium-ion cell used in the mobile equipment without an amplifier circuit.

Dielectric Loss in a Piezoelectric Ceramic Transducer under High-Power Operation; Increase of Dielectric Loss and Its Influence on Transducer Efficiency

Dielectric loss in a piezoelectric ceramic transducer is related to the vibration, and increases markedly under high-power operation. When PZT ceramics is used over the vibration velocity of about 0.25 (m/s), the dielectric loss becomes larger than the mechanical vibration loss. In this paper, the values of the resistances indicating the dielectric loss and mechanical vibration loss in the equivalent circuit are shown. If an equivalent electric circuit including these resistances is utilized, efficiency of the transducers operating at a high-power level may be calculated with more accuracy. By calculation of the efficiency, the maximum efficiency was obtained at the anti-resonance frequency, not at the resonance frequency. These facts cannot be explained by the ordinary equivalent circuit which does not involve dielectric loss related to the vibration.