Sadayuki Takahashi

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.

Multilayer ceramic actuators

Abstract Piezoelectric and electrostrictive ceramic materials have now become key components in smart actuator/sensor systems used as precision positioners, miniature ultrasonic motors and adaptive mechanical dampers. In particular, multilayer structures have been intensively investigated in order to improve their reliability and to expand their applications. There have been recent developments in the USA, Japan and Europe.

Internal electrode piezoelectric ceramic actuator

Abstract A piezoelectric ceramic actuator element with multilayer internal electrodes has been investigated. It was fabricated by multilayer ceramic capacitor techniques. An individual internal electrode has the same area as the element cross section area. It has no piezoelectric inactive part, so that it shows original strain/field characteristics in the material. It can be driven by a relatively low votlage (< 200V) and has a semi-permanent life under successive voltage pulse application. Typical properties of the element using 0·65Pb(Mg1/3Nb2/3)O3-0·35PbTiO3 ceramics are 8·7 × 10−4 strain, over 3·5 × 107 N/m2 force, within 100 μsec response time and 70% electromechanical couplig factor driven by 1 × 106 V/m field.

Effects of Impurities on the Mechanical Quality Factor of Lead Zirconate Titanate Ceramics

The values of mechanical quality factor Qm are determined for lead zirconate titanate ceramics containing various oxides as impurities in various amounts. Impurities are found to be classified into two groups with respect to the change of Qm values, viz., (1) Qm decreases in the presence of impurities (e. g. Nb2O5), (2) Qm increases in the presence of minor additions (e.g. Cr2O3). The values of Qm are found to increase when both the amount of space charge and specific resistivity increase. This seems to be caused by the suppression of domain wall motion resulting from the prevention of space charge migration. An empirical formula is obtained for Qm as a function of the reduced amount of space charge and specific resistivity.

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.

Internal Bias Field Effects in Lead Zirconate-Titanate Ceramics Doped with Multiple Impurities

The effects of doping with multiple impurities on the electromechanical properties of lead zirconate-titanate ceramics have been investigated from the viewpoint of the internal bias field. The internal bias field is strengthened by doping with the multiple acceptors K and Fe, but weakened by the multiple donors La and Nb. Simultaneous doping with donor and acceptor prevents the field from being enhanced by the latter. These facts suggest that the internal bias field is caused by a complex of an acceptor impurity and an oxygen vacancy. The properties of ceramics can be varied by controlling this field, and the mechanical quality factor and the aging change in the frequency constant are proportional to it.

Ultrasonic transducers with functionally graded piezoelectric ceramics

Ultrasonic transducers used for measurement systems are required having a capability of generating a short time waveform ultrasonic pulse, i.e., a broadband frequency spectrum. In order to obtain the broadband transducer, functionally graded piezoelectric ceramics with a ceramic backing are fabricated and their ultrasonic performances are examined. Gradient of the piezoelectric parameter is realized by sintering a layer-structured ceramic green body composed of piezoelectric ceramic calcined powder layers with various compositions or composed of green sheets containing calcined powder mixed with some organic materials. It has been found that the above transducer generates an ultrasonic wave with a broader frequency spectrum compared with that of the conventional one.

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.

Design of Ultrasonic Transducers with Multiple Acoustic Matching Layers for Medical Application

For high-efficiency wide-band piezoelectric transducers, a design method based on the synthesis theory of multiple-mode filters is presented. This design method has the advantages that it retains phys- ical intuition and can find optimum values of these matching layers by using iterative calculation techniques. An air-backed disk transducer with triple matching layers has been built to illustrate this design ap- proach, and good agreement between theory and experiment has been achieved. The transducer has SS-percent 6-dB fractional bandwidth, 3.2-dB round trip insertion loss, and less than l-dB passband ripple. Moreover, a prototype linear array probe with triple matching layers has been produced and has been used in an ultrasonic diagnostic equip- ment. Ultrasonograms with high resolution were obtained.