Electromechanical transformation device and method for manufacturing the same

Abstract

An electromechanical transformation device comprises an alkaline niobate piezoelectric ceramic composition and a rigid body adhered onto the major surface of the piezoelectric ceramic composition. The piezoelectric ceramic composition is made of crystal structures such as orthorhombic crystals formed at the side where the temperature is lower than the orthorhombic-to-tetragonal phase transition temperature, tetragonal crystals formed at the side where the temperature is higher than the orthorhombic-to-tetragonal phase transition temperature as well as at the side where the temperature is lower than the tetragonal-to-cubic phase transition temperature, and the cubic crystals formed at the side where the temperature is higher than the tetragonal-to-cubic phase transition temperature. Young's modulus of the rigid body is 60 GPa or more and the volume percent of the piezoelectric ceramic composition existing within a range where the distance from the adhesion point of the piezoelectric ceramic composition and the rigid body is 40% or more.

1 . An electromechanical-transformation device using crystal structures that include an orthorhombic crystal formed at the side where the temperature is lower than the orthorhombic-to-tetragonal-phase transition temperature and that include a tetragonal crystal formed at the side where the temperature is higher than the orthorhombic-to-tetragonal-phase transition temperature and at the side where the temperature is lower than the tetragonal-to-cubic-phase transition temperature and that include a cubic crystal formed at the side where the temperature is higher than the tetragonal-to-cubic-phase transition temperature, and wherein that the electromechanical-transformation device comprises a rigid body having a Young's modulus of 60 GPa or more and comprises a piezoelectric-ceramic composition of which a volume-percentage, being within the range of which the distance from the point of attachment of the rigid body to the piezoelectric-ceramic composition is two mm or less, is 40% or more as compared to the whole piezoelectric-ceramic composition and the piezoelectric-ceramic composition has a major surface acting as an acoustic radiation surface, that the rigid body is directly adhered to the major surface of a piezoelectric-ceramic composition or indirectly to the major surface by the intermediary electrodes and acts as an acoustic-matching layer to emit ultrasonic waves, and that the thickness of the rigid body is formulized as t={v/(4f)}±10% or t=[v/(2f)]±10% of which f means the resonance-frequency of the piezoelectric-ceramic composition and v means the acoustic-velocity of the rigid body and t means the thickness of the rigid body. 
     
     
         2 . An electromechanical-transformation device according to  claim 1 , whereof the orthorhombic-to-tetragonal-phase transition temperature is within the range of the operating temperature of said device and/or within the range of the storing temperature of said device, and that the tetragonal-to-cubic-phase transition temperature is within a temperature range higher than the operating temperature. 
     
     
         3 . An electromechanical-transformation device, according to  claim 1 , whereof a rigid body is adhered to the piezoelectric-ceramic composition by a thermosetting resin-adhesive. 
     
     
         4 . An electromechanical-transformation device, according to  claim 1 , whereof the rigid body is adhered to the piezoelectric-ceramic composition by an epoxide-based adhesive. 
     
     
         5 . An electromechanical-transformation device, according to  claim 3 , whereof the adhesive that adheres the rigid body to the piezoelectric-ceramic composition has a curing temperature within the range exceeding the orthorhombic-to-tetragonal-phase transition temperature by 50 degrees Celsius or more and that is falls below the tetragonal-to-cubic-phase transition temperature by 50 degrees Celsius or more. 
     
     
         6 . An electromechanical-transformation device, according to  claim 1 , whereof the piezoelectric-ceramic composition is formulized as {Li x (K 1-y Na y ) 1-x } a (Nb 1-z-w Ta z Sb w )O 3  within the composition-range of 0.90≦a≦1.2, 0.02≦x≦0.2, 0.2≦y≦0.8, 0≦z≦0.5, 0≦w≦0.2. 
     
     
         7 . An electromechanical-transformation device, according to  claim 1 , whereof the rigid body is made of a ceramic composition containing silica, alumina, or silica-alumina in major proportions. 
     
     
         8 . (canceled) 
     
     
         9 . A method for manufacturing the electromechanical-transformation device, according to  claim 1 , with the method comprising a polarization-process in which a pair of electrodes is formed on the piezoelectric-ceramic composition, and in which polarization is provided on said composition by impressing a direct current of electricity between the electrodes; and comprising an adhesion-process in which the piezoelectric-ceramic composition and the rigid body are adhered together by a thermosetting-adhesive of a curing temperature-range exceeding the orthorhombic-to-tetragonal-phase transition temperature by 50 degrees Celsius or more and falling below the tetragonal-to-cubic-phase transition temperature by 50 degrees Celsius or more, and that in the adhesion-process the thermosetting-adhesive is heated within the curing temperature-range after completion of the foregoing polarization-process.