Showing papers on "Piezoelectricity published in 1972"

Elasticity, Piezoelectricity and Crystal Lattice Dynamics

Abstract: A review of some recent developments in the area between the dynamical theory of crystal lattices, in the harmonic approximation, and the classical, linear theories of elasticity and piezoelectricity.

Electromechanical Properties of Oxygen‐Octahedra Ferroelectric Crystals

Abstract: A phenomenological theory of the electromechanical properties of various types of oxygen‐octahedra ferroelectrics is presented. The electrostrictive constants reduced to those of the perovskite‐type oxide are nearly constant with the values Q11p≈0.10 m4/C2, Q12p≈−0.034 m4/C2, and Q44p≈0.029 m4/C2. These constants are obtained by assuming that the piezoelectric effect in the ferroelectric phase is due to the electrostrictive effect in the paraelectric phase biased by the spontaneous polarization. The oxygen‐octahedra ferroelectrics can be treated approximately as elastically isotropic and the stiffnesses normalized to those of the perovskite‐type oxide c11p and c44p are shown to be proportional to their melting points TM, i.e., c11p≈1.3×108TM(°K) N/m2 and c44p≈0.47×108TM(°K) N/m2. The potential usefulness for ultrasonic applications of oxygen‐octahedra ferroelectrics is discussed for dielectrically isotropic plates under perpendicular field excitation. The orientation of the plate which has the largest cou...

Stabilization effects in piezoelectric lead titanate zirconate ceramics

Abstract: The effect of stabilizing the properties of piezoelectric Pb(ZrTi)O3-ceramics by addition of the oxides of Mn, Cr or U is studied. Some ordering of the polarization is found to be preserved after heating the material above the Curie temperature. A model for the mechanism is presented, the basic idea of which is the trapping of charge carriers compensating the grain surface charges caused by the spontaneous polarization.

Elastic and piezoelectric constants of the cuprous halides

Abstract: Elastic and piezoelectric constants of CuCl, CuBr, and CuI have been measured. The elastic constants of zinc‐blende‐structure materials when plotted on a reduced scale indicate a striking instability as the Phillips critical ionicity (0. 785) is approached. CuCl is the most piezoelectric of these materials with a piezoelectric constant e14=0.41 C/m2 at 80°K.

Elastic and Piezoelectric Properties of Ferroelectric 5PbO · 3GeO2 Crystals

Abstract: The elastic, piezoelectric, and dielectric constants of a new ferroelectric crystal 5PbO · 3GeO2 have been measured. The measurements involve mostly the use of thickness modes in small plates of various crystallographic orientations. The electromechanical coupling factors turn out to be small, which makes this material unattractive for ultrasonic applications. The temperature characteristics of some piezoelectric constants are presented. The piezoelectric constant d31 vanishes above the Curie point (177 °C), while d22 remains constant above and below the Curie point.

Piezoelectric-type electroacoustic transducer

Abstract: A piezoelectric-type electroacoustic transducer composed of two convex or concave piezoelectric polymer films each having electrodes on both surfaces thereof, said two polymer films being so connected to electric wiring that, when the one of the piezoelectric polymer films elongates by the action of an electric field in one direction, the other shrinks by the action of the same electric field.

Pressure wave piezoelectric sensor of continuous structure

Abstract: Pressure wave sensor formed of at least one elongated piezoelectric element having two faces, each associated to a flexible conducting electrode substantially over the whole length of the sensitive element. When the sensor is formed of a plurality of sensitive elements the latter are electrically connected to one another.

Polymer type electroacoustic transducer element

Abstract: A piezoelectric type electroacoustic transducer element having a high sensitivity in a high frequency region is composed of a piezoelectric polymer sheet having on one surface thereof a backing of a material having a larger elasticity (Young''s Modulus) and mass than the elasticity and mass of the piezoelectric polymer sheet.

Piezoelectric, Elastic and Dielectric Properties of LiGaO2

Abstract: A single crystal of lithium meta-gallate is synthesized by means of the Bridgman technique. The values of all tensor components of piezoelectric constant d, elastic compliance sE and dielectric constant eT are determined. The variations of the electromechanical coupling factor k'31 in the length-extensional mode of LiGaO2 resonators with crystallographic orientation are determined numerically by use of the values of the tensor components obtained. In order to determine the variations of the temperature coefficient of resonance frequency Tfr in the length-extensional mode of the resonators with orientation, the values of temperature coefficients both of elastic compliance and thermal expansion are measured. The maximum of k'31 is found to be 0.23, the value of Tfr being in the range from -40 to -65 ppm/°C.

Electrostatic-piezoelectric transducer

Abstract: An electrostatic type electroacoustic transducer having improved acoustic characteristics is composed of a piezoelectric polymer-type oscillator having a stretching-type piezoelectric effect, such as a polarized polyvinylidene fluoride film having electrodes vacuum-coated on both surfaces and at least one fixed electrode disposed facing the oscillator and spaced therefrom.

Piezoelectric transducer and noise making device utilizing same

Abstract: A noise making device, using a piezoelectric transducer, includes a piezoelectric element mechanically coupled to a substrate and an electrical circuit for energizing the transducer. The piezoelectric element includes a piezoelectric crystal, first and second electrode means carried by the crystal, and means dividing one of the electrode means into electrically isolated areas so as to provide a third electrode means.

Elastic, Piezoelectric, and Dielectric Constants of Bi12 GeO20

Abstract: In order to resolve conflicting published results concerning the values of the elastic, piezoelectric, and dielectric constants of Bi12GeO20, an exhaustive study of this material has been made. Over 45 samples of material grown by three independent sources were tested. The piezoelectric constant was determined using three different techniques. In addition, the first accurate measurements of the dielectric constant of Bi12GeO20 at microwave frequencies have been made. Recommended values of the material constants are as follows: c11E=1.28×1011 N/m2, c12E=0.305×1011 N/m2, c44E=0.255×1011 N/m2, e14 = 0.99 C/m2, and e11S=34.2×10−11 F/m.

Electrical-mechanical coupling due to charged dislocations

Abstract: A theory for the relationship between the mechanical damping, compliance defect, piezoelectric moduli and electric susceptibility due to charged dislocations is discussed. A damping and piezoelectric (direct and converse) experiment on a single crystal of KCl at 40 kHz and strain amplitudes of 1·6 × 10−10 to 1·5 × 10−5 is reported. The method is shown to be suitable for the measurement of a piezoelectric modulus as small as 5 × 10−19 coulomb/newton. The mechanical damping, compliance defect and piezoelectric modulus are found to be strongly amplitude dependent above a strain of 3 × 10−7. From this experiment the charge on the dislocations is calculated to range between 1 and 3% of the maximum allowed on a dislocation. The behaviour of this measured charge with strain amplitude suggests that the damping is due to charged dislocations interacting with their compensating charge clouds. The charge cloud radius of 13 A calculated from the impurity concentration agrees favourably with the value o...

Linear transducer array for ultrasonic image conversion

Abstract: An ultrasonic transducer comprising a linear array of piezoelectric elements for converting a single line from a compressional acoustic image field to electrical impulses which, in turn, provide a means for converting the incident compressional image field to a visual representation. In order to match the configuration of the acoustic image field, the array of piezoelectric elements, in a preferred embodiment, has the configuration of an arc, that is, the array is arranged in a straight line in one plane and in an arc in a plane orthogonal to the first. The transducer is made up of a plurality of assemblies each of which is composed of segments of piezoelectric material each held in a supporting slot in a length of metal plate which slot is filled with a material selected to provide impedance matching between the piezoelectric material and the transmission medium. The array of piezoelectric elements is made from the piezoelectric segments by making fine cuts therein perpendicular to the supporting slot to form a plurality of piezoelectric "islands" and each island is electrically connected to utilization circuitry. In a preferred embodiment, an ultrasonic cylindrical lens is affixed to the supporting structure along the supporting slot and intermediate the piezoelectric array and the compressional acoustic image field to broaden the angular sensitivity pattern in the direction to compensate for the disparity between length and width (greater length) of piezoelectric elements or islands.

Acoustic surface wave resonator

Abstract: A piezoelectric resonator including body of piezoelectric material capable of propagating acoustic surface waves in response to electrical signals applied thereto. The surface waves are confined to a predetermined area on the surface of the piezoelectric material by bonding to the piezoelectric material a layer of acoustically transmissive material having an acoustic transmission velocity lower than the acoustic transmission velocity of the piezoelectric material. The dimension of the resultant laminate along the direction of propagation of the acoustic surface waves determines the resonant frequency of the laminate. The electrical characteristics of the resonant laminate are similar to those of quartz crystals commonly used in oscillators and filters.

Acoustic modulation of light by nematic liquid crystals

Abstract: An acoustic modulator using a liquid crystal and a piezoelectric driver is described. The response time of the modulator is less than the time needed for the onset of mechanical stress. Actually it is governed only by the electromechanical properties of the piezoelectric driver used.

One‐Dimensional Theory of Polarization by Shock Waves: Application to Quartz Gauges

Abstract: Laplace transform techniques were used to solve for the current generated by an air‐backed quartz gauge impacted by a much thicker disk of equal mechanical impedance. A nonlinear equation of state, which considers the variations of the piezoelectric factor h11 with strain and electric displacement, the dielectric impermeability β11S with strain, and the elastic stiffness c11D with electric displacement, was used in this solution. The differences between theoretical values of the current and values obtained in shock compression experiments to 18 kbar were on the order of ± 1% for time less than twice the transit time of the gauge. The effects of electromechanical coupling on shock reverberation experiments utilizing active quartz reverberation disks are discussed.

Acoustic-wave detection via a piezoelectric field-effect transducer.

Abstract: An oriented piezoelectric film has been incorporated in the insulator region of a silicon insulated‐gate field‐effect transistor to provide a sensitive high‐frequency strain transducer. With this device, strains as low as 10−8 have been detected and gauge factors of roughly 7000 have been attained for applied ac strains at 5.6 MHz.

Piezoelectric oscillator system

Abstract: A piezoelectric oscillator system includes a coupling oscillator having a piezoelectric transducer and a plate for vibration in a bending mode. The coupling oscillator is mechanically connected to a second plate which is also caused to vibrate in a bending mode upon energization of the piezoelectric transducer by an AC voltage. The second-mentioned plate may carry a second piezoelectric transducer for generating an electrical output signal. The system includes means for effecting self generation of the AC voltage through the provision of a tap electrode associated with the piezoelectric transducer for taking off a feedback control signal for a transistor switching circuit which may be constructed to provide an AC rectangular waveform.

Theory of the Piezoelectricity of Zinc-Blende-Type and Wurtzite-Type Crystals

Abstract: A theory of piezoelectricity in zinc-blende-type and wurtzite-type crystals is given. The charge-transfer effect contributes mainly to the piezoelectric constant. The assumption of the second-nearest-neighbor electron interaction $\ensuremath{\pi}$-electronic energy) in the crystal enables us to predict theoretically the charge-transfer value, so that the piezoelectric coefficients can be calculated. The $\ensuremath{\pi}$-electronic interaction energy is found to be 0.5 \ensuremath{\sim} 0.8 times the $\ensuremath{\sigma}$-bonding (tetrahedral-bonding) energy in wurtzite crystals.

Use of Piezoelectric Crystals as Sensitive and Specific Detectors for So2

Abstract: A general purpose gas chromatograph using a piezoelectric crystal as detector has been constructed and a piezoelectric crystal detector sensitive and selective for sulfur dioxide has been designed and developed. From 1 to 100 ppm of SO2 can be quickly and easily determined.

Pyroelectric and Nonlinear Optical Properties of Poled Polyvinylidene Fluoride Films

Abstract: Oriented films of polyvinylidene fluoride [(CH,CF,),] can be made significantly pyroelectric and optically nonlinear by polingin a field N lo6 voltjcm. Pyroelectric coeflicients as large as 24 nCjcm2"C (comparable to single-crystal LiNbO,) and nonlinear optical coefficients comparable to d, of crystal quartz are observed. Simple. inexpensive and fairly rugged pyroelectric detectors for electromagnetic radiation of any wavelength can be made from the poled lilms. Polyvinylidene fluoride (PVF,) crystallizes in a polar phase and it is found that its polarization can be switched. In the sense that it is a switchable pyroelectric PVF, can be regarded as a ferroelectric polymer. piezoelectric,' pyroelectric' and optically nonlinear' by poling them in a strong electric field. The Polyvinylidene Fluoride (PVF,) is a highly crystal- piezoelectric and nonlinear optical coefficients are line polymer having repeat unit CH,CF,. Rolling comparable to those of crystalline quartz, and the and stretching this material produces well-oriented pyroelectric coefficient is comparable to that of (textured) polycrystalline films. It has recently been single-crystal LiNbO,. X-ray and nuclear magnetic found that these films can be made significantly resonance measurements3 indicate that PVF, can