Piezoelectric generator coefficient

The piezoelectric generator coefficient d indicates the mechanical strains that are induced by electric potentials and the piezoelectric motorcoefficient e is a measure of the dipole moments that are created by strains. These two parameters are similar in nature and proportional to one another. The electromechanical coupling coefficient k is proportional to both d and e, its square giving the efficiency of conversion between mechanical and electrical energy that can be achieved with the ferroelectric... 

The piezoelectric effect stems from hydrogen and fluorine atoms in the VDF, which are positioned perpendicularly to the polymer backbone. Fig. 5.7A shows a typical molecular structure of PVDF with different crystalline phases (Chang et al., 2012). The piezoelectric performance of PVDF is dependent on the nature of the crystalline phase (Crossley et al., 2014). Typically, PVDF has three crystalline phases, namely a, p, and y, and it is the a-phase that typically forms in most situations. While it is polar p-phase that shows the strongest piezoelectric behavior so this material needs to be electrically poled using an electric field with the order of 100 MV m or mechanically stretched. A higher P-phase crystalline can lead to a higher piezoelectric coefficient Note that the copolymer of P(VDF-TrFE) [(CH2-CF2) -(CHF-CF2)ml crystallizes more easily into the P-phase due to steric factors (Furukawa, 1989). So, the most applied material in piezoelectric generator is P(VDF-TrFE). 

If a piezoelectric transducer is simply being used as a displacement or strain indicator, then the relationships described above are sufficient to allow the calculation of the electrical signal which will be generated upon perturbation of a device. All that must be known are the stiffness constants (elastic properties), the piezoelectric strain coefficients (piezoelectric properties) of the transducer material, and the strain induced. If however, acoustic waves are being employed for mass sensing applications, then one must consider the dynamics of particle motion and how wave propagation is affected by the finite boundaries of a transducer. 

Sensitivity. The sensitivity of a piezoelectric material is taken to be equal to the generated open-circuit voltage that drop>s across to the contact with the distance t (= thickness) divided by the applied stress or the product g t, where g is the relevant piezoelectric voltage coefficient. The voltage coefficient g is connected with the charge coefficient d via the dielectric permittivity = CrCo according to... 

Piezoelectric voltage coefficient (gffi The tensor that defines the generation of strain on application of electric field is known as the piezoelectric voltage coefficient. 

Bias-induced reverse piezoelectric response Broadband dielectric spectroscopy (BDS) Dielectric permittivity spectrum Dielectric resonance spectroscopy Elastic modulus Ferroelectrets Electrical breakdown Acoustic method Characterization Dynamic coefficient Interferometric method Pressure and frequency dependence of piezoelectric coefficient Profilometer Quasistatic piezoelectric coefficient Stress-strain curves Thermal stability of piezoelectricity Ferroelectric hysteresis Impedance spectroscopy Laser-induced pressure pulse Layer-structure model of ferroelectret Low-field dielectric spectroscopy Nonlinear dielectric spectroscopy Piezoelectrically generated pressure step technique (PPS) Pyroelectric current spectrum Pyroelectric microscopy Pyroelectricity Quasistatic method Scale transform method Scanning pyroelectric microscopy (SPEM) Thermal step teehnique Thermal wave technique Thermal-pulse method Weibull distribution... 

The compounds K5Nb3OFi8 and Rb5Nb3OFi8 display promising properties for their application in electronics and optics. The compounds can be used as piezoelectric and pyroelectric elements due to sufficient piezo- and pyroelectric coefficients coupled with very low dielectric permittivity. In addition, the materials can successfully be applied in optic and optoelectronic systems due to their wide transparency range. High transparency in the ultraviolet region enables use of the materials as multipliers of laser radiation frequencies up to the second, and even fourth optical harmonic generation. 

CB04. The spontaneous polarisation was measured by the pulse pyroelectric technique (Ps = 46 nC/cm ). The piezoelectric coefficient evaluated for CB04 was dsi = 1.6 pC/N. The estimation of the efficiency of the second harmonic generation for compound CB04 gives the value three times more than for quartz. 

A typical measuring circuit is shown in Fig. 9.15. A signal generator supplies a sinusoidal signal with 600 fl output impedance. The current is amplified at sensitivity of 10 AfV. The ac voltages are measured by ac digital voltmeters. The experiment is performed with a PZT-4 tube, provided by EBL, Inc., with L = 25.4 mm, D = 12.7 mm, h = 0.50 mm, and Y= 7.5 X 10 N/m. The lowest resonance frequency is 5 kHz. The results of measurements are shown in Fig. 9.16. The current, about 1 xA, can easily be measured with 1% accuracy. The current from the two x quadrants agrees well with that from the two y quadrants. In terms of the units mentioned, the piezoelectric coefficient dn can be obtained from directly measurable quantities as ... 

There are several methods that have been implemented for measurements of thin film piezoelectric coefficients. In looking at the relative accuracy of the techniques, it is important to consider the differences between thin film and bulk samples. Firstly, thin films are, by definition, thin. Since the maximum strain that can typically be generated is <1 %, the film displacements, themselves are quite small. The second, rather obvious, difference is that thin films are not amenable to fabrication of unsupported samples. A limited amount of information is available on the piezoelectric coefficients of thin films released by dissolving away the... 

Alternatively, in piezoelectric crystals, apphed electric fields, generate mechanical strains, s , that are also related by the piezoelectric coefficients ... 

Crytal chemitry. The effect of solid solution on the transition behavior of perovskite (ABX3) structures has been intensively scrutinized for more than 50 years. These materials have merited continuous attention because of their enormous technological versatility. As multilayer capacitors, piezoelectric transducers, and positive temperature coefficient (PTC) thermistors they generate a market of over 3 billion every year (Newnham 1989, 1997). In addition to ease of fabrication, these compounds exhibit a number of attributes required of ideal actuators (1) They display very large field-induced strains (2) They offer quick response times and (3) Their strain-field hysteresis can be chemically controlled to be very large or negligibly small, depending on the application. Details of their technical applications can be found in Jaffe et al. (1971) and Cross (1993). 

Piezoelectric sensors are generally based on the use of AT-cut quartz crystals (+ 35°15 orientation of the plate relative to the crystal plane) because of their excellent temperature coefficients [3]. The generated acoustic wave depends on the crystal cut, thickness of the material used, and the geometry and configuration of the metal electrodes used to produce the electric field [5]. 

The charge Q generated on the PVDF film is proportional to the bending displacement Z of the beam, Q = GZ, where G is a constant dependent on the transverse piezoelectric coefficient dsi, and the dimensions and Young s moduli of individual layers of the composite beam [Shen et al. (2004)]. The transfer function from Z s) to the measured voltage V/(s) can then be written as... 

A deformation of the smectic C structure should produce variation in the tilt angle, 0, and therefore in the polarization, P. Thus, a piezoelectric response is generated and can be measured. To date, only two components of the piezoelectric tensor have been studied for FLCPs (Fig. 23) the cl coefficient, which describes the electric response in the z direction to the acoustically induced deformation along... 

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