4.8.1 Piezoelectric effect When a piezoelectric cut is applied simultaneously with many forces a complex stress field will be generated inside it. Thus both the longitudinal and transverse effects may occur Q=LDF (487 Where o, D, and F are matrices, andl is a column vector, whose magnitudes depend on both the different forces and the cut size
• When a piezoelectric cut is applied simultaneously with many forces, a complex stress field will be generated inside it. Thus both the longitudinal and transverse effects may occur. 4.8.1 Piezoelectric effect Q = LDF (4.87) Where Q , D , and F are matrices, and L is a column vector, whose magnitudes depend on both the different forces and the cut size
4.8. 1 Piezoelectric effect A quartz crystal is a kind of crystallite of Sio2. As is shown in fig. 4.58, each crystalline unit contains hree Si atoms and six o atoms. and the o atoms lie in pairs against each other. Each Si atom has four unit positive charges, while each O, atom has two unit negative charges. In the crystalline unit the si and o atoms form a hexahedral structure and they reach a state of charge equilibrium
• A quartz crystal is a kind of crystallite of SiO2 . As is shown in fig. 4.58, each crystalline unit contains three Si atoms and six O2 atoms, and the O2 atoms lie in pairs against each other. Each Si atom has four unit positive charges, while each O2 atom has two unit negative charges. In the crystalline unit, the Si and O2 atoms form a hexahedral structure and they reach a state of charge equilibrium. 4.8.1 Piezoelectric effect
4.8.1 Piezoelectric effect Crystal structure(simplified) Crystal structure(simplified) unloaded loaded unloaded loaded 交 n-discs (a) Fig. 4.58 The piezoelectric effects in crystalline quartz. (a) Longitudinal effect and(b)transverse effect, each showing the charge displacement Q caused by crystal deformation resulting from force F. Also shown are typical electrical connections and sketches of typical transducers
4.8.1 Piezoelectric effect Fig. 4.58 The piezoelectric effects in crystalline quartz. (a) Longitudinal effect and (b) transverse effect, each showing the charge displacement Q caused by crystal deformation resulting from force F. Also shown are typical electrical connections and sketches of typical transducers
4.8.2 Operating principle of piezoelectric transducer and associated circuitry U To measure the generated electrical charges on two faces of the piezoelectric crystal, electrodes must be made on these two faces a metal film usually silver or gold one, is evaporized on the crystal surface to form an electrode
❑To measure the generated electrical charges on two faces of the piezoelectric crystal, electrodes must be made on these two faces. A metal film, usually silver or gold one, is evaporized on the crystal surface to form an electrode 4.8.2 Operating principle of piezoelectric transducer and associated circuitry
4.8. 2 Operating principle of piezoelectric transducerand associated circuitry a piezoelectric transducer can be considered as a charge generator or as a capacitor, whose amount of capacitance is E。EA 0 Where dielectric constant of piezoelectric material, a=As for quartz, E dielectric constant for vacuum. and En=885×1012F.m-1 distance between two electrodes, (
A piezoelectric transducer can be considered as a charge generator or as a capacitor, whose amount of capacitance is: A c 0 = Where = dielectric constant of piezoelectric material, = 4.5 for quartz, 0 = dielectric constant for vacuum, and 1 2 1 0 8.85 10 − = F m , = distance between two electrodes, (m ). 4.8.2 Operating principle of piezoelectric transducer and associated circuitry