35/51 4.3 Relative Displacement:Translational and Rotational C VIll.Capacitance Pickups 0 o≈0 Operational amplifier eo= 1/j@Cx 1/jωCf eex C is a fixed capacitor eex 二 Any C is the displacement-varying capacitor Cx conducting surfoce- Metal guard ring to improve Cfex linearity of electric field 0.225A Insulator Figure 4.37 Probe Feedback-type Capacitive Pickups capacitor plote (a 36/51 4.3 Relative Displacement:Translational and Rotational IX.Piezoelectric Transducers When certain solid materials are deformed,they generate within them an electric charge and it is reversible; 4 groups of materials exhibit a significant and useful piezoelectric effect:natural and synthetic[人造的；（人工） 合成的]crystals,polarized ferroelectric(铁电的)ceramics and certain polymer films. Respond to mechanical deformations (motion to voltage transducers) The ultimate purpose of piezoelectric transducer is generally force,pressure,or acceleration measruement.4.3 Relative Displacement: Translational and Rotational VIII.Capacitance Pickups Figure 4.37 Feedback-type Capacitive Pickups 35/51 ࢞ ⁄ ࡯࣓࢐ ૚ = ࢕ࢋ ࢌ ⁄ ࡯࣓࢐ ૚ ࢞ࢋࢋ ࢌ࡯ = ࢞࡯ ࢞ࢋࢋ ࢞ࢋࢌ࡯ = ࢞ ࡭૞૛૛ .૙ 4.3 Relative Displacement: Translational and Rotational IX. Piezoelectric Transducers ‹ When certain solid materials are deformed, they generate within them an electric charge and it is reversible; ‹ 4 groups of materials exhibit a significant and useful piezoelectric effect: natural and synthetic [人造的；(人工) 合成的] crystals, polarized ferroelectric (铁电的) ceramics and certain polymer films. ‹ Respond to mechanical deformations (motion to voltage transducers) ‹ The ultimate purpose of piezoelectric transducer is generally force, pressure, or acceleration measruement. 36/51