The piezoelectric effect was first discovered by Pierre and Jacques Curie in 1880. Certain materials were observed to generate a voltage when subjected to a mechanical strain, or undergo a change in physical dimensions under an applied voltage. Quartz, lead zirconate titanate (PZT), potassium sodium tartarate (Rochelle salt) and ordinary sugar are capable of exhibiting the piezoelectric effect.
Piezoelectric materials that are usable in transducer design must exhibit the following properties: stability, high output, insensitivity to temperature and humidity changes and the ability to be worked into the desired configuration or shape. As no material is optimal for all the above properties, transducer design requires certain compromises.
In response to a mechanical strain the piezoelement generates a charge which is temporarily stored in the inherent capacitance of the piezoelement. With time the charge dissipates due to leakage. This makes piezoelements most useful for dynamic measurements, such as acceleration.
The relationship between an applied force and the surface charge generated is:
Q = DF
where Q is the surface charge, D is the piezoelectric constant and F is the applied force. The different modes of deformation for piezoelectric sensors and an equivalent circuit are shown in Figure 14.
Figure 14 Deformation of piezoelectric plates and an equivalent circuit for a piezoelectric element
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Support for the development of this module was provided by the National Science Foundation and The Cooper Union for the Advancement of Science and Art.
Please send questions or comments to Professor Ron Adrezin or Professor Daniel Raichel.