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Engineering LibreTexts

2.1: Prelude to Capacitors and Piezoelectric Devices

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  • This chapter begins with a discussion of material polarization, and then it discusses capacitors and piezoelectric devices. The next chapter discusses pyroelectric devices and electro-optic devices. All of these devices are all constructed from a thin dielectric layer, and operation of all of these devices involves establishing a material polarization, charge build up, throughout this dielectric material. In piezoelectric materials, mechanical strain causes a material polarization. As with many energy conversion devices, piezoelectric devices can work both ways, converting mechanical energy to electricity or converting electricity to mechanical vibrations. In pyroelectric devices, a temperature gradient causes the material polarization, and in electro-optic devices, an external optical electric eld causes the material polarization.

    Why start the discussion of energy conversion devices with a discussion of capacitors? Capacitors are familiar to electrical engineers, and they are energy storage devices. How do capacitors work? What are the components of a capacitor? What materials are capacitors made out of? What are the differences between different types of capacitors such as mica capacitors and electrolytic capacitors? In an introductory circuits course, a capacitor is a device where the relationship between the current \(i\) and voltage \(v\) is given by \[i = C \frac {dv} {dt} \]

    and the capacitance \(C\) is just a constant. The only difference between one capacitor and another is the capacitance value. In order to answer these questions further, we need to go beyond this model. Through this study, we will gain insights into piezoelectric devices, pyroelectric devices, and electro-optic devices too.