Physics for Electrical Engineering: Unit I: Dielectric Materials and Insulation
Piezo-Electricity
These materials have the property of becoming electrically polarized when mechanical stress is applied. This property, known as piezoelectric effect and has an inverse.
PIEZO-ELECTRICITY
These
materials have the property of becoming electrically polarized when mechanical
stress is applied. This property, known as piezoelectric effect
and has an inverse.
According
to inverse piezoelectric effect when an electric
stress (voltage) is applied, the material becomes strained. The strain is
directly proportional to the applied field E.
When
piezoelectric crystals are subjected to compression or tension, opposite kinds
of charges are developed at the opposite faces perpendicular to the direction
of the applied force. The charges produced are proportional to the applied
force.
This
property is utilized in conversion of mechanical energy into electrical energy
and vice versa. The quartz crystal is a very good example of one such
transducer material. Crystal faces are to be cut in proper direction and shaped
to achieve maximum efficiency.
Explanation
A
rectangular slab is cut from a quartz crystal such that two opposite faces ABCD
and EFGH are perpendicular to optic axis.
The
other two opposite faces AEHD and BFGC are parallel to optic axis.
When
the mechanical stress is applied to two opposite faces ABCD and EFGH, then
opposite electrical charges (electrical field) are developed on the other pair
of opposite faces AEHD and BFGC. This is known as piezo-electric effect. (Fig.
1.29 (a)).
When
the electrical field is applied across the opposite faces parallel to optic
axis AEHD and BFGC (fig. 1.29 (b)), then thickness of the crystal (faces ABCD
and EFGH) along the optic axis changes ie., there is expansion or contraction
of the crystal. This is known as inverse piezo-electric effect.
•
The electric charges produced is directly proportional to the stress applied.
•
Piezo-electric effect is well exhibited on natural crystals cut in a suitable
direction with respect to optic axis.
• Piezo Electricity
Electricity
produced by means of piezo-electric effect is known as piezoelectricity.
Physics for Electrical Engineering: Unit I: Dielectric Materials and Insulation : Tag: : - Piezo-Electricity
Physics for Electrical Engineering: Unit I: Dielectric Materials and Insulation
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Physics for Electrical Engineering
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