7.3. A Beam Bimorph

7.3. A Beam Bimorph

An electric field in a piezoelectric material causes strain but not curvature. Therefore, in the previous two sections, different electric fields on opposite sides of a beam are needed to produce flexure. Another way of producing flexure in a beam is to use a bimorph. Consider the gyroscope shown in Fig. 7.3.1 [80].

Fig. 7.3.1: A ceramic bimorph piezoelectric gyroscope.

The part in 0< x ₁< a ₁ is the driving portion and a ₁< x ₁< l is the receiving or sensing portion. The polarizations in the two layers are opposite. When a driving voltage V ₁ is applied across the electrodes at x ₃= c, one layer extends while the other contracts due to switched polarizations. This allows the beam to be driven into the lowest flexural mode in the x ₃ direction with a proper driving frequency. If the beam is rotating about the x ₁-axis with a constant angular rate ?, the Coriolis force causes a flexural motion in the x ₂ direction. This Coriolis force generated flexure produces a voltage V ₂ in the receiving portion which can be picked up by the sensing electrodes. Flexure in the x ₃ direction alone does not cause any output voltage.