Sensor Technology Ltd.’s BM300 is a modified lead titanate. While it has good piezoelectric performance in the axial (thickness) direction, it has very low planar (radial) performance. For all practical purposes, BM300 exhibits no transverse response. This is a great advantage for applications in which planar sensitivity is unwanted.
Consider a comparison: Soft PZT exhibits an axial to planar coupling coefficient ratio (k33 : k31) of approximately 1.9 : 1. For BM300 the planar coefficient is so small that ratio is 17 : 1.
This anisotropy leads to another useful performance characteristic: high gh values. The hydrostatic piezoelectric voltage constant, gh, is a direct indicator of hydrophone sensitivity. It is related to the g coefficients for each axis by the equation
gh = g33 + g32 + g31
g33: axial (thickness) voltage constant
g32, g31: planar voltage constants
For piezoelectric ceramics g33 is positive, while g32 and g31 are negative, resulting in small (but usable) gh values. For lead titanate however, g33 is high while g32 and g31 are negligible, resulting in high gh values.
While the unique anisotropy of modified lead titanate is perhaps its most compelling feature, the material offers other useful performance characteristics. BM300 has a low dielectric constant and excellent stability over time.
With its negligible response to side loading, high gh and g33, lead titanate is ideal for receiving sensors under hydrostatic load or when the response to transverse modes needs to be minimized. Examples include: