Piezoelectric
Materials Applications for Cardiovascular Devices
Website designed by: Luis
Alonzo
Piezoelectricity
Piezoelectricity
is
defined as the ability of certain materials to develop a dielectric
displacement due to an applied stress and, conversely, develop a strain
in
response to an electric field [1]. Normally, the charges within a
piezoelectric
material are well balanced regardless of their distribution. This
balance
results in no net charge on the material faces. The piezoelectric
effect relies
on the asymmetric charge distribution within individual crystalline
units. Upon
application of a mechanical force on the material, the positive and
negative
charges are displaced with respect to one another. The displacement
results in
a change in polarization of the material, which yields a measurable
electrical
potential. This effect can be represented graphically in the animation
below [2]:
Similarly,
when a
piezoelectric material is exposed to an electric field, it experiences
a
lengthening or shortening according to the polarity of the field, and
in
proportion to the strength of the field [1].
The physical basis of
piezoelectricity (i.e. electrical and mechanical
behavior) is best described by combined
relations of Gauss’ Law and Hooke’s Law. The relationship between the
electrical and mechanical properties of piezoelectric materials is governed by
the following equations [3]:
where i, j, m = 1, . . ., 6
and k, l, n = 1, 2, 3. Also, S, D, E, and T are the strain, dielectric
displacement, electric field, and stress, respectively. And sijE,
dkl, and elnT are the elastic compliances, the piezoelectric
constants, and dielectric permittivities.
Materials exhibiting the
piezoelectric effect include a variety of naturally occurring crystals, natural
materials, manufactured crystals, manufactured ceramics, and special man-made
polymers. The ideal material may be selected based on the application, since
certain materials are more efficient than others. The table below describes the
properties of some commonly used piezoelectric materials [4]: Since their discovery in
the 19th century, piezoelectric materials have been used for a
variety of applications, from power sources to actuators. In medicine, one of
their main uses is in the field of imaging, such as in piezoelectric ultrasound
imaging. This technology relies in the change of shape of piezoelectric
materials due to an applied electrical current or sound/pressure waves hitting
the material. Recently, new and potential applications have emerged for
piezoelectric materials within the field of cardiology. This website will focus
on two of these recent developments within cardiovascular devices, among which are:
ventricular assist devices, and artificial heart
valve sensors.