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Piezoelectricity
The word piezoelectricitymeans electricity resultingfrom pressure and latentheat.
Piezoelectricity was discovered in 1880
by French physicists Jacques and
Pierre CurieJacques (1856-1941,
left) with his brother
Pierre (1859-1906)
and his parents
Piezoelectricity
Piezoelectricity is the electric
charge that accumulates in
certain solid materials (such as
crystals, certain ceramics, and
biological matter such as bone,
DNA and various proteins) in
response to applied mechanical
stress.
A piezoelectric disk
generates a voltage
when deformed
Piezoelectricity is exploited in a number of
useful applications, such as the production
and detection of sound, generation of high
voltages, electronic frequency generation,
microbalances, et cetera.
It forms the basis for a number of scientific
instrumental techniques with atomic
resolution, the scanning probe microscopies,
such as STM, AFM, MTA, and SNOM.
It also finds everyday uses such as being
used as the time reference source in quartz
watches.
Piezoelectric effect
The piezoelectric effect is understood as the
electromechanical interaction between the
mechanical and the electrical state in
crystalline.
The piezoelectric effect is a reversible process in
that materials exhibiting the direct piezoelectric
effect also exhibit the reverse piezoelectric
effect.
Oscillation of the crystal excited by an alternating
voltage (black), unreformed quartz (grey);
Direct piezoelectric effect,
The internal generation of electrical charge
resulting from an applied mechanical force.
Reverse piezoelectric effect,
The internal generation of a mechanical
strain resulting from an applied electrical
field.
an applied
mechanical
force
the internal
generation
of electrical
charge
the internal
generation of
a mechanical
strain
an applied
electrical
field
DPE
RPE
Oscillation
Oscillation is the repetitive variation, typically
in time, of some measure about a central value
(often a point of equilibrium) or between two
or more different states.
Oscillatory system
An undamped spring–mass
system is an oscillatory system
Two pendulums with the same period
fixed on a string act as pair of coupled
oscillators.
The oscillation alternates between the
two.
Oscillation current
Oscillation current Oscillation circuit
LC circuit
Capacitor
LC circuit diagram
LC circuit
Inductor
Quartz Crystal Microbalance
QCM
Quartz crystal microbalance
is a very sensitive mass
deposition sensor based on
the piezoelectric properties
of the quartz crystal.
The QCM is a widely used acoustic
sensor. The QCM is applied for the
analysis of surface attached polymers,
adsorbates, biomolecules, and cells.
It is a noninvasive tool to measure
interfacial processes insitu.
When the QCM was first developed,
natural quartz was harvested, selected for
its quality and then cut in the lab.
The crystals are cut and polished into
hair-thin discs which support thickness
shear resonance in the 1-30 MHz range.
The AT-cut are widely used in
applications.
This technique uses the changes in
resonance frequency of the crystal to
measure the mass on the surface
because the resonance frequency is
highly dependent on any changes of
the crystal mass.
A QCM measures a mass variation per
unit area by measuring the change in
frequency of a quartz crystal resonator.
A QCM is capable of measuring mass
deposition down to 0.1 nanograms.
Sauerbrey equation
The Sauerbrey equation was developed by
Prof. Dr. Günter Sauerbrey from Tiefenort,
Germany, in 1959.
It is a method for correlating changes in the
oscillation frequency of a piezoelectric crystal
with the mass deposited on it.
Sauerbrey equation
The Sauerbrey equation is defined as:
Photograph of typical quartz crystal resonators as usedfor QCM, metallized with gold electrodes (left: frontelectrode, right: back electrode) by vapor deposition.
Economic ways of driving a
QCM make use of oscillator
circuits.
Modes of operation
The only design criterion of thickness–shear
mode resonators for frequency control is
frequency stability.
The AT-cut is most appropriate.
AT-cut quartz crystals are also typically used as
sensor elements, although the requirements for
sensor applications are more complex.
Only maximum frequency shift is not anappropriate measure. A better value isthe limit of detection, which depends onthe signal-to-noise ratio.
Temperature dependence is small forAT-cut crystals. In liquid applications,the most temperature-sensitive value isthe liquid viscosity.
Sensitivity to mechanical perturbationsis smaller for thicker crystals, i.e., lowerresonance frequencies.
Noise and systematic errors introducedby the electronic circuitry must be alsotaken into account.
Homework （Materials for the Seminar course）
• Please select a piezoelectric material and illustrate its use with a example.
• You need to report them in the seminar course.
THANK YOU!
