piezoelectric sensor part 1 - uni-frankfurt.de

LECETURE 4

Piezoelectric sensor

Part 1

Prof. Dr. YU GU

GU@chemie.uni-Frankfurt.de

Office Room: N160/517

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!