Piezoelectric Sensors

Seth R. Hills

ECE5320 Mechatronics Assignment #1

Outline

Reference list Links for more information Major applications Basic working principle illustrated A typical sample configuration in application Major specifications Limitations Selection Criteria Cost information Where to buy

References:

http://www.sensorsmag.com/articles/0204/27/main.shtml

http://www.media.mit.edu/resenv/classes/MAS836/Readings/MSI-techman.pdf

http://www.princeton.edu/~cml/html/publicity/TRN20001122/Piezoelectric%20sliver%20.htm

http://www.sensorsweb.com/taxonomy/term/46 http://www.davidson.com.au/products/

pressure/pcb/theory/piezo-theory.asp

To Explore Further Visit these websites or check out these articles:

http://www.iupac.org/publications/pac/2004/pdf/7606x1139.pdf

http://www.ndt.net/article/yosi/yosi.htm

Major applications • Sonar• Hearing Aids. Low frequency • Ultrasound. Ultrasonic actuator• Night vision. Pyroelectric sensor effect• Traffic Sensors • Music Pickups • Machine Monitoring • Bearing Wear Sensors• Thread Break Sensor • Accelerometers• Aerospace. Modal testing, wind tunnel, and shock tube instrumentation; • Ballistics. Combustion, explosion, and detonation • Engine Testing. Combustion and dynamic stressing • Shock/Vibration• Implantables: Pacemaker Activity Monitor, Implantable Switch, Vascular Graft

Monitor, Micropower Source

• And many, many more!

http://www.sensorsmag.com/articles/0204/27/main.shtml#sidebar1

Specific Applications

• To detect sound, e.g. piezoelectric microphones (sound waves bend the piezoelectric material, creating a changing voltage) and piezoelectric pickups for electrically amplified guitars.

• Piezoelectric elements are also used in the generation of sonar waves. Piezoelectric microbalances are used as very sensitive chemical and biological sensors.

• Piezoelectric elements are used in electronic drum pads to detect the impact of the drummer's sticks.

http://www.sensorsweb.com/piezoelectric_sensors

Basic working principle

In 1880, brothers Pierre and Jacques Curie demonstrated the relationship between a mechanical load on a crystal and the electric charge resulting from it.

Piezoelectricity is a linear electromechanical interaction between the mechanical and electrical states of a material.

The piezoelectric effect results from a deformation of the crystal lattice by some external force that pushes the positive and negative lattice points against one another and thus produces a dipole moment and an electric charge.

http://www.sensorsmag.com/articles/0204/27/main.shtml#sidebar1

Electrets Electrets are solids which

have a permanent electrical polarization. The electrical analog of magnets (Figure 3). In general, the alignment of the internal electric dipoles would result in a charge which would be observable on the surface of the solid. In practice, this small charge is quickly dissipated by free charges from the surrounding atmosphere which are attracted by the surface charges.

http://ccrma.stanford.edu/CCRMA/Courses/252/sensors/node7.html

Figure 3: Internal Structure of an electret

Piezoelectric Crystals Permanent polarization as in the case of the electrets is also

observed in crystals. Each cell of the crystal has an electric dipole, and the cells are

oriented such that the electric dipoles are aligned. Again, this results in excess surface charge which attracts free charges from the surrounding atmosphere making the crystal electrically neutral.

If a sufficient force is applied to the piezoelectric crystal, a deformation will take place. This deformation disrupts the orientation of the electrical dipoles and creates a situation in which the charge is not completely canceled. This results in a temporary excess of surface charge, which subsequently is manifested as a voltage which is developed across the crystal.

http://ccrma.stanford.edu/CCRMA/Courses/252/sensors/node7.html

Description Continued…

In a piezoelectric crystal, the positive and negative electrical charges are separated, but symmetrically distributed, so that the crystal overall is electrically neutral. When a stress is applied, this symmetry is disturbed, and the charge asymmetry generates a voltage. A 1 cm cube of quartz with 500 lb (2 kN) of correctly applied pressure upon it, can produce 12,500 V of electricity.

http://www.sensorsweb.com/taxonomy/term/46

A typical sample configuration in application

A piezoelectric film vibration sensor, mounted to a thin steel beam, monitors the acoustic signal caused by the abrasion of the thread running across the beam, analogous to a violin string. The absence of the vibration instantly triggers the machinery to stop. Thread tension and defects in man-made fibers are also monitored with piezo film textile sensors.

http://www.media.mit.edu/resenv/classes/MAS836/Readings/MSI-techman.pdf

Piezo Film Textile Sensors

THE PIEZOELECTRIC ACCELEROMETER (Compression Type)

The sensing element is a crystal which has the property of emitting a charge when subjected to a compressive force.

In the accelerometer, this crystal is bonded to a mass such that when the accelerometer is subjected to a 'g' force, the mass compresses the crystal which emits a signal. This signal value can be related to the imposed 'g' force

http://www.sensorland.com/HowPage003.html

piezoelectric cantilevers to measure viscosity

Description:  This sliver of piezo- electric material forms a cantilever that can be used to measure the density of a liquid. Forces acting on the microcantilever cause corresponding changes in its’ electrical resistance.

http://www.princeton.edu/~

Major specifications 1. Electro-Mechanical Conversion

(1 direction) 23 x 10-12m/V, 700 x 10-6N/V(3 direction) -33 x 10-12m/V

2. Mechano-Electrical Conversion(1 direction) 12 x 10-3V per microstrain, 400 x 10-3V/(3 direction) 13 x 10-3V/N

3. Pyro-Electrical Conversion8V/ o K (@ 25 o C)

4. Capacitance1.36 x 10-9F; Dissipation Factor of 0.018 @ 10 KHz;

5. Maximum Operating VoltageDC: 280 V (yields 7 µm displacement in 1 direction)AC: 840 V (yields 21 µm displacement in 1 direction)

6. Maximum Applied Force (at break, 1 direction)6-9 kgF (yields voltage output of 830 to 1275 V)

http://www.media.mit.edu/resenv/classes/MAS836/Readings/MSI-techman.pdf

Pros and Cons

Piezoelectric sensors offers unique capabilities which are typically not found in other sensing technologies.

There are certain advantages: wide frequency and amplitude range

and disadvantages: no static measuring capability

This all depends on the particular application. Therefore, when choosing a specific sensor or sensor technology, it is important to pay close attention to the performance specifications.

http://www.davidson.com.au/products/pressure/pcb/theory/piezo-theory.asp

Limitations

Low frequency performance (below 500Hz) tends to be limited

Limited displacements Quasistatic force sensing Requires high impedance amplification of

signal

Selection Criteria Dependent on Application Range Resolution Sensitivity Error Repeatability Linearity and Accuracy Impedance Nonlinearities Static and Coulomb Friction

Selection Criteria

Eccentricity Backlash Saturation Deadband System Response First-Order System Response Underdamped Second-Order System Response Frequency Response

Cost InformationThere are many manufacturers and distributors of

piezoelectric devices here are a few:

Piezoelectric microphone: $94.84 – digikey.com Piezoelectric axle sensor: Request a quote -

www.triggindustries.com 28 Micron Piezo Film Sheet: $55.00+ at

www.msiusa.com

Where to Buy:

http://www.triggindustries.com/piezoelectric_sensors.htm

http://www.piezo-products.com/?mp-pvid=1-1gLgd-0iQ-1D8vA9

http://www.sparklerceramics.com/www.msiusa.comwww.digikey.com