Piezoelectric Sensors

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Piezoelectric Sensors

• Seth R. Hills
• ECE5320 Mechatronics Assignment 1

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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

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References

• http//www.sensorsmag.com/articles/0204/27/main.sh
  tml
• http//www.media.mit.edu/resenv/classes/MAS836/Rea
  dings/MSI-techman.pdf
• http//www.princeton.edu/cml/html/publicity/TRN20
  001122/Piezoelectric20sliver20.htm
• http//www.sensorsweb.com/taxonomy/term/46
• http//www.davidson.com.au/products/pressure/pcb/t
  heory/piezo-theory.asp

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To Explore Further Visit these websites or check
out these articles

• http//www.iupac.org/publications/pac/2004/pdf/760
  6x1139.pdf
• http//www.ndt.net/article/yosi/yosi.htm

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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.sh
tmlsidebar1
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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
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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.sh
tmlsidebar1
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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.

Figure 3 Internal Structure of an electret
http//ccrma.stanford.edu/CCRMA/Courses/252/sensor
s/node7.html
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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/sensor
s/node7.html
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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
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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.

Piezo Film Textile Sensors
http//www.media.mit.edu/resenv/classes/MAS836/Rea
dings/MSI-techman.pdf
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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
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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/
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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 Conversion
• 8V/ o K (_at_ 25 o C)
• 4. Capacitance
• 1.36 x 10-9F Dissipation Factor of 0.018 _at_ 10
  KHz
• 5. Maximum Operating Voltage
• DC 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/Rea
dings/MSI-techman.pdf
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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/t
heory/piezo-theory.asp
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Limitations

• Low frequency performance (below 500Hz) tends to
  be limited
• Limited displacements
• Quasistatic force sensing
• Requires high impedance amplification of signal

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Selection Criteria

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

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Selection Criteria

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

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Cost Information

• There 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

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Where to Buy

• http//www.triggindustries.com/piezoelectric_senso
  rs.htm
• http//www.piezo-products.com/?mp-pvid1-1gLgd-0iQ
  -1D8vA9
• http//www.sparklerceramics.com/
• www.msiusa.com
• www.digikey.com