In this chapter we are going to study the working principle, application and rumble spectrum analysis of piezoelectric sensor.

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Chapter Six Piezoelectric sensor

• In this chapter we are going to study the
  working principle, application and rumble
  spectrum analysis of piezoelectric sensor.

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The First Section The Working Principle Of
Piezoelectric Sensor

• The piezoelectric sensor is one
  kind of electricity-generating sensor. Based on
  the piezoelectric effect of certain dielectrics,
  the external force will help to generate electric
  charge on the surface of the dielectric, thus
  achieving the purpose of non-electrical quantity
  measurement.
• The element of piezoelectricity
  sensor is sensitive to forces. It can measure the
  non-electric quantities that can finally be
  transformed into forces, for example, dynamic
  force, dynamic pressure, vibration acceleration,
  and so on. But it cannot be employed in measuring
  the static parameter.

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First, piezoelectric effect

• The shape of natural quartz crystal
  is hexagon crystal column. When it is cut by a
  diamond knife into a piece of square thin slice
  and the slice is pressured, the crystal slice
  will be distorted, and the positive charge will
  appear on the surface. The proportion of electric
  charge Q and the force F is positive, which is
  called piezoelectric effect. The piezoelectric
  effect can also be found in some man-made
  materials
• If there is alternating voltage in
  the polarization direction of the dielectric, the
  mechanical deformation will happen to the
  dielectric. If there is no outer electric field,
  the deformation of the dielectric will disappear,
  which is called counter-piezoelectric effect
  (electrostriction effect).

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The piezoelectric effect demonstration of
quartz crytal

• When the force direction varies, the polarity
  of the charge will change with it, and the output
  voltage frequency is the same as the one of
  dynamic force when the dynamic force becomes
  static, the charge will soon leak and disappear
  due to leakage on the surface.

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Second, the classification and properties of
piezoelectric materials

• Generally there are three kinds of
  piezoelectric part material in making
  piezoelectric sensor one is piezoelectric
  crystal (for example, the above quartz crystal),
  one piezoelectric ceramics after polarized
  processing, and another is polymer
  piezoelectricity material.

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(First) Quartz crystal
The shape of natural quartz crystal
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The shape of natural quartz crystal(continued)
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Quartz crystal slice and packaging

• Quartz crystal slice

The two-sided silver-platings and seal
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Quartz crystal oscillator (crystal oscillator)
Crystal oscillator

• When the quartz crystal functions in the
  oscillating circuit, the piezoelectric effect and
  counter piezoelectric effect work one by one,
  which yields steady oscillating output frequency.

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(Second) Piezoelectric ceramics

• The piezoelectric ceramics is
  man-made polycrystalline piezoelectric material,
  with higher piezoelectric sensitivity than quartz
  crystal and lower production cost. Therefore it
  is widely used in producing the current
  piezoelectric parts throughout the world. The
  commonly used piezoelectric ceramics material is
  lead zirconium titanic piezoelectric ceramics
  (PZT) and non-lead piezoelectric ceramics (for
  example, BaTiO3 and so on).

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The shape of piezoelectric ceramic

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The shape of non-lead piezoelectric ceramics and
transducer (developed by Shanghai Silicate
Research Institute)

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Polymer piezoelectric film and drawing
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(Third) Polymer piezoelectric materials

• The typical polymer piezoelectric
  material includes polyvinylidene fluoride (PVF2
  or PVDF), polyvinyl-fluoride (PVF), modified
  polyvinyl-chloride (PVC), and so on. It is one
  kind of soft piezoelectric material, and can be
  made into forms like film or cable tube in
  accordance with the requirements. Being
  waterproof, it is not easy to break and suitable
  for massive and continuous drawing. And the
  finished products can be large size or area, with
  low price and relatively wide frequency response
  scope. The measurement dynamic range can be 80dB.

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Piezoelectric film and cable made by polymer
piezoelectric materials

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The polymer piezoelectric footboard that can be
used in waveform analysis and alarm.

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Piezoelectric treading alarm

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Piezoelectric loudspeaker made by polymer
piezoelectric film (counter piezoelectric effect)
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The Second Section The measurement conversion
circuit of piezoelectric sensor

• The output voltage of the charge
  amplifier is only influenced by the input charge
  and feedback capacity, and rarely influenced by
  such factors as the cable length.

The electric charge amplifier can the charge
conversion which outputs the piezoelectric
pick-up for the voltage (the Q/U switch), but the
non-enlargement electric charge's function, is
only one custom calls the law.
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The appearance of four-channel charge amplifier

• .

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The indicator of the above shown four-channel
charge amplifier (reference material from the
Oriental Vibration and Noise Technology Research
Institute)

• Sensitivity 0.11000mV/pC
• frequency range 0.3100KHz
• Noise (maximum gain)
• Equivalent to the input less than 5µV
• 1 accuracy 1
• 10V/10mA maximum output 10V/10mA
• 220V/50Hz power 220V/50Hz
• controlling mode Computer or manual

Welding type electric charge amplifier
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Mini charge amplifier module
Major targets or quotas

•        Sensitivity 1, 10, 100mV/pC (optional)
• Frequency range 0.3100KHz (the range is
  optional)
• Noise (maximum sensitivity) The out-put terminal
  is less than 1mV
• Normalization External resistance adjustment
• Linearity Error 1
• maximum output 5V or 10V
• power 6V15V
• Characteristics the economical multi-point test
  system can be developed

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The appearance of other charge amplifiers
Kneading board type electric charge amplifier
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the appearance of multi-channel charge amplifier
appearance
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The Third Section The application of
piezoelectric sensor

• First, the application of polymer piezoelectric
  materials

• 1. The glass destroys the alarm device
• Presses the electrical measurement the
  high polymer to inspire the thin film glue on the
  glass, the vibration which may feel the glass is
  stave when will send out, and transmits the
  voltage signal for the centralism alarm system.

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The broken glass sensor made by polymer
piezoelectric materials
Will be thick approximately about the 0.2mm PVDF
thin film to keep under control 10 20mm sizes.
In its pro and con various spray coatings
transparent tin peroxide electric conduction
electrode, uses in again the ultrasonic welding
two soft contact conductors. And covers with the
protective film. When use, with flickers
the dry glue its glue on the glass. When the
glass suffers the instantance which the violence
destroys, the piezoelectricity thin film feels
the fierce vibration, the surface produces
electric charge Q, produces the narrow pulse
alarm between two output pins.

• mass block

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The piezoelectric sensors can only be used in
dynamic measurement

• Since the charge on the piezoelectric part
  caused by the external force can only be
  preserved when no leakage occurs, which means the
  input resistance of the measurement circuit is
  maximized. That is impossible. So the
  piezoelectric sensor can not be used in static
  measurement. The charge can be complemented when
  the alternating force functions on the
  piezoelectric parts, which can provide certain
  current to the measurement circuit. So it is only
  suitable for dynamic measurement (generally it
  ought to be above 100Hz, but the sensitivity will
  drop when it exceeds 30 Hz).

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2. Piezoelectric perimeter alarm system (used at
the entrance and exit of important places as well
as perimeter security)

• Bury the long piezoelectric cable in
  the shallow surface of earth, and it can play the
  role of distributional underground microphone or
  listening gear. It can distinguish human steps,
  wheel or tracked vehicle with the scope of dozens
  of meters through signal processing system. The
  figure on the right is the output wave form of
  the measurement system.

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3. Traffic monitoring
Buries the high polymer piezoelectricity electric
cable on the road, may gain the vehicle type
category message

• (including axis number, wheel base, single
  and double tire), the vehicle speed monitoring,
  the weighing bridge of toll station, rushing red
  light monitor, the parking area monitoring,
  traffic data collecting (road monitoring), the
  airport taxiway, and so on.

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The application demonstration of polymer
piezoelectric cable
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Second, the application of piezoelectric ceramic
sensors

• The parallel connecting method of
  piezoelectric film

The piezoelectric ceramics makes the laminated
shape, is called the piezoelectricity piece. The
piezoelectricity piece usually is two pieces (or
above two pieces) cakes in together, what
generally is commonly used is the paralled
connection. Its total area is monolithic two
times, on pole plate's total electric charge Q
and is monolithic electric charge Q two times.
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The piezoelectric dynamic sensor and its
application in measuring dynamic cutting force in
the lathe

Integrated lathe tool dynamic strength survey
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The application of piezoelectric dynamic sensor
in the dynamic measurement in sports
The piezoelectric pick-up survey both legs jump
dynamic strength
The piezoelectricity type gait analysis runs
Taiwan
The piezoelectricity type vertical jumps the
training analysis installment
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The Fourth Section Vibration Measurement and
Spectrum Analysis

• First, the basic concept of vibration

The vibration may divide into the
mechanical vibrations, the construction structure
vibration, the transport means to vibrate the
impact vibration which, the weapon, the
detonation cause and so on. Divides from
the vibration frequency range, has the high
frequency vibration, the low frequency vibration
and the ultra low frequency vibration and so on.
Looking from the vibration signal's
statistical nature, may vibrate divides into the
periodic vibration, the non-periodic vibration as
well as the random vibration and so on.
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The enormous power of the earthquake
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Seismic waveform
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Second, the classification of vibration sensor

• The vibration sensor is also called
  vibration pickup. It is divided into two types
  contact and the non-contact. The contact type
  includes electromagnetic type, inductance type,
  piezoelectricity type and so on the non-contact
  type includes eddy current type, electric
  capacity type, the Hall type, electro-optical
  type and so on. The following is an introduction
  and application of piezoelectric vibration sensor.

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Third, the structure and shape of piezoelectric
vibration acceleration sensor
Transverse vibration oscillation pickup
Longitudinal oscillation oscillation pickup
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Fourth, the performance index of piezoelectric
vibration acceleration sensor (take a small-sized
internal IC piezoelectric acceleration sensor
as an example)

• Technical specification
• Sensitivity 500mV/g
• Measuring range 10g
• Frequency range 4-4000Hz
• Installment resonance point 15kHz
• Resolution 0.00004g
• Weight 40g
• Installation ThreadM5 mm
• Linearity 1

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Fifth, the installment and application of
piezoelectric acceleration sensor

• a) Fixing the stud b) magnet adsorption c) glue
  water caking d) grasps the probe type
• 1- piezoelectric acceleration sensor 2- stud 3-
  magnet steel 4- caking agent 5- thimbles

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Fifth, the application of piezoelectric
acceleration sensor (continued)
Handhold vibration meter
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Fifth, the application of piezoelectric
acceleration sensor (continued)
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Sixth, the application of piezoelectric vibration
acceleration sensor in automobile

• The acceleration sensor can be used
  in judging automobile's collision, making the air
  bag gasify rapidly and thus saving life. It can
  also be installed on the sidewall of the
  cylinder, with a view to making the ignition
  moment close to detonation area and avoiding
  detonation, but at the same time to ensuring the
  output torque of the engine as much as possible.

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Detonation wave form

• The ignition moment of the engine
  cylinder must be very precise. If the ignition
  time can be advanced properly, that is, an
  advance angle is offered, the mixture of air and
  gas in the cylinder can burn completely, increase
  torque and reduce pollution discharge. But if the
  advance angle is too much, the mixing air will
  burn by itself, yield shockwave and give out
  sharp metal-knocking noise, which is called
  detonation, and may melt and damage the spark
  plug and piston ring. It may also make the
  cylinder cover, connecting rod and crank overload
  and distort. These can be measured and controlled
  by the piezoelectric sensor.

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Detonation measurement
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Seventh, the spectrum analysis and instrument of
vibration
What survey time domain graph with is the
oscilloscope, the survey frequency range graph
uses the spectrometer

• Time-domain chart

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Spectrum analyzer

• Frequency domain chart (Spectrogram)

Spectrograph or frequency range chart
Its abscissa is frequency f, the y-coordinate may
be an acceleration, may also be the oscillation
amplitude or the power and so on. It had
reflected in the frequency range, corresponds to
each frequency component peak-to-peak value.
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The shape of spectrum analyzer (continued)

• Frequency domain chart (Spectrogram)

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Frequency domain graphics

• The spectrum graph corresponding to the
  time-domain waveforms (distorted sine wave)

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Vibration time-domain / frequency domain graphics
(reference materials from the Oriental Technology
Institute of Vibration and Noise)
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Vibration time-domain / frequency domain graphics
(continued) (reference materials from the
Oriental Technology Institute of Vibration and
Noise)
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Fundamental and third harmonic spectrum
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Waveform synthesized by fundamental and 3rd
harmonic
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Square wave can be decomposed into same frequency
fundamental and odd harmonics like 3,5,7 ... ...
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Fault diagnosis based on spectral analysis

• Reduction gearbox fault analysis

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Blasting vibrograph
Printer
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Tsunami early warning system
The earthquake initiates one of Tsunami primary
causes. The epicenter fault migration causes
between the fault to produce the cavity, when the
sea water fills this cavity has the giant sea
water fluctuation. This kind of sea water
fluctuation when from the deep sea passes on to
the epicontinental sea, the ocean waves suddenly
rise to several meter high, and by each second
several hundred meter speed dissemination. After
the ocean waves rush to the ashore, will create
the significant destruction. The Tsunami early
warning system through the seabed vibration
pressure transmitter record ocean waves change's
data, and transmits to the information buoy,
transmits from the information buoy to the
meteorological satellite, transmits again from
the meteorological satellite to the satellite
earth station.
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Have a rest!