SYSTEM ON CHIP FOR MICRO-VIBRATION MEASUREMENT

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SYSTEM ONCHIP FOR MICRO-VIBRATION MEASUREMENT

• Prepared by
• Tarun Mishra
• Department of Electrical and Computer Engineering
• Utah State University
• Email tarun.mishra_at_aggiemail.usu.edu
• Ph No 510-364-9864

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OUTLINE

• Introduction
• Bi-Morph Sensor
• Basic Design and Structure
• Specifications Results
• Advantages
• Limitations
• Proposed System

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INTRODUCTION

• Advances in precision micro-machining has led to
  an interest in micro-robotics.
• Applications of micro-robotics range from
  micro-assembly, to biomedics (inner space), to
  land mine sweeping, to city water system
  analysis.
• As with conventional robotics one of the biggest
  challenges is making robots that are mobile and
  can traverse a wide variety of terrain.
• Furthermore, in micro-robotics there is the
  problem that as the robot gets smaller the
  terrain obstacles seem bigger.

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• A pebble is no problem for a six meter long HMV,
  but it is real challenge for a ten millimeter
  surveillance robot. Actuation systems for mobile
  micro-robotics must meet the following
  challenges
• Traverse terrain with obstacles bigger than robot
• Low power/ high efficiency
• Simple control
• Withstand harsh environments
• Simple mechanics for both scalability and ease of
  manufacturing

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Bi-Morph Sensor

• Piezoelectric crystal or element primarily
  responds to force -input.
• Multiple forces can also be applied
• To increase the charge sensitivity more than one
  element can be used to form a transducer system
  and such combinations are known as bimorphs.

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Bimorph Continued.

• A bimorph actuator is composed of two thin panels
  of ceramic elements bonded together with a
  flexible metallic panel as it's central
  electrode. By wiring these two elements in such a
  way as to make one elongate and the other
  contract by applying voltage, inflection
  deviation occurs conforming to the waveform of
  the applied voltage.

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Basic Designs of Piezoelectric Positioning
Elements

• Bender Type Actuators A Piezo bimorph operates
  similarly to a bimetallic strip in a thermostat.
  When the ceramic is energized the metal substrate
  is deflected with a motion proportional to the
  applied volt-age. Bimorph actuators providing
  motion up to 1000 µm are available and greater
  travel range is possible. Apart from the
  classical strip form, bimorph disk actuators are
  available, where the center arches when a voltage
  is supplied.

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Two Electrode and Three Electrode Bimorph

• Instead of a Piezo/metal combination Piezo/Piezo
  combinations are possible where individual Piezo
  layers are operated in opposite mode
  (contraction/expansion).
• Two basic versions are available the two
  electrode bimorph (serial bimorph) and the three
  electrode bimorph (parallel bimorph).

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Two Electrode Bimorph (Serial Bimorph)

• Here one of the two ceramic plates is always
  operated opposite to the direction of
  polarization.
• To avoid depolarization, the maximum electric
  field is limited to few hundred volts per
  millimeter.
• These type of actuator is widely used in
  accelerometers and force sensors.

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Three Electrode Bimorph (Parallel Bimorph)

• Here the two piezoelectric plates are of the same
  polarization directions and the actuator is
  driven by applying electrical field between
  surface electrodes and the bonding layer

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Diagrammatic Representation
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Basic Characteristics of Bimorph
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Bimorph Structure

• Bimorphs are composed of two sheets of
  Piezo-electric electrodes securely glues together
  and there are two different ways to do so.
• The first is to have electrodes on both sides of
  the sheets. Then the sheets are glued together
  with their poled directions in the same direction
  as seen below.  Equal but opposite electric
  fields are then applied to the two sheets.  One
  of the sheets shrinks in length and the other
  expands causing the bimorph to bend.

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Bimorph Structure

• The second way to create bimorphs is to put
  electrodes on just one side of the electrode
  sheet and glue them so that the poled directions
  are in the opposite direction. The electrodes are
  on the outer sides of the bimorph and the
  electric field is applied across the entire as
  seen below.

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Electric Field Across Bimorph

• When an electric field is applied across a
  bimorph one of the electrode sheets expands while
  the other shrinks causing the bimorph to bend,
  below. In the picture the deflection of a bimorph
  is represented by the arrow.
• The deflection distance can be measure to
  determine the performance of the bimorph. 

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Electrostrictive curve for Applied Electric Field
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Some Results

• Some results are shown below for DC voltages
• AC voltages produce different displacements than
  the DC, it depends what the frequency is. At
  resonance the AC deflection is more than double
  that of the DC
• Video of bimorph under AC voltage at resonance
  (Fig.2)

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Displacement vs Voltage
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Specifications

• For bimorph actuator specifications, we need to
  take into account the following parameters
• Maximum Displacement (mm/V)
• Blocked Force (N)
• Maximum Voltage (volts)
• Stiffness (N/mm)
• Resonance Frequency (Hz)
• Capacitance (F)
• Compliance
• Response Time (ms)

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Specifications

• There are other factors to be considered too
  along with this specifications like
• Youngs Modulus
• Operating Temperature
• Storage Temperature
• Mechanical quality factor etc.

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Applications

• Microphone, acoustic pressure sensor, micro
  speaker, acoustic transducers, vibration
  measurement
• MEMS piezoelectric sensors and actuators
  (numerous arbitrarily shaped structures on
  silicon substrate)
• High performance and low cost parts in Audio
  system, communication system, multimedia system,
  hearing aid system
• High sensitive and biomedical compatible acoustic
  and ultrasonic transducers

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General Advantages

• Size miniaturization with extremely small weight
• Little power consumption and no polarization
  voltage needed
• Potentially low cost due to the batch processing
  and possibility of integrating microphones and
  circuits on a single chip

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Unique Advantages

• Easier control of the neutral plane position than
  a uni-morph structure and effective conversion of
  mechanical strain into electrical voltage and
  vice versa
• Simple structure containing only piezoelectric
  film, electrodes and very flexible parylene (does
  not introduce any significant stiffness in the
  diaphragm, nor residual stress)
• With larger sensitivity and signal/noise ratio
  and higher fundamental resonant frequency, it has
  inherently higher figure of merit than a
  uni-morph device.
• Conformal deposition allowing various diaphragm
  shapes

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Limitations

• There are three major limitations to the bimorph
  piezoelectric actuator.
• The shaping of the electrodes and laminate.
• The bandwidth.
• Blocking force.
• The Shaping of the electrodes and laminate can be
  in several forms
• C-shape
• Bar, rectangular
• Disk
• Each shape will have a different response time
  and force when a specific voltage is applied.

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Limitations (cont.)

• Shaping can also effect bandwidth.
• A larger laminar area will cause the bandwidth to
  drop. As the bandwidth drops the response time
  also drops.
• This could either be an advantage or a
  disadvantage depending on the plant.
• Blocking force is also determined by the
  deflection and compliance of the two laminar
  surfaces.
• This ends up being inversely proportional to the
  length which indicates longer the lamina the less
  force it is able to exert.

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MEM System-On-Chip

• A typical SoC consists of
• One microcontroller, microprocessor or DSP 
  core(s)
• Memory blocks
• Analog interfaces including ADCs and DACs
• External interfaces including industry standards
  such as USB, FireWire, Ethernet, USART
• Voltage regulators and power management circuits.

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SoC
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FPGA

• FPGAs contain programmable logic components
  called Configurable logic blocks (CLBs)
• CLBs cab be configured to perform
  complex combinational functions
• FPGA configuration is usually specified using any
  HDL
• Costs between 10 10,000

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FPAA

• Analog counter parts of FPGA
• They are programmed using a bit-stream
• various analog functions can be implemented using
  a set of configurable analog block (CAB) and
  programmable interconnect networks
• Each CAB can implement a number of analog signal
  processing functions

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Proposed System
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CONCLUSION

• As low vibration amplitude cannot be
  neglected in any design. With the help of some
  reconfigurable SoC, vibration estimation in the
  can be done easily. This system can be used for
  rapid adaptation to any function, guaranteeing
  both low cost and short design times.

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REFERENCES

• TRANSDUCERS AND SENSORS, Murthy. D.V.S, PHI
• A. M. Flynn, Piezoelectric Ultrasonic
  Micromotors, MIT PhD. Thesis, Thesis in
  Electrical Engineering and Computer Science, June
  1995.
• Craing L. Horn and Natarajan Shankar, "Modeling
  the Dynamic Behavior of Electrostrictive
  Actuators", SPIE Conference Procedings Vol. 3041,
  pp.268-280, 1997.
• "Basis of Piezoelectric Positioning", Products
  for Microposionting Catalog, Physik Instrumente
  Co., 1995.
• http//www.physikinstrumente.com/tutorial/
• http//www.americanpiezo.com/products_services/str
  ipe_actuators.html