Thermal and Motion Systems Overview
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Questions and Answers

Which piezoelectric material has the highest relative permittivity?

  • ZnO
  • Lithium niobate
  • Quartz
  • PZT-5A (correct)

    • What is the main issue associated with the Curie temperature of piezoelectric materials?

  • It affects the material density.
  • It determines the frequency response.
  • It is responsible for power output efficiency.
  • It defines the temperature range for maintaining piezoelectric properties. (correct)

    • Which of the following piezoelectric materials has the lowest density?

  • Quartz (correct)
  • PVDF
  • PZT-4
  • Lithium niobate

    • What is a significant drawback of bulk piezoelectric materials compared to thin films?

    <p>Incompatibility with MEMS or IC integration</p> Signup and view all the answers

    Which material has the highest coupling factor k?

    <p>PZT-5A</p> Signup and view all the answers

    What primarily causes the lower response speed in systems due to the thermal time constant?

    <p>Thermal charging and dissipation</p> Signup and view all the answers

    What characteristic is notable in the motion range of a parallel plate capacitor?

    <p>Range of motion is minimal</p> Signup and view all the answers

    Which best describes a biomimetic ciliary transport system?

    <p>Employs numerous distributed actuators</p> Signup and view all the answers

    In the context of the Seebeck effect, what happens when there is a temperature differential across a material?

    <p>An electrical potential is generated</p> Signup and view all the answers

    What does the Seebeck coefficient represent?

    <p>The voltage generated per unit temperature difference</p> Signup and view all the answers

    What occurs in electrostatic sensors when the distance between moving and fixed plates changes?

    <p>Capacitance changes</p> Signup and view all the answers

    What fundamental principle underlies the actuation of electrostatic systems?

    <p>Electrostatic force of attraction</p> Signup and view all the answers

    In a thermal couple with different Seebeck coefficients, what voltage difference is developed due to a temperature change?

    <p>A voltage difference based on the difference in Seebeck coefficients</p> Signup and view all the answers

    What equation represents the stored energy in a capacitor?

    <p>U = CV^2 / 2</p> Signup and view all the answers

    What is the correct expression for the force exerted by a capacitor actuator?

    <p>F = - εA / 2d^2</p> Signup and view all the answers

    Which of the following is a merit of capacitor actuators?

    <p>Low power consumption</p> Signup and view all the answers

    What must be small to achieve a larger force in capacitor actuators?

    <p>Distance</p> Signup and view all the answers

    Which is a demerit of using capacitor actuators in applications?

    <p>They may stick due to molecular forces</p> Signup and view all the answers

    In capacitor actuators, the actuation is primarily driven by which parameter?

    <p>Voltage</p> Signup and view all the answers

    What is the typical thickness of the proof mass area in a capacitive accelerometer as stated?

    <p>5 µm</p> Signup and view all the answers

    What is the main reason for needing packaging in certain applications of capacitor actuators?

    <p>They are vulnerable to sticking due to small spacing</p> Signup and view all the answers

    What are the two main categories of external magnetic fields?

    <p>Uniform and Non-uniform</p> Signup and view all the answers

    How do permanent hard magnets behave in a magnetic field?

    <p>They behave similarly to a compass needle.</p> Signup and view all the answers

    What phenomenon do soft magnetic materials exhibit when subjected to a magnetic field?

    <p>Shape anisotropy</p> Signup and view all the answers

    What is a key process for depositing magnetic materials in the fabrication of magnetic MEMS?

    <p>Electroplating</p> Signup and view all the answers

    What is a significant limitation of 2D spiral micro-inductors?

    <p>They have low magnetic permeability of air.</p> Signup and view all the answers

    What negatively affects the efficiency of in-plane micro-inductors?

    <p>Eddy currents in the conductive substrate</p> Signup and view all the answers

    What is the main advantage of fabricating magnetic cores at the center of micro-inductors?

    <p>It enhances the strength of the magnetic field.</p> Signup and view all the answers

    Which aspect of soft magnetic materials is emphasized when subjected to a magnetic field?

    <p>Their shape dependence for magnetic moment development</p> Signup and view all the answers

    What is the nature of the strain components generated in the described setup?

    <p>No longitudinal strain components</p> Signup and view all the answers

    In the context of the described piezoelectric transducer, what role do the electrodes play?

    <p>They are used to apply a voltage across the material.</p> Signup and view all the answers

    What is the configuration change of the electrode application in the context of the transducer?

    <p>The electrodes are positioned to force axis-3 in the longitudinal direction.</p> Signup and view all the answers

    Which aspect of the strain formula is specifically noted to be zero?

    <p>The longitudinal strain components</p> Signup and view all the answers

    What happens to axis-3 in the new configuration of the piezoelectric transducer?

    <p>It is forced to lie in the longitudinal direction.</p> Signup and view all the answers

    What is the significance of applying a voltage across two electrodes in this setup?

    <p>It creates an electric field that influences the material properties.</p> Signup and view all the answers

    What is the expected outcome regarding the displacement of the piezoelectric transducer when voltage is applied?

    <p>End displacement occurs along the longitudinal direction.</p> Signup and view all the answers

    What type of material is mentioned in the example that interacts with the electrodes?

    <p>ZnO (zinc oxide)</p> Signup and view all the answers

    Study Notes

    Thermal Time Constant

    • Lower response speed is a consequence of thermal time constant
    • Construction and fabrication of simple devices is easier due to their dissipation and thermal charging
    • Range of motion for parallel plate capacitors is relatively small

    Micro Ciliary Motion System

    • Utilizes a biomimetic micro-motion system
    • Ciliary transport system utilizes a large number of distributed actuators to achieve macroscopic motion

    Thermal Couples

    • Thermal electric effect refers to the generation of electrical potential when a temperature differential exists across a piece of material
    • More electrons are excited into the conduction band at the high-temperature end and diffuse into the colder region
    • Seebeck effect is characterized by the Seebeck coefficient
    • A working thermal couple with two different Seebeck coefficients develops a voltage difference when subjected to a temperature change

    Electrostatic Sensors and Actuators

    • Sensors utilize the change in capacitance between moving and fixed plates due to distance and position changes or media replacement
    • Electrostatic force (attraction) drives actuators between moving and fixed plates when voltage is applied

    Forces of Capacitor Actuators

    • Stored energy is the product of capacitance and voltage squared, divided by two
    • Force is the energy derivative with respect to the pertinent dimensional variable
    • The expression for force incorporates the capacitance equation and the derivative of the stored energy

    Merits and Demerits of Capacitor Actuators

    • Merits include universal sensing and actuation, low power, high speed, and efficient and clean removal of sacrificial materials
    • Demerits include inverse scaling of force and distance, vulnerability to particles due to small spacing, vulnerability to sticking phenomena, and the use of sacrificial release

    Capacitive Accelerometer

    • Proof mass area is 1x0.6 mm2 and 5 m thick

    Common Piezoelectric Materials

    • Materials like ZnO, PZT-4, PZT-5A, Quartz, Lithium tantalate, Lithium niobate and PVDF are commonly used in piezoelectric devices
    • Materials are characterized by their relative permittivity, Young’s modulus, density, coupling factor, and Curie temperature

    Issues with Piezoelectric Materials

    • Curie temperature is the temperature above which the piezoelectric property is lost
    • Piezoelectric constant is sensitive to the material composition and can be damaged by defects
    • Frequency response of most materials is limited due to leakage and cannot "hold" a DC force
    • Bulk materials are easy to form but not easily integrated with MEMS or ICs
    • Thin-film materials are not as thick and overall displacement is restricted

    Piezoelectric Strain

    • Strain is described by a matrix equation
    • No longitudinal strain components are generated in this manner

    Piezoelectric Transducer Example

    • Derives the expression for end displacement of a piezoelectric transducer configured with electrodes to pole the ZnO material
    • Axis-3 is forced to lie in the longitudinal direction of the beam length
    • Voltage V is applied across two electrodes

    Magnetic Dipoles in Magnetic Fields

    • External magnetic fields are classified as uniform or non-uniform
    • Hard magnets behave similarly to a compass needle in magnetic fields
    • Soft magnetic materials exhibit shape anisotropy and develop a magnetic moment based on their shape rather than field orientation

    Fabrication of Magnetic MEMS

    • Thin-film process technologies are required to make magnetic micro-devices
    • Electroplating is an important process for depositing magnetic materials

    Fabrication of Micro-inductors

    • Micro-inductors are passive devices with applications in microelectronics and MEMS
    • Micro-inductors are fabricated as spirals or square spirals in 2-D layouts

    2D Spiral Micro-inductors

    • 2-D micro-inductors are simple to fabricate but not very effective due to their spiral shape and low magnetic permeability of air
    • Magnetic cores have been fabricated at the center to improve performance
    • In-plane micro-inductors have poor efficiency due to their in-plane fabrication with the substrate
    • Magnetic flux passing through the conductive silicon substrate creates eddy currents that degrade device performance

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    MEMS Sensors and Transducers Part 1 PDF

    Description

    This quiz covers critical concepts related to thermal time constants, micro ciliary motion systems, thermal couples, and electrostatic sensors and actuators. You'll explore the effects of temperature differentials on electrical potential and the mechanisms behind biomimetic motion systems. Test your understanding of these essential principles in physics and engineering.

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