Piezoelectric Resonators ME 2082

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Emery Oliver
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1 Piezoelectric Resonators ME 2082

2 Introduction K T : relative dielectric constant of the material ε o : relative permittivity of free space (8.854*10-12 F/m) h: distance between electrodes (m - material thickness) A: area of the electrodes (m 2 ) C 0 : measured capacitance at 1kHz (F)

3 Topics of Discussion Equivalent Circuit of a Ceramic Element (Non-resonant operation)

4 Mechanical Q Mechanical Q Equation F r : resonance frequency (Hz) F a : anti-resonance frequency (Hz) Z m : resistance at F r (ohm) C 0 :static capacitance (Farad) Alternatively, Q M can also be determined using the equation: where F 1, F 2 are -3dB points on the frequency/impendance curve from the resonance frequency F r.

5 Piezoelectric Modes of Vibration The frequency constant, N, is the product of the resonance frequency and the linear dimension governing the resonance. The various modes of resonance are shown schematically for: N 1 =F r D (Hz.m) Radial Mode Disc N 2 =F r l (Hz.m) Length Mode Plate N 3 =F r l (Hz.m) Length Mode Cylinder N 4 =F r h (Hz.m) Thickness Mode Disc, Plate N 5 =F r h(hz.m) Shear Mode Plate

6 Variation of Coupling Coefficients as a Function of Relative Frequency Interval between Series and Parallel Resonant Frequencies

7 Equivalent Circuit of a Piezoelectric Resonator

8 Measurement of Resonant Frequencies - Circuits Constant Voltage Circuit: Constant Current Circuit:

9 Measurement of Resonant Frequencies - Variations Variation of Impedance with Frequency: Variation of Admittance with Frequency:

10 Measurement of Resonant Frequencies - Variations Variation of Phase Angle with Frequency:

Piezoelectric Composite Transducers 1-3 Composites Property 1-3 Composites Monolithic Ceramic Dielectric Constant K 33 T 890 ±20% 3250 Dissipation

11 Piezoelectric Composite Transducers 1-3 Composites Property 1-3 Composites Monolithic Ceramic Dielectric Constant K 33 T 890 ±20% 3250 Dissipation factor Frequency Constant N ± 5% 1850 Kε 0.62 Q (unloaded) 5 70 Ceramic Volume 25-30% 100 Frequency 150 KHz-1.5MHz 150 KHz-5 MHz

12 Piezoelectric Flexure Elements Bimorph: Flexure elements have two layers of PZT material bonded together, with electrodes in series or parallel configuration. These elements offer large displacements for positioning devices or actuators. Series configuration:

13 Piezoelectric Flexure Elements Parallel configuration:

generation, structural deformation, inspection systems and scanning microscopes.

14 Piezoelectric Actuators An actuator is a device that produces a displacement (movement) when voltage is applied. Actuators are used for many functions, including canceling vibration, tool adjustment and control, micropumps, mirror positioning, wave generation, structural deformation, inspection systems and scanning microscopes. When a voltage is applied to the assembly, it produces small displacements with a high force capability. These actuators can be built from wide ranging piezoelectric materials offered by Sensor, depending on the various end uses.

15 Piezoelectric Actuators Bending mode actuators

16 Piezoelectric Actuators Multilayer piezoelectric actuator is a device consisting of a number of piezoelectric elements in a stack. The elements are generally connected in parallel either through the electrode structure or the insertion of brass electrodes between the elements

17 Piezoelectric Actuators Diaphragm actuators:diaphragm actuators consist of a piezoelectric washer bonded to a metal diaphragm. This configuration provide a low cost but good displacement actuator. In applications, the diaphragm must be clamped on its edges to produce the deflection.

18 Piezoelectric Actuators Tube actuators: A piezoelectric tube element with electrodes on its curved surfaces can be used as an actuator element. The elements offer good structural rigidity, but are more difficult to manufacture. They are often used in such applications as scanning tunnelling microscopes (STMs). A tube actuator is generally poled through the wall, but other configurations involving split electrodes and segments are also used as actuator elements. The extension of the piezoelectric tube element under a DC voltage V applied in the direction of polarization is given by the formula: Displacement = [L/W]d 31 V Where: L is the length of the tube W is the thickness of the wall d 31 is the piezoelectric coefficient V is the applied voltage

19 Piezoelectric Actuators Electrode Configurations for Tube Elements:

20 Igniter Elements Operating Principle: High voltages are generated when piezoelectric materials are impacted. When this voltage is applied across an air gap, an arc is generated whenever the voltage exceeds the breakdown voltage of the air gap. The voltage V generated during the impact can be expressed as: V=L x g 33 x S Where L is the length of the element, g 33 is the piezoelectric voltage coefficient and S is the mechanical load in the axial direction. A spring-loaded mechanism is generally used to produce the mechanical load on the ceramic element. The energy E is then determined by the equation: E= 1/2 CV 2

PIEZOELECTRIC TECHNOLOGY PRIMER

PIEZOELECTRIC TECHNOLOGY PRIMER James R. Phillips Sr. Member of Technical Staff CTS Wireless Components 4800 Alameda Blvd. N.E. Albuquerque, New Mexico 87113 Piezoelectricity The piezoelectric effect is