Piezoelectric Material A presentation by Travis Heffernan Monique

Piezoelectric Material A presentation by Travis Heffernan & Monique Furtado Engineering 45 Properties of Materials Santa Rosa Junior College Fall 2007 Younes Ataiiyan

Direct Piezoelectric Effect Piezoelectric Material will generate electric potential when subjected to some kind of mechanical stress.

The direct Effect : Generator F F • Compression Effect: Decrease in volume and it has a voltage with the same polarity as the material • Tension Effect: Increase in volume and it has a voltage with opposite polarity as the material

Inverse Piezoelectric Effect If the piezoelectric material is exposed to an electric field (voltage) it consequently lengthens or shortens proportional to the voltage.

The Inverse Piezoelectric Effect • If the applied voltage has the same polarity then the material expands. • If the applied voltage has the opposite polarity then the material contracts.

The History of Piezo • The name Piezo • originates from the Greek word piezein, which means to squeeze or press. The piezoelectric effect was first proven in 1880 by the brothers Pierre and Jacques Curie.

Developing theories… • Pierre and Jacques Curie predicted and • • demonstrated the piezoelectric effect using tinfoil, glue, wire, magnets, and a jeweler’s saw. They showed that crystals of tourmaline, quartz, topaz, cane sugar, and Rochelle salt generate electrical polarization from mechanical stress. The converse effect was mathematically derived by Gabriel Lippman in 1881 using fundamental thermodynamic principles and was later experimentally confirmed by the Curies.

How are Piezoelectric ceramics made? • Fine powders of the component metal oxides are mixed • • • in specific proportions, then heated to form a uniform powder. The powder is mixed with an organic binder and is formed into structural elements. The elements are fired according to a specific time and temperature program, during which the powder particles sinter and the material attains a dense crystalline structure. The elements are cooled, then shaped or trimmed to specifications. Electrodes are applied to a conducting material, which is connected to the elements.

Crystal Structure and Dipole Moments • A traditional piezoelectric ceramic is a • mass of perovskite crystals. Each crystal consists of a small tetravalent metal ion, usually titanium or zirconium, in a lattice of larger divalent metal ions, usually lead or barium, and O 2 - ions At temperatures below the Curie point, however, each crystal has tetragonal or rhombohedral symmetry and a dipole moment. Above the Curie point each perovskite crystal in the fired ceramic element exhibits a cubic symmetry with no dipole moment.

Polarizing Piezoelectric Material • Adjoining dipoles form regions of local alignment called domains. • • The alignment gives a net dipole moment to the domain, and thus a net polarization. The direction of polarization among neighboring domains is random, however, so the ceramic element has no overall polarization. The domains in a ceramic element are aligned by exposing the element to a strong, direct current electric field, usually at a temperature slightly below the Curie point When the electric field is removed most of the dipoles are locked into a configuration of near alignment

Types of Piezoelectric Materials • Naturally occurring crystals: Berlinite (Al. PO 4), cane sugar, Quartz, Rochelle salt, Topaz, Tourmaline Group Minerals, and dry bone (apatite crystals) • Man-made crystals: Gallium orthophosphate (Ga. PO 4), Langasite (La 3 Ga 5 Si. O 14) • Man-made ceramics: Barium titanate (Ba. Ti. O 3), Lead titanate (Pb. Ti. O 3), Lead zirconate titanate (Pb[Zrx. Ti 1 -x]O 3 0<x<1) - More commonly known as PZT, Potassium niobate (KNb. O 3), Lithium niobate (Li. Nb. O 3), Lithium tantalate (Li. Ta. O 3), Sodium tungstate (Nax. WO 3), Ba 2 Na. Nb 5 O 5, Pb 2 KNb 5 O 15 • Polymers: Polyvinylidene fluoride (PVDF)

Sonic and Ultrasonic Applications • Sonar with Ultrasonic time • • • -domain reflectometers Materials testing to detect flaws inside cast metals and stone objects as well as measure elasticity or viscosity in gases and liquids Compact sensitive microphones and guitar pickups. Loudspeakers

Pressure Applications • Transient pressure measurement to • • • study explosives, internal combustion engines (knock sensors), and any other vibrations, accelerations, or impacts. Piezoelectric microbalances are used as very sensitive chemical and biological sensors. Transducers are used in electronic drum pads to detect the impact of the drummer's sticks. Energy Harvesting from impact on the ground Atomic force and scanning tunneling microscopes. Electric igniters and cigarette lighters

Consumer Electronics Applications • Quartz crystals resonators as • • frequency stabilizers for oscillators in all computers. Phonograph pick-ups Accelerometers: In a piezoelectric accelerometer a mass is attached to a spring that is attached to a piezoelectric crystal. When subjected to vibration the mass compresses and stretches the piezo electric crystal. (i. Phone)

Motor Applications • Piezoelectric elements can be used • • in laser mirror alignment, where their ability to move a large mass (the mirror mount) over microscopic distances is exploited. By electronically vibrating the mirror it gives the light reflected off it a Doppler shift to fine tune the laser's frequency. The piezo motor is viewed as a high-precision replacement for the stepper motor. Traveling-wave motors used for auto-focus in cameras.

Our Experiment

Procedure 1) Attach a mirror to the piezoelectric buzzer. Position that laser so 2) 3) 4) 5) 6) that the beam can reflect off of the mirror and hit the wall across the room. Connect the function generator to the Piezoelectric device. Find the resonant frequency of the device by slowly increasing the frequency at 10 Vp-p. The laser will vibrate the most at the resonant frequency. Measure the diameter of the laser without any signal. Then measure the diameter of the laser with the AC signal applied. Calculate the displacement of the laser and divide it by two to get the amplitude of the magnified change in volume for the piezoelectric material. Measure the distance from the piezo to the wall and to the laser. Also measure the height of the laser and reflected beam in relation to the piezo. Calculate the change in volume for the piezoelectric material.

Piezo Material at Resonance

Error Analysis The laser’s diameter expands over a distance. The quality of the mirror scatters the laser. The sinusoidal vibration of the material amplifies the laser’s displacement.

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