 BY:- DIPANKAR BAIDYA  ME IInd YEAR weight FORCE Electric field

The need for electrical power supply to remote installations without the use of diesel generating set or without installing power transmission line has spurred on interest on piezoelectric energy harvesting, or the extraction of electrical energy using a vibrating piezoelectric device. Installation of power transmission line in inhospitable terrain and its maintenance are costly. Use of DG set produces sound signature, which can be easily picked up by the enemy in case of defence installation. It also produces pollution, which is not to the liking of astrophysicists. Piezoelectric power generators overcome all these problems.

 Discovered in 1880 by Jacques and Pierre Curie during studies into the effect of pressure on the generation of electrical charge by crystals (such as quartz).  Piezoelectricity is defined as a change in electric polarization with a change in applied stress (direct piezoelectric effect).  The converse piezoelectric effect is the change of strain or stress in a material due to an applied electric field. Piezoelectric effect ▶Two main types of piezoelectric materials are used today: Quartz Crystals Polycrystalline Ceramics

PHYSICAL PROPERTIES OF PVDF(Polyvinylidene Floride)  Specific gravity: ;  melting point: C;  water absorption: %;  tensile strength at break: Mpa;  elongation at break: %,  hardness shores D: 70-82;  low temperature embrittlement; -62 to 64 0 C.

How are piezoelectric ceramics made? A traditional piezoelectric ceramic is perovskite crystal, each consisting 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. Under conditions that confer tetragonal or rhombohedral symmetry on the crystals, each crystal has a dipole moment.

 Mechanical compression or tension on a poled piezoelectric ceramic element changes the dipole moment, creating a voltage.  Compression along the direction of polarization, or tension perpendicular to the direction of polarization, generates voltage of the same polarity as the poling voltage. Generator and motor actions of a piezoelectric element

 These piezoelectric crystals can be cut and stressed in different ways: ◦ Shear ◦ Flexural ◦ Compression

The Piezoelectric Effect  Resulting force produces a strain on the crystal causing charge to accumulate on opposing surfaces. F F Si O O O QUARTZ CRYSTAL

 PRELOAD STUD INCREASES STIFFNESS OF ELEMENT CAUSING HIGH RESONANCE THERMAL TRANSIENTS CAUSE METALS TO EXPAND AND CONTRACT STRESSING CRYSTALS ALONG SENSITIVE AXIS STRAIN WAVES TRAVEL UNIMPEDED DIRECTLY INTO CRYSTAL