Piezoelectric Generator Harvesting Bike Vibrations Energy to Supply Portable Devices E. Minazara , D. Vasic and F. Costa Fundamentals of piezoelectric material The conversion of mechanical energy into electrical one is generally achieved by converters alternator type or commonly known dynamo. But there are other physical phenomena including piezoelectricity that can also convert mechanical movements into electricity. The piezoelectric effect exists in two domains, the first is the direct piezoelectric effect that describes the materials ability to transform mechanical strain into electrical charge, the second form is the converse effect, which is the ability to convert an applied electrical potential into mechanical strain energy figure 1.

The direct piezoelectric effect is responsible for the materials ability to function as a sensor and the converse piezoelectric effect is accountable for its ability to function as an actuator. A material is deemed piezoelectric when it has this ability to transform electrical energy into mechanical strain energy, and the likewise transform mechanical strain energy into electrical charge.The piezoelectric materials that exist naturally as quartz were not interesting properties for the production of electricity, however artificial piezoelectric materials such as PZT (Lead Zirconate Titanate) present advantageous characteristics. Piezoelectric materials belong to a larger class of materials called ferroelectrics. One of the defining traits of a ferroelectric material is that the molecular structure is oriented such that the material exhibits a local charge separation, known as an electric dipole. Throughout the artificial piezoelectric material composition the electric dipoles are orientated randomly, but when a very strong electric field is applied, the electric dipoles reorient themselves relative to the electric field; this process is termed poling. Once the electric field is extinguished, the dipoles maintain their orientation and the material is then said to be poled. After the poling process is completed, the material will exhibit the piezoelectric effect.

Staircase Power Generation Using Piezo-Electric Transducers V. Prasannabalaji, R. Rakesh, S. Sairam and S. Mahesh Piezoelectric generator principle The vibrations energy harvesting principle using piezoelectric materials is illustrated in figure 4. The conversion chain starts with a mechanical energy source: bike. Bike vibrations are converted into electicity via piezoelectric element. The electricity produced is thereafter formated by a static converter before supplying a storage system or the load (electrical device).

Electrical Power Generation Using Piezoelectric Crystal Anil Kumar mechanical stresses applied to piezoelectric materials distort internal dipole moments and generate electrical potentials (voltages) in direct proportion to the applied forces. These same crystalline materials also lengthen or shorten in direct proportion to the magnitude and polarity of applied electric fields.Because of these properties, these materials have long been used as sensors and actuators. One of the earliest practical applications of piezoelectric materials was the development of the first SONAR system in 1917 by Lan- gevin who used quartz to transmit and receive ultrasonic waves [1]. In 1921, Cady first proposed the use of quartz to control the resonant frequency of oscillators. Today, piezoelectric sensors (e.g., force, pressure, acceleration) and actuators (e.g., ultrasonic, micro positioning) are widely available. The same properties that make these materials useful for sensors can also be utilized to generate electricity. Such materials are capable of converting the mechanical energy of compression into electrical energy, but developing pie- zoelectric generators is challenging because of their poor source characteristics (high voltage, low current, high impedance). This is especially true at low frequencies and relatively low power output. Other projects have used piezoelectric films to extract electrical energy from mechanical vibration in machines to power MEMS devices [4]. This work extracted a very small amount of power (