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Name-Anshuman Samantray 7th semester Electrical EngineeringCollege of Engineering and Technology
PATTERN OF EXPLANATION1. Introduction2. What is piezoelectric effect?3. What is a crystal?4. How piezoelectricity works?5. What are piezoelectric generators?6. What are the advantages of piezoelectric generators?7. What is piezoelectric car?8. Diagrammatic presentation of piezoelectric car.9. Operation of piezoelectric car.10. Advantages of piezoelectric car.11. Disadvantages of piezoelectric car.
INTRODUCTION The battery range for many electric vehicles is limited, meaning that such methods of transportation can only be used for short trips. In extended range vehicles manufacturers provide an internal combustion engine that uses conventional fuels to recharge batteries in motion & hence extend their range. But in order to reduce environmental pollution, a piezoelectric energy assisted car, using piezoelectric effect for charging the batteries in motion, can be taken as a better alternative.
HISTORY Piezoelectricity was discovered in 1880 by two brothers, Pierre and Paul-Jacques Curie ,who found that when a certain type of crystals, including Quartz, Tourmaline And Rochelle salt were compressed along certain axes, a voltage was produced on the surface of the crystals. This effect is known as piezoelectric effect. White Quartz Rochelle Salt
What is a crystal? A class of material arranged in a definite geometrical pattern in three dimensions (table salt and sugar are common examples) Quartz Crystal is silicon and oxygen arranged in a crystalline structure (SiO2). SiO2 is also found abundantly in nature in a non- crystalline structure (“amorphous”) as sand.
A method for predicting the behavior of acrystal: The unit cell + Represents silicon atom - Represents oxygen atom Not actually correct, but this method allows a good understanding of quartz crystals
The unit cell of crystal silicon dioxide - + + - - +As we can see that there is no inversion centre & hence aquartz crystal shows piezoelectric effect………
How piezoelectricity works Normally, the charges in a piezoelectric crystal are exactly balanced, even if theyre not symmetrically arranged. The effects of the charges exactly cancel out, leaving no net charge on the crystal faces. (More specifically, the electric dipole moments—vector lines separating opposite charges—exactly cancel one another out.) If you squeeze the crystal , you force the charges out of balance. Now the effects of the charges (their dipole moments) no longer cancel one another out and net positive and negative charges appear on opposite crystal faces. By squeezing the crystal, youve produced a voltage across its opposite faces—and thats piezoelectricity!
The Piezoelectric Effect Crystal material at rest: No forces applied, so net current flow is 0 Crystal +-+-+- Current Meter =0 Charges cancel +-+-+- each other, so no current flow
The Piezoelectric Effect Crystal material with forces applied in direction of arrows……….. Crystal ----- Force Current Meter +++++ deflects in + directionDue to properties of symmetry,charges are net + on one side &net - on the opposite side: crystal getsthinner and longer
The Piezoelectric Effect Changing the direction of the applied force……….. Crystal ++++ Force Current Meter deflects in - direction -----…. Changes the direction ofcurrent flow, and the crystal getsshorter and fatter.
The electromechanical nature of piezoelectric material In general, if you deform a piezo crystal by applying a force, you will get charge separation: Think of a simple battery. Taking it one step further, what would happen to the crystal if you applied an electrical force that results in the exact same current flow from the proceeding circuit?
The electromechanical effect Now, replace the current meter with a power source capable of supplying the same current indicated by the meter…. Crystal switch +-+-+-charges cancel power source +-+-+-…. With the switch open, the crystal material is now at rest again:the positive charges cancel the negative charges.
The electromechanical effect When the switch is closed, and we apply the exact amount of power to get the same current that was detected when the crystal was squeezed , then the crystal should deform by the same amount!! Crystal ++++ + side power source (battery) ----- - side…. and, the crystal should get shorter and fatter.
The electromechanical effect What will happen if you switched the battery around?? Crystal ----- - side power source (battery) +++++ + side…. the crystal should get longer and skinnier.
PIEZOELECTRIC GENERATORS Piezoelectric generator is nothing but a piezoelectric crystal sandwiched between two metallic electrodes. So when a mechanical pressure/stress is applied on the crystal , an emf is generated across the metallic plates provided.
IMPORTANCE The converse effect is also possible i.e. when the emf is applied along certain electrical axes in the crystal ,this crystal produces mechanical vibrations. This effect, known as converse piezoelectric effect, is used in many practical devices such as buzzers , Ultrasonic filters & sonar for producing Ultrasonic waves.
IMPORTANCE This effect is implemented in a variety of practical devices such as microphones, phonograph pick-ups and wave filters in telephone communications systems and electric power generation etc.
PIEZOELECTRIC CAR Each of these piezoelectric car tires is equipped with an array of highly bendable PZT benders covering most of the inner surface .The output due to deformation of tires, which is an AC waveform has to be converted into DC signal by a rectifier before it can be cached in a capacitor . Each row of benders, running across the width of tire is taken as one generator & is rectified separately with all PZT lines connected in parallel. At any given time only three or four rows , depending on the length of AN ARRANGEMENT OF the contact patch , generate power. PZT BENDERS IN A TIRE
Since rectifiers provide very high resistance for reverse flow of current the remaining PZT benders behave as disconnected & hence inverse piezoelectric effect can not occur. The following curve shows Voltage and Power across a 1000Ω load at various rotations per minute.
Power is extracted from the tire-wheel system using a commutator-like assembly i.e. one that continuously maintains the electrical contact between the chassis and the wheel while allowing the latter to spin freely . Such a setup permits the extraction of tire-generated power to run on-board electronics. The energy obtained in this method depends on two factors –tire surface area , rpm at 100 km/h. So greater the surface area more will be the output. If a huge amount of power can be extracted so as to charge the batteries of an all-electric engine then no fossil fuel will be required to provide power reducing the pollution . Such a concept vehicle is named as P-Eco.
DIAGRAMATIC PRESENTATION OF A PIEZO-CAR Piezoelectric generator
ADVANTAGES 1. Reduces environmental pollution. 2. By using Lead Zirconate piezoelectric crystals, we can generate until 10000 volts by small deformations of the tire. 3. It helps increase a car’s efficiency.
IMPROVEMENTS However piezoelectric materials’ output has only been sufficient for low-energy-consumption gadgets. To obtain high-power output, a large area of tires’ inner surface must be filled with PZT benders. Since PZT elements have limited flexibility ,high deformation areas of the tire such as sidewalls could not be covered . So a more flexible polyvinylidene fluoride is being developed for increasing power output.