Piezoelectric Materials

Piezoelectric materials The piezoelectric effect describes the relation between a mechanical stress and an electrical voltage in solids. It is reversbile: an applied mechanical stress will generate a voltage and an applied voltage will change the shape of the solid by a small amount (up to a 4% change in volume). The piezoelectric effect occurs only in non conductive materials. Piezoelectric materials can be divided in 2 main groups: crystals and cermaics. The most well-known piezoelectric material is quartz (SiO2).

Piezoelectric materials have the special property of producing an electrical voltage in response to an applied force. Usually crystals or ceramics, piezoelectric materials have a variety of uses including sonar, sound detection and high-voltage generation in addition to everyday uses, such as cigarette lighter ignition sources and barbecue-grill igniters.

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The piezoelectric effect is found in a number of natural and man-made materials. Commonly used naturally-occurring crystals include quartz, topaz, tourmaline, Rochelle salts and cane sugar. Man-made crystals include the quartz-like langasite and gallium orthophosphate. Common piezoelectric man-made ceramics include barium titanate, lead titanate and lead zirconate titanate, the most common piezoelectric ceramic in use. Other naturally-occurring piezoelectric materials include dry bone, tendons, silk, some woods, enamel, dentin and collagen. Applications

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There is a large array of applications for peizoelectric materials, particularly quartz, which can generate thousands of volts of electricity. One of the most common applications of piezoelectricity is in the electric cigarette lighter. Other common applications include sensors on electric guitars like pick-ups and contact microphones, ultrasound machines, sonar wave detection and generation devices, engine management systems in cars, loudspeakers, fuel injectors for diesel engines and quartz clocks.

Common Material Used for a Photovoltaic Solar Cell Photovoltaic (PV) solar cells are devices that capture solar energy and generate electricity from it. Silicon is the most commonly used material in a photovoltaic solar cell. Materials other than silicon, such as CIGS (a mixture of elements), are also gaining popularity. 1. Silicon:Traditional photovoltaic solar cells use silicon as their main ingredient. Silicon is refined to 99.99 percent purity in order to make it a good conductor. A traditional

photovoltaic solar cell is made up of layers of silicon wafers that have been doped with other substances. CIGS: CIGS is a mixture of the elements copper, indium, gallium and selenide and is used to manufacture thin-film photovoltaic devices. CIGS is applied in a thin layer to plastic components. This can be used to generate power using nanotechnology and advancedmaterials science. Solar Cell Characteristics There's a natural synergy: modern humans need energy and sunlight is everywhere. The trick is to harvest that energy in a useful and efficient way. Photovoltaic cells are designed to do just that: they convert sunlight into the most versatile form of energy, electricity. Their performance characteristics are an indication of how, and how well, they do that job. 1. Composition o

Photovoltaic cells are built of semiconductor material that absorbs sunlight and transfers the energy of the light photon to an electron, which then can power an electrical circuit. The choices for bulk semiconductors include silicon, germanium, cadmium telluride, copper indium selenide and copper gallium selenide. Bandgap and Absorption Spectrum

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Semiconductors absorb best when the energy in the light they absorb is just enough to transfer their electrons from a localized valence state to a conduction band in the semiconductor, where they are free to move. Each material has specific valence and conduction band energies; the difference between them is called the bandgap. The energy carried in a photon depends upon its wavelength. Each material will absorb different wavelengths best. Quantum Efficiency

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Quantum efficiency (QE) is a measure of how well a semiconductor transfers energy from photons to electrons. It is given in percent, so a QE of 87 percent means that 87 out of every 100 photons is absorbed by electrons within the semiconductor. A semiconductor's QE is best when a photon has an energy just above the semiconductor's bandgap energy, so QE will vary with wavelength. A QE curve will show the absorption efficiency over the whole solar spectrum. Conversion Efficiency

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Unfortunately, not every electron that absorbs energy is available to power a circuit. Some "recombine," which means they drop down to the valence band, giving up their energy and getting tied to a specific atom once again. Some crash into other atoms along the way, giving up their energy in the form of heat -- electrical resistance in the semiconductor and the electrical contacts is the culprit here.

The I-V Curve o

The maximum amount of power a solar cell can put out is determined by measuring its performance under different circuit loads. The maximum current (I) is put out when there is no load; the maximum voltage (V) builds up when there's an open circuit, that is, no connection at all. Somewhere between these two extremes is a point where the current times the voltage is a maximum. Power is the product of current and voltage, so this point is called the maximum power point. Dielectric Constant

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The dielectric constant is defined as the property of a particular dielectric material indicating the material's capacity to store electrical energy. It is usually expressed as a ratio. The ratio expressed is relative the dialectical constant of a vacuum. It may also be described as the ratio of the permittivity of a particular material to the permittivity of free space. Loss Tangent

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The dielectric loss tangent refers to the product of the dielectric constant of a particular material and the tangent of the material's dielectric loss angle. The dielectric loss angle is defined as the difference between 90 degrees and the dielectric phase angle. The dielectric phase angle is the angular difference in phase between the sinusoidal alternating potential difference applied to a dielectric material and the part of the resulting alternating current with the same period as the potential difference.

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What Materials Are Capacitor Plates Made Out Of? 

By definition, capacitor plates are made of conducting materials. This usually means metals, though other materials are also used. In addition to being conducting, capacitor plates need mechanical strength and resistance to deterioration from electrolytic chemicals. On top of that, most capacitors need extremely thin plates to pack the most capacitance in a small package. Manufacturers use ductile metals to make thin plates from foils. The materials must also be inexpensive and have good availability to be suitable for mass production. 1. Aluminum Aluminum is a workhorse material for making the majority of capacitors. It's inexpensive, highly conductive and easily formed into plates or foils. Tantalum o

Capacitors that use tantalum are more temperature and frequency stable than those using aluminum, though tantalum costs more. Silver Silver appears in silver-mica capacitors. These also cost more than aluminum plate capacitors, and are used in high-accuracy audio applications.