History :

The piezoelectric effect was discovered in 1880 by the Jacques and Pierre Curie brothers. They found out that when a mechanical stress was applied on crystals such as tourmaline, tourmaline, topaz, quartz, Rochelle salt and cane sugar, electrical charges appeared, and this voltage was proportional to the stress.

First applications were piezoelectric ultrasonic transducers and soon swinging quartz for standards of frequency (quartz clocks).

Piezoelectric materials :

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).

Applications of Pizoelectric Effect :

Piezoelectric generators :

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when compressed or expanded or otherwise changing shape a piezoelectric material will output some voltage. This effect is also possible in reverse in the sense that putting a charge through the material will result in it changing shape or undergoing some mechanical stress. These materials are useful in a variety of ways. Certain piezoelectric materials can handle high voltage extremely well and are useful in transformers and other electrical components

Personal Energy Generator :

Some of the most obvious applications of piezoelectric materials for energy collection are personal energy generators that are enough to power phones, MP3 players, etc. The sole of your shoe could be constructed of piezoelectric materials and every step you took would begin to generate electricity. This could then be stored in a battery or used immediately in personal electronics devices.

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Pizoelectric R/C :

a remote control that works by harnessing the piezoelectric power generated by, well, bending and twisting the remote itself. Called the Leaf Grip Remote Controller, the remote looks mostly like two handles with a transparent screen between them. That screen, or, more accurately, that film, has two layers of piezoelectric sensors, one of which detects bending, while the other detects a twisting motion.

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Car's Airbag Sensor :

The material detects the intensity of the shockexternal image composite_draft_bag_a.jpg and sends an electricla signal which triggers the airbag.

Shape Memory Alloys ( SMAs)

Shape memory alloys are metals that "remember" their original shapes. SMAs are useful for such things as actuators which are materials that "change shape, stiffness, position, natural frequency, and other mechanical characteristics in response to temperature or electromagnetic fields"

History :

In 1961, Nitinol, which stands for Nickel Titanium Naval Ordnance Laboratory, was discovered to possess the unique property of having shape memory. William J. Buehler, a researcher at the Naval Ordnance Laboratory in White Oak, Maryland, was the one to discover this shape memory alloy. The actual discovery of the shape memory property of Nitinol came about by accident. At a laboratory management meeting, a strip of Nitinol was presented that was bent out of shape many times. One of the people present, Dr. David S. Muzzey, heated it with his pipe lighter, and surprisingly, the strip stretched back to its original form.

Metal Programing :

The material can also be ‘programmed’ to remember a shape. This can be achieved by folding the wire to a particular shape and external image sma2.gifclamping it in position. The wire is then heated for a approximately five minutes at precisely 150 degrees or pass an electric current through the SMA wire. If the wire is now folded into another shape and then placed in hot water it returns to the original ‘programmed’ shape.

Applications :

A clever use of muscle wire and a PIC micro-controller circuit is seen below. A robotic hand has ‘stretched muscle wires’ attached to the base of each finger. When current is applied to the muscle wire it contracts to its ‘natural’ length, pulling on the ordinary wire ,making the fingers look as if they are moving.

A PIC micro-controller can be programmed so that outputs are switched ON or OFF. When switched ON the muscle wire contracts (shrinks) to its original length. In the example, five of the outputs have been programmed to switch on and off, making the fingers of the hand move.

Nitinol actuators as engine mounts and suspensions can also control vibration. These actuators can helpful prevent the destruction of such structures as buildings and bridges.

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Future Applications :

Future applications are envisioned to include engines in cars and airplanes and electrical generators utilizing the mechanical energy resulting from the shape transformations. Nitinol with its shape memory property is also envisioned for use as car frames. (Kauffman and Mayo, 7) Other possible automotive applications using SMA springs include engine cooling, carburetor and engine lubrication controls, and the control of a radiator blind ("to reduce the flow of air through the radiator at start-up when the engine is cold and hence to reduce fuel usage and exhaust emissions") .


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MR fluids are oils that are filled with iron particles. Often, surfactants surround the particles to protect them and help keep them suspended within the fluid. Typically, the iron particles comprise between 20 and 40 percent of the fluid's volume.

The particles are tiny, measuring between 3 and 10 microns. However, they have a powerful effect on the fluid's consistency. When exposed to a magnetic field, the particles line up, thickening the fluid dramatically. The term "magnetorheological" comes from this effect. Rheology is a branch of mechanics that focuses on the relationship between force and the way a material changes shape. The force of magnetism can change both the shape and the viscosity of MR fluids.

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Smart Structure Buildings :

Modern dampers adapt to the force of an earthquake, shifting with each shockwave to reduce the impact on the building's structure, in effect "dampening" the overall effect on the building.Modern dampeners are constructed with the Magnetorheological fluid which can change from liquid to solid with the application of a MagneticField. The Magnetorheological fluid inside modern dampeners are kept solid in normal conditions, but change to liquid and back as sensors activate and deactivate a magnetic field during an earthquake, allowing the dampeners to absorb the shockwaves and reducing damage to the structure.

The Magnetorheological fluid inside the dampeners changes a building from a rigid structure that must absorb the shockwaves to a 'smart' structure which adapts instead.

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Auxetic Materials

Auxetics are materials that have a negative Poisson's Ratio. When stretched, they become thicker perpendicular to the applied force. This occurs due to their hinge-like structures, which flex when stretched.

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The term "Auxetic" was not used to refer to these materials until about 1991. It was derived from the Greek word Auxetikos, which means "that which tends to increase."

Auxetic materials are not natural, and no known biological examples exist. The first auxetics were foams with specifically engineered microstructures. Depending on the size of the air gaps in the microstructure, the auxetic effect in these materials can be more or less extreme. Most auxetic foams expand by a factor of about 30 percent or so before shredding because of the stretching force.

Applications :

Key areas of application are seen in the biomedical field. Prosthetic materials, surgical implants, suture/muscle/ligament anchors and a dilator to open up blood vessels during heart surgery are all possible.

piezoelectric sensors and actuators. Auxetic metals could be used as electrodes sandwiching a piezoelectric polymer, or piezoelectric ceramic rods could be embedded within an auxetic polymer matrix. These are expected to increase piezoelectric device sensitivity by at least a factor of two, and possibly by ten or a hundred times.

Future :

leading to materials with extreme properties such as high modulus and strength, these advanced materials will have potential in sensor, drug-release and separations applications. By accepting a negative Poisson's ratio as a positive property we are truly expanding the applications of these fascinating materials

References :