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August 23, 2011

When an element is stretched in one direction, it tends to get thinner in the other two directions. Hence, the change in longitudinal and lateral strains are opposite in nature (generally). Poisson’s ratio ν, named after Simeon Poisson, is a measure of this tendency. It is defined as the ratio of the contraction strain normal to the applied load divided by the extension strain in the direction of the applied load. Since most common materials become thinner in cross section when stretched, Poisson’s ratio for them is positive.
For a perfectly incompressible material, the Poisson’s ratio would be exactly 0.5. Most practical engineering materials have ν between 0.0 and 0.5. Cork is close to 0.0, most steels are around 0.3, and rubber is almost 0.5. A Poisson’s ratio greater than 0.5 cannot be maintained for large amounts of strain because at a certain strain the material would reach zero volume, and any further strain would give the material negative volume.

Some materials, mostly polymer foams, have a negative Poisson’s ratio; if these auxetic materials are stretched in one direction, they become thicker in perpendicular directions.Foams with negative Poisson’s ratios were produced from conventional low density open-cell polymer foams by causing the ribs of each cell to permanently protrude inward, resulting in a re-entrant structure.
An example of the practical application of a particular value of Poisson’s ratio is the cork of a wine bottle. The cork must be easily inserted and removed, yet it also must withstand the pressure from within the bottle. Rubber, with a Poisson’s ratio of 0.5, could not be used for this purpose because it would expand when compressed into the neck of the bottle and would jam. Cork, by contrast, with a Poisson’s ratio of nearly zero, is ideal in this application.

It is anticipated that re-entrant foams may be used in such applications as sponges, robust shock absorbing material, air filters and fasteners. Negative Poisson’s ratio effects can result from non-affine deformation, from certain chiral microstructures, on an atomic scale, or from structural hierarchy. Negative Poisson’s ratio materials can exhibit slow decay of stress according to Saint-Venant’s principle. Later writers have called such materials anti-rubber, auxetic (auxetics), or dilatational. These materials are an example of extreme materials.
Categories: MECHANICS
Tags: Air, air filters, cell, change, common materials, contraction, contrast, cork, cross, cross section, decay, dilatational, element, engineering materials, EXAMPLE, fasteners, Lateral, load, low density, nature, negative poisson, opposite in nature, perpendicular directions, polymer, polymer foams, practical application, practical engineering, protrude, ribs, rubber, Saint, simeon poisson, sponges, steels, stress, structure, value, wine, wine bottle, zero volume
Comments: 3 Comments
August 23, 2011

When an element is stretched in one direction, it tends to get thinner in the other two directions. Hence, the change in longitudinal and lateral strains are opposite in nature (generally). Poisson’s ratio ν, named after Simeon Poisson, is a measure of this tendency. It is defined as the ratio of the contraction strain normal to the applied load divided by the extension strain in the direction of the applied load. Since most common materials become thinner in cross section when stretched, Poisson’s ratio for them is positive.
For a perfectly incompressible material, the Poisson’s ratio would be exactly 0.5. Most practical engineering materials have ν between 0.0 and 0.5. Cork is close to 0.0, most steels are around 0.3, and rubber is almost 0.5. A Poisson’s ratio greater than 0.5 cannot be maintained for large amounts of strain because at a certain strain the material would reach zero volume, and any further strain would give the material negative volume.

Some materials, mostly polymer foams, have a negative Poisson’s ratio; if these auxetic materials are stretched in one direction, they become thicker in perpendicular directions.Foams with negative Poisson’s ratios were produced from conventional low density open-cell polymer foams by causing the ribs of each cell to permanently protrude inward, resulting in a re-entrant structure.
An example of the practical application of a particular value of Poisson’s ratio is the cork of a wine bottle. The cork must be easily inserted and removed, yet it also must withstand the pressure from within the bottle. Rubber, with a Poisson’s ratio of 0.5, could not be used for this purpose because it would expand when compressed into the neck of the bottle and would jam. Cork, by contrast, with a Poisson’s ratio of nearly zero, is ideal in this application.

It is anticipated that re-entrant foams may be used in such applications as sponges, robust shock absorbing material, air filters and fasteners. Negative Poisson’s ratio effects can result from non-affine deformation, from certain chiral microstructures, on an atomic scale, or from structural hierarchy. Negative Poisson’s ratio materials can exhibit slow decay of stress according to Saint-Venant’s principle. Later writers have called such materials anti-rubber, auxetic (auxetics), or dilatational. These materials are an example of extreme materials.
Categories: MECHANICS
Tags: Air, air filters, cell, change, common materials, contraction, contrast, cork, cross, cross section, decay, dilatational, element, engineering materials, EXAMPLE, fasteners, Lateral, load, low density, nature, negative poisson, opposite in nature, perpendicular directions, polymer, polymer foams, practical application, practical engineering, protrude, ribs, rubber, Saint, simeon poisson, sponges, steels, stress, structure, value, wine, wine bottle, zero volume
Comments: 3 Comments
August 23, 2011

QTC is a composite made from micron-sized metallic filler particles (Silicone Rubber) mixed into an elastomeric matrix. Quantum tunnelling composite is a flexible polymer that exhibits extraordinary electrical properties. In its normal state it is a perfect insulator, but when compressed it becomes a more or less perfect conductor and able to pass very high currents.

History:
First produced in 1996, QTC is a composite material made from conductive filler particles combined with an elastomeric binder, typically silicone rubber. The unique method of combining these raw materials results in a composite which exhibits significantly different electrical properties when compared with any other electrically conductive material.

Types of QTC:
1. Elastomeric (Material: Silicone Rubber) (The particle move close together)
2. Ink / Coating Solvent or Aqueous Polymer
3. Granular Sensors
Working of Quantum tunnelling composite:

QTC usually comes in the form of pills or sheet. QTC pills are just tiny little pieces of the material. The sheets are composed of one layer of QTC, one layer of a conductive material, and a third layer of a plastic insulator. While QTC sheets switch quickly between high and low resistances, QTC pills are pressure sensitive variable resistors.
Application:

– Touch switches (sheet)
– Force/pressure sensors (pills)
– Motor speed control using force (pills)
Benefits:
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QTC is a pressure/force sensing material. It can be easily integrated into existing products to enable force sensing opportunities and solutions.
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Product surfaces can be incorporated, coated or impregnated with QTC to impart the properties of force sensing into or onto the host surface.
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QTC material can be formed or moulded into virtually any size, thickness or shape, permitting redesign of product interfaces and providing improved ergonomics, aesthetics and user comfort.
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QTC is an enabling technology which is simple and reliable to use.
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QTC material is durable – it has no moving parts to wear out.
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QTC material is mechanically strong.
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QTC material can be made to withstand extreme temperatures limits.
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QTC material is versatile, both electrically and physically e.g. Its range and sensitivity can be altered. QTC material is also intrinsically safe – the material is a contactless switch, ideal for sparkless operation.
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QTC material can be directly interfaced to standard electronic and electrical devices.
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QTC material and/or technology can be customized for customer requirements, applications and products.
Categories: LATEST TECHNOLOGICAL NEWS
Tags: aesthetics, close, composite material, control, customer, elastomeric, electrical properties, enabling technology, existing products, filler, flexible polymer, form, host, Ink, insulator, little pieces, material types, motor speed control, move, operation, particle move, plastic, polymer, pressure sensors, product interfaces, product surfaces, quantum tunnelling, resistances, Sensors, silicone rubber, Surface, technology, thickness, Touch, touch switches, Types, variable resistors, versatile, working
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August 23, 2011

After six years of intensive effort, scientists are reporting development of the first commercially viable Nano generator, a flexible chip that can use body movements — a finger pinch now en route to a pulse beat in the future — to generate electricity.
This development represents a milestone toward producing portable electronics that can be powered by body movements without the use of batteries or electrical outlets.
The latest improvements have resulted in a Nano generator powerful enough to drive commercial liquid-crystal displays, light-emitting diodes and laser diodes. By storing the generated charges using a capacitor, the output power is capable to periodically drive a sensor and transmit the signal wirelessly.

If we can sustain the rate of improvement, the Nano generator may find a broad range of other applications that require more power.
Example:
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Personal electronic devices powered by footsteps activating Nano generators inside the sole of a shoe;
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Implanted insulin pumps powered by a heart beat; and
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Environmental sensors powered by Nano generators flapping in the breeze.

Preparation:
The key to the technology is zinc oxide (ZnO) nanowires. ZnO nanowires are piezoelectric — they can generate an electric current when strained or flexed. That movement can be virtually any body movement, such as walking, a heartbeat, or blood flowing through the body. The nanowires can also generate electricity in response to wind, rolling tires, or many other kinds of movement.

The diameter of a ZnO nanowire is so small that 500 of the wires can fit inside the width of a single human hair. Scientist found a way to capture and combine the electrical charges from millions of the Nano scale zinc oxide wires. They also developed an efficient way to deposit the nanowires onto flexible polymer chips, each about a quarter the size of a postage stamp. Five Nano generators stacked together produce about 1 micro Ampere output current at 3 volts — about the same voltage generated by two regular AA batteries (about 1.5 volts each).
While a few volts may not seem like much, it has grown by leaps and bounds over previous versions of the Nano generator. “Additional nanowires and more Nano generators, stacked together, could produce enough energy for powering larger electronics, such as an iPod or charging a cell phone.”
Categories: LATEST TECHNOLOGICAL NEWS
Tags: ampere, body, body movements, electrical charges, electrical outlets, electricity, Environmental, flexible polymer, future, heart, heart beat, human hair, insulin, insulin pumps, intensive effort, iPod, key, Laser, laser diodes, light emitting diodes, liquid crystal, many other kinds, movement, nano scale, nanowire, personal electronic devices, phone, polymer, portable electronics, postage, power, pulse beat, sensor, shoe, sole, technology, width, wirelessly, zinc oxide, ZnO
Comments: 2 Comments