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Leakage describes an unwanted loss, or leak, of something which escapes from its proper location. In everyday usage, leakage is the gradual escape of matter through a leak-hole. In different fields, the term may have specialized meanings.

Chemistry

In chemistry, leakage is a process in which material is lost, intentionally or accidentally, gradually through the holes or defects of their containers. The material lost is usually fluid, usually liquid or powder and sometimes gas, from an imperfectly sealed container. Often, leakage can be disastrous if the leaked material is harmful or corrosive.

A zinc-carbon battery is an example of an easy-leaking system. The electrolytes inside the cell sometimes leak out of the cell shell, and cause damage to an electronic appliance.

Economics

In economics, leakage is the non-consumption uses of income, including saving, taxes, and imports. In the Keynesian injection-leakage or circular flow model, leakages are combined with injections to identify equilibrium aggregate output. The model is best viewed as a circular flow between national income, output, consumption, and factor payments. Savings, taxes, and imports are "leaked" out of the main flow, reducing the money available in the rest of the economy.

The simple model of credit creation assumes all loans borrowed from banks in a fractional-reserve banking system are re-deposited to the system. This allows simple calculation of amount of credit created. Therefore, in credit creation, cash leakage refers to the sums of money borrowed from banks but not re-deposited. Cash leakage, in this case, lowers the ability of credit creation.

Electronics

In electronics, leakage refers to a gradual loss of energy from a charged capacitor. It is primarily caused by electronic devices attached to the capacitors, such as transistors or diodes, which conduct a small amount of current even when they are turned off. Even though this off current is an order of magnitude less than the current through the device when it is on, the current still slowly discharges the capacitor. Another contributor to leakage from a capacitor is from the undesired imperfection of some dielectric materials used in capacitors, also known as dielectric leakage. It is a result of the dielectric material not being a perfect insulator and having some non-zero conductivity, allowing a leakage current to flow, slowly discharging the capacitor.

Leakage may also mean an unwanted transfer of energy from one circuit to another. For example, magnetic lines of flux will not be entirely confined within the core of a power transformer; another circuit may couple to the transformer and receive some leaked energy at the frequency of the electric mains, which will cause audible hum in an audio application.

Leakage in a high-voltage system can be fatal to a human in contact with the leak, as when a person accidentally grounds a high-voltage power line.

Semiconductors

In semiconductor devices, leakage is a quantum phenomenon where mobile charge carriers (electrons or holes) tunnel through an insulating region. Leakage increases exponentially as the thickness of the insulating region decreases. Tunneling leakage can also occur across semiconductor junctions between heavily doped P-type and N-type semiconductors. Other than tunneling via the gate insulator or junctions, carriers can also leak between source and drain terminals of a Metal Oxide Semiconductor (MOS) transistor. This is called sub-threshold leakage. The primary source of leakage occurs inside transistors, but electrons can also leak between interconnects. Leakage increases power consumption and if sufficiently large can cause complete circuit failure.

Leakage is currently one of the main factors limiting increased computer processor performance. Efforts to minimize leakage include the use of strained silicon, high-k dielectrics, and/or stronger dopant levels in the semiconductor. Leakage reduction to continue Moore's law will not only require new material solutions but also proper system design. A good overview of leakage and leakage reduction methods are explained in Leakage in Nanometer CMOS Technologies.

Retail

Retail leakage occurs when members of a community spend money outside that community or when money spent inside that community is transferred outside the community. For example, crossing a border to buy goods forgoes the same purchase that could have been made inside the community. Many chain stores have high leakages rates due to the transferring of sales revenue to a corporate headquarters.

In addition, in retail trade, leakage, or shrinkage can also mean the loss of stock without payment, typically due to theft by employees or shoplifters.

Sound recording

In sound recording, leakage (also called spillage) occurs when audio intended for one track is picked up inadvertently by another track's microphone in a multitrack recording.

Multitrack recording is at its optimum when there is sufficient isolation between individual tracks to allow freedom in remixing each track to a desired sound level. Reasonable isolation can be achieved (even in a live recording) by careful microphone placement, or by the separation of sound sources. Sound leakage can limit or even ruin the remixing and overdubbing potentials of a multitrack recording, when one sound interferes with another sound on a track.

Other fields

Leakage may also have the following meanings in other fields:

• In medicine, anal leakage is a condition of faecal incontinence.
• In tourism, leakage refers to the loss of tourist revenue from a country. (See leakage effect).

References

1. Merriam-Webster
2. WordNet
3. Cheng, E. et al, Chemistry - A Modern View 2, Aristo-Wilson, Hong Kong, 2004
4. EconPlace
5. Ngai, J. et al, Economics and You 5, Manhattan, Hong Kong, 2005.
6. Associated Research Tech Info
7. Glossary from Electric Fence
8. Glossary from System Connection
9. WordSpy - Retail Leakage
10. About.com - Retail Theft and Inventory Shrinkage
11. Sorcerer Sound Recording Studios
12. Eargle, J. The Microphone Book, Second Edition, ISBN-0240519612

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