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User:Ererics41/sandbox/Mobius Resistor

A moebius resistor is an electronic component shaped like a loop with a 180 degree twist in the middle which limits the flow of electricity in a circuit, or creates resistance, without causing any magnetic interference (inductance) patented by Richard L. Davis. This forms a resistor in the shape of a moebius strip. This unique mathematical shape with one continuous side allows electricity to flow continuously and in opposite directions. Thus the component becomes non-inductive, creating no magnetic interference.[1] Due to these properties, moebius resistors are used in high frequency pulse devices such as radar which would malfunction due to inductance generated from electronic components. However, there are several drawbacks to the moebius resistor which would later be addressed in a new non-inductive resistor.

History

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As electronic devices increased in power and radar technology began to develop electrical engineers faced a new challenge. Inductance generated by electronic components in the circuit interfered with radar frequencies and caused frequent malfunctions. This was especially true in devices which used larger amounts of power and at higher frequencies.[1] The early solutions to this problem, included bending resistors into a hairpin shape in order to cancel out inductance by making electricity flow in both directions. Later resistors would be wound into loops designed to cancel out inductance which had a similar effect. However, these techniques failed to completely cancel out inductance and proved insufficient as technology advanced. Physicist Richard L. Davis worked to solve this problem and used mathematical concepts to create a new resistor. After thinking about the moebius loop, a mathematical construct, he realized the unique shape could be used to cancel out induction more effectively than previous solutions. Davis proceeded to invent the moebius resistor and filed a patent on May 1, 1964 which was published on Aug 16, 1966. [2]

How it works

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In a circuit a resistor is used to create resistance which reduces the flow or current of electricity. Resistance defined by Ohm's law is voltage divided by current. Thus if the ratio of voltage to current increases resistance increases. To do this, resistors must impede the flow of electricity which is commonly done by wire-wounding in which a long wire is wrapped around a non-conductive rod. [3] Resistance is then created as electricity travels through turns of the wire which have areas of low capacitance. Capacitance can be defined as charge per volt or the inverse of resistance. Thus as the ratio of current to voltage(capacitance) decreases, the inverse increases which means resistance in generated.[4] A moebius resistor produces resistance in a similar manner as electricity travel through bends in the moebius loop. This loop also contains areas of low capacitance which in turn causes resistance. These two methods of generating resistance are very similar; however, a typical resistor is inductive meaning the component creates a magnetic interference caused by electricity flowing through the component. A moebius resistor prevents this problem as the electricity flows in two opposite directions. This is because the moebius resistor has only one surface which the electricity flows through. As the electricity flows in two different directions the magnetic force generated are opposites which cancel each other out, thus creating a net of zero inductance. [1]

Assembly

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The resistor is assembled using two ribbons of conductive material of equal length separated by a ribbon of dielectric material to form a strip which will become the body of the resistor. This strip is then bent 180 degrees once and the ends are soldered together. Resistor terminals, which allow the component to attach to the circuit, are then added on opposite sides of the strip on the soldered area.[5]

Potential conductive materials used:

  • Tophet A - nickel-chrome alloy
  • Manganin - copper, manganese, nickel alloy
  • Aluminum - for very low resistance[1]

Conductive materials used may vary depending on target resistance as electrical resistivity is different depending on the metal. For the above examples, manganin, tophet A and aluminum have resistivity values of 482 microhm • cm, 108 microhm • cm, and 28.2 microhm • cm respectively. Thus resistors made using manganin would have high resistance values, while those made using tophet A and aluminum would have lower resistance values.[6][7]

Applications

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The moebius resistor is used in circuits containing high voltage and frequency due to its non-inductive ability. Such circuits are found in pulse devices and devices which use ultra-high frequency waves(UHF) or microwave frequencies. Example devices include radar, and broadcasting equipment. These devices may be negatively affected by inductance thus it is important to reduce inductance generated by circuits. Low resistance resistors is a major culprit in production of inductance and are thus replaced by moebius resistors which generate no inductance. [8] Moebius resistors can be used in these devices without signifcant increases in the size of the device. This is because the moebius resistor can be added compactly in the form of a coil. In fact, once the moebius resistor has been assembled, it no longer needs to stay in one shape to function. Thus the resistor can be shaped into more compact forms which minimize space taken and allow for smaller devices.[1]

Drawbacks

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The major drawback of moebius resistor is its variable resistance value. Over time, the resistance generated by a moebius resistor may change due to the differences in tension at different areas of the component. In assembly two strips of identical length are soldered together and form one continuous loop, however the strip that makes up the outer side of the loop typically has a slightly higher tension then the inner strip. This difference in tension can cause stretching over time and thus change the resistance value. Although this change may have a small impact on high resistance resistors, it is very apparent in low resistance resistors and can cause large margins of error.[9] Additionally, due to the time period of the creation of the moebius resistor flame-proofing was not considered thus the component has very little measures for flame proofing which limit the applications. However, since the creation of the moebius resistor a new non-inductive resistor, the non-inductive film-type cylindrical resistor, has been invented which addresses some of these problems. Thus the new cylindrical resistor has replaced the moebius resistor in many devices and is now more commonly used.

See also

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References

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  1. ^ a b c d e US patent 3,267,406, R. L. Davis, "Non-Inductive Electrical Resistor", issued 1966-08-16
  2. ^ "Making Resistors With Math." Time 25 Sept. 1964
  3. ^ Woodford, Chris. "How Do Resistors Work? What's inside a Resistor?" Resistors. Explain That Stuff, 30 May 2016. Web. 24 Oct. 2016. <http://www.explainthatstuff.com/resistors.html>.
  4. ^ VujeviÊ, Duπan, Dr. "Application of the Möbius Strip in Electrical Engineering." Journal of Energy 56.6 (2007): 704-07. Web. 23 Oct. 2016.
  5. ^ Moebius Resistor Is Noninductive And. Nonreactive. Issue brief no. 68-10267. N.p.: NASA, 1968.
  6. ^ "ENDMEMO." Resistance Calculator. N.p., n.d. Web. 05 Nov. 2016. <http://www.endmemo.com/physics/resistance.php>.
  7. ^ "80/20 Ni Cr Nickel-Chrome Resistance Wire." Tophet A Electrical Resistance Wire. N.p., n.d. Web. 05 Nov. 2016. <http://www.alloywire.com/products_RW80_Tophet_A.html>.
  8. ^ Hyypia, Jorma (November 1969), "At Ultra-High Frequencies Electronic Components Take On Weird Shapes!", Electronics Illustrated, 12 (5), pp. 76, 77, 117
  9. ^ "Strengths and Weaknesses of Common Resistor Types | EE Times." EETimes. N.p., n.d. Web. 05 Nov. 2016. <http://www.eetimes.com/document.asp?doc_id=1256482>.
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