Suppose you have a current source with magnetic fieldand you want to reduce it by adding a metal near itto induce opposite magnetic field to cancel the onefrom the source (partially). What coil configurationmust you use? Is this possible?Don't reply by telling me to use particular wireshielding or bend the source wire. I'm justinterested in the theoretical rationale of puttingmetal or coil configuration near the magnetic fieldsource to create reverse magnetic field to cancela part of it. How much magnetic field do you thinkis reduced (or cancelled)?? This is assuming the metalor coil put near it doesn't have any voltage orcurrent source itself but just from the inducedcurrent from the magnetic field of the source.qude

All electrical circuits have a return path. The best you can do is to use asecond wire for the return path and to twist it around the signal wire. Younow have equal currents flowing in opposite directions in close proximity.The magnetic fields almost cancel out.

magnetic field reducer?

Jun 19, 2005 24 Replies

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Don Kelly 21 years ago

-----snip---------

---------- Induction motors can be modified (essentially open circuited rotor windings) to give an output that depends on speed. Thus a 60Hz motor with a synchronous speed of 3600rpm, if driven at 2400 rpm, will have a rotor frequency of 20Hz. Note that this is not a stationary device. However it is easier to get the desired frequency by electronic means. A static device such as some copper sheet will not do this.

However, this has nothing to do with a "third" waveform. Electrosensitivity is one thing but the "shields" or other devices which claim great protection, etc, are typically designed to do one thing -extract money from suckers.

--------- There are electric devices- it is possible to build an electromechanical device that depends on fields. An electrostatic voltmeter is one such device. However, the typical energy density of electrostatic devices is much lower than that of electromagnetic devices so that for a given power level, the electrostatic device is very much larger (and generally involves rather nasty voltage levels)

Don Kelly dhky@peeshaw.ca remove the urine to answer

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qude 21 years ago

Do you have samples of how a diode can be used in a circuit to adjust the frequency of the incoming magnetic field and output another one with different frequency? Do you have any schematics of the tags that use this principle? Can this also work when the diode is put inside an IC with copper foil stick on it as the magnetic field sensor?

I know changing magnetic field can induce current. But what law have you heard that changing electric field can also induce current? Pls. elaborate. Thanks.

qude

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Dave 21 years ago

a diode can not 'adjust' the frequency. it can rectify an incoming sine wave which creates all sorts of harmonics that can then be filtered out to get multiples of the incoming signals frequency. the subharmonics is a bit tougher, requiring a tuned circuit that is pumped by the rectified incoming wave at the right rate to produce the desired output.

for the rfid tags you would have to contact one of the manufacturers... i'm sure they would gladly share their schematics with you.

a diode in an ic is still a diode. to detect a magnetic field you normally use a loop not a stick.

time to go study the basics a bit more my friend... i'm not going to give you all the answers, if you really want to understand this you need to get a good book on electromagnetic fields and waves. study maxwell's equations, especially the one with the dE/dt and =J as parts of it.

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Gerald Robinson 21 years ago

How would you maximise the heating effect?

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Dave 21 years ago

study electromagnetics for a few years so i knew how to model the eddy currents at different frequencies and field strengs, then some material science to learn about the different types of materials and their properties, then probably some thermodynamics thrown in because the flow of the heat once its induced in the material will affect it also. then i would figure out the best frequency and field strength to heat whatever the specific material was that i was working with.

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