Faraday Shielding - What Is It? How Does It Work?

Electrostatic. A field like that which builds up in a relay or solenoid. A Tesla coil is an extreme example of an electrostatic field. A metal detector TX coil and field have no chance of transmitting across a room with any degree of repeatability. An EMF field does in most cases, unless it is snubbed. A capacitive start AC motor is an example of a snubbed EMF where almost all of the energy is converted to either motion or heat. Heat is considered a loss in motor terms.

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		Quote:			Posted by kabier2
	it will produce electromagnetic wave like in rf transmitters were it use space to travel.in our case in detectors we are sending this wave to Earth which is an absorber of this field. that is way we use low freq. for ib and pulses for pi.

It's an electrostatic field, not an RF field. There are fundamental differences in a field used as a sensing field and one used to broadcast. We are not broadcasting. We are creating a field to set up eddy currents inside of metal objects so we can sense them.

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		Quote:			Posted by kabier2
	well RF means radio freq. which is not used in detectors but the is the same electromagnetic phenomena a field for low freq. a wave for radio freq.

RF is designed to emit and travel great distances using the two components of a radio wave. The electrical component and the magnetic component. They are 90 degrees from each other in physical orientation. If you hold your hand out with your index finger pointing away from you, your thumb up to the sky and your middle finger to your left or right, you will get the orientation. The index finger will indicate the directiion of RF radiation travel, your thumb indicates the orientation of the electrical component as it travels along the direction of travel and your middle finger will indicate the magnetic component. This is the "rule of thumb" of the expression. Marconi was the first to use it as a descriptor for an RF signal.

In a metal detector coil, there is only one field and that is an electrostatic field generated by a pulse of sine waves which, because they are alternating, turn a static field on or off using voltage but no current to speak of to propel the wave. Therefore, it is not at all like an RF signal.

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Thanks for the comment Mudflap. Something I neglected to mention is that an RF antenna is a highly AC reactive element cut to the right size to develop equal fields and therefore obtain great distances of transmission while a TX coil is part of a closed loop, improperly tuned tank circuit that emits a field that is basically leakage. In a perfectly tuned tank circuit, there would be no leakage at all. Zero. It is the coil mismatch, precisely tuned to that mismatch, that gives us a field we can use to detect metal.

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		Quote:			Posted by kabier2
	hi and i need yr comments for the alu. foil shield i used for idx-pro cc 24cm coil i followed DON way as using foam for the coil form i posted pictures in the geotech1 idx-pro thread

If you are adressing me, I have no idea what you are talking about.

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