Is there a conductor that conducts well at low frequencies, but surprisingly badly at higher frequencies?

Question

I know there is the skin effect, which is sometimes ameliorated by silver plating a copper conductor. I want to know if there is a conductor that conducts well at low frequencies, but surprisingly badly at higher frequencies, or vice versa.

Answer 1

There are not conductors but you can use conductors to make such a thing. Its called a coil or inductor. A capacitor is the opposite, it conducts better at higher frequencies.

These components on their own or in networks are called filters (high pass or low pass). You can also network them to attenuate below and above certain frequencies (band pass)

Answer 2

As far as I know, choice of material doesn't affect the relative conductivities at different frequencies; I'll admit that I didn't know about the skin effect before now, but even there, the specific properties of the material just add a scaling factor to the equation.

If you really want your circuit's conductivity to drop off sharply at high frequencies, you should put an inductor in it.  If instead you want low conductivity at low frequencies, put in a capacitor.

Answer 3

First, let's make it clear you are asking about an increase with resistance with frequency, not the increase in impedance due to the presence of inductance.

The resistance of most materials increases with frequency, but you don't get any dramatic changes until the frequencies get really high (terahertz and above). Quantized energy can match internal energy transitions, (rotational, translational, vibrational and once you get into the visible spectrum, electron shell transitions). When this happens,you get sharp absorption bands.

This might sound a little odd to you, but there is in fact a close relationship between the absorption spectrum of a material and its conductivity at the optical frequency. Conductive materials reflect light (e.g. silver),  insulating materials are transparent to light (e.g. glass) and resistive materials absorb light (e.g. graphite). For those three materials, the conductivity at optical frequencies is very similar to their conductivity at DC, but that is not true for all materials at all frequencies. For example, glass is a resistor in the infra-red, and so absorbs light.

If you are talking about lower frequencies, I don't have any data on this but I  suspect that electrolytes or ionised gases might show a marked increase in resistance with frequency. RF Conduction will require the reversal of the momentum of ions that are thousands of times heavier than electrons