Some people believe that wearing a tinfoil helmet will protect them from mind-control rays (or other forms of secret coercion). But if their intent is to create a “Faraday cage” to protect the brain from intrusive electromagnetic rays, wouldn’t it be more effective to use something a little more solid–say, an infantry helmet? And even then, wouldn’t it have to be grounded to work? Admittedly, looking for logical consistency in a conspiracy theory isn’t the wisest thing in the world, but usually they have a semblance of internal coherence. –L. Hammer, Tucson

A lot of people probably think helmets to ward off mind-control rays were invented by some smart-ass having a little fun with the feebs. Uh-uh. Check out the detailed instructions for creating your own helmet (using metal window-screen mesh) at “What I did was make a hood like you see on a hooded sweatshirt,” inventor Leia Jessira Starfire writes, “and to make this thing look ‘natural’ you can actually attach this hood to a sweatshirt so that you don’t stand out like a sore thumb and look like a dork. The more odd we look the easier it is for others to justify their claims that we are just a bunch of loonies making this all up. Even if we do have miles of evidence and X-ray proof….I also put a drawstring under this as well to cinch the back down because this is the important area where most transmitter/receivers seem to be.” One more thing: “Duct tape–very important.”

Ms. Starfire says the shield works. “For me this has been such a relief. As for the telepaths, I have learned to recognize them and ignore them and without their transmitters to force me to acknowledge them and force me to open up to them I can keep all the voices out because of the [radio frequency] shield hood!!!”

See, scoffers? It works. Every bit as effective as homeopathic pills. Still, you have to wonder whether this is truly a cost-effective solution. As Straight Dope Science Advisory Board stalwart Jill notes, “I just ignore the telepaths. The worst thing you can do is block them and piss them off. When it gets to be too much, I put my fingers in my ears and sing, ‘FLINTSTONES, MEET THE FLINTSTONES.'”

Moreover, from an engineering standpoint, the Starfire shield frankly bites. What these people need is professional help. A Faraday cage can protect against radio-frequency energy, but only if properly designed. The Faraday cage was originally conceived as a shield against static electricity: the free electrons carrying whatever charge the cage has repel each other and spread out along the cage’s convex conductive surface, leaving the interior electrically neutral. In a dynamic electromagnetic environment (radio waves), things are a little more complicated, but you do have something called the “skin effect,” in which a Faraday cage will cause significant attenuation of an incoming signal, depending on the cage’s construction and the signal’s frequency. To work properly, however, the cage must fully enclose the shieldee. If, like a dork (excuse me, Ms. Starfire, but one must call a spade a spade), you cover only a portion of yourself with the helmet, not only will the cage not shield you, the edges of the helmet will serve as an antenna, broadcasting your innermost thoughts (or electromagnetic traces thereof) to the world.

A partial solution is to ground the cage. Initially I thought one might drag a chain for this purpose, in the manner of the old gasoline trucks, but Uncle Al, the well-known sci.physics guru, sternly informed me, “Dragging a chain won’t do it. You must drive a thick steel spike into the water table and connect to it with a substantial copper or aluminum cable.” There’s also cage construction to consider. Uncle Al recommended “multiple layers of grounded conductive foil interleaved with electrically resistively lossy high-dielectric-constant stuff as per stealth plating (ferrite in carbon-loaded polymer).”

Clearly he’s thinking of increasing the cage’s capacitance, with obvious salubrious consequences. “One might add further interleaved layers of carefully annealed Co-Netic alloy or mu-metal, too, to bleed off magnetic fields,” but admittedly this is tougher to come by at the supermarket than Reynolds Wrap.

Some prefer a completely different approach. Check out from New Age author Eileen Nauman (courtesy of Straight Dope friend of science James Carr): “Whenever I go on the road and have to give seminars or talks, I always pack my trusty Saran Wrap! It is three sheets or layers, one on top of the other. I tuck it beneath my bra so that it hangs over and covers my solar plexus….[If] my attention is too scattered and pulled and I can’t focus like I need to, then I excuse myself and go slap on my Saran Wrap and there’s a happy ending. The only bad thing about this is: you’ll sweat like a pig beneath it.” But at least your solar plexus will be safe.

Art accompanying story in printed newspaper (not available in this archive): illustration/Slug Signorino.

Cecil Adams is the world’s most intelligent human being. We know this because: (1) he knows everything, and (2) he is never wrong. For more, see The Straight Dope website and FAQ.