Introduction: Faraday Pockets
Hide your cell phone by blocking any incoming or outgoing radio frequencies with a Faraday pocket. Whether you're looking for an easy way to immediately silence your phone when at a movie theater or stop those annoying incoming calls from your crazy ex-lover, Faraday pockets have you covered.
By lining your pocket with a special fine mesh metallic fabric you can reflect incoming fields and absorb energy. The effect of protecting something with a conductive fabric is called a Faraday cage and is named after Michael Faraday, whom first discovered the phenomena.
Making your own is easy, and a fun way to experiment with a neat scientific property of electrical field cancellation.
Ready to make the best pants ever? Let's make!
You'll need a pair of pants which you are willing to modify. Luckily the modification is just to the pocket, and even then isn't much of a modification, so you won't be ruining your clothes with this project.
Along with scissors, a fabric marker, and a sewing machine you'll also need conductive fabric, I used nickel/copper rip-stop as it has a high shielding rating and is easy to work with. There's loads of other options available, so experiment and have fun!
Luckily, the shield layer of conductive fabric doesn't have to be very thick:
The conductive layer can be very thin because of something known as the skin effect. That term describes the tendency of current to flow primarily on the skin of a conductor. As long as the conducting layer is greater than the skin depth, it will provide excellent shielding because the absorption loss will be large. The skin depth is a function of the frequency of the wave and the conductor material. As an example, consider that for a frequency of 200 MHz, the skin depth of aluminum is only about 21 microns. EMP pulses can have frequency content that ranges up to 1,000 MHz. Therefore, wrapping a box in a couple of layers of heavy duty aluminum foil (typically about 24 microns thick) provides the necessary conductor thickness to protect against high-frequency radiated fields. (source)
Step 2: Outline of Pocket
Turn pants inside out and place a corner of the conductive fabric under the pocket flap making sure that you're getting the corner of the conductive fabric all the way up into the underside of the pocket as far as it will go.
Using your fabric marker trace the outline of the pants pocket on the conductive fabric.
Step 3: Cut
Remove the conductive fabric from under the pocket flap and cut along the traced outline, then use the cutout as a pattern to cut a corresponding piece for the other side of the pocket.
Cut a generous outline outside the traced outline for you to sew into, you can always trim it down later.
Step 4: Pin
Place the cut sections of conductive fabric on either side of the pockets on your inside out pants.
Pins were used to located the conductive fabric where I wanted. It's important to cover as much of the pocket as possible - completely is possible.
Step 5: Sew
I used a sewing machine with regular thread to do the majority of the sewing. Each conductive pocket side was sewn together onto the existing pants pocket, the more difficult sections to sew were finished by hand with a needle and thread.
Check to make sure the pocket edges are sealed, and that as much of the pocket is covered as possible.
Can it have holes or openings?
Yes, as long as the holes are small with respect to the wavelength of the incident electromagnetic wave. For example, a 1 GHz wave has a wavelength of 0.3 meters in free space. As long as the holes are significantly smaller than that dimension (i.e., a few millimeters), they won’t let in much of the incident wave. This is why fine conductive mesh can be used when constructing a Faraday cage. In practice, the cage’s lid or door usually causes the most leakage. Taping the seam with conductive tape helps to reduce this leakage. (source)
With your pocket modified you're ready to turn your pants right side out and test out your Faraday pocket.
For best results, your phone should sit entirely inside the conductive fabric lined pocket. Any opening will allow signal to be transmitted to or from the device and nullify the Faraday cage effect.
Have you made your own Faraday cage?I want to see it!
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