Introduction: Signal-Blocking Glove Box
Imagine you're headed out on a big road trip with your favorite songs blasting on the radio and a cool breeze is blowing in through the window. You've finally found peace... until your cellphone begins to ring. Sure, you could've turned it off, or maybe even taken out the battery (if the manufacturer will even allow it!), but what if you want real freedom from your phone without having to compromise it or, dare I say, leave it at home? With the Signal-Blocking Glove Box, you won't have to do either of the above. As a powerless RF-blocking container, you'll be free from the constant connectivity that distracts and ties you down to the modern world. Say goodbye to GSM, GPS, Bluetooth, WiFi, and NFC. The government can't track you and your peeps can't text you, but who needs 'em? You've got the open road...
Step 1: How to Block RF Signals
In technical terms, the "Signal-Blocking Glove Box" is a Faraday cage. At its most basic, a Faraday cage is simply a conductive enclosure. The physical structure of the enclosure determines how effective it is at absorbing electric charge or attenuating RF signals. We're interested in the RF blocking aspects of the Faraday cage, so we'll need to figure out what kind of material we can use.
Most modern cell phones and other personal gadgetry contain a variety of radios that operate up to 2.4 gigahertz, the exception being 802.11ac for Wi-Fi which operates at 5 gigahertz. Let's use this higher measurement as our goal to ensure even greater success at attenuating the lower frequencies. In order to properly block a 5 GHz signal, we'll need to figure out the wavelength and how tight our enclosure needs to be, which we can do with the following equations:
λ = c / f
x = λ / 10
λ = wavelength in meters
c = velocity of light in meters per second
f = frequency in Hertz
x = maximum diameter in meters of any holes in the surface of our Faraday cage
Plugging everything in gives us:
λ = 299,792,458 / 5,000,000,000
λ = 0.0599584916 m
x = 0.0599584916 / 10
x = 0.00599584916 m (~6 mm)
In order to block a 5 GHz signal from entering or leaving our box, we'll need to make sure there are no holes or gaps greater than 6 mm in diameter. Ideally, the box would also have a conductive path to ground, but seeing as how we'll be stuffing ours into a plastic compartment within a moving vehicle, we'll have to do without (but this won't limit our RF blocking abilities; grounding would just be an added benefit)
I designed a self closing box that would fit snugly into my glove compartment. The compartment dimensions were about 10 inches wide by 7 inches deep by 4 inches tall, so I settled on making my box 9 by 6 by 4 inches to make things fit snugly while maximizing storage space. The box is pulled tightly closed by extension springs to ensure a tight, conductive seal is always made.
I used special RF blocking fabric (linked on the next page) as my conductive layer for the box, but it was by no means the only way. Aluminum foil is cheap, plentiful, and effective in layers, however the constant crinkling noise seemed unpleasant and the long term durability questionable.
Step 2: Parts and Materials
Step 3: Assemble Box
I cut my box out of 3mm thick black acrylic using a laser cutter. I've attached the file for my box above if you wish to copy it, but you could also easily modify a premade box. The most important feature is making sure the door of your box forms a tight compact seal to ensure a fully conductive shell around the interior. If you decide to make the box from my vector files, you can see how to assemble it above. If you decide to sew the interior shell with conductive fabric of your box, be sure to use a tight stitch; regular thread will work just fine too!
Step 4: Installation
Installation is pretty straightforward, but it will certainly vary depending on the interior of your glove compartment. I affixed my box to the little shelf inside with double stick tape on the bottom of the box (Command strips to the rescue!). The door of the Faraday cage is physically attached to the glove compartment door by strings wrapped around the exterior screw heads. This way, the door to the interior box will open automatically with the glove compartment door, making it easier to use if you only have one hand free.
Step 5: Final Thoughts
I'm quite happy with the mechanism and the effectiveness of the box (I've successfully failed to call myself during every test!). If you plan on making your own Faraday cage, let me know and show off your work in the comments!