Zone of silence [cellphone jammer]
Erico Guizzo · IEEE Spectrum · 2005
This paper presents a gadget that jams a cellphone's radiofrequency bands with a junk signal of a few milliwatts. Called the Wave Bubble, it creates a cellphone-free bubble of silence four meters in diameter. The Wave Bubble works by generating a range of voltages in a circuit that tunes an oscillator. This voltage-controlled oscillator's amplified output, in turn, spews out signals between 800 megahertz and 2.5 gigahertz, a range wide enough to cover the bands for CDMA and GSM cellphones, radiofrequency identification tags, Wi-Fi networks, and the Global Positioning System.