A Faraday Cage (http://en.wikipedia.org/wiki/Faraday_cage) blocks electromagnetic waves from passing through it. A Microwave uses this concept (to stop said micro waves from hitting the user), and aluminium foil has also been used as a shield (hence the gag with conspiracy theorists wearing them as helmets). I have a background in robotics and mechatronics engineering and can go into greater detail or assist you in designing a product which could incorporate such a shield if you would like to give me a call. A while ago, I was researching the difficulty of extracting data from RFID cards and found it incredibly easy. Thus, I think such a shield could have quite a few valuable applications.