An add-on cartridge structure for electronic devices having a housing formed from upper and lower case sections. The upper case is typically made from plastic and has a conductive layer formed on inside surfaces, while the lower case is made from a metallic material such as aluminum. A wall-like mating...http://www.google.com/patents/US6404639?utm_source=gb-gplus-sharePatent US6404639 - Cartridge for electronic devices
