Passive device shield with proximity change alert
A method of making a fuel for a portable heater comprises heating a salt of iron with a carboxylic acid at a temperature from about 400° C. to about 700° C. under an inert or reducing atmosphere to produce a composite material comprising carbon and iron nanoparticles. The fuel may be mounted to a substrate, such as a mesh or foil, and incorporated into a self-heating packaging. Typically, the packaging comprises a wall defining a chamber that, in use, contains a substance to be heated, e.g. a food-stuff or liquid. A heating manifold in thermal communication with the chamber contains the fuel in the inert atmosphere to initially inhibit production of heat otherwise arising from substantial oxidation of substantially all the fuel in the manifold in an exothermic reaction. A vent in the manifold is initially sealed and air-tight, but selectively opening of the vent allows oxidation of the iron nanoparticles. The chamber is then heated by the transfer of heat from the fuel to the chamber, the transfer of heat being by at least one of direct thermal conduction through the wall, thermal convection or indirect thermal heating arising from heating of a fluid medium that is introduced into the chamber.
1. A shield for a passive device and a receiver remotely coupled to the shield, the shield being adapted to provide radio frequency shielding to block selected radio frequencies, the shield further comprising a transmitter to send a coupling signal to the receiver, the coupling signal being of at least one non-blocked frequency, the receiver having means to monitor the distance between the receiver and transmitter and an alert means to indicate when the measured distance exceeds a predetermined value.
2. A shield according to claim 1 , wherein the shield is adapted to be selectively removable from a passive device it shields.
3. A shield according to claim 1 wherein at least one of the transmitter or receiver has means to adjust the predetermined value, the transmitter has means to act as a locating device to search for the shield and provide an alert signal when in range, and the receiver has means to selectively deactivate the coupling.
4. A shield according to claim 1 , wherein the alert means comprises an indication of at least one of time and date that the predetermined distance was exceeded, and means to indicate the last time the shield and receiver were paired.
5. A shield according to claim 1 , wherein the receiver has means to search for the shield in order to pair the receiver with the transmitter, the receiver having additional means to activate the alert means if the transmitter cannot be found.
6. A shield according to claim 1 , wherein the alert means comprises at least one of a vibrating alert, a sound alert, a visual alert, an alert that increases in pitch and intensity.
7. A shield according to claim 1 , wherein the shield is provided with a stiffner, at least in the vicinity of the transmitter, wherein the stiffner is in the form of a coating to the shield, the coating being in the form of at least one laminated surface.
8. A shield according to claim 1 , wherein the shield provides the shielding by the provision of a shielding layer, the shield having a further thin surface provided on the shielding layer, the further thin layer enabling the provision of printed messages on the shield.
9. A shield according to claim 1 , wherein the predetermined value is between 3 to 100 meters.
10. A shield according to claim 1 , wherein the receiver is incorporated in a mobile phone.
11. A shield according to claim 1 , wherein the receiver has means to detect signals from a plurality of coupled transmitters.
12. A shield according to claim 1 , wherein the coupling signal is in the form of at least one of the radio frequency signal, a blue tooth signal, low-powered blue tooth signal and Wi-Fi signal.
13. A shield according to claim 1 , wherein the receiver has means to indicate the presence of the transmitter when in range, thereby ensuring the user that the device is working properly.
14. A shield according to claim 1 , wherein the shield has means to enable information to be stored thereon, the information means being in the form of at least one of a printable layer, a re-printable layer, thermoplastics layer, writable memory, and rewritable memory.
15. A shield according to claim 1 , wherein a further receiver is provided adapted to read the coupling signal of the transmitter and which enables identification of the shield, wherein the further receiver has means to link the transmitter whose coupling signal it reads to an identification pass and means to provide details of that pass to the shield.
16. A shield according to claim 1 , wherein plurality of further receivers are provided which are linked in a network and have means to track the location of the shield, wherein the network of receivers has means to enable at least one of the identification and tracking of a plurality of different shield transmitters, and has means to activate the tracking and location of a particular shield transmitter, and wherein the activation means is activated when a particular shield has not been presented for inspection within a set period of time.
17. A shield according to claim 1 , wherein the shield has fastening means to selectively attach it to a device incorporating a passive chip the fastening means being in the form of at least one of a shield being incorporated on a band which is adapted to wrap around and retain a plurality of items to be shielded or a clamp which enables the shield to be clipped to a device.
18. A shield according to claim 1 , wherein the shield is incorporable in at least one of the following a bag, wallet, purse, item of clothing, document, book and passport.
19. A shield according to claim 1 , wherein the shield comprises a shield of sheet material and incorporates a shielding layer having a maximum thickness of 0.4 mm and being constructed of a material adapted to provide radio frequency shielding with an attenuation of at least 50 dB.
20. A shield according to claim 1 , wherein the shield is specifically adapted to shield frequencies of 13.56 MHz.