Sheet articles of non-conductive material marked for identification purposes, and method and apparatus for identifying such articles

Claim 3

A method according to claim 1 wherein the said output signal is representative of the value of such excess, and in which additionally the energy reflected is measured and transformed into a second output signal which is representative of the value of the energy reflected.

Claim 4

A method according to claim 1 or 2 wherein the sheet articles used are paper foils in which said fibers have a length not greater than 40 mm and a thickness below 50μ, and have a conductivity of less than 10% of the copper standard, and in which said paper has less than 5% by weight of said fibers.

Claim 5

A method according to claim 3 wherein said fibers are equally distributed and randomly oriented in the plane of the sheet article.

Claim 6

A method according to claim 3 wherein said fibers are made of stainless steel.

Claim 7

Apparatus for use in a method according to claim 1 which comprises an emitter of an unguided beam of microwaves, means for positioning the article to be identified with the part of the sheet article in which the very thin conductive fibers are incorporated in the path of an unguided beam from the said emitter, a first receiver positioned so that in use it receives energy from the part of said beam which passes through the said article and is neither absorbed nor reflected, a second receiver positioned so that in use it receives energy from the part of the said beam which is reflected by the very thin conductive fibers incorporated in the said article, and a comparator connected to the output of both receivers, adapted to deliver an output signal in response to a significant excess of the energy arrested, as measured by the first receiver, over the energy reflected, as measured by the second receiver.

Claim 8

Apparatus according to claim 6 wherein said emitter and first receiver comprise a horn-antenna, placed at a distance of maximum one wavelength from each other, the antenna of the emitter being connected via a directional coupling toward a sensor for measuring the microwaves entering said antenna, which constitutes additionally the antenna of the second receiver.

Claim 9

Paper sheet article adapted for being treated by a method according to claim 1 wherein said article is capable of allowing microwave radiation impinging thereon to pass therethrough, which article is marked for identification purposes by the incorporation therein of a small quantity of very thin conductive fibers which are capable of absorbing and reflecting certain proportions of the energy of microwave radiation impinging thereon.

Claim 10

A paper sheet article according to claim 8 having less than 5% by weight of said fibers which have a length not greater than 40 mm and a thickness below 50μ, and have a conductivity of less than 10% of the copper standard.

Claim 11

A paper sheet article according to claim 9 wherein said fibers are equally distributed and randomly oriented in the plane of the foil.

Claim 12

A paper sheet article according to claim 9 or 10 in which said fibers are made of stainless steel.