Abstract: Security strips or threads are provided which are suitable for at least partial incorporation in and/or for mounting on security documents or means for identification, such as labels, and which comprise the following deposited or laminated layers: at least one layer of a plastic substrate; a layer of a first security detection feature made up of identifying marks or indicia; and a layer of a second security detection feature comprising a generally invisible, optionally repeating pattern. The repeating pattern comprises at least one very thin conductive region and at least one electrically isolating region. Also provided is a security paper having such a security thread at least partially embedded therein and/or mounted on a surface thereof and a process for making the security paper. Further provided is a method of verifying the authenticity and reading the coded information of a security paper employing such a security thread.

Abstract: A security thread for use in a paper-based value document, such as currency or banknote paper, includes a plastic substrate coated with one or more regions of "soft" magnetic material. A device for verifying both the authenticity and the denomination of the document includes a coil that is driven by an alternating current to thereby provide a uniform magnetic field within a predetermined spatial region. As the document passes in proximity to the drive coil, the applied magnetic field saturates the regions of magnetic material on the security thread. The magnetic regions provide a response magnetic field that, because of the saturation of the magnetic regions, is a non-linear response containing a multiple of frequency components, including a component at the fundamental or drive frequency and various harmonic frequency components. A receive coil senses the response magnetic field.

Abstract: An electronic article surveillance system for detecting articles carrying or containing magnetically responsive markers is disclosed, which system comprises a transmitting antenna in the form of a large loop of current-carrying material through which the articles are passed, and one or more receiving antenna units, which detect the electromagnetic response of the markers to an interrogating electromagnetic field generated by the transmitting antenna.

Abstract: An electronic article surveillance system is provided having a transmitter for generating two alternating magnetic fields by way of a single transmitter coil fed with a transmitter signal current, and a receiver that detects harmonics and intermodulation products of the alternating magnetic fields by way of a receiver coil that generates a receiver signal current. The receiver comprises a wide-bandwidth phase detector locked on to a frequency p.f.sub.2 .+-.q.f.sub.1, where p and q are positive integers, one of which may be zero, and a digital signal processor adapted to carry out a full time-domain analysis of the waveform of the receiver signal current, and wherein the transmitter signal current corresponds to the linear super position of two alternative currents with a relatively low frequency f.sub.1 and high frequency f.sub.2 respectively.