Abstract: The present invention provides an intrusion barrier for protecting against mechanical or chemical intrusion into an electronic assembly, especially one containing volatile memory. It includes a screen material surrounding the electronic assembly which screen material has formed thereon fine conductive lines in close proximity to each other. The lines are formed of conductive particles of material dispersed in a solidified matrix of a material which loses its mechanical integrity when removed from the screen. An electrical supply and signal detection circuit is provided which generates an output signal responsive to a given change in resistance of the conductive lines, such that if the resistance changes are a result of a mechanical or chemical attack, a signal is generated which can cause the erasure of the volatile memory.

Abstract: The present invention provides an intrusion barrier for protecting against mechanical or chemical intrusion into an electronic assembly, especially one containing volatile memory. It includes a screen material surrounding the electronic assembly which screen material has formed thereon fine conductive lines in close proximity to each other. The lines are formed of conductive particles of material dispersed in a solidified matrix of a material which looses its mechanical integrity when removed from the screen. An electrical supply and signal detection circuit is provided which generates an output signal responsive to a given change in resistance of the conductive lines, such that if the resistance changes are a result of a mechanical or chemical attack, a signal is generated which can cause the erasure of the volatile memory.

Abstract: A system for authenticating components in a communications system using cryptographic techniques to determine if each has the proper key without disclosing information which would be useful to an imposter in deriving the key. A random number generated at a first terminal is encrypted under its key for transmission as a first value to a second terminal whose identity is to be authenticated. The second terminal decrypts the transmitted first value using its key deriving a second value (which equals the random number if the keys are identical.) The second terminal then encrypts its key using the second value as the key, generating a third value which is transmitted back to the first terminal for verification. The first terminal then verifies the third value, either by decrypting it using the random number as the key to obtain its key or by encrypting its key using the random number as key to derive the third number (if the two keys are identical.

Abstract: In hand-held magnetic readers, it is desirable that the magnetic read head be able to detect flux transitions on the surface of a magnetic media without requiring that the head have a specific orientation to the media. The present invention provides such a read head in which a thin planar magnetoresistive element is mounted so as to be perpendicular to the surface of the media. A thick yoke which is coplanar with the element provides a pole face adjacent the media surface which is sufficently wide as to extend over adjacent flux transitions when the plane of the element is skewed with respect to the flux transitions. A further pole face of the yoke is adjacent the edge of the element remote from the surface.

Abstract: A time base signal for controlling the recording of binary data is developed by measuring the velocity of a magnetic record. The velocity is measured by determining an average velocity by the time interval required for a mark recorded by a write head to move a predetermined distance to a read head and correcting the average velocity as a function of the acceleration of the record. The acceleration is determined by recording a reference frequency pattern at a first station, reading the pattern at a second station, and measuring the difference between the written and read patterns.

Abstract: A nuclear magnetic resonance (NMR) magnet assembly includes two pole faces spaced to provide a gap in which is established a uniform magnetic field. The pole pieces have pole faces that are flat and parallel. The pole pieces are mounted on support plates one of which is fixed and the other of which is movable about a pivot point with two degrees of freedom of movement in response to adjustment of two adjustable mechanisms. Each adjustment mechanism includes a differential screw that produces a transverse movement and a longitudinally inclined pin or pins that translates such transverse movement into a much greatly reduced longitudinal movement. The combination of a differential screw and inclined pin provides a very fine adjustment of the parallelism of the pole faces. Each mechanism further includes means for providing a coarse adjustment.