Abstract: A high-speed field emission vacuum switching device comprises a cathode tip formed on a substrate, an extraction grid close to the cathode tip, and a modulator grid spaced from the cathode tip by a dielectric layer. The grids have apertures aligned with the cathode tip. An anode is spaced from the modulator grid by a dielectric layer. By use of the modulator grid, a substantial improvement in high-frequency switching performance can be achieved. A collector grid may be provided between the extraction grid and the modulator grid, and a cut-off grid may be disposed between the modulator and collector grids.

Abstract: The array is highly suitable for producing a spacially wide output “beam” (comprising a number of individual beams). It suffers less from problems of hotspots and filamentation since each tapered laser supports a limited number of modes, or even a single mode. Therefore it produces a semiconductor laser which is especially suitable for pumping of other lasers and to be used in materials processing.

Abstract: An acoustic imaging system comprises a plurality of piezoelectric elements in a piezoelectic array. The array comprises a plurality of physically separate sub-arrays which are assembled together. It is supported on an interconnect layer. The elements are connected to the interconnect layer by a plurality of electrically conductive paths. The elements receive acoustic energy and convert it into electrical signals. The signals are transmitted along the plurality of electrically conductive paths and through the interconnect layer to an image processor which processes the signals to produce an image.

Abstract: A separation method, a method for detection, a sensor, and a test-kit find application in immunological detection. The separation method provides for separation of a primary species which separation method is suitable for use in an immunoassay method for the detection of an analyte species and includes the use of a first auxiliary species capable of being formed into a second auxiliary species which second auxiliary species is capable of interacting with a third species to facilitate separation.

Abstract: A number of electronic modules 82, 82′, 83, 83′ are mounted on a cold finger 100 disposed within a sealed housing 104, 110, the interior 210 of which is evacuated. To minimize heat transfer by conduction, gaps are provided in the dielectric substrates carrying the input and output transmission lines providing signal paths between the modules and electrical connectors on the exterior sidewalls 106, 108 of the housing. The gaps are bridged by thin conductive wires, thereby providing low electrical, but high thermal, impedance at the gaps. A number of module assemblies may be stacked on a single cold finger. To allow modules to be adjusted under actual operating conditions, a cover having a number of spring-loaded screwdrivers extending through vacuum tight seals and aligned with adjustable components of the modules, may be temporarily substituted for the enclosure lid 110. The springs urge the screwdrivers out of engagement when no adjustment is being made to minimize heat transfer.

Abstract: A bridge deck (10) is supported by tensile supports (11 and 12) and stabilized to reduce the overall aerodynamic lift on the deck (10) by the addition of aerofoil stabilizers (19 and 20) pivotally secured about respective axes (21) generally longitudinal of the deck (10). The stabilizers (19 and 20) are driven by a mechanism (21 to 26) operable by angular movement between the deck (10) and the tensile supports (11 and 12) to articulate the stabilizers (19 and 20) to a position which will generate a force, in the presence of a cross wind, to reduce the overall aerodynamic lift on the deck (10).

Abstract: A continuous wave radar system, for example a radar altimeter, comprises a memory (24) for storing an array of return signals, means for performing a time integration (25) of the array to improve its signal-to-noise ratio, means responsive to the time integrated array (26) to compare (30) the noise level (28) thereof with the peak level (27) thereof to obtain the signal-to-noise ratio of the array, and control means (31) responsive to the signal-to-noise ratio thus obtained to set either the period over which the said time integration is performed for each renewal of the time integrated array (26), or the power of the transmitted signal, of both, in accordance with predetermined criteria to the minimum necessary to ensure an adequate signal-to-noise ratio.

Abstract: A mine neutralisation vehicle comprises a first portion to which propulsion units are attached by which propulsion units the vehicle is positioned. Pivotally connected to the first section is a second section containing a shaped charge warhead. By means of the pivot connection the shaped charge can be directed at a mine, for example a buried mine, while the main body of the vehicle is maintained in a horizontal direction.

Abstract: A communications system includes a plurality of interfaces (20) each of which can receive and/or transmit data to a common transmission network (21). Each interface (20) transmitting data to the network (21) attaches a classification code to the transmitted data, and each interface (20) receiving data from the network (21) retrieves the classification code and restricts access to the associated data in dependence upon that classification code. The invention alleviates the need to employ "secure" and "clear" communications networks in parallel, and is especially applicable to aircraft communications.

Abstract: A scratch resistant coating for the window of an infra red sensor comprises a layer of zirconium oxynitride or hafnium oxynitride. The formula of the coating is M.sub.1-(y+z) O.sub.y N.sub.z where y and z are both in the range 0.1 to 0.4. The coating and the window are both transmissive in the infra red and visible ranges of the spectrum.

Abstract: A night vision viewing system (13a or 13b) suitable for mounting on an observer's headgear (11) wherein light rays from a forward scene pass to the observer's eye (E) via a path comprising a forward looking objective lens (19), a first inclined reflector (23) which directs the rays upwardly onto the input face of a downward-looking image intensifier (25). Intensified rays from the image intensifier pass, in turn, via a fibre optic stub image rotator (27), a second inclined reflector (29), a relay lens arrangement (31) and third and fourth inclined reflectors (33) and (35), the fourth reflector directing the rays downwardly into an eyepiece (15) which is in the observer's forward line of sight. The eyepiece (15) incorporates an internal surface (39) having both light reflective and light transmissive properties which directs rays entering the eyepiece (15) from the intensifier (25) to the observer's eye.

Abstract: A terrestrial flight telephone system comprises a number of air stations which communicate on a common frequency with a ground station. The ground station can handle calls from a number of air stations in respective slots of sequential frames defined by the ground station. Accurate synchronisation is critical to the functioning of the system and drift in an oscillator of the air station, which controls the timing of transmissions from the air station, is corrected by signals received from the ground station.

Abstract: An imaging system is provided which comprises an objective lens arrangement, a linear array of detector elements within a detector the array comprising a row of time delay an integrate (TDI) channels and a scanning optic arranged to scan an image over the array detector elements, the system further comprises means for rotating the scanning optic about an axis (N) normal to an optical surface of the scan optic when the scan optic is in the center of its field of view position, the scan optic being rotated about this axis (N) in dependence on the rate at which the imaging system is panned across a scene, such that a received image is vector scanned across the linear array of detector elements to compensate for loss in image resolution due to the panning action of the imaging system occurring during the period in which an image frame is detected.

Abstract: A method of fabricating a microbridge structure for a thermal detector array comprises growing a planarising layer on a substrate, growing a ferroelectric material layer on the planarising layer and then etching the planarising layer away, either wholly or partially, to leave a ferroelectric microbridge having a uniform thickness. The planarising layer may be a sacrificial layer or may comprise a sacrificial layer as well as other layers.

Abstract: An electron field emission device includes a field emissive cathode which may include a plurality of sharp field emitter tips 2. First and second grids 4 and 7 are located between the cathode and an anode. The grids comprise parallel strips of electrically conductive material, those of the first grid being arranged orthogonal to those of the second. Applications of suitable voltages to the grids enable selected regions of the cathode to be made electron emissive and produce collimated electron beams. The anode may be phosphor coated to produce a visible display or an infra-red image may be produced. Relatively low voltages may be used to switch the regions on and off. As the beams are collimated, the anode may be located a relatively large distance from the cathode, enabling high voltage phosphors to be used.

Abstract: An optical backplane is formed by defining channels in the plane of a polyimide layer 55, laying optical fibres 56, 57 in each channels, retaining the fibres 56, 57 using an adhesive and bonding an epoxy resin layer 58 to the polyimide layer 55 to form a flexible structure 54. The flexible structure 54 is made rigid by bonding epoxy glass FR4 layers 60, 61 to either side of the flexible structure 54. A flexible ribbon 53 with an optical fibre 57 contained therein is formed as an integral portion of the flexible structure 54 using spacers 59, 62 to define a ribbon region and to aid removal of the rigid layers 60, 61 in the ribbon region.

Abstract: The invention provides a system and method whereby a mobile station of telecommunications system selects one of a number of fixed ground stations by which the mobile station communicates with the public switched telephone network or other such system, selection being made by the mobile station receiving selected criteria and deriving from a plurality of these criteria a score for each of a plurality of the fixed stations, the fixed station via which communication is to be made being selected in dependence upon the score derived for that fixed station.

Abstract: A continuous wave radar altimeter comprises a pulsed power control (4), operable when the signal-to-noise ratio of the received signal is likely to be too low, to pulse the transmitted power so that the power varies between a non-zero base level and a higher level. The receiver channel (13, 14) is switched off during each transmitted pulse.

Abstract: It is known to use a rigid cone to provide stability to a body being towed by an aircraft. However, such cones are useful over a limited range of speeds. The invention provides a drag-producing aerodynamic device in which the cross-sectional area of the structure producing drag is variable. The cross-sectional area of the structure producing drag decreases as the towing speed, and hence the dynamic air pressure acting on the structure producing drag, increases and vice versa.

Abstract: A thermal imager referencing system comprises two rotating cranks in the form of discs (7, 8) each pivotally attached to connecting member (9). The discs (7, 8) are rotated at a constant speed causing two mirrors laterally displaced along connecting member (9) to intercept an optical path X of a thermal imager associated with the referencing system. Each rotation through 360 degrees of the discs (7, 8) causes each mirror to pass once through the optical path, the mirror surfaces being respectively arranged to cause a linear array of detector elements (not shown) of the thermal imager to view alternately thermo-electric devices (14, 16), which are at different temperatures, during the flyback time associated with the thermal imager. The referencing system enables processing means of the thermal imager to normalize the detector array, compensating for DC offset and differences in gain between different elements of the detector array.