Abstract: A method for producing a polymeric material, said method comprising subjecting a starting material which includes two multiple bonds which are activated so that they will take part in a polymerisation reaction and wherein the multiple bonds are sufficiently close togeter to ensure that cyclopolymerisation will preferentially occur; to suitable conditions under which said polymerisation reaction will occur, provided that the starting marerial is other than triallyamine hydrochloride. The method can be used to produce polymers for various processes including adhesives, network polymers, liquid crystal polymers etc.

Abstract: A liquid crystal device comprises a layer of nematic or long pitch cholesteric liquid crystal material contained between two cell walls. One wall (A) carries a surface treatment giving a first azimuthal alignment direction with or without a surface pretilt to liquid crystal molecules. The other wall (B) carries a surface treatment (17) capable of separately providing both a preferred, substantially homeotropic alignment of the adjacent liquid crystal, and a defined azimuthal second alignment direction to the adjacent liquid crystal dependent upon liquid crystal molecular arrangement. The first and second alignment directions are approximately orthogonal. Polarisers may be arranged on either side of the cell walls with their polarisation axes parallel or perpendicular to the two azimuthal directions. Alternatively an amount of dichroic dye may be incorporated in the liquid crystal material, and the device operated with one or two polarisers.

Abstract: An infra-red imaging system has two variable focal length optical components (6, 7) whose positions are fixed relative to one another. The system also comprises an image detector (8). Control means (13) is provided such that the focal length of one of the variable focal length optical components (7) can be varied in relation to the focal length of the other variable focal length optical component (6). The system can be used to produce an image of variable magnification while maintaining an in-focus image at the detector (8). The control means (13) may comprise a mechanical linkage, an electronic circuit, or a computer program. In an alternative embodiment the optical system is a beam expander. Controlling a focusing mirror can achieve a dither effect. Controlling a focusing mirror can also de-focus the image, giving a mean scene temperature evaluation.

Abstract: A method of fabricating a dielectric medium comprising two materials with discrete interfaces between the two materials and media formed from the dielectric medium.

Abstract: A semiconductor device of the invention in the form of a superlattice-heterojunction bipolar transistor (SL-HBT) 10 incorporates a superlattice region 16 within an emitter mesa 21. The superlattice region 16 provides a non-linear response to a sufficiently high level of device current to counteract thermal runaway. This protects the device from damaging levels of current. The device 10 may be a radio-frequency SL-HBT with performance equivalent to that of a conventional heterojunction bipolar transistor. The invention may also be implemented as a semiconductor laser.

Abstract: A bistable nematic liquid crystal device cell is provided with a surface alignment grating on at least one cell wall and a surface treatment on the other wall. Such treatment may be a homeotropic alignment or a planar alignment with or without an alignment direction, and zero or a non zero pretilt. The surface profile on the monograting is asymmetric with its groove height to width selected to give approximately equal energy within the nematic material in its two allowed alignment arrangements. The monograting may be formed by a photolithographic process or by embossing of a plastics material. The cell is switched by dc pulses coupling to a flexoelectric coefficient in the material, or by use of a two frequency addressing scheme and a suitable two frequency material. Polarisers either side of the cell distinguish between the two switched states. The cell walls may be rigid or flexible, and any coated with electrode structures, e.g.

Abstract: A sensor system (10) for locating transmitters incorporates three vehicle-mounted patch antennas (30 to 34), a signal processing unit (40), a navigation unit (50) and a computer (60). The navigation unit (50) measures sensor system position using the Global Positioning System. The antennas (30 to 34) receive radiation from a transmitter (210) to be located and respond by generating output signals which are frequency downconverted and processing coherently by a digital signal processing unit (230). This produces elevation and azimuth phase data for the computer (60), which determines measured phase differences. The computer (60) also calculates expected phase differences from antenna positions and trial transmitter positions. It determines transmitter location from correlation between measured and expected phase differences. The position of a transmitter (210) is determined for a number of sensor system positions.

Abstract: Apparatus for detecting a metal object comprises a transmitter for generating a pulsed or an alternating magnetic field in the vicinity of the metal object to be detected and a detector for detecting the secondary magnetic field induced in the metal object by the transmitted magnetic field. The detector measures at least three magnetic field gradient components of at least first order of the secondary magnetic field. The apparatus also comprises a processor for determining at least one of the position or the electro-magnetic cross-section or an estimate of the shape of the metal object from the measured magnetic field spatial gradient components. The processor fits the measured components to dipole, multiple dipole, multipole, or extended source models. In a preferred embodiment, the invention may comprise three or more pairs of gradiometric coils, or other sensing means.

Abstract: Temperature sensing apparatus comprises a source of electromagnetic radiation (1), a wavelength-selective element (3) which interacts with radiation emitted from the source (1) and a detection system (6) which monitors radiation from the wavelength-selective element (3). The wavelength-selective element (3) is fixedly mounted on a substantially rigid substrate (not shown). The apparatus can be used for temperature sensing in aquatic environments.

Abstract: An imager is disclosed comprising: one or more detectors, a shutter adapted to open and close periodically to modulate the radiation incident upon the detector element to produce a sequence of alternating open fields and closed fields, said detector being adapted to produce a first pair of output signals Vo1 and Vc1 comprising an open field and a closed field, and a second pair of output signals Vo2 and Vc2 comprising an open and a closed field, a reset device adapted to reset the output of the detecting element to a predetermined voltage after the output signals of Vo1, Vc1, Vo2 and Vc2 have all been obtained, there being no reset of the output of the detecting element between the output signals Vo1, Vc1, Vo2 and Vc2, and a processor adapted to process said first and second pairs of output signals to produce a first and a second processed image signal from the detecting element, the first processed image signal corresponding to the first pair of fields and the second processed image signal corresponding to t

Abstract: A signature recognition system for identifying an article with a distinctive diffraction element (or elements) and verifying the presence of that element or elements comprising: an article with one or more diffraction gratings impressed thereon, the grating(s) exhibiting periodic wave surface profiles having a depth-to-pitch ratio &dgr; of between 0.1 and 0.5, a source of polarized electromagnetic radiation of wavelength &lgr; such that the pitch G of the periodic wave surface profile of the grating(s) is comparable to an integer multiple n of that wavelength, a device for directing the source of polarized electromagnetic radiation to the surface of the grating(s) at a plane of incidence substantially normal to the plane of the surface of the diffraction grating and at an angle of approximately 45° azimuth to the alignment of the grooves on the surface, and a device for detecting radiation reflected from the grating(s) surface which is oppositely polarized to the incident radiation.

Abstract: Compounds of the formula: where X3 is: other variables are defined in the description, and the rectangular box is a mesogenic group, are used in a variety of devices including liquid crystal devices piezoelectric, pyroelectric devices and in optical recording media.

Abstract: A buffer circuit includes a MOSFET source follower (M54) and a floating gate MOSFET (MFG53) connected in series with the phototransistor (PT51) to control current through it at an input circuit node (D53). The source follower (M54) buffers the phototransistor (PT51), having a gate (G54) connected to its emitter (PC51). The floating gate (F53) is programmable with charge to preset the phototransistor current under prearranged illumination conditions to counteract unwanted signal contributions (e.g. fixed pattern noise) or non-optimum circuit characteristics. The floating gate MOSFET (MFG67) may alternatively be connected in series with the source follower output (D65) to control current at an output circuit node. The circuit may be a member of a pixel circuit array and may include programming circuitry (M84, M85) to select it for programming and to isolate it to enable other array members to be programmed.

Abstract: A multi-element fuel cell system comprises a substantially cylindrical former (2), a rechargeable hydrogen fuel source (3) and a plurality of fuel cell elements (4). The former comprises a series of interconnecting modules each perforated to allow passage of fuel to the fuel cell elements. Each fuel cell element (4) is positioned radially outwardly of the former (2) and is provided with channels, arranged to receive and direct fuel gas, an anode current collector, a gasket (12), a first diffusion backing layer (8), a membrane electrode assembly (10), a second diffusion backing layer (9) and a cathode current collector (11). The cathode current collector applies even compression to the fuel cell element, such that good electrical contact is maintained within each fuel cell element. The fuel cell elements are electrically connect in series via respective anode and cathode current collectors and then capped at each end of the former for connection to equipment.

Abstract: Apparatus for the identification of articles (5) endowed with device for changing the polarization properties of the radiation, comprising a source (1) of non-randomly polarized microwave radiation, and a detector (3) for detecting the change in polarization properties of the radiation. The microwave radiation may have a first plane of polarization and, in use, the device for changing the plane of polarization properties of radiation may change the first plane of polarization to a second plane of polarization. The detector (3) for detecting the change in polarization properties of radiation may comprise a receiving antenna (4c) connected to suitable microwave detector (3), where the receiving antenna (4c) is arranged to favour reception of radiation having the second plane of polarization. For example, the transmitting (4b) and receiving (4c) antennas may be waveguide antennas.

Abstract: A single electron on hole field effect transistor fabricated from a narrow band gap semiconductor. The transistor is such that the valence and conduction bands have sufficiently similar energy levels such that a top region of the valence band at one point (37), e.g. under a gate electrode (34), within the current path of the transistor can be forced to be higher than the bottom region of the conduction band at another point within the transistor, allowing Zener tunelling to occur. The transistor is fabricated from semiconductors with band gaps narrow enough to allow this to occur, for instance InSb and InAISb, CdTe and CDxHg1−xTe.

Abstract: A hole boring charge assembly suitable for explosively forming a wide borehole in a concrete target consists of a detonatable array of at least three hollow charges (12) having recessed, lined forward faces (14) facing towards the target in the same general direction as a fore-and-aft line of target penetration. Simultaneous detonation of the charges (12) produce individual jet penetrators derived from the charge liners (16) which penetrate the target and together produce a wide multi-sided borehole therein suitable for the subsequent emplacement of a blasting charge. The charges (12) may be focussed forward of the array to produce a single, coalesced penetrator which is capable of producing a wide, tapered, approximately axisymmetric hole in concrete.

Abstract: An analogue to digital converter generating at least two threshold levels and a comparator for comparing each of the levels with the input signal and generating a primary digital output signal to provide an indication that the input signal has crossed one of the threshold levels. The converter comprises a timer for determining the elapsed period of time between the input signal crossing a first level and the input signal crossing a second level and for generating a secondary output signal representing the elapsed time, whereby the secondary digital output signal and the corresponding primary output signal are used to provide a digital representation of the analogue input signal. The converter may also comprise a receiver of the primary digital output signal from the comparator and for providing an UP/DOWN digital output signal to indicate in which direction the input signal crossed the threshold level.

Abstract: Metalorganic precursors for deposition of strontium tantalum and strontium niobium oxides by MOCVD techniques have the formula Sr[M(OR1)6-xLx]2 wherein x is form 1 to 6; M is Ta or Nb; R1 is a straight or branched chain alkyl group; and L is an alkoxide group.

Abstract: A dispersion strengthened mechanically alloyed aluminium based alloy is provided which is prepared by mechanical alloying and is characterized by improved isotropic strength, fracture toughness and corrosion resistance. The alloy system contains by weight 1.2 to 1.6% lithium, 4.0 to 6.0% magnesium, 0.15 to 0.7% carbon, up to 1% oxygen and up to 2.0% in total of one or more grain controlling elements to provide microstructural optimization and control, the balance aluminium save for incidental impurities.