Abstract: An eye tracking apparatus for monitoring the movement of a user's eye, the apparatus including: a display for displaying an image; an eye imaging sensor for monitoring the user's eye and for providing an output indicative of the user's point of regard in the user's field of vision; an optical combiner arranged, in use, in optical communication with the display, the eye imaging sensor and the user's eye: said optical combiner arranged to receive the displayed image from the display, to project said image into the user's field of vision, to receive electromagnetic radiation reflected from the user's eye and to pass said reflected radiation to the eye imaging sensor; wherein the optical combiner is adapted to substantially correct for aberrations in the reflected radiation introduced therein by the optical combiner.

Abstract: This invention relates to optoelectronic devices of improved efficiency. In particular it relates to light emitting diodes, photodiodes and photovoltaics. By careful design of periodic microstructures, e.g. gratings, associated with such devices more efficient light generation or detection is achieved.

Abstract: A beam forming apparatus for forming a beam in a forward direction including a first reflector arranged to receive light from said source and to reflect it rearward, and a second reflector arranged to receive light from said first reflector and to reflect it forward. The rearmost reflector is hyperbolic in form, and the front reflector is advantageously elliptical. This arrangement offers multiple different beam patterns of varying and controllable concentration to be achieved in a consistent and predictable manner.

Abstract: An apparatus is provided for compensating for the effect of a stray ferromagnetic object moving past but not through a sensing region of a ferromagnetic object detector. The ferromagnetic object detector is of a type to produce a plurality of sensor signals, each sensor signal being influenced by the presence of a genuine ferromagnetic object moving through the sensing region but also liable to be influenced by the presence of the stray object. The apparatus comprises: an input for receiving the plurality of sensor signals and first means for analysing the received signals to determine whether there is a substantially same time-varying component present in each of the signals. The apparatus also comprises second means for determining whether the plurality of signals without the contribution of that time-varying component are each or collectively below a predetermined level of significance.

Abstract: A ship's radiated noise monitoring system includes a plurality of arrays of spaced vibration-responsive detectors, the arrays being adapted for location adjacent to the ship's hull in the region of possible noise sources; summing amplifiers for receiving the detectors output signals from respective arrays and providing output signals representative of the average vibration signals received by each array; an analyzer connected to the output of each summing amplifier to perform a spectrum analysis; and computer apparatus to receive the noise spectrum from each array, apply respective weighting factors to the noise spectra and combine the weighted noise spectra to produce a predicted radiated noise spectrum. Preferably each array comprises a regular distritution of nine accelerometers attached to hull frames in groups of three. The system is used in conjunction with sonar equipment to enable self-noise to be monitored to optimise the sonar performance.

Abstract: A semiconductor device comprises the following elements: an active layer comprising a quantum well structure and a buffer layer beneath the active layer adapted to form a confinement layer for charge carriers in the active layer. The buffer layer is adapted so as not to increase an overall strain in the active layer. The active layer is already strained as a result of a lattice mismatch between the active layer and the buffer layer. Strain in the buffer layer may be controlled by use of a strain control buffer layer and by appropriate choices of material and composition for the buffer layer and for a substrate on which the buffer layer is grown.

Abstract: A semiconductor device comprises an active layer above a first confinement layer. The active layer comprises a layer of ?-Sn less than 20 nm thick. The first confinement layer is formed of material with a wider band gap than ?-Sn, wherein the band gap offset between ?-Sn and this material allows confinement of charge carriers in the active layer so that the active layer acts as a quantum well. A similar second confinement layer may be formed over the active layer. This semiconductor device may be a p-FET. A method of fabricating such a semiconductor device is described.

Abstract: A firewall system employs signature validation hardware communicating via low level communication protocols and with inner and outer host computers, which have network protocol stacks and for implementing complex communication protocols with remote source and destination computers. The source computer has data checker and signature functionalities, which respectively check data and generate digital signatures for data to be transmitted. The inner host computer receives transmitted data and converts it to a lower protocol level at which the hardware operates. The hardware uses digital circuitry for protocols and checking. It validates signatures in data at a software application level, but only requires protocols that are simple and low level. The firewall system communicates with the source and destination computers via high performance connection media.

Abstract: A plurality of sensors output information into a distributed acoustic sensing (DAS) system via acousto-mechanical signals. The sensors are coupled to the optic fibre at the centre of the DAS system indirectly, the acousto-mechanical signal being transmitted via an intermediary body, such as the ground or a conduit.

Abstract: A semiconductor device structure comprises an active layer and a buffer layer. The active layer is a quantum well structure. There is a lattice mismatch between the buffer layer and the active layer which places the active layer under biaxial compressive strain. Uniaxial tensile strain is applied to the active layer to reduce compressive strain on the active layer in a second direction but not in a first direction. This favours hole and electron mobility in the first direction, rendering the semiconductor device structure suitable for the formation of both p-channel and n-channel devices.

Abstract: A low noise axial flow impeller has a multi cellular form of construction comprising a multiplicity of individual axial flow channels disposed in a circumferential and radial array with respect to the axis of rotation. This increases the “blade passing frequency” as compared to a conventional impeller and since higher frequencies have lower energy for a given flow output the total amplitude of the noise generated can be reduced. For high total flow area coupled with low structural weight the channels are arranged in tessellating rings of equal numbers of channels, with channel cross sections based on hexagons (or truncated hexagons in the case of the channels in the innermost and outermost rings).

Abstract: This invention relates to the use of vermiculite and layer minerals in general release films.

Abstract: A method for processing returns from a sensor, such as a radar system, in order to identify targets is provided. The method uses a track before detect routine to integrate data from several scans in order to give better discrimination. In running the track before detect routine however a number of possible target motions are postulated and the data combined accounting for such motions. A result above a threshold may then be indicative to a target present and moving with the postulated velocity. The method gives more accurate target detection as the combined data at the correct target motion postulate is more consistent than transient noise and clutter. Once a target has been identified it is preferably removed from the data set in searching for additional targets.

Abstract: Integration of ionospheric models in over the horizon radars (OTHR) is achieved with very little or substantially no change to existing coordinate registration systems or software by specifying a virtual transponder at a target location and generating a signal which appears to have emanated from a transponder at that location. A return path to said virtual transponder is ray-traced through the ionospheric model to produce propagation parameters; and an appropriately delayed virtual transponder signal is inserted into the receiver. The result produced at the receiver is used to perform coordinate registration for further received signals.

Abstract: A munitions casing including an annulus of a shape memory alloy disposed around said casing where the shape memory alloy has been subjected to a combination of mechanical and thermal treatments so as to impart a memory, and a cutter located between the annulus and the casing wherein heating of the shape memory alloy to a predetermined temperature causes said annulus to contract radially inwardly and rupture the said munitions casing.

Abstract: A fibre optic accelerometer particularly intended for use with an interferometer using the compliant cylinder approach but further providing a seismic mass at the core of the cylinder resulting in improved sensitivity and rejection of out-of-axis inputs.

Abstract: This invention relates to a pattern recognition correlator and method for correlating input data with one or more reference data sets. The input data, which may be for instance digital amplitude modulated optical data, is used to modulate an optical signal to form a phase modulated optical signal. This temporal phase modulated optical signal is then converted into a parallel optical phase signal, preferably through use of an optical delay, and modulated by an optical phase modulator. When there is a correlation between the input data and the reference data the emerging wavefront is plane and can be strongly coupled to a detector. In the absence of correlation the emergent wavefront is not plane and so is not coupled as strongly to the detector. The detector output can therefore be used as an indication of correlation.

Abstract: The present invention relates to a system and method for processing imagery, such as may be derived from a coherent imaging system e.g. a synthetic aperture radar (SAR). The system processes sequences of SAR images of a region taken in at least two different passes and generates Coherent Change Detection (CCD) base images from corresponding images of each pass. A reference image is formed from one or more of the CCD base images images, and an incoherent change detection image formed by comparison between a given CCD base image and the reference image. The technique is able to detect targets from tracks left in soft ground, or from shadow areas caused by vehicles, and so does not rely on a reflection directly from the target itself. The technique may be implemented on data recorded in real time, or may be done in post-processing on a suitable computer system.

Abstract: Methods for coded aperture imaging, and processing the data from coded aperture imaging are taught. Several snapshots of an image are acquired, each using a different coded aperture array. The several snapshots are combined together with appropriate weightings to form a single equivalent frame as are the aperture functions for the coded aperture arrays used. Combining several frames of data can improve the signal to noise ratio of the decode image and increase the resolution of the image. Preferably a balanced weighting system is used and image reconstruction is performed by inverting the covariance matrix formed by the covariance of the signals from a number of estimated trial points. Using a balanced weighting system reduces the covariance matrix to a diagonal or near diagonal matrix with a corresponding reduction in computational load. The techniques also reduces additive noise.