Abstract: In imaging apparatus particularly for use in intra-oral dental applications, a solid state imager is continually clocked out during a wait period prior to irradiation from an X-ray source. A signal derived from the CCD is compared with a threshold at to determine the onset of irradiation by the X-ray source which will appear as a rapid change in the signal level. The threshold conditions are varied to follow changes in ambient conditions and particularly temperature changes to allow for increase of dark current with a rise in temperature. This permits the threshold at which the CCD is triggered to begin image acquisition to be set at a relatively low level whilst minimising the risk of false triggering.

Abstract: In an electron beam tube such as a klystron, a vacuum seal comprises a ceramic cylindrical wall on which are brazed metal rings which are welded to flares and fixed to electrodes and of a collector. Ceramic rings and are located between the metal ring and the electrodes. The cylindrical wall includes inner flanges which overlap the inner peripheries of the metal rings hence reducing the likelihood of arcing occurring between them and other parts of the arrangement at different potentials. In other embodiments of the invention, the ceramic rings are extended to shield the inner edges of the metal rings or a separate ceramic tube is positioned within the metal rings to provided shielding.

Abstract: An electron gun arrangement includes an electron gun having a longitudinal axis and including first and second electrodes longitudinally spaced apart for generating an electron beam in a longitudinal direction. A first support member supports the first electrode and includes a first slot arrangement presenting a first pair of surfaces longitudinally spaced apart. A second support member is longitudinally spaced apart from the first support member for supporting the second electrode and includes a second slot arrangement presenting a second pair of surfaces longitudinally spaced apart. The surface of the first pair of surfaces that is closer to the second support member constitutes a first clamping surface and the surface of the second pair of surfaces that is closer to the first support member constitutes a second clamping surface.

Abstract: In an electron beam tube, such as an IOT, ferrite loaded silicone rubber or some other ferrite loaded dielectric material, is carried by a wall of an input cavity. The material absorbs r.f. energy, reducing coupling between different parts of the tube which could otherwise result in undesirable oscillation. Furthermore, its provision on part of the input cavity wall enables easy access to be made for replacement and servicing requirements.

Abstract: An electron beam tube arrangement in an inductive output tetrode. The arrangement comprises a resonant cavity circuit having two cavities, and includes an element for coupling high frequency energy between the two cavities. The coupling element includes a coupling dome projecting into one of the two cavities from a wall thereof. The coupling dome has a base portion which is adapted to be connected to a dome completion member selected from a set comprising at least one dome completion member for adjusting a coupling level between the two cavities.

Abstract: A linear electron beam tube has voltages provided thereto, an electron gun, and an output resonant cavity operatively arranged together. An internal body portion, an external body portion and an insulating portion are provided. The internal body portion, external body portion, and insulating portion at least partially define an annular input resonant cavity. The internal body portion is provided with a high voltage, with respect to the external body portion, and the internal and external body portions are separated by the insulating portion so that the internal and external body portions have no electrically conductive connection therebetween. The internal body portion is in electrical contact with the electron gun. The annular input resonant cavity at least partially defined by the internal and external body portions surrounds the electron gun.

Abstract: An inductive output tetrode includes a cylindrical ceramic envelope within which is located an electron gun including a cathode and grid. An annular resonant input cavity into which a high frequency signal is coupled surrounds the envelope and is located adjacent the electron gun so as to provide a modulating electric field in the cathode-grid region to density modulate the electron beam. The input cavity is connected to two metal cylinders arranged immediately adjacent to the outside of the envelope. Metallic portions located within the envelope are co-extensive with cylinders with the material of the envelope 1 being located between them. These structures act as r.f. chokes to reduce high frequency losses from the input cavity. Tuning of the resonant cavity may be achieved by adjusting a tuning member which is at distance of quarter of a wavelength at the resonant frequency from the cathode-grid region.

Abstract: A magnetron comprises a cathode and an anode, the anode comprising a substantially cylindrical anode block having a plurality of internal resonant cavities. A pair of enclosed channels extend about the block, a coolant inlet being present in one of the channels and a coolant outlet being present in the other of the channels, the channels being connected to each other along their length by one or more connecting passageways dimensioned relative to the channels to provide a restriction so as the enhance coolant flow velocity, in use, through the connecting passageway.

Abstract: A firing arrangement for initiating a secondary explosive includes a switch, a charge storage circuit for storing an electrical charge, a power supply for charging the charge storage circuit, an initiator electrically connected to the charge storage circuit through the switch, for directly initiating the secondary explosive, and a common unit. The common unit is hand held during initiation and houses the initiator and at least one of the switch, the charge storage circuit, and the power supply. The common unit includes a manual activator for causing discharge of the charge storage circuit through the switch and initiator, to directly initiate the secondary explosive.

Abstract: Metal vapor laser apparatus includes a laser tube and a reactor chamber in which is contained metal which may be copper in the form of granules. Neon is introduced via one input port of the chamber and a halogen or halogen donor gas through another input port. A coil surrounds the reactor chamber and provides heating to its interior. The gas passes over the metal to form metal halide at its surface and is vaporized by the heating effects. The buffer gas and metal halide are then transmitted via a conduit into the laser tube where dissociation of the metal halide and subsequent excitation of metal vapor is carried out to produce laser radiation.

Abstract: A charge-coupled device (CCD) having a light-sensitive image section (40) and two readout registers (42, 44), situated at opposite ends of the image section, the device being arranged so that light-induced pockets of charge in the image section may be read out along either of the two registers, the outputs of the two registers being merged (46) to provide one common output for the device.

Abstract: A metal vapor apparatus comprising a laser tube within which laser action occurs during operation of the apparatus, and means for applying a liquid metal coolant to the tube.

Abstract: In a klystron, or other device which uses modulation of an electron beam to produce amplification of an applied high frequency signal, a collector is used to receive electrons of the beam after the amplified signal has been coupled from the device. Any secondary electrons produced by the impact of high energy electrons on the collector surface are prevented from returning back along the klystron by a periodic magnetic field produce by magnets which coaxially surround the collector.

Abstract: An amplifying arrangement employs both density and velocity modulation of an electron beam in order to produce amplification of a high frequency signal. In one embodiment, density modulation is produced at the cathode region, a first carrier signal being applied between a cathode and a modulation grid to produce bunching of electrons. The density modulated electron beam is then velocity modulated at a first resonant cavity. It is preferred that the first carrier signal is twice the frequency of the carrier signal producing the velocity modulation. The arrangement may be such that, at the final resonant cavity, adjacent electron bunches produced by density modulation combine, thus giving a high efficiency amplifying arrangement.

Abstract: An electron beam tube arrangement has an output cavity resonator circuit which includes a first output cavity, a second output cavity being coupled thereto by means of a coupling loop. The coupling loop is located in the first cavity and connected to said second cavity. In one embodiment of the invention, the second cavity also contains a coupling loop which is electrically connected to that in the first output cavity.

Abstract: An output of a magnetron operating in the TM.sub.01 /mode has a ceramic output window which is planar. As ceramic material may have a higher dielectric constant than glass a longer output probe can be used which, combined with the fact that the window is planar, gives good mode purity thus reducing heating and arcing in the window. Ceramic also has a higher melting point than glass which means that cooling of the window is less critical.

Abstract: A magnetron having a rising sun anode includes a slot which is extensive in a plane transverse to the axis and in which a tuning member is located. The tuning member may be moved inwardly and outwardly to control the frequency of the magnetron output radiation, the member being arranged such that it can intercept the anode cavities by a variable amount to change their resonant characteristics.

Abstract: The high voltage power supply of an image intensifier is operated intermittently to minimize the effect on a resulting intensified image of interference produced by the power supply, the input capacitance of the intensifier maintaining the high voltage at an acceptable level when the power supply is not operating. When used in conjunction with a video camera, the power supply may be allowed to operate only during the frame synch and/or line synch periods. A shutter may inhibit operation of the image intensifier while its power supply is operating.

Abstract: A magnetron includes a cathode assembly which comprises a helically wound wire supported by a ceramic cylindrical member. Emissive material is located between adjacent turns of the conductor and connection is provided to the conductor via a rod and tube. When current is passed through the conductor (2), the emissive material (4) is directly heated.

Abstract: The contrast or absolute brightness of a multiplexed LCD is maintained at its preselected value using a feedback arrangement which includes an LCD element functioning as a reference element. The reference element is not used to display information but is continually driven ON and OFF. The average transmissivity of the ON and OFF states is determined and compared with a reference value, the result of the comparison being used to control the voltage levels of the drive waveforms applied to the LCD. By selecting appropriate ratios between the ON and OFF times of the reference element, the LCD can be operated to give optimum contrast, or may have its absolute brightness varied. Control may be effected remotely by reprogramming the microprocessor which determines the timing of the drive waveforms.