Abstract: A conductive polymer PTC device includes upper, lower, and center electrodes, with a first PTC conductive polymer layer between the upper and center electrodes, and a second PTC conductive polymer layer between the center and lower electrodes. Each of the upper and lower electrodes is separated into an isolated portion and a main portion. The isolated portions of the upper and lower electrodes are electrically connected to each other and to the center electrode by an input terminal. Upper and lower output terminals are provided, respectively, on the main portions of the upper and lower electrodes and are electrically connected to each other. The resulting device is, effectively, two PTC devices connected in parallel, thereby providing an increased effective cross-sectional area for the current flow path, and thus a larger hold current, for a given footprint.

Abstract: The method is used to produce a varistor which has a cylindrical resistance body (1) made from a material based on metal oxide, and two electrodes (2, 3) which are each arranged on one of two mutually parallel end faces of the cylindrical resistance body (1). In a first method step, a layer of electrode material is applied to both end faces, as far as their outer boundary (9), which is designed as a sharp edge. In a -second method step, a circular ring (4), which is delimited by the outer boundary (9), runs to as far as the end face of the resistance body (1) and has a width of from approx. 10 to 500 &mgr;m, is removed from the electrode, or the resistance body (1) and electrode are beveled (5′) at the outer boundary. The method allows simple and economic manufacture of a varistor.

Abstract: A chip resistor includes a spaced pair of main top electrodes on an insulating substrate, a resistor layer formed on the insulating substrate to bridge between the main top electrodes, an overcoat layer formed over the resistor layer, and a pair of auxiliary top electrodes formed on the main top electrodes in contact with the overcoat layer. Each of the auxiliary top electrodes contains a glass material in addition to a metal material for integration with the overcoat layer.

Abstract: A piezoresistive pressure sensor (30) has four resistive diffused regions (32) coupled into a bridge configuration (33) with four junctions (36) and four inside corners (40). Each of the diffused regions has a first end connected to one of the four junctions and a second end connected to a different one of the four junctions. There are four contact diffusion terminals (34) disposed in contact with the bridge configuration, and each of the diffusion terminals is disposed at one of the four junctions such that the diffused regions are electrically connected essentially only by the contact diffusion terminals and an overlap (44, 46) is provided between each of the diffusion terminals and the inside corners to accommodate mask misalignment during manufacture. Thus, no tap is required to electrically connect the contact diffusion terminals to the resistive diffused regions of the bridge, which results in increased sensor sensitivity.

Abstract: An improved surface mount resistor and method for making the same includes a body comprised of an elongated strip of electrically resistive material and a resistor terminal formed at each end of the resistive material. The resistive material is machined with a laser beam to create a current path having a desired resistance. The pattern cut is determined by partitioning the resistive material into a plurality of squares forming a current path through the resistive material with the correct resistivity. The resistive material is cut primarily with axial cuts so that the beam strength of the resistive material is maintained.

Abstract: A thick-film resistor and a process for forming the resistor to have accurate dimensions, thereby yielding a precise resistance value. The resistor generally includes an electrically resistive layer and a pair of terminals, a first of which is surrounded by the second terminal, so as to form a region therebetween that surrounds the first terminal and separates the first and second terminals. The terminals are preferably concentric, with the second terminal and the region therebetween being annular-shaped. The resistive layer electrically connects the first and second terminals to complete the resistor. Each of the terminals has a surface that is substantially parallel to an upper and/or lower surface of the resistive layer and contacts the resistive layer. The surfaces of the terminals may be embedded in the resistive layer by printing the resistive material over the terminals, or may contact the upper or lower surface of the resistive layer by locating the terminals above or below the resistive layer.

Abstract: The present invention relates to making sensors by cutting pieces from a boule or ingot of a metal oxide single crystal. The sensors produced are also described.

Abstract: An electrical connection for a ceramic hot surface element in which the ends of the hot surface element are essentially interference fit within a pair of metallic termination sleeves, and electrical connection to the hot surface element is provided by an active metal braze which is directly chemically bonded to the metallic termination.

Abstract: A resistor may be embedded into a substrate. A portion of the resistor may be exposed, by segmenting the substrate, for instance, so that the resistor may be trimmed to a desired resistance level. Alternatively, a portion of a resistor may be embedded into a substrate, with another portion of the resistor being disposed on the outer surface of the substrate. The portion of the resistor on the outer surface may be trimmed to adjust the resistance of the resistor to a desired level.

Abstract: A chip-like network resistor is disclosed which is reduced in variation in resistance of terminal electrodes. A substrate (1) is formed on both ends (3, 5) with a plurality of recesses (7), at each of which a terminal electrode (17) connected to a thick-film electrode (9) is arranged. The terminal electrodes (17) each are constituted of a thin metal film electrode layer (19) and two plated layers (21, 23). The thin metal film electrode layer (19) includes a front surface electrode section (19a) formed on a front surface (1a) of the substrate (1) so as to overlap with the thick-film electrode (9), a side surface electrode section (19b) connected to the front surface electrode section (19a) and arranged so as to entirely cover an inner surface of the recess (7) and a rear surface electrode section (19c) formed on a rear surface (1b) of the substrate (1) and connected to the side surface electrode section (19b).

Abstract: The temperature coefficient of resistance (TCR) of a resistor having a layer of a resistance material on a surface of a substrate and a termination layer of a conductive material at opposite ends of the resistance layer is adjusted by changing the area of at least one of the termination layers. The area of the termination layer is changed by removing a portion of the termination layer. The portion of the termination layer can be removed by making a cut through the termination layer which extends along a line across at least a portion of the termination layer. This method can be used to form matched pairs of resistors by first adjusting the resistance value of at least one of a pair of the resistors at room temperature to provide the resistors with substantially the same resistance values. The TCR of one of the resistors is then adjusted by removing a portion of one of the terminations of the resistor until both resistors have substantially the same TCR.

Abstract: A thin film surface-mount fuse having two material subassemblies. The first subassembly includes a fusible link, its supporting substrate and terminal pads. The second subassembly includes a protective layer which overlies the fusible link so as to provide protection from impacts and oxidation. The protective layer is preferably made of a polymeric material. The most preferred polymeric material is a polyurethane gel or paste. In addition, the most preferred supporting substrate is an FR-4 epoxy or a polyimide.

Abstract: An electrical device comprising a resistive element having a first electrode in electrical contact with the top surface of the resistive element and a second electrode in electrical contact with the bottom surface of the resistive element. An insulating layer is formed on the first and second electrodes. A portion of the insulating layer is removed from the first and second electrodes to form first and second contact points. A conductive layer is formed on the insulating layer and makes electrical contact with the first and second electrodes at the contact points. The conductive layer has portions removed to form first and second end terminations separated by electrically non-conductive gaps. The wrap-around configuration of the device allows for an electrical connection to be made to both electrodes from the same side of the electrical device.

Abstract: A novel current limiting PTC polymer device comprising a conductive polymer composition with electrodes attached thereto characterized by having a low contact resistance and a method of producing the same. The invention provides for the selective treatment of portions of the surface of the conductive polymer composition by at least one of plasma/corona etching and plasma sputtering/plasma spray to create a site for attachment of the electrodes resulting in a low contact resistance. The electrical devices of the invention are particularly useful in circuit protection applications.

Abstract: An electrical device comprising a resistive element having a first electrode in electrical contact with the top surface of the resistive element and a second electrode in electrical contact with the bottom surface of the resistive element. An insulating layer is formed on the first and second electrodes. A portion of the insulating layer is removed from the first and second electrodes to form first and second contact points. A conductive layer is formed on the insulating layer and makes electrical contact with the first and second electrodes at the contact points. The conductive layer has portions removed to form first and second end terminations separated by electrically non-conductive gaps. The wrap-around configuration of the device allows for an electrical connection to be made to both electrodes from the same side of the electrical device.

Abstract: An apparatus for winding a heating wire on a core for forming the inner periphery of an electric melt-bonding joint which comprises a core in a generally cylindrical shape which is capable of rotating around its axial center, the core being relatively moved in the axial direction with respect to a heating wire, an engaging piece mounted on the core, which has a holding portion for holding a heating wire, and a fixing means to fix a terminal pin to the leading end of the heating wire. The engaging piece has a holding portion for holding the terminal pin, whereby the heating wire is wound on an outer peripheral portion of the core by rotating the core.

Abstract: A method for fabricating a thin film resistor comprises applying a tantalum nitride layer over a dielectric layer, applying a metallization layer over the tantalum nitride layer, and patterning the metallization layer with a first portion of the metallization layer situated apart from a second portion of the metallization layer and both the first and second portions being at least partially situated on the tantalum nitride layer. In one embodiment, after patterning the metallization layer, the resistance value between the first and second portions of the metallization layer is determined and compared to a predetermined resistance value, and at least one of the first and second portions is trimmed to obtain a modified resistance value between the first and second portions that is closer to the predetermined resistance value than the determined resistance value.

Abstract: A process for making an integrated terminating resistor on a two-conductor data bus includes making a series of individual resistor elements and assembling the resistor elements in a stack of parallel, spaced array of elements. The elements are soldered together between end portions of the two conductors of the data bus at both ends thereof by inserting the conductors into two diametrically opposed, axially aligned notches in all of the resistor elements and heating solder in the notches to reflow the solder to bond the conductor in the notches. A parallel electrical and mechanicalconnection is thereby established, connecting the elements together electrically and mechanically in a closely spaced array. The array is sealed in a shock absorbing and abrasion resistant enclosure.

Abstract: A dielectric ceramics contains, at least, two kinds of metal ions and a dielectric constant changes continuously or step by step as a function of position. The metal ions contained in the dielectric ceramics are, at least, two kinds which are selected from Mg, Ca, Sr, Ba, Zn, Pb, Bi, Y, La, Ce, Nd, Sm, Gd, Er, Ti, Zr, Sn, Si and Mn, and the dielectric constant .epsilon. changes in the range of 7.ltoreq..epsilon..ltoreq.90. This dielectric ceramics is used in a dielectric substrate for stripline device, a dielectric substrate for monolithic IC and a dielectric block for polarizer. For example, when used as the dielectric substrate for stripline device, it is so formed that a dielectric constant at its center portion is constant, and that those at an outer portion becomes smaller step by step or continuously towards ends.

Abstract: A surface mount resistor is formed by joining three strips of material together in edge to edge relation. The upper and lower strips are formed from copper and the center strip is formed from an electrically resistive material. The resistive material is coated with epoxy, and the upper and lower strips are coated with tin or solder. The strips may be moved in a continuous path and cut, calibrated, and separated for forming a plurality of electrical resistors.

Abstract: A vaporizing device including a heating unit having a pair of electrical connector terminals staked to a substantially rigid substrate having a serpentine resistance type heating element printed thereon and electrically connected to the terminals. An insulating conformal layer coats the heating element, and wicks into the interstices of the region between said electrical terminals and the openings in the substrate receiving the terminals to significantly enhance the structural strength of the device. This provides an inexpensive and yet sturdy and rugged vaporizing device which may be discarded after each use.

Abstract: A method of making an electrical connection of a conductor (1) to a thick film track (2) mounted on a substrate (3) includes the steps of heating the conductor (1) to a temperature at which it may melt the glass constituent of the track (2), and inserting it into the track (2) such that it sinks in and contacts the metallic constituent of the track. The glass sets, fixing the conductor in place. Thus the need for a second firing operation is avoided.

Abstract: When resistor elements, common electrodes and individual electrodes are formed on a substrate, a disconnected portion, i.e., open portion is formed in one of the common electrodes. After the respective resistor elements are trimmed, the disconnected portion of the one common electrode is bridged by a conductor.

Abstract: An ignitor for fuel gas burners formed of a plurality of spaced parallel filaments of SiC coated Carbon (C) high temperature brazed with Chromium Silicide in grooves provided in a refractory base block of Aluminum Oxide and Silicon Oxide. Terminal posts of IVIoSi are embedded in the high temperature braze. Stainless steel lead attachment pads are nickel-chrome brazed to the posts at a lower temperature. Removable notched graphite bridges and graphite hold-down blocks position the filaments during the high temperature brazing.

Abstract: A trimmable resistor which is prepared with additional electrical contacts between the resistor and the substrate. These contacts are usually not connected electrically to the electronic circuit. Moreover, they do not extend across the entire width of the resistor. If the resistor is over trimmed, its resistance can be reduced by wire bonding a selected one of the additional electrical contacts to an end contact of the resistor. Multiple contacts may be placed along the substrate, both on the side of the resistor where trimming is to take place and on an opposite side.

Abstract: PTC (positive temperature coefficient) thermistors of a novel configuration and a method for their manufacture. The PTC thermistors have a PTC element sandwiched between two electrodes for which leads are formed as an extension of each of the two electrodes protruding beyond the edge of the PTC element. Several manufacturing methods avoid undue thermal and physical stress to the PTC composition while providing PTC thermistors having a variety of shapes and configurations.

Abstract: A network-type resistor array in which a plurality of resistors are successively arranged, in which electrode portions of the resistors are respectively separated by angular electrode-separating notches, so as to prevent the short-circuit between the adjacent electrode portions due to the flowing along of molten solder for electrode connection.

Abstract: A printed circuit board includes a wiring pattern formed on an insulating board according to a predetermined electric circuit, and a cover member covering a portion of the wiring pattern used as a contact, the cover member being formed of an electrically conductive and non-solderable material. Due to the presence of the covering member, the wiring pattern portion is not covered with solder when the printed circuit board is subjected to dip soldering to attach various electric components to the printed circuit board. Since the covering member is electrically conductive, the wiring pattern portion can readily be used as a contact when the dip soldering is completed.

Abstract: The invention is a thermistor comprising a thermistor element, a fixed product of a resistive film on an axial surface of the thermistor element and a conductor material on the terminal surfaces of the thermistor element. The fixed resistive film extends to the peripheral edges of the axial surface, thereby influencing conductance from the thermistor element except at its terminal ends.

Abstract: A positive temperature coefficient ("PTC") device body is formed by compression molding of an organic PTC composition consisting of a crystalline polymer with conductive particles dispersed therein. The body is sandwiched between electrodes to which terminals are attached by spot welding or soldering. The PTC device body is aged at normal pressure and at a temperature higher than the peak resistance temperature, that is, the temperature at which its resistance is a maximum, and lower than 250.degree. C. The resistance of the PTC device does not change either before or after exposure to high temperatures, that is, temperatures substantially greater than 250.degree. C., and the PTC characteristics of the device do not decrease despite aging. Therefore PTC devices made according to the present invention can be surface-mounted.

Abstract: For the manufacture of finished, self-stabilizing resistors, i.e. provided with leads, having PTC elements as the active parts, as well as such resistors, particularly on coil windings, such as those of electric motors, the invention provides a method according to which on a metallic carrier strip contact and top surfaces for the PTC elements are punched, a PTC element is placed and fixed to each contact surface, the top surface is bent over the PTC element, the contact and top surfaces are provided with leads and the top and contact surfaces are separated from the remaining carrier strip.

Abstract: A method of making a compact high-voltage, high-power, thick-film screen-printed cylindrical resistor. A V-serpentine pattern is formed and adapted to fit on a cylindrical substrate having a diameter range of about 1/10 inch to about 1/2 inch. Such pattern is caused to have adjacent sections at a small acute angle to each other. Furthermore, the pattern is caused to have gaps at the open ends of the loops that are substantially wider than the gaps at the closed ends of the loops. In addition, the pattern is caused to have a sufficient number of undulations, and sufficient gap size, to achieve a predetermined voltage rating. Thereafter, the height of the pattern is changed to achieve a voltage coefficient substantially corresponding to the desired voltage coefficient. Furthermore, the resistive film material is altered to cause it to have a different resistivity, said latter resistivity being such that the same resistance value is achieved.

Abstract: A thermal print head comprises: a thermally resistant insulating substrate; a glazed glass partially formed on the substrate at one end side thereof; a heating element formed on the glazed glass; a first common electrode formed on the heating element; and a protective film formed on the first electrode; a second common electrode a part of which is formed between the insulating substrate and the glazed glass, the first and second electrodes being connected to each other; wherein the insulating substrate has a chamfer on the one end side where the first and second common electrodes are arranged, the chamfer being formed closely from the glazed glass, a part of the first and second common electrode being arranged on the chamfer.

Abstract: SMD fuses having consistent operating characteristics are fabricated by forming a repeating lithographic fuse element pattern on an insulative substrate, passivating the structure, bonding a protective glass plate over the passivation layer, slicing the assembly so formed, terminating the slices and cutting the slices into individual fuses. Fuses thus manufactured may be of any desired dimensions, including standard and non-standard chip sizes.

Abstract: Filamentary material having a core of elemental carbon covered with a coating of silicon carbide material with a thin outer layer of elemental carbon is heated in air to cause the outer layer to oxidize. The filament is then cut to segments of a desired length, bundled and the ends metallized. A tubular metal connector is crimped over each of the metallized ends of the bundle with a conductive lead extending therefrom. The bundle assembly is then mounted onto a refractory holder.

Abstract: A method for manufacturing a sensor with an attached leadwire (10) fastened to an adaptor block (18) which is attached to a gage shim (24). The sensor is deposited on an insulated layer (28) placed on the gage shim (24) in electrical contact with the electrical leads (16) of the leadwire (10). One or more passivation layers (36) are applied over the upper surface of the entire sensor to provide a complete seal.

Abstract: A variable power resistor includes a heat sink having a front face and a back face with an electrically insulating, thermally conductive ceramic coating bonded directly onto the front face such that the ceramic coating is in direct thermal contact with the heat sink. A plurality of discrete thick film conductive circuit pads are positioned on the electrically insulating, thermally conductive ceramic coating and a thick film resistive layer is positioned over portions of the conductive circuit pads such that the pads are electrically connected in series. The variable power resistor also includes a moveable contactor capable of contacting the circuit pads in order to vary the resistance of the resistor and an electrical connection between the resistor and an electrical circuit. The electrically insulating, thermally conductive ceramic coating may be plasma sprayed onto the heat sink, while the resistive circuit may be screen printed onto the ceramic coating.

Abstract: An extended resistance temperature sensor formed of a plurality of lengths of pre-insulated resistance temperature detector (RTD) wire. The RTD wire is either unheated, self heated or is heated by means of strands of heater wire integrated with or placed closely adjacent to the RTD wire. The RTD wire itself, or together with the heater wire, is bonded together in one embodiment. Alternatively, the RTD wire, or with the heater wire, may be encased in insulated shrink tubing, thin wall metal tubing or both. Connectors are provided to supply electrical current for heating purposes or to connect the RTD wire to detection circuitry, or both. Protective sheaths are provided over the connectors.

Abstract: A temperature sensor and fabrication technique for making the sensor. An insulating substrate supporting a conductive resistive pattern is laser trimmed until the pattern has a desired resistance. Back and forth movement of the laser is controlled at an automated laser trimming station. The laser trimmer compares the sensed resistance of the conductive resistance pattern with a sensor pattern that has already been precisely trimmed to a desired resistance and is used as a standard.

Abstract: A thermal print head is provided having a substrate with an arcuate edge ground to a selected radius upon which a layer of glaze is deposited and precision ground. Resistive film is patterned onto the glaze and conductive film is applied in electrical connection therewith.

Abstract: An inductor for noise reduction characterized in that wire is wound around a core member formed of a magnetic substance and the magnetic substance is composed of a material having insulation resistance of 0.5 to 5 kilo-ohms.

Abstract: A substantially rectangular insulating substrate is prepared. Next, pairs of lead electrodes are formed on the substrate such that they extend in parallel with regular intervals and slantwise with reference to the longitudinal direction of the substrate. The electrodes are formed by use of a lithography technology, including deposition and etching. Then, a resistor material is pasted on the substrate and the electrodes by screen printing, to thereby form a strip-shaped resistor extending in the longitudinal direction. Finally, a protective layer is formed on the resultant structure, so as to prevent the resistor and the electrodes from being oxidized or worn away, thereby completing the fabrication of a thermal head. In this thermal head, each of those portions of the strip-shaped resistor which are defined by a pair of adjacent lead electrodes serves as a parallelogrammatic heating resistor used for recording one pixel.

Abstract: A flexible elongated resistance heating element of improved uniformity and ease of termination has a continuous strip of resistance wire formed about a flexible elongated strand of insulating material in a generally helical pattern of nonuniform pitch with regions of increased pitch and correspondingly reduced turns density which regions experience little increase in temperature when the element is energized. The pitch of the helical resistance wire pattern varies as it approaches each of the ends of the element to provide a region of increased pitch followed by a region of decreased pitch at each end. Shorting wires may thereby be eliminated. An insulating coating surrounds the resistance wire and strand and electrical terminals are connected by crimping to the regions of decreased pitch of the resistance wire at the ends. The heating element may be bonded to a support member in a serpentine pattern with the cool end regions extending freely from the support member.

Abstract: A rotary digital contacting encoder (FIG. 1) including a base (5), comprising--a base epoxy disk (501) with three external, pre-molded in place, connector pins (P.sub.1 -P.sub.3) on its exterior side extending through it, and a conductive layer in the form of two concentric layer rings (502 & 503; FIG. 4); and--an encoder element made of a "Kapton" insulating substrate (510) carrying two, like concentric cog rings (511A & 511B; FIGS. 3 & 7) on its top side. Conductive vias (512 & 513) electrically interconnect each respective cog ring with its respective conductive layer ring and its respective external connector pin, the vias forming conductive paths through the insulating substrate between the conductive layer and the cog rings. The presence of the conductive layer 502/503, which can be screen printed on the base disk, greatly simplifies the relative alignment of the encoder element, conductor pads and terminals.

Abstract: A method of making a thermistor comprising the steps of making a layer of thermistor ceramic material comprised substantially of Mn.sub.2 O.sub.3, NiO, Co.sub.3 O.sub.4, Al.sub.2 O.sub.3, CuO, or Fe.sub.2 O.sub.3, having upper and lower surfaces. A first dielectric material comprised of low K Al.sub.2 O.sub.3 or the like is placed on the upper and lower surfaces of the layer, and then is cut into a plurality of elongated strips. The layer is created by blading a slurrey of the ceramic material to create a plurality of uncured sheets; placing the sheets in superimposed position, and then making the monolithic layers from the sheets by applying heat and pressure thereto, and then firing the monolithic layer with heat of increased magnitude. The strips are encapsulated in an envelope of the dielectric material, and terminal connections comprised of silver, Ni, Sn and Pb are imposed thereon. A thermistor chip or strip comprising an elongated ceramic thermistor body with an outside surface and opposite ends.

Abstract: A multipurpose electrical shunt, formed from an integral body of material, includes a first and second electrical connectors spaced apart for mating with a first terminal of a main circuit breaker and a first terminal of a branch circuit breaker. The shunt further includes an electrically resistive material integrally connected to the first and second electrical connectors for providing a voltage drop thereacross proportional to the current flowing therethrough and first and second output terminals extending beyond the resistive material for connection to a current sensing means such as an electrical meter. The shunt provides a current carrying conductor connecting a main circuit breaker to the branch circuit breaker and further provides sensing of the current flow between the main circuit breaker and the branch circuit breaker.

Abstract: A surface mount wirewound resistor having a conventional wirewound resistor embedded in a plastic body member with terminal axial leads of the resistor being severed at the opposite ends of the body member. A U-shaped metallic terminal pad and clip is secured to the ends of the body member and is in electrical contact with the severed ends of the axial leads. The upper and lower portions of the terminal pad are in coplanar relationship with the upper and lower surfaces of the body member. An alternate surface mount wirewound resistor has metallic tabs that extend from the resistance element embedded in the plastic body member, with the tabs being bent upwardly from the ends thereof and into coplanar relationship with the upper surface of the body member.

Abstract: A thick film resistor type printed circuit board including an insulating substrate, a plurality of pairs of terminal electrode layers made of silver and formed on the insulating substrate, a plurality of resistor layers formed on the terminal electrode layers so as to connect the pairs of the terminal electrode layers, respectively, a plurality of wiring conductive layers made of copper and connected to predetermined ones of the terminal electrode layers so as to coat the predetermined ones of the terminal electrode layers and a protective layer for covering at least a portion of the insulating substrate, in which portion the terminal electrode layers and the resistor layers are formed.

Abstract: An improved connector pad stack structure for use in microstructure devices having a silicon nitride surface in which the sensor metal such as platinum or Ni-Fe is eliminated from the pad bonding site and only adhesion promoting metals are used on the Si.sub.3 N.sub.4 to provide a stronger, more durable and reliable pad stack.

Abstract: A double molded over method of manufacturing a lightning arrester in which a central core 1 is made of zinc oxide in a first step, then two metal end fittings 5, 6 are molded onto the end faces and over the side thereof, and finally a coating of elastomer material 7 is molded around the side wall of the central core and over side portions of the end fittings. The core may be formed of a plurality of smaller section bars of zinc oxide regularly disposed about a longitudinal axis with the end fittings molded onto the end faces and about the sides of the end bars whose end faces are partially metallized. In a further variant, a stack of zinc oxide based pellets having the same cross-sectional area as the core in the first example, with the stack having the same overall length as the core if stiffened by thermal compression with fusible metal inserted between pairs of pellets. The stack assembly is then compressed mechanically in conjunction with heat treatment to effect very good mechanical bonding.