Abstract: A semiconductor device having a semiconductor substrate or an insulation layer, an integrated circuit on each of the opposite sides, or main surfaces, of the semiconductor substrate or insulation layer, and a path for an ultrasound signal interconnecting the integrated circuits. The path is afforded by an ultrasonic transducer on each of the opposite sides of the semiconductor substrate or insulation layer. A plurality of paths may be provided in the same semiconductor substrate or insulation layer without crosstalk by transmitting ultrasound signals having different frequencies through the respective paths. The paths may be one-way or two-way. The ultrasonic transducers each contain a piezoelectric material; the thickness of the piezoelectric material in the ultrasonic transducer, at least on the receiver side in each path, is such that the resonant frequency of the ultrasonic transducer corresponds to the frequency of the ultrasound signal signal transmitted through the path.

Abstract: An Ultrasonic Catheter Guidance System which overcomes the inadequacies, dangers, and difficulties encountered by previously available medical guiding apparatus is disclosed. The present invention utilizes a novel technique for coupling ultrasonic energy into an optical fiber that can be used within a blood vessel of patient's body. The present invention includes a transducer [44] which is precisely located on a thin slab of piezoelectric material [10] that generates ultrasonic acoustic surface waves [62] that propagate on the surface [13] or within the bulk of the slab [10]. The transducer [44] may be selected from a set of the many novel alternative configurations that are disclosed in the specification and illustrated by the drawings. The operating power and frequency of the present invention can be predetermined by altering the configuration of the transducers [44].

Abstract: A surface acoustic wave device comprises a piezoelectric substrate, a plurality of input transducers, formed on the substrate, for generating surface acoustic waves corresponding to input signals, a plurality of waveguides which are juxtaposed on a region of said substrate where the surface acoustic waves generated by said input transducers overlap each other, and in which signals are generated due to an interaction of the surface acoustic waves, the waveguides generating surface acoustic waves corresponding to the signals due to the interaction, and an output transducer for receiving the surface acoustic waves generated from the waveguides, converting the signals due to the interaction into electrical signals, and extracting the electrical signals, the output transducer being constituted by a plurality of portions, juxtaposed in a widthwise direction of the surface acoustic waves generated from the waveguides, for receiving some components of the surface acoustic waves generated from the waveguides, and outp

Abstract: A surface acoustic wave device includes a substrate having a surface which supports surface acoustic wave propagation and having a pair of interdigitated transducers disposed thereon. Each of the pair of interdigitated transducers has a set conductive members. To improve the ratio of devices having acceptable long-term frequency stability characteristics to those without such acceptable characteristics, the conductive members of the pair of interdigitated transducers have a larger than conventional thickness.

Abstract: An SAW convolver is disclosed, in which a pair of input transducer means disposed at the left and right end portions on a piezoelectric substrate having a velocity dispersion consists of a plurality of pairs of input transducers and the distance between different pairs of input transducers differs from each other so as to compensate the velocity dispersion.

Abstract: A surface acoustic wave (SAW) chirp signal processor having a piezoelectric substrate, an array of input transducers and an array of output transducers. In its chirp compression mode, the device has chirp signals applied in parallel to its input transducers and produces compressed output pulses at its output transducers, corresponding to selected chirp rates. The input transducers are successively offset with respect to a focal point on the array of output transducers, by distances that successively and linearly increase or decrease from transducer to transducer, consistent with the increase or decrease in the wavelength of the chirp signals. The device may also be used in a pulse expansion mode, by inputting a broadband pulse into a selected one of the output transducers. The input transducers then produce a chirp signal having a rate corresponding the selected to output transducer.

Abstract: A SAW device comprises a substrate, input and output interdigital electrodes provided on the substrate alternately to form a row of electrodes, and a pair of open strip reflectors disposed at both ends of the row, the input interdigital electrodes having a first pair number representing the number of pairs of opposing finger electrodes forming the input electrode, the output interdigital electrodes having a second pair number representing the number of pairs of opposing finger electrodes forming the output electrode, wherein the first pair number and second pair number are set different in the adjacent input and output electrodes with a predetermined ratio therebetween, the first pair number is changed in each input electrodes in the row, and the second pair number is changed in each output electrodes in the row.

Abstract: A surface acoustic wave apparatus wherein a reflector for reflecting a surface acoustic wave is provided on both sides of at least one of an input interdigital transducer and an output interdigital transducer, or, on one side of one of the input interdigital transducer and the output interdigital transducer.

Abstract: An acoustic transducer for an acoustic wave device which includes an acoustic wave propagating substrate, the transducer adapted to couple to an electrical load and/or source. The transducer includes at least a pair of comb electrodes formed on the substrate. It includes apparatus for applying an electrical load and/or source across the pair of comb electrodes. The first of the combs has a plurality of electrode fingers. The second comb has at least one electrode finger. The widths of the electrode fingers are the same. Gaps of at least two different widths are disposed between the electrodes.

Abstract: An ACT (acoustic charge transport) filter comprises a plurality of SAW (surface acoustic wave) transducers and an interleaved filter bank coupled on either transversal side of the SAW transducer. Each interleaved filter bank comprises two filters, and the electrodes of the two filters are interleaved. Isolation between the interleaved electrodes is supplied by a meadering ground. The electrodes are apodized to facilitate weighted sampling of the delayed signal. Multiple frequency characteristics may be extracted from a single ACT filter by cascading the SAW transducer/interleaved filter bank combinations. Weighted sampling of the delayed signal may also be accomplished through weighted withdrawal of the ACT filter.

Abstract: Biasing electrodes on a piezoelectric acoustic vibrator alter the sensitivity of the acoustic vibrator and can be used to compensate for external stresses applied to the acoustic vibrator. The biasing electrodes and the circuitry providing electric signals to them are separate from the RF circuitry feeding the RF signal electrodes of the acoustic vibrator. Biasing electrodes can be used on bulk acoustic wave devices or surface acoustic wave devices. The biasing electrodes can be energized by a static D.C. voltage source, or can be used in a dynamic biasing arrangement to provide instantaneous compensation for changing environmental conditions.

Abstract: A surface acoustic electric wave device of the type comprising, over a large face of a planar piezo-electric substrate, a first row of parallel conductive fingers having an individual geometry chosen and distributed according to a chosen distribution arrangement along this row, a second row of parallel conductive fingers having an individual geometry chosen and distributed according to a chosen distribution arrangement along this row, the second row being interspaced from the first so as to allow a propagation of surface acoustic waves between the fingers of the first row and those of the second, which imparts to the device spectral and/or temporal characteristics defined by the acoustic propagation and the frequency selectivity due to the geometry of the fingers.

Abstract: A dispersive surface acoustic wave delay line device consists of a plurality of delay line elements which are disposed parallely so that a propagating path of a delay line element is not co-owned by the other delay line elements, in order to reduce secondary effects caused by electrode fingers.

Abstract: A SAW (surface acoustic wave) device tapped delay line comprises a continuous pattern of bifurcated inter-digital fingers having a constant pitch of .lambda./2 and forming a first IDT (inter-digital transducer), a plurality of second IDTs, substantially identical to one another and arranged with a predetermined pitch P for consecutively receiving a SAW propagated from the first IDT with respective propagation delays, and grounded dummy fingers in regions between adjacent IDTs. The first IDT is apodized in accordance with a Hermitian response to provide it with a pass band centered at a first frequency, and .lambda. is the wavelength of a SAW at a second frequency different from the first frequency and within the pass band. P is an integral multiple of .lambda./2, so that there is a constant finger periodicity throughout the SAW device whereby reflections between the second IDTs are avoided.

Abstract: This invention features a method for encoding surface acousting wave (SAW) delay lines. The method uses a split-electrode transducer as a programmable reflector. When shorted out, it does not reflect surface waves. When open-circuited, it partially reflects incident surface waves. As manufactured by conventional photolithographic methods, each of several such transducers is shorted out by a fusible link. In the as-manufactured state, the array of shorted transducers produces no reflection of surface waves. If a fusible link is destroyed by passage of electric current or other means, the corresponding transducer becomes a partial reflector. The status of these switchable reflectors may be read by exciting a separate launch transducer with a burst of electromagnetic energy containing substantial energy at the basis operating frequency of the SAW transducers or at suitable harmonics.

Abstract: The correlation between a PN code pattern of the synchronization preamble data of an incoming spread spectrum signal and a reference PN code pattern generated on the reception side is detected by using an SAW convolver. The gate length of the SAW convolver is shorter than the preamble data length. However, an apparatus which can obtain the true correlation output by calculating the logical multiplication of the correlation output from the SAW convolver and the validation pulse is constituted.

Abstract: A surface acoustic wave device comprises a piezoelectric substrate and a plurality of electrode fingers which are located on the piezoelectric substrate along the progagation direction of a surface acoustic wave. The electrode fingers are located on the piezoelectric substrate at a pitch of about 1.5.lambda.o/2 (where a symbol .lambda.o indicates a wavelength of a surface acoustic wave with a frequency equivalent to the center frequency of the surface acoustic wave device). The width of each of the electrode fingers is about 1.5.lambda.o/4. The electrode fingers are located on the substrate so as to be electrically independent of an external circuit and each other.Since the width of electrode fingers is about 1.5.lambda.o/4, the surface acoustic wave device can be produced without fine processing techniques.

Abstract: An electrode structure for use with a surface acoustic wave device which has the same velocity as the transducers and the gratings forming the device but no reflections and which can be used to vary structure reflectivity.

Abstract: In a method and apparatus for encoding signals, signals are passed through a body of a material that modifies a characteristic of signals passing therethrough, such as an acousto-electromagnetic. Energy is applied to the body for establishing a standing wave therein, so that the standing wave controls the passage of signals through said body. The energy may be applied by a piezoelectric element. The body or the piezoelectric element may be removable, to form an encoding key.

Abstract: An electrode structure for use with a surface acoustic wave resonator which has the same velocity as the transducers and gratings but no reflections; a second embodiment provides an electrode structure having a velocity equal to the velocity of the transducers and gratings but that has a coefficient of reflectivity that can be predetermined by varying the width of the electrodes in the electrode structure.

Abstract: A SAW device tapped delay line includes an apodized input IDT (inter-digital transducer) and a plurality of substantially identical unapodized output IDTs arranged to receive, after delays which successively increase by an amont T, a SAW propagated from the input IDT. Each output IDT is terminated with a low impedance which is constituted by the low input impedance of a buffer amplifier, to minimize acoustic regeneration by the output IDTs. Grounded dummy fingers with the same metallization ratio as the output IDTs are provided between adjacent output IDTs to provide a constant SAW velocity. The delay line is particularly suited to use in an equalizer of a microwave radio transmission system, in which the delay T is the inverse of the symbol rate of the system. Intermediate frequency automatic time domain equalizer (IF ATDE) arrangements using the SAW device tapped delay line are described.

Abstract: A surface acoustic wave device having interdigitated transducers comprised of an improved metalization system including copper and titanium doped aluminum transducers. A method of producing the interdigitated transducers includes deposition of the metals on a quartz substrate and subsequent heat treatment. The metalization system provides SAW devices having improved long-term frequency stability, particularly when operated at high power levels. The surface acoustic wave device may be incorporated in a feedback loop of an amplifier to form an oscillator circuit.

Abstract: An acoustic charge transport device (ACT) alters the intersection of an associated surface acoustic wave (SAW) electric potential with the static depletion potential and the input contact potential to correct the timing variations inherent in conventional ACT devices. The ACT device incorporates a pair of correcting electrodes secured to the ACT channel on either side of an input electrode. The electrodes vary the depth of the electric potential of the SAW which ensures sampling of the input signals at consistent times.

Abstract: A strip coupled type convolver includes an aluminum nitride (AlN) layer and a semiconductor layer both provided on a single sapphire substrate, and includes many metal strips extending across a surface wave propagating path on a surface of the AlN piezoelectric layer to transmit a potential on the piezoelectric surface to a Schottky diode array provided on the semiconductor surface to cause a nonlinear interaction.

Abstract: A SAW (surface acoustic wave) device includes a substrate having thereon at least one apodized IDT (inter-digital transducer). The axis of the apodization pattern is inclined towards a driven conductive rail of the IDT at the ends of the pattern, whereby the driven end fingers have a low capacitive coupling to a ground plane on which the substrate is supported. The capacitive coupling to the ground plane may also be reduced by supporting the substrate on the ground plane via an insulating support, whereby an air gap or the insulating support decreases the capacitance between the IDT and the ground plane.

Abstract: A SAW resonator includes resonating SAW transducer units formed on a piezoelectric substrate and juxtaposed in a direction of propagation of acoustic waves, and a unidirectionally reflecting SAW transducer unit provided in each end of the juxtaposed resonating SAW transducer units on the substrate. Each resonating SAW transducer unit includes first and second SAW transducers connected in series and/or in parallel with each other.

Abstract: A surface acoustic wave convolver comprises a piezoelectric substrate, a plurality of input transducers formed on the substrate and adapted to respectively generate surface acoustic waves in response to input signals, and a plurality of wave guide paths parallelly provided on the substrate in a superposing area of the surface acoustic wave generated by the input transducers to each generate a convolution signal of the input signals by non-linear interaction of the surface acoustic waves therein. The convolution signals generated in neighboring wave guide paths are mutually different by 180.degree. in phase, and the wave guide paths are adapted to generate surface acoustic waves corresponding to the convolution signals and an output transducer receives the surface acoustic waves generated by the wave guide paths and converts the convolution signals into an output electrical signal.

Abstract: A surface acoustic wave device according to the present invention can be molded surely with resin, leaving a free space over exciting portions and a propagating portion by disposing a recess portion formed over the exciting portions and the propagating portion on a piezoelectric substrate without using any metallic package.

Abstract: A balance-to-unbalance matching network for a surface acoustic wave device is provided in the form of a transmission line wound around a toroidal coil and having a length shorter than 1/4 the wave length at the frequency of induced acoustic waves, to provide an inductance component to cancel the susceptance of the transducer. In one embodiment the lines are would and connected to the magnetically coupled to the core so that magnetic fields are produced in the same direction by means of currents flowing into the line sections.

Abstract: A surface acoustic wave (SAW) device and a related method, for providing improved frequency response characteristics from a SAW spectrum analyzer or channelizer. The device includes a spectrum analyzer with a preprocessing SAW device configured to provide output signals with narrower passbands, lower sidelobe components, or both. The preprocessing SAW device is a tapped delay line in one embodiment, to simulate positional offsets in the placement of input transducers of the analyzer. The tapped delay line can also be used to provide amplitude weighting or can be configured in a chirp spacing, to transform the spectrum analyzer into a chirp analyzer. Another embodiment employs a thinned-electrode prefilter as the preprocessing device, to yield a frequency response with multiple narrow passbands, which are used to narrow the individual channel passbands of the spectrum analyzer or to suppress sidelobes in the frequency response.

Abstract: The invention features a theft resistant security system for motor vehicles. The system has receptacle with a coupling coil. A SAW (surface acoustical wave) device associated with the receptacle for relative movement thereto is also provided. The SAW device has a code and its own coupling coil for interaction with the receptacle coupling coil. A testing mechanism is connected to the receptacle for determining whether the code of the SAW device is valid for operation of the motor vehicle. Problems of crosstalk and wave reflection may produce spurious code pulses in systems of this type. The invention provides techniques for eliminating or reducing these unwanted pulses.

Abstract: A SAW slanted array correlator (SAC) comprises a piezoelectric substrate, input and an output interdigital transducer deposited on the piezoelectric substrate, a reflective array aligned with the transducers, and an acoustic absorbing film disposed on the substrate between the output transducer and the reflective array. The input and output transducer are slanted at equal and opposite appropriate angles to each other. The reflective array is disposed on the substrate at an angle the same as the angle of emplacement of the output transducer. The transducers comprise a number of interdigital electrodes with varying periodicity, the periodicity being the same for corresponding portions of the two transducers. The reflective array comprises a number of shorted electrodes having a periodicity corresponding to the periodicity of the output transducer. The acoustic absorbing film has a non-uniform width with selected portions having little or no width.

Abstract: A surface acoustic wave (SAW) device for converting multiple parallel signals to a smaller number of serial signals. The device includes a piezoelectric substrate and a surface acoustic wave (SAW) input transducer for propagating periodic surface acoustic waves across the substrate. The parallel signals are input to the device through an array of acoustic charge transport (ACT) input transducers, which convert the signals into packets of electrical charge that are transported across the device with the surface acoustic waves generated at the SAW input transducer. An ACT output transducer converts the charge packets back into electrical signals, but in serial rather than parallel form. The converter of the invention can be usefully combined with a SAW channelizer or spectrum analyzer, to provide serial outputs from the analyzer.

Abstract: A surface acoustic wave device characterized in that in addition to linear first bus-bar electrodes which connect in alignment the edges of the same potential electrodes of interdigital electrodes, second bus-bar electrodes are provided which connect the same potential electrodes in the vicinity of the overlapping positions. Also disclosed is a surface acoustic wave device characterized in that the metalized ratio g/p, which is the ratio of the width of an electrode and the intercentral distance between the adjacent electrodes in an irregular pitch electrode group, is varied between 0.1 to 0.4 or between 0.6 to 0.9.

Abstract: A Surface Wave Acoustic (SAW) is constructed with hyperbolically curved electrode fingers. The transducers consist of relatively narrower inner electrode fingers and relatively wider outer electrode fingers, and may also be divided into a plurality of tracks with each of the tracks being subdivided into a plurality of subtransducer elements which are capacitively coupled in electrical series.

Abstract: In a surface acoustic wave elastic convolver capable of showing sufficiently high convolution efficiency with a simple structure, the convolver comprises a piezo-electric substrate, plural input transducers formed on the substrate for respectively generating surface acoustic waves corresponding to input signals, an output transducer for obtaining a convolution signal of the input signals, from a surface acoustic wave generated by non-linear interaction, of the surface acoustic waves generated by those input transducers, and a dielectric film of a non-linear effect larger than that of the substrate, formed on the substrate in at least an area where the output transducer is formed.

Abstract: A surface-acoustic-wave device includes a glassy layer provided on a piezoelectric layer and having periodic grooves (gratings) so as to be used as a reflector exhibiting an excellent reflection ratio.

Abstract: A surface wave acoustic delay line is formed of a set of electrode assemblies disposed on the surface of a block of crystalline material propagative of a surface acoustic wave. In each of the assemblies, the electrodes are arranged in an interdigitated pattern. Reflected waves are cancelled by the construction of an additional electrode in each of an electrode assembly, the additional electrode extending only one-half the distance of the other electrodes and being spaced from an adjacent electrode by one-quarter wavelength. This introduces a 180.degree. phase shift between portions of relected waves which then cancel to remove the reflection. Also, in the case of closely spaced electrode assemblies, additional electrodes, equal in shape and size to the electrodes of the assemblies, are introduced between the assemblies in the form of a grid which propagates surface waves without reflection.

Abstract: The disclosure relates to a microstrip circuit which is used to combine the energy output from the convolving plate of a surface acoustic wave (SAW) monolithic elastic convolver. The convolving plate is tapped at its two ends and a Wilkinson combiner is used to sum the signals that propagate to the ends of the plate. The Wilkinson combiner is a three-port device with the two arms that couple to the convolver plate having their characteristic impedances set to match that of the acoustic waveguide. In view of the impedance match, no electromagnetic reflections are produced at the end of the convolving plate and all of the energy incident on the Wilkinson combiner is summed and delivered to the output port of the combiner. Additionally, the microstrip circuit has an impedance transformer to transform down to an impedance suitable for driving an output amplifier chain of a receiving system.

Abstract: A surface acoustic wave device having a single crystal aluminum nitride film wherein when the direction of propagation of the surface acoustic wave is expressed by (.lambda.,.mu.,.theta.) according to the Euler angle notation, .theta. is set to 90 degrees, .lambda. to a desired angle, and .theta. to an angle in the range of 30 to 150 degrees. In a surface acoustic wave device having a c-axis-oriented aluminum nitride film, the direction of c-axis orientation of the piezoelectric film is inclined within a plane containing the direction of propagation of the surface acoustic wave and perpendicular to the surface of the piezoelectric film at an angle in the range of about .+-.30 degrees to about .+-.150 degrees with respect to a normal to the piezoelectric film. The devices are 1.122% in maximum coupling coefficient.

Abstract: A SAW device includes aligned IDTs (inter-digital transducers) with a continuous pattern of fingers between their front edges. Each IDT may be symmetrical about its center, and includes front and back edge reflection suppressing regions of fingers of successively decreasing length, which serve to suppress surface acoustic wave reflections at the respective edges. Optional shield regions between the two front edge suppressing regions, and between the back edge suppressing regions and acoustic absorbers, include fingers of successively increasing length complementary to and adjacent the fingers of successively decreasing length of the reflection suppressing regions. The IDTs may be apodized or unapodized, and each IDT may include dummy fingers between its active region and each reflection suppressing region.

Abstract: In an acoustic surface wave multimode filter comprising a pair of acoustic surface wave resonators and a bus bar on a piezoelectric substrate with the bus bar shared by the resonators, the bus bar is rendered thicker than the resonators. Preferably, the bus bar should be about twice as thick as the resonators.

Abstract: A SAW dispersive delay device comprises a high-coupling piezoelectric substrate such as lithium niobate, an input and an output metallic transducer deposited on the piezoelectric substrate, and a pair of coextensive metallic reflective arrays deposited on the same substrate and respectively aligned with the transducers. The arrays comprise a number of "shorted" and "open" reflectors which are alternately interleaved. The reflectors are inclined substantially 45.degree. with respect to the aligned tranducer propagation direction. The periodicity of the reflectors varies along the length of each reflective array so that different frequencies are reflected at different locations along each array to thereby provide a different delay path. The periodicity variation is the same in the two arrays. The periodicity of these reflectors varys in a manner consistent with a prescribed dispersion characteristic.

Abstract: In order to present an asymmetric frequency characteristic in an unidirectional acoustic surface wave device with a simple external phase shifter, a transducer formed on a substrate have three interaction areas (acoustic sources) defined by different three electrodes, first electrode being common, second electrode being connected to one end of the phase shifter, third electrode being connected to another end of the phase shifter, and distances between interaction areas being unequal to 2n (n:integer).

Abstract: A delay line with multiple taps is provided in which a hyperbolically tapered input transducer directs a wave to a plurality of hyperbolically tapered partial reflectors. A plurality of hyperbolically tapered output transducer taps are aligned with each of the partial reflectors so that varying delays may be obtained over a wide frequency band.

Abstract: A simple compact, high performance SAW multiplexer is provided by utilizing an input transducer in which hyperbolic tapered electrode fingers are provided. These hyperbolic electrode fingers provide a low frequency output acoustic wave at locations where the spacing between the fingers is relatively large, and a higher frequency signal at points where the spacing is relatively closer. A series of pickup taps which are preferably located on both sides of the input transducer which are also constructed with hyperbolically tapered fingers, but these pickup elements are separated into segments, and isolated by ground straps so that each pickup finger pad will be responsive only to a portion of the frequencies launched by the input transducer. The frequency of the pickup pads varies from a low frequency to a high frequency in alternate manner from one side of the multiplexer to the other.

Abstract: The surface acoustic wave device includes a plurality of output gate electrodes provided between two signal input transducers on a piezoelectric layer on a semiconductor substrate, so that each output gate electrode receives a bias voltage unique to it and supplies an output signal based on the unique bias voltage.

Abstract: A "passive interrogator label system" (PILS) is disclosed with passive, SAW transponders which are capable of receiving an interrogation signal, processing this signal and transmitting a reply signal that is derived from the interrogation signal and contains encoded information. The SAW transducers employed in the transponders are operated at their third harmonic and comprise split fingers which reduce SAW reflections. These transducers are also shaped to increase their bandwidth and to reduce their capacitance. The bus bars connecting the transducers are formed of double thickness to reduce ohmic resistance losses and these bus bars as well as the transponder phase delay pads have two levels of serrations on their edges to substantially cancel reflections. SAW reflectors in the transponder are provided with shorts between successive fingers to reduce ohmic resistance losses and to render them less susceptible to fabrication errors.

Abstract: A single mode waveguide dispersive surface acoustic wave (SAW) delay line is formed by aligning an elongated input transducer, which has a pattern of interdigital electrode fingers which launches a wideband SAW, with a beam compressor that feeds an input waveguide. The input SAW passes down the waveguide to a 3 dB coupler which extracts one-half of the power of the incoming SAW and feeds it in the direction opposite to the input wave. Both portions of the SAW are passed to dispersive reflective arrays along a folded path. A series of additional couplers and reflective dispersive arrays that form the folded path serve to further delay the SAW until it reaches a beam expander at the output end which feeds the SAW to an output transducer that is constructed in a manner similar or analogous to the input transducer.

Abstract: In a directional transducer for SAW filters on a piezoelectric substrate, the transducer is formed of a plurality of groups which are connected in half-groups to busbars for two phases. The half-groups are alternately distributed into two or more channels such that the finger electrodes of each phase form a more or less gap-free series as viewed over all channels. A common, meandering busbar for both phases is associated with each channel.