EP1410502A1

EP1410502A1 - Converter for surface waves with improved suppression of interfering excitation

Info

Publication number: EP1410502A1
Application number: EP02729899A
Authority: EP
Inventors: Werner Ruile; Thomas Bauer; Michael Jakob; Ulrike RÖSLER
Original assignee: Epcos AG
Current assignee: SnapTrack Inc
Priority date: 2001-07-24
Filing date: 2002-05-21
Publication date: 2004-04-21
Also published as: US20040247153A1; DE10135871A1; JP4284175B2; DE10135871B4; US7170372B2; JP2004537235A; WO2003012987A1

Abstract

An electroacoustic converter (1) for a component operating with surface waves, in particular for a surface wave filter, is disclosed, whereby a variation in the gaps (4), in the gap region, with regard to at least one feature selected from transverse arrangement, size and form is carried out in order to suppress interfering excitation. As a result of the limited dimensional change ( DELTA D) in relation to the finger length the desired main excitation in the converter remains essentially unchanged, the interfering excitations on the other hand are rendered ineffective by shifting or splitting up.

Description

description

Transducer for surface waves with improved suppression of disturbing excitation

A surface acoustic wave component comprises at least one electroacoustic transducer, which is arranged on a crystalline or ceramic piezoelectric substrate or on a piezoelectric thin film. The electroacoustic transducer has a periodic finger structure, the fingers usually being alternately connected to two different collecting electrodes (bus bars). The period of the finger structure determines the resonance frequency of the transducer, which corresponds to the frequency at which the electroacoustic conversion takes place with the greatest efficiency.

In the case of a surface wave resonator, the impedance of the resonator is almost zero at the resonance frequency.

The important properties of the transducer are essentially determined by the number, width, distance and connection sequence of the electrode fingers as well as by the aperture of the transducer. As a rule, these are selected such that, as far as possible, only an acoustic oscillation mode is excited, to which the design is optimized with respect to the aforementioned variable parameters.

One application for surface wave components is the construction of reactance filters from surface wave single gate resonators. An important parameter of these reactance filters is the insertion loss, which corresponds to the maximum attenuation of a signal passing through the filter in the pass band. Anything that increases the insertion loss deteriorates the performance of the overall system, so that even the slightest losses can be avoided.

Resonators used in the parallel branch of reactance filters should have one above their resonance frequency have as small as possible a real part of the input admittance. A real part of the input admittance of the parallel resonator, which is different from Mull there, leads to an undesired conductivity in the passband of the reactance filter and thus to an outflow of signal energy and thus to an increased insertion loss. The input admittance of a single-gate resonator commonly used today now shows a shoulder in precisely this area, which therefore leads to increased insertion loss in a reactance filter. So far, no measures are known for this shoulder, which has already been recognized by others, in order to effectively suppress it.

It is therefore an object of the present invention to provide an electroacoustic transducer for a component working with surface areas, in which this loss mechanism is suppressed, and with the aid of which surface wave filters in particular can be produced which have improved insertion loss.

This object is achieved according to the invention by an electroacoustic transducer with the features of claim 1. Advantageous embodiments of the invention are specified in the subclaims.

The invention is based not least on the fact that the loss mechanism mentioned could be assigned by the inventors. You have recognized that the area of the transverse gaps, ie the area of the finger ends of the transducer fingers, creates a residual conductivity of the transducer. This residual conductivity could be assigned to a disturbing excitation in the area of the transverse gaps, which leads to an additional conductance that lies between the resonance and the center of the stop band. This direct excitation only partially takes part in the reflection process, since with a normal finger transducer there is a gap on every second finger in the gap area and therefore every second finger as a reflection point fails. Nevertheless, the excitation takes place via stray fields, which leads to an excitation in the gap area with an approximate (sin x) / x behavior. This excitation, which manifests itself as a parallel conductance, must be taken into account in the admittance of the main excitation.

The invention now specifies a transducer in which this disturbing excitation in the gap area is modified in such a way that it is either suppressed or shifted to a frequency position at which it does not interfere, e.g. sufficiently removed from the passband, or if there is already sufficient attenuation. For this purpose, a transducer according to the invention is constructed in a conventional manner with regard to the number, width, longitudinal position and connection sequence of the fingers and with regard to its aperture, whereby the essential properties of the transducer, which determine its main vibration mode, are defined. To suppress the disturbing excitation, however, the gaps are subjected to a variation with respect to at least one feature which is selected from the transverse arrangement, size and shape of the gaps. The change in dimension of the gaps or the amount of displacement of the gaps caused by the variation is kept small in comparison to the finger length.

Every variation of the gaps along the transducer leads to a disturbance of the excitation in the area of the gaps, which leads to a shift or damping of the undesired excitation. This makes it possible to remove the unwanted excitation from the disturbing area of the stop band.

A preferred method for suppressing the disturbing excitation is obtained when the gaps are not varied statistically, but periodically or quasi-periodically. This is already achieved when one of the gap features to be varied can be expressed as a one-dimensional quantity, which then varies from gap to gap in such a way that the individual Gap features follow a periodic envelope over the length of the transducer.

According to the invention, it is also possible to combine at least two gaps into a group in the converter and to carry out the periodic variation from group to group. Each group can include the same or a different number of gaps. Each group can have a pattern formed by the total number of gaps belonging to the group, which pattern is defined by the relative transverse arrangement, the size and / or the shape of the gaps within the group. The periodic variation can now take place by changing at least one parameter from group to group. However, it is also possible to provide a pattern which at least largely corresponds in each group, but which varies from group to group with regard to its absolute transverse position in the transducer and, in particular, has a periodic variation over the length of the transducer.

With the invention it is possible to suppress the undesirable excitation or to shift it so far that it no longer occurs in a disruptive manner. The main mode, which determines the essential properties and in particular the passband of the filter, remains practically unchanged. The invention can therefore be used regardless of a given transducer design in all types of transducers which have a plurality of interdigitated electrode fingers. The invention makes use of the fact that the disturbing excitation in the gap area has a (sin x) / x behavior which, like normal excitation, can also be changed and influenced accordingly. In particular, the assignment of at least two gaps to a group and their periodic change across all groups means that the excitation function (in this case, the disturbing excitation in the gap area) is multiplied in the time domain by a function whose period corresponds to the length of a group , For example, If groups are formed into two gaps each and these groups are transversely and alternately offset from one another, the disturbing excitation results in a convolution in the frequency domain, which leads to a splitting of the excitation. The original admittance that is disruptive in the stop band thus becomes two new admittances that are considerably reduced in strength compared to the originally disruptive and are far from the stop band and therefore no longer interfere.

Other periodic variations of gaps or gap groups in the transducer according to the invention lead to a more complex splitting of the original disturbing excitation in the gap area. Regardless of the type of modification, this leads both to a shift and to a reduction in the disturbing excitation or the disturbing conductance of the transducer.

Variables are gap spacing, transverse position and shape of the gap. The variation can affect one, several or all of these features. During transverse position and

Gap distance (size of the gap or transversal distance of the finger ends) can be represented as one-dimensional values, over which any envelope curve can be laid over the length of the transducer as a periodic or aperiodic variation, the shape of the gaps represents only a zero dimension sional size at which the variation is undirected or cannot follow a variation function. Variations on the gap shape alone are preferably carried out so that groups of gaps each having the same shape of the gaps or a pattern of different gap shapes are formed, and that the gap shape or the pattern of the gap shapes varies from group to group. The shape of the gaps is determined by the two-dimensional design of the finger ends, which is rectangular in conventional transducer fingers. Transducers according to the invention can have finger ends of any shape, for example rounded or beveled, or have another shape. Although the invention also includes a variation in the gap spacing, it is preferably designed with a minimal size, since in this way the disruptive excitation that arises only through the gaps can be further suppressed.

According to a further embodiment of the invention, finger sections that are not galvanically connected to the other electrode fingers or to the busbars are provided in the gap area.

Another easy way to vary is to simultaneously vary the transverse gap position and gap distance. Such a variation is obtained if the finger ends of the transducer fingers and the associated stub fingers of the opposite busbar are viewed independently of one another and, viewed over the length of the transducer, are varied independently according to a function in the transverse arrangement. The variation of the transverse position of the electrode finger ends and stub finger ends can take place independently, but preferably with the same period.

A possible embodiment of the invention also relates to transducers in which the gaps are not between each

Butt finger end and the corresponding electrode finger end are formed, but between the electrode finger end and the corresponding adjacent bus bar. In this case, the position of the electrode finger ends can be varied via the transducer to vary the gap size. The variation of the transverse gap position in transducers according to the invention without a stub finger is also achieved by varying the width of the busbar. The edge of the busbar pointing towards the end of the finger can follow the position of the end of the finger, so that the area of a short electrode finger of the busbar is of the same degree wider and there is a constant gap distance. Different gap distances are also ne variation of the gap shape possible with such transducers without stub fingers.

Transducers according to the invention can have a variation in the gap area on only one side of the converter, that is to say in the area of only one busbar, but preferably on both sides. The variation is preferably carried out in the same way on both sides. In the case of strongly different transducer environments on different sides, however, it can also be advantageous to design the variation of the gaps on both sides accordingly differently.

In a further embodiment of the invention, the gaps are combined into groups, each of which in turn comprise at least two subgroups. Each subgroup has a subgroup pattern formed from the size and / or shape of the gaps and / or from the relative transverse position of the gaps within the subgroup. At least two different subgroup patterns are provided in each group, which occur alternately at least once per group. In addition, each subgroup pattern can also have a periodic variation with respect to at least one feature. In this way, it is possible to modulate the excitation in the gap area with at least two different functions that have different periods. This leads to a multiple splitting of the interfering admittance and thus to a further improved suppression of the interfering signal in the excitation behavior of the converter according to the invention.

Periodic variations within a subgroup or within a group with regard to the transverse arrangement and / or size of the gaps can be carried out sinusoidally, triangularly, sawtoothedly, semicircularly or following other periodic functions. The variation can also be linear or comprise a combination of several linear variations. For example, the variation in the absolute transverse position of the gaps in the Transducer or be linear with respect to the relative transverse position of the gaps within a group or subgroup. A periodic variation can also include, for example, a combination of linearly increasing and linearly decreasing gap positions. In the same way, such a variation can of course also affect the gap size, ie the distance from the electrode finger ends to the stub finger ends.

The linear variations or combinations of linear variations of at least one feature of the gaps can also be combined with other variations, for example the sinusoidal or semicircular variations. With a variation in the gap distance, the shape of the finger ends and thus also the shape of the gaps can follow the envelope curve for the gap distances plotted along the transducer length.

As already mentioned, the properties of the converter remain essentially unchanged due to the variations in the gap area. This is achieved by keeping all dimensional changes in the variation of the gaps relatively small compared to the transducer finger length. A completely sufficient effect is achieved if the dimensional change in the variation of the gaps is twice the finger width of a transducer finger. This means that the variation is far below the variations used to weight the converter and thus to shape the transfer function of the converter. On the contrary, with the invention, the admittance of the transducer should remain unchanged and only be reduced by the disturbing excitation, which has nothing to do with the desired excitation. Completely without interaction with the

The excitation function remains a variation of the gaps, which is only obtained by varying the stub fingers. The overlap length of the transducer fingers can be kept unchanged and in particular constant over the transducer length. However, it is also possible to combine the variation in the gaps with a normal phase or omission weighting. Likewise, the variation according to the invention in the gap area is not limited to normal finger transducers. It is also possible to vary reflection-free split finger transducers according to the invention. Periodic variations have a period of four gaps because of the doubling of the number of fingers compared to a normal finger converter. A minimum period of two wavelengths for periodic variations is thus achieved, which then leads to a folding of the disruptive excitation function in the gap area, as already explained above.

Likewise, transducers according to the invention can be designed as recursive transducers whose reflectivity is set such that the transducer has a preferred direction of wave propagation. In the case of transducers which preferably allow wave propagation in only one direction, one speaks of SPUDT transducers which are also designed according to the invention in such a way that they have a variation in the gap area. Since recursive transducers are characterized by different widths of the electrode fingers and / or spacings of the electrode fingers, uniform variations of the gaps with respect to at least one gap feature are not possible with directional transducers. In the case of recursive transducers, however, it is possible in a simple manner to divide the gaps into groups, each of which can be assigned a specific group pattern, which can be varied according to the invention in terms of type or transverse position over the transducer length.

Also with converters due to the beam steering effect

(Energy propagation direction of the surface wave is not vertical to the electrode fingers), the invention is applicable, since a variation of the gaps is also possible here.

A transducer according to the invention finds a preferred application in a surface acoustic wave filter, for example is designed as a resonator filter. For example, the invention can be used in longitudinal dual mode resonator filters, so-called DMS filters. However, it is also possible to design the interdigital transducers of single-gate resonators according to the invention and to use the latter in a reactance filter. It is already advantageous if only one filter has a resonator with a transducer according to the invention within a reactance filter comprising several single-gate resonators. One-port resonators with transducers according to the invention are preferably used in the serial branch of reactance filters, since the additional conductance of known filters, which is switched off with the invention, has a particularly disruptive effect there.

A transducer according to the invention can be formed on a piezoelectric film, which in turn is applied to a substrate. Such a film can be produced in thin film processes. However, a converter according to the invention is preferably formed on single-crystalline substrates, for example on the known materials quartz, lithium niobate, lithium tantalate or langasite. In addition to these customary substrates, the invention can, however, also be used on all other piezoelectric substrates in which surface areas can be produced and spread.

A transducer according to the invention can have a metallization made of a uniform material, in particular aluminum and its alloys. However, it is also possible to construct the converter from several layers, at least some of the individual layers being aluminum, at least

Main component has. The remaining layers can be made of Cu, Mg, Ti, Zr, Sc or other metals. In this way, the converter becomes more stable if an electrical signal with high power is coupled in and converted into a surface wave. Transducers according to the invention are not restricted to uniform finger periods. Transducers according to the invention can therefore also have increasing or decreasing finger widths and / or finger spacings (= finger period) in the longitudinal direction. Such converters are also called chirped converters. Due to the periodicity changing over the transducer length, such a transducer has an increased bandwidth.

A broadband converter can also be obtained and modified according to the invention if it has finger widths and / or finger spacing that change in the transverse direction. Such types of converters are also referred to as FAN converters. The variation of finger widths and / or finger distances can be linear or hyperbolic, for example. In addition, transducers can have varying finger widths and / or finger spacings when viewed in the transverse direction, this change being irregular.

It is also possible to design the converter as a focusing converter and to modify it according to the invention.

Another transducer according to the invention is constructed as an irregular or non-periodic transducer and is composed, for example, of different cells, each of which differ in terms of finger widths and / or finger spacing. Such an irregular transducer is obtained if the excitation function of the transducer is modulated and all degrees of freedom, including finger distances and finger widths, are used for the modulation.

The invention is explained in more detail below with reference to exemplary embodiments and the associated figures.

Figure 1 shows a section of an inventive

Converter with rectangular variation of the transverse position of the gaps, FIG. 2 shows a transducer according to the invention with a further rectangular variation of the transverse gap position,

FIG. 3 shows a transducer with a sinusoidal variation in the transverse gap position,

FIG. 4 shows a converter with a sawtooth-like variation of the transverse gap position,

FIG. 5 shows differently shaped electrode finger ends,

FIG. 6 shows a converter with a combined linear variation of gap position and gap size.

FIG. 7 specifies several functions for varying one-dimensional gap parameters.

FIG. 8 compares the input admittance of single-gate resonators with transducers according to the invention with the admittance of single-gate resonators with known transducers.

FIG. 9 shows the insertion loss of a filter using single-gate resonators with transducers according to the invention.

Figure 1 shows a simple embodiment of the invention. A section of a normal finger converter 1 is shown in the area of a busbar 3. This converter has two electrode fingers 2 per wavelength. In this embodiment, the transducer is varied with respect to the transverse gap position. The absolute amount ΔD by which the gaps 4 are shifted to a maximum is less than two electrode finger widths, that is, in the case of a normal finger converter, less than a distance which corresponds to half a wavelength at the center frequency. By pairing two adjacent gaps against the two adjacent pairs of gaps the disruptive excitation in the gap area in the time domain is multiplied by a further excitation function that has a period of four SAW wavelengths. This results in a convolution in the frequency range and thus a splitting of the excitation, which then disappears from the stop band range.

As a second exemplary embodiment, FIG. 2 likewise shows a rectangular variation of the transverse gap position in a converter which is shown in sections. The gaps are grouped into groups G1, G2, G3, .... to form four gaps, each offset transversely by a small amplitude. Here too there is a convolution of the original excitation in the frequency range, which in turn leads to a splitting, with the result that the admittance of the interfering excitation disappears from the stop band range.

FIG. 3 shows a further embodiment of the invention, in which the transverse position of the gaps 4 is also varied. The transverse position of the gaps 4 follows a sine function as the transverse coordinate over the length of the transducer. This variation is also periodic and has a period length of around 12 gaps, for example.

FIG. 4 shows a further embodiment of the invention with variation of the transverse gap position. Seen over the length of the transducer, the gaps 4 are combined in groups G1, G2, G3, ..., each group Gn having a uniform pattern. The pattern here consists of the combination of the gap positions of the gaps 4 belonging to the group in the region of the busbar 3 shown. Each group here comprises four gaps corresponding to a period of four wavelengths. Each pattern is identical here and has a linear variation in the transverse gap position in the group. Seen across all groups Gn, this results in a sawtooth-shaped variation in the gap position. In the embodiment according to FIG. 4, all group patterns are identical and with respect to the transverse arrangement at the same height. However, it is also possible to use identical group patterns, but to offset them transversely from group to group. This in turn can be done, for example, with a rectangular function, as is shown for groups of gaps in FIGS. 1 and 2. However, it is also possible to shift the patterns against one another in accordance with any other variation, preferably a periodic variation, with respect to the transverse position.

In the exemplary embodiments described above and the figures belonging to them, the electrode finger ends, which determine the shape of the gaps, are shown as rectangular, so that a rectangular gap shape also results with the same finger ends. However, it is also possible to vary the shape of the finger ends and thus also to change the shape of the gaps. FIG. 5 shows an example of five possible shapes of finger ends, the known rectangular shape being shown in FIG. 5a. FIGS. 5b and 5c show two forms of finger ends in which the finger ends are cut off at an angle. FIG. 5d shows a rounded finger end, while the finger end according to FIG. 5e follows a concave function. According to the invention, however, the finger ends can have any shape.

FIG. 6 shows a transducer according to the invention, in which the gaps, viewed over the length of the transducer, vary with respect to the gap position, the gap size and the gap shape or the shape of the electrode finger ends. A variation in this regard is obtained if the fingers 2a (stub fingers) connected to the lower busbar 3 have a position of their finger ends which, viewed over the length of the transducer, follows a combined linear function. In section a, the length of the stub fingers 2a decreases linearly in the direction x. This naturally shifts the position of the finger ends. In section b, the length of the stub fingers 2a increases again linear. Regardless of this, but preferably with the same period, the position of the ends of the fingers 2b, which are connected to the opposite busbar 5 (only indicated in the figure), changes. The change in the finger end position is also linear here, so that there is a gap distance increasing linearly in the direction X in section a. A linearly decreasing gap distance is realized in section b. In addition, the shape of the finger ends can be varied so that the contour of the finger ends follows the contour of the envelope for all gaps. However, it is also possible to use finger ends of the same or different shapes for these or other embodiments.

FIG. 7 shows a number of exemplary functions, for which gap features such as gap position and gap size which can be expressed as one-dimensional variables can be varied. The rectangular function according to FIG. 7a corresponds to a variation as has already been shown for the variations of the gap position with the aid of FIGS. 1 and 2. However, such a variation can also be applied to the size of the gaps. Likewise, the functions of FIGS. 7b and 7c correspond to possible variations, as has already been implemented in FIGS. 3 and 4 for the variation of the gap position. Further exemplary functions are shown in FIGS. 7d, 7e and 7f.

However, it is also possible to vary a transducer according to the invention simultaneously with respect to two features according to a periodic function, the selected function being able to be different for each of the gap features. For example, while in FIG. 6 the position and spacing of the gaps are varied according to a function 7d, the two gap features can also be varied simultaneously with any other combination of functions. The same period is preferably used for the simultaneous variation of different features. While in the previous exemplary embodiments the variation was only described in the area of one busbar, a converter according to the invention preferably also has the same or a similar variation in the area of the second busbar. If the variation of the gaps in the area of the other conductor rail is carried out with the same function, but with a different period or a different phase or with a completely different function, the disturbing conductance of the upper and lower gaps is carried out differently and thus shifted differently.

The invention can also be used in cascaded one-gate resonators. These include a converter that is divided into sub-converters connected in series. Such a partial transducer comprises at least one electrode finger, but preferably groups of electrode fingers, which are connected to a common, correspondingly long, connecting bus bar that is located transversely in the middle of the transducer. The variation according to the invention can also include the gap size and / or the gap position and / or the shape of the finger ends. Particularly when the gap position varies, the connecting busbar can follow the gap position. The middle busbar arranged between two connected partial transformers can then be designed with different widths or with steps.

A converter according to the invention can be used, for example, in single-gate resonators. FIG. 8 shows the input admittance of a one-gate resonator with an example according to

Figure 1 trained transducer according to the invention. The admittance of the resonator with the transducer according to the invention is shown by curve A, while a transducer which is identical in its other dimensions but not provided with the gap variation according to the invention has an input admittance according to curve B. The entrance admittance of the known resonator shows an interfering conductance at position S, which acts as a hump in the curve. Single-gate resonators with transducers according to the invention show a steeply falling course in this area, which corresponds to an ideal excitation with the desired main mode.

The simplest version (one basic element) of two interconnected single-gate resonators is used in a ladder-type reactance filter. If a one-gate resonator with a transducer according to the invention is used in the transverse branch (= parallel branch) of the reactance filter, an improved transmission behavior of the filter with an improved because of the steeper left flank is obtained. If a one-gate resonator with a transducer according to the invention is used in the longitudinal branch (= serial branch) of the reactance filter, an improved transmission behavior of the filter with improved, because less insertion loss is obtained in a range above the center frequency.

FIG. 9 shows the transmission behavior of such a reactance filter on the basis of the function S ₂ ι- plotted over the wavelength (center frequency). Here, too, curve B corresponds to the transmission behavior of a reactance filter with known single-port resonators, while curve A shows the transmission behavior of a filter that both has a single-gate resonator with a transducer according to the invention in the longitudinal branch and also in the transverse branch. It can be clearly seen that the left flank (see arrow) is designed to be significantly steeper, while the bandwidth of the filter is only insignificantly reduced according to curve A. The lower insertion loss above the center frequency (see arrow on the right) can also be seen. At the same time, the transmission curve A is also flatter and shows a lower one

Insertion loss. This shows that improved filters can be constructed with transducers according to the invention, which are improved in terms of slope and insertion loss. A similar result is obtained if a converter according to the invention is used to construct a strain gauge filter, that is to say a longitudinal dual mode resonator filter (DMS filter). Such a filter then has, for example, three transducers according to the invention, which are arranged between two reflectors.

It is also possible to use transducers according to the invention in transversal modes coupled resonator filters (TMR filter). Such filters have such a high aperture that the acoustic wave can propagate in the form of several transverse modes. Even in such cases, disturbing suggestions occur in the area of the gaps, which can be avoided with the invention.

The invention is also used for identification marks in surface wave technology. These include a converter according to the invention and at least one reflector. An electrical signal applied to the converter is converted into a surface wave, reflected on the reflector and converted back into an electrical signal in the same converter. The signal, which is generally unchanged after the double conversion, is less affected by disturbing excitations with a converter according to the invention or with a delay line with a converter according to the invention.

Since the invention could only be illustrated with the aid of a few selected exemplary embodiments, further variations with regard to the function used for the variation are also conceivable, as well as combinations of variations of several gap features in parallel with one another, which are not shown here.

Claims

claims

1. Electroacoustic transducer for a component working with surface waves, in particular for a surface wave filter, in which the number, width, longitudinal position and connection sequence of the fingers (2) of the transducer (1) and the aperture are specified and essentially the properties of the transducer determine - in which the different gaps (4) have a variation with respect to at least one feature selected from the transverse arrangement, size and shape in order to suppress disturbing excitation occurring in the region of the finger ends, - the dimensional changes or displacements of the gaps caused by the variation (4) are small compared to finger length.

2. Converter according to claim 1, wherein the variation of the gaps (4) takes place periodically.

3. Transducer according to claim 1 or 2, in which at least some of the gaps (4) are combined into groups (Gl, G2, G3, ..) with a predetermined number of at least two gaps each, so that each group extends over a length of at least two wavelengths, each group (Gl, G2, G3, ..) having a pattern with respect to the relative transverse arrangement, size and / or shape of the gaps (4), the patterns in all groups at least largely matching, but are shifted with respect to their absolute transverse position in the transducer, or the patterns each show a group-to-group variation that is periodic across all groups.

4. Converter according to one of claims 1 to 3, in which the periodic variation with respect to the transverse arrangement and / or size of the gaps (4) is sinusoidal.

5. Transducer according to one of claims 1 to 3, in which the periodic variation with respect to the transverse arrangement and / or size of the gaps (4) is triangular.

6. Converter according to one of claims 1 to 3, in which the periodic variation with respect to the transverse arrangement and / or size of the gaps (4) is semicircular.

7. Converter according to one of claims 3 to 6, in which a number of groups (Gl, G2, G3, ...) of gaps (4) are divided into subgroups, each having a subgroup pattern, with at least two within each group Different subgroup patterns occur alternately at least once per group.

8. Transducer according to one of claims 3 to 7, wherein the pattern of the group or the subgroup pattern comprises a linear variation in the direction of wave propagation of the transverse position and / or the size of the gaps (4) or a combination of several linear variations.

9. Transducer according to one of claims 3 to 8, in which per group (Gl, G2, G3, ...) at least two subgroups with the same subgroup pattern with respect to the relative transverse arrangement in the subgroup, as well as with respect to size and / or shape the gaps (4) are provided, the patterns of the subgroups each being arranged transversely offset from one another.

10. Converter according to one of claims 7 to 9, in which at least two subgroups are provided, with only the same gaps (4) occurring within a subgroup with respect to the transverse arrangement, size and / or shape, and wherein the different subgroups differ with respect to at least one feature.

11. andler according to one of claims 1 to 10, wherein the amplitude of the variation of transverse arrangement and size of the gaps (4) does not exceed twice the finger width of the transducer (1).

12. Transducer according to one of claims 1 to 11, in which finger widths, finger spacing and finger connection sequences are designed such that the converter has a directed wave propagation or is designed as a SPUDT converter.

13. Converter according to one of claims 1 to 11, wherein the converter (1) is delimited on both sides by reflectors and is part of a single-gate resonator or a longitudinal dual mode resonator filter - DMS filter.

14. Converter according to one of claims 1 to 13, arranged on a piezoelectric film, which is arranged on a substrate thereof different material.

15. Converter according to one of claims 1 to 13, arranged on a piezoelectric substrate made of quartz,

Lithium niobate, lithium tantalate or langasite.

16. Transducer according to one of claims 1 to 15, which has a uniform structure comprising aluminum or a single layers with aluminum as the main component comprising a multilayer structure.

17. Converter according to one of claims 1 to 16, designed as a split finger converter.

18. Converter according to one of claims 1 to 17, with increasing finger widths and / or finger spacing in the longitudinal direction.

19. Transducer according to one of claims 1 to 17, with increasing finger widths and / or finger spacing in the transverse direction.

20. Converter according to one of claims 1 to 19, designed as a focusing converter.

21. Transducer according to one of claims 1 to 19, with regularly or irregularly changing finger widths and / or finger spacing in the transverse direction.

22. Converter according to one of claims 1 to 17, with irregular finger widths and / or finger spacing in the longitudinal direction.

23. Transducer according to one of claims 1 to 22, wherein the variation in size and / or transverse arrangement of the gaps (4) in the vicinity of the busbars (3, 5) is provided on both sides of the transducer.

24. Converter according to one of claims 23, wherein the gaps (4) in the area opposite one another

Finger ends are varied differently.

25. Converter according to one of claims 1 to 24, in which the variation of the gaps (4) takes place statistically.

26. Converter according to one of claims 1 to 25, designed as a cascaded converter with series-connected partial converters.

27. Reactance filter, made up of SAW one-gate resonators, wherein at least one one-gate resonator has a transducer according to one of claims 1 to 26.

28. Reactance filter, made up of OFW single-gate resonators, which have only single-gate resonators with transducers according to one of claims 1 to 26 in the shunt arm.

29. Reactance filter, made up of OFW single-gate resonators, which have both single-ended resonators with transducers according to one of claims 1 to 26, both in the longitudinal branch and in the transverse branch.

30.Transversal filter with transducers according to one of claims 1 to 26.

3l.DMS filter with transducers according to one of claims 1 to 26.

32.Transversalmoden coupled resonator filter with transducers according to one of claims 1 to 25.

33. Surface wave delay line with a transducer according to one of claims 1 to 25.