Electro-acoustic transducer and electro-acoustic component comprising an electro-acoustic transducer

Abstract

An electro-acoustic transducer and an electro-acoustic component including an electro-acoustic transducer are disclosed. In an embodiment the transducer includes a first and a second bus bar, a plurality of electrode fingers and a plurality of two or more sub tracks, wherein each electrode finger is electrically connected to one of the bus bars, wherein each sub track extends along a longitudinal direction, wherein all sub tracks are arranged one next to another in a transversal direction, wherein at least a first of the sub tracks includes segments of the electrode fingers and has an associated sub track with segments of the electrode fingers, wherein the segments of the electrode fingers of the first sub track are shifted by a distance S=/2 along the longitudinal direction relative to the segments of the electrode fingers of the associated sub track, and wherein is an acoustic wavelength.

Claims

1. An electroacoustic transducer comprising: a first bus bar and a second bus bar; a first plurality of electrode fingers and a second plurality of electrode fingers; and a plurality of sub tracks, wherein each of the first plurality of electrode fingers is electrically connected to the first bus bar and each of the second plurality of electrode fingers is electrically connected to the second bus bar, wherein each sub track extends along a longitudinal direction, wherein all sub tracks are arranged one next to another in a transversal direction, wherein at least a first of the sub tracks comprises segments of the first plurality and second plurality of electrode fingers and has an associated sub track with segments of the first plurality and second plurality of electrode fingers, wherein the segments of the first sub track are shifted by a distance S=/2 along the longitudinal direction relative to the segments of the associated sub track, wherein a distance (D) between adjacent sub tracks is 4D6 in the transversal direction, and wherein is an acoustic wavelength.

2. The transducer of claim 1, wherein the first and second bus bars and the first plurality and second plurality of electrode fingers are arranged on a piezoelectric substrate comprising LiTaO.sub.3, LiNbO.sub.3 and/or Quartz.

3. The transducer of claim 1, wherein the first and second bus bars and the first plurality and second plurality of electrode fingers are arranged on a LT42 piezoelectric substrate.

4. The transducer of claim 1, wherein the transducer is configured to utilize a leaky wave mode.

5. The transducer of claim 1, further comprising slanted conductor segments as electrical connections between the segments of adjacent sub tracks.

6. The transducer of claim 1, wherein the transducer comprises 2-10 sub tracks.

7. The transducer of claim 1, wherein each of the plurality of sub tracks has an associated sub track within a shifted distance S=/2 along the longitudinal direction.

8. The transducer of claim 1, wherein the transducer is arranged next to another transducer.

9. The transducer of claim 1, wherein different metallization ratios of the first sub track and an intermediate section between the first sub track and the associated sub track establish a wave guiding structure.

10. An electroacoustic component comprising: two transducers wherein at least one transducer is the transducer of claim 1.

11. The component of claim 10, further comprising two additional transducers, wherein the transducers are arranged in a 22 matrix layout.

12. An electroacoustic component, comprising: a first bus bar and a second bus bar; a first plurality of electrode fingers and a second plurality of electrode fingers; and a plurality of sub tracks, wherein each of the first plurality of electrode fingers is electrically connected to the first bus bar and each of the second plurality of electrode fingers is electrically connected to the second bus bar, wherein each sub track extends along a longitudinal direction, wherein all sub tracks are arranged one next to another in a transversal direction, wherein at least a first of the sub tracks comprises segments of the first plurality and second plurality of electrode fingers and has an associated sub track with segments of the first plurality and second plurality of electrode fingers, wherein the segments of the first sub track are shifted by a distance S=/2 along the longitudinal direction relative to the segments of the associated sub track, wherein is an acoustic wavelength, and wherein acoustic waves configured to leave the first sub track in the longitudinal direction and acoustic waves configured to leave the associated sub track interfere destructively.

13. An electroacoustic transducer comprising: a first bus bar and a second bus bar; a first plurality of electrode fingers and a second plurality of electrode fingers; and a plurality of sub tracks, wherein each of the first plurality of electrode finger is electrically connected to the first bus bar and each of the second plurality of electrode fingers is electrically connected to the second bus bar, wherein each sub track extends along a longitudinal direction, wherein all sub tracks are arranged one next to another in a transversal direction, wherein at least a first of the sub tracks comprises segments of the first plurality and second plurality of electrode fingers and has an associated sub track with segments of the first plurality and second plurality of electrode fingers, wherein the segments of the first sub track are shifted a distance S=/2 along the longitudinal direction relative to the segments of the associated sub track, wherein is an acoustic wavelength, wherein the first and second bus bars and the first plurality and second plurality of electrode fingers are arranged on a LT42 piezoelectric substrate, and wherein the transducer is configured to utilize a leaky wave mode.

14. The transducer of claim 13, where a distance D between adjacent sub tracks is: 4D6 in the transversal direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The working principle of the transducer and non-limiting embodiments are described in the schematic figures.

(2) FIG. 1 illustrates a transducer with N subtracks and the relation of the longitudinal direction X and of the transversal direction Y relative to the orientation of the transducer.

(3) FIG. 2 shows an embodiment with two subtracks.

(4) FIG. 3 shows an embodiment with a virtually infinite number (N=infinity) of subtracks realized by slanted electrode fingers.

(5) FIG. 4 illustrates the concept of a wave guiding structure.

(6) FIG. 5 illustrates the application to an RF-filter with four transducers.

(7) FIG. 6 shows a graph of improvements in the out-of-band rejection obtained by an improved transducer.

(8) FIG. 7 shows a graph of further positive aspects of improved transducers.

(9) FIG. 8 shows a graph of further positive aspects of improved transducers.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(10) FIG. 1 shows a transducer TD comprising two bus bars BB. A plurality of electrode fingers EF is connected in such a way that each electrode finger EF is connected to exactly one of the two bus bars BB. The transducer comprises a plurality of N subtracks. The subtracks are electro-acoustic active regions of the transducer. Each subtrack has segments of electrode fingers perpendicular to the bus bars BB. The segments of the electrode fingers of the corresponding subtracks are electrically connected to respective corresponding segments of adjacent subtracks by slanted conductor structures. Adjacent electrode fingers electrically connected to different bus bars transform RF-signals applied to the bus bars to acoustic waves and vice-versa. The acoustic velocity and the distance between adjacent electrode fingers mainly determine a resonance frequency and an anti-resonance frequency of the transducer. The acoustic waves excited by the electrode fingers propagate along the longitudinal direction X. The subtracks ST, thus, establish stripes extending along the longitudinal direction X and the stripes of adjacent subtracks are arranged one next to another in the transversal direction Y. For at least one of the subtracks, the first subtrack and its associated subtrack the shift S along the longitudinal direction X equals /2. Acoustic waves emitted by the first track, here ST.sub.2, and its associated subtrack, here STN, interfere destructively at a position along the longitudinal direction X where another transducer may be arranged. The number N is mainly not limited. An increase of N and a transition into infinity results in a transducer as shown in FIG. 3.

(11) FIG. 2 shows a transducer TD having two subtracks ST.sub.1 and ST.sub.2. Thus, the total number of subtracks N equals 2. The shift between the two subtracks along the longitudinal direction X equals /2. The distance between the two subtracks along the transversal direction Y is denoted as D.

(12) FIG. 3 shows a transducer TD which is obtained mathematically by a transition N.fwdarw. and which is obtained by arranging slanted electrode fingers which have an angle other than 90 relative to the extension of the bus bars. The shift S along the longitudinal direction X between two finger ends of each finger is preferably .

(13) FIG. 4 shows the concept of building a wave guiding structure by varying the mass loading in different sections of the acoustic track. Here, the number of subtracks is N=2 and the metallization ratio in the region between the two subtracks is chosen relative to the metallization ratio in the two subtracks in such a way that the wave velocity V is increased between the two subtracks along the transversal direction Y. Further, stub fingers can be connected to the respective bus bars to further form the wave guiding structure. The wave velocity may have a maximum value in a gap region, i.e. in the region separating an electrode finger of one polarity from the electrode structure of the respective opposite polarity.

(14) FIG. 5 shows a concept of a layout of a piezoelectric substrate PSU on which transducers according to the above ideas TD are arranged. Each transducer TD comprises a first subtrack ST.sub.1 and a second subtrack ST.sub.2 mainly shifted by a distance of /2 along the longitudinal direction. Positioned next to the two transducers on the right-hand side and at a position along the longitudinal direction are arranged further transducers which may be electrically connected to the transducers on the left-hand side. In any case, the transducers on the right-hand side are acoustically coupled to the transducers on the left-hand side, but due to the split-track nature of the transducers on the left-hand side, the negative influences of the acoustic coupling is vastly decreased.

(15) The piezoelectric substrate PSU may comprise further contact pads for ground connections GND or for signal connections SIG.

(16) Thus, with the present concept, the distances between adjacent transducers can be minimized while the negative effects of acoustic coupling are reduced.

(17) FIG. 6 shows the frequency dependent insertion loss (matrix element S.sub.21) of a duplexer comprising transducers as described above. For comparison, the insertion loss of the conventional duplexer is also shown. Although the improved duplexer has 0.3 dB more insertion loss due to diffraction effects in the pass band spikes in the corresponding rejection band of the conventional duplexer (curve IL1) are reduced or eliminated (curve IL2).

(18) FIG. 6 shows the curves for a band V filter and for a band VIII filter.

(19) Similar improvements are shown in FIG. 7 where curve IL3 shows the insertion loss of a conventional band V filter while curve IL4 shows the insertion loss of an improved band pass filter comprising a transducer with slanted electrode fingers, e.g. with an infinite number of subtracks.

(20) Further, FIG. 8 shows the improvement in a frequency range below a pass band where curve IL5 shows the insertion loss of a conventional band pass filter, whereas curve IL6 shows the insertion loss for an improved band VIII filter with slanted electrode fingers.

(21) The present concept is not restricted to described embodiments or transducers or components shown in the figures. Transducers and/or components comprising further electrode structures such as reflectors, dummy fingers, split finger electrodes, etc. are also comprised.