RU1818680C - High-frequency transducer of surface acoustic waves - Google Patents

Abstract

The invention relates to electronics. The purpose of the invention is to increase the reproducibility of the amplitude-frequency characteristic of a high-frequency conversion 4r2V5. tp f U0 / 2 of the surface acoustic wave (SAW) companion when expanding the operating frequency range. In each three-electrode section 4, the passive sections 6 of the electrodes are made of three parallel segments 7, the longitudinal axes of which coincide with the longitudinal axes of the corresponding active sections 5 of the electrodes. The width of sections 5 and 6, the distance between the longitudinal axes of adjacent electrodes in each section 4, the spatial placement period of sections 4 is selected depending on the length of the surfactant. This provides a high efficiency of excitation of the surfactant, operation of the transducer at frequencies higher than the frequencies of acoustic synchronism of sections 4 and compensation of the surfactant reflected from the edges of sections 5 and 6 of the electrodes. 4 ill. ё 00 00 O 00 about a / g /

Description

The invention relates to the field of electronics and can be used in devices for the frequency selection of signals on surface acoustic waves

The purpose of the invention is to increase the reproducibility of the frequency response while expanding the operating frequency range.

This goal is achieved by the fact that in the proposed high-frequency transducer surfactant containing a piezoelectric sound duct, on the working edge of which is placed a periodic sequence of three-electrode sections with alternating polarity of the active sections of the electrodes in each section, the first and second summing buses combining the passive sections of the electrodes of one pol -. In accordance with the invention, in each section, the passive sections of the electrodes are made of three parallel segments, the longitudinal axes of which coincide with the longitudinal axes of the corresponding active sections of the electrodes, the width of the active and passive sections of the electrodes selected from the expression

b To / 3, (t) b - width of active and passive sections of electrodes, m;

To - PAZ length at the average frequency of the converter, m,

the distance between the longitudinal axes of adjacent antiphase electrodes in each section is selected from the expression

Lc 2- Do / 3- Ds / 2, (2) where C is the distance between the longitudinal axes of adjacent electrodes, m;

1 s is the length of the surfactant at the frequency of the acoustic synchronism of the sections, m, and the spatial period of the sections is selected from the expression

Lp n-V2, (3) p - 4, 5.6 ... is the number of the working harmonic.

In FIG. 1 and 2 show the process of forming the frequency response of the converter; in FIG. 3 and 4, respectively, are a diagram of the occurrence of reflected SAWs and a vector diagram of their compensation.

The SAW high-frequency transducer contains a piezoelectric sound guide 1, first 1 and second 3 antiphase summing buses, sections 4 of interdigital electrodes (HSE), alternating polarities with active 5th passive b sections, the latter from sections 7.

The surfactant converter operates as follows. When applying electric

of the signal, each section of antiphase electrodes 4 excites surfactants propagating to the left and right along the surface of the piezoelectric sound duct 1 (Fig. 1).

Each electrode in section 4 can be considered as an elementary source of a surfactant, the amplitude of which is proportional to the mutual overlap of the active sections 5 of the adjacent electrodes connected to the summing buses 2 and 3. The spectral function of the elementary source (or the acoustic frequency response of the electrode) is described, for example, for a modified model d. sources

Ael (t) 2 | Dsoz (D-1), (4)

where D f / fc is the relative frequency;

fc is the frequency of the acoustic HSE in the section.

Since the distances between the centers of neighboring HSEs in section 4 are chosen the same from expression (2), i.e., Ts 2 Lo / 3

 Ac / 2, then the condition of acoustic synchronism will be satisfied at the frequency fc - K / 2C - 2 / 3fo,

where fo is the average frequency of the converter, V is the speed of the surfactant, and the phases of neighboring elementary sources will differ by l.

in turn, each section 4 is an IDT containing N - 1.5 electrode pairs and having a linear phase. In accordance with the properties of this kind of IDT with the same overlap

electrodes of the frequency response section will

/Mn-M.fN-OAAf.f.T.-SEgl l

COS (rf-Tc) / 2J (5)

-stnfaAV8 1

) cos (l / 2-A)

where Tc w- is the sampling period for them & YC,

pulse characteristic section 4.

Since sections 4 form a periodic sequence with a spatial period Ql, n, 5, 6, 7 .... and the mutual overlap of the electrodes and the polarity of sections 4 are determined by the algebraic values of the weight coefficients corresponding to the given frequency response of the 5 frequency converter, at the frequency of each anharmonic satisfying condition (3), frequency responses appear, and the frequency response of the converter, for example, with constant overlapping of the electrodes inside a separate section, is described by the equation:

A (t) Ael (t) Ac (f) i hk -e ik TP L, (b)

k 1.

where k 1.2.3 ...;

k is the current section number;

hk is the weight coefficient of the section; Tr Lp / U is the sampling period of the impulse response of the converter;

Lp is the spatial placement period of sections 4;

L 2 p (f to) - frequency detuning.

The frequency response of the converter is shown in FIG. 2.

The mid frequency fo converter can be selected to match any of the anharmonics. At the same time, converters operating on the anharmonics of p 1,2.3 are not physically implemented, since the adjacent HSE sections merge. However, from the viewpoint of the efficiency of excitation of surfactants, and therefore, from the point of view of ensuring minimum losses when operating at high frequencies, it is preferable to work on the anharmonic of step 5. i.e., at fo t2. In this case, the SAW excitation efficiency is 20–25% higher than the prototype device (L 3. fo fl) and 30–35% higher than the third anharmonic (n 6, fo t). Since the frequencies of non-working anharmonics fa, fa lag far enough from the average frequency fo f2i, it is not difficult to feed these parasitic anharmonics using the second IDT in the device or using matching circuits.

Thus, the choice of the widths of the electrodes, the distances between the electrodes and the distances between the sections, respectively, from relations (1-3) allows us to ensure the operation of the transducer at frequencies higher than the frequencies of the acoustic synchronism of sections 4 with high accuracy of reproduction of a given frequency response.

The choice of the widths of the active 5 and passive 6 sections of the electrodes, their placement on the same longitudinal axis and the choice of the distance between their longitudinal axes from the ratio LC 2 To / 3 allows the compensation of surfactants, not only reflected from the same edges of the active sections of the electrodes, as takes place in the prototype, but also from the edges of the passive sections of the electrodes (Fig. 3), which improves the reproduction of the frequency response.

Indeed, in the converter between surfactants reflected from the same edges of both active 5 and passive sections of electrodes inside the section, the phase shift is 240 ° and, therefore, the total amplitude of the surfactant reflected from

separate section 4, is equal to zero at the average frequency fo h (see Fig. 3, 4).

At frequencies near f2, only

partial compensation of reflected surfactants. However, taking into account that the average frequency fa is significantly (25%) higher than the frequency of acoustic synchronism fc of the HSE, at which maximum reflection is observed,

0 it can be assumed that due to reflections of distortions, the frequency response of the converter in the passband is negligible.

In addition, the implementation of passive 5 sections of electrodes in the form of three segments

5 with a width of Up to / 3 each and the placement of these segments on the same longitudinal axis with the active sections of the 6 electrodes makes it possible to ensure uniform metallization along the aperture and thereby reduce the distortion of the frequency response due to the non-uniformity of the surfactant phase front,

Thus, the use of the proposed Converter allows you to. To achieve the objective of the invention, 5 increase the phase response performance while expanding the operating frequency range.

In order to form a given frequency response in the proposed converter, various methods of weighing both electrodes in sections and sections can be used by changing: overlapping active and passive sections, selective removal of sections, etc.

As an example of use, a SAW bandpass filter was manufactured, containing a sound duct made of quartz ST-cut with a size of 15 x 6 x 1 mm, on the working surface of which there were two sectioned surfactant converters of the proposed design. One of the transducers was made with amplitude apodization of the sections (with weighing of the overlap) of the electrodes), the second with weighing by removing the electrodes. The number of sections in the transducers is 109 and 76, respectively. The section period was 11.8 microns. the width of the electrodes and gaps of 1.6 μm, the aperture of 0.55 mm.

The filter parameters are as follows: 5 average frequency 666.5 M Hz, corresponding to n 5 ;,

2 dB bandwidth - 2.5 MHz;

attenuation in the boom band of more than 40 dB;

frequency response unevenness in the passband of 0.3 dB;

insertion loss of 17 dB when matched by series inductors with RH - Rr 50 Ohms.

Claims (1)

The claims A high-frequency transducer of surface acoustic waves (SAW), containing a piezoelectric sound guide, on the working edge of which there is a periodic sequence of three-electrode sections with alternating polarity of the active sections of the electrodes in each section, the first and second summing buses combining the sections of electrodes of the same polarity, which is different the fact that, in order to increase the reproducibility of the amplitude-frequency characteristics while expanding the working frequency range, in each section passive stki electrodes are made of three parallel segments. 0 the longitudinal axes of which coincide with the longitudinal axes of the corresponding active sections of the electrodes, the width of the active and passive sections of the electrodes selected from the expression b Lo / 3, where b is the width of the active and passive sections of the electrodes, m; The surfactant length is at the mid-frequency of the transducer, m, the distance between the longitudinal axes of adjacent electrodes in each section is selected from the expression Lc - 2, where C is the distance between the longitudinal axes of adjacent electrodes, m; The dc is the length of the surfactant at the frequency of the acoustic synchronism of the sections selected from the expression Lp - n Up / 2, where n - 4. 5, 6 ... is the number of the working anharmonic. 1 - / Ll (D-frequency acoustic function;. Electrode, 2 - (U (/) -АЧ1 CCMVHK fe accounting fit (f), 3- Яе№. Frequency response section е accounting А-fl У) AFC of converting 5oV. 5- frequency response of the prototype at, ЈP45 / U Fmg. 2 h L tf tig 5 s1 YaRigCh