JPH09130195A - Surface acoustic wave converter and surface acoustic wave reflector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To excite only the desired higher harmonic with high efficiency by dividing each electrode finger into 3 steps, regardless of the order number of the desired higher harmonic to be excited. SOLUTION: Each electrode finger 4 of a sending surface acoustic wave converter 2 is divided into 3 steps 1, 2 and 3. The shift value is defined D1 =2λ0 in the propagation direction of an SAW of step 2 against step 1, and the shift value is defined as D2 =4λ0 /5 in step 3 against step 1. The electrode finger lengths of steps 1, 2 and 3 are referred to as W1 , W2 and W3 , respectively. If the center of step 1 is decided as a reference point, the signals of 5th-order higher harmonics excited in each step are added together in the same phase at the reference point to strengthen with each other. In regard to a basic wave, the amplitudes of SAWs excited in steps 1 to 3 are proportional to the lengths W1 to W3 , respectively. Therefore, the length W1 to W3 can be decided so as to set the sum of signals at zero for the basic wave.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave converter and a surface acoustic wave reflector for the purpose of operating at higher harmonics of a surface acoustic wave (hereinafter referred to as SAW).

[0002]

2. Description of the Related Art Conventionally, as a surface acoustic wave converter for the purpose of operating with this kind of higher harmonics, there is, for example, the one shown in FIG. This device is a step electrode finger transducer (STE
PPED FINGER IDT), and on the piezoelectric substrate 1, a pair of electrode terminals 2, 2 and a plurality of electrode fingers 3, 3, ... In the crossed finger type surface acoustic wave transducer (hereinafter, simply referred to as IDT) in which is formed, when each crossed width of the electrode fingers 3 is W, each electrode finger 3
Is divided into M steps 1, 2, ... Corresponding to the order M of the harmonic to be excited, and the electrode finger length Ws of each step is divided.
To

[0003]

(Equation 3)

In addition to the above, each step is shifted by a length D and connected. The fundamental wave of this IDT is determined by the period of the electrode finger 3 and the propagation velocity of the SAW, and its wavelength is equal to the period λ _{0 of the} electrode finger, and D is the wavelength λ _{0 of} this fundamental wave.

[0005]

(Equation 4) Is set to

FIG. 15 shows, as a specific example, a configuration example using a single electrode finger that excites harmonics of order M = 5. The operation of this configuration will be described below with reference to FIG. 16 using this as an example. Now step 1
When the center of is the reference point, the impulse signal in step 1 is expressed by the following equation.

[0007]

(Equation 5)

Here, A (f ₅ ) represents the SAW excitation amplitude at the frequency f ₅ of the _fifth harmonic. Then step 2
The signal S _{2 at} the reference point of the impulse signal excited at the electrode finger center of is the fifth harmonic wave number k ₅ is k ₅ = 5.2π
/ Lambda ₀ and can be expressed, and because the distance of the electrode finger center and the reference point of the step 2 is x = λ _0/5,

[0009]

(Equation 6)

## EQU1 ## Similarly, the signals S ₃ to S _{5 at} the reference points of the impulse signals in steps 3 to 5 are similarly processed.
Is expressed as follows.

[0011]

(Equation 7)

Therefore, all SAWs from S ₁ to S ₅ are added in phase at the reference point and reinforce each other. Next, considering the case of the fundamental wave, the impulse signal in step 1 is

[0013]

(Equation 8) And for step 2

[0014]

(Equation 9) It is expressed as Similarly, the following is expressed.

[0015]

(Equation 10)

When this is vector-displayed on the complex plane, it can be expressed as shown in FIG. At the reference point at the center of the electrode finger in step 1, as a result of vector-wise addition of these five waves, the amplitude becomes zero as a whole, and the fundamental wave is not excited. Similarly, for harmonic components other than the 5th harmonic, the wave excited from each step is
As a result, they are not all in-phase, so the result is 5
Only the second harmonic will be excited efficiently.

[0017]

However, in such a conventional surface acoustic wave converter intended to operate at higher harmonics, as the order M of the harmonics to be excited becomes larger, The number of vectors required to realize the vector sum = 0, which is the condition required to suppress the fundamental wave shown in 17, also increases. Along with this, the precision required for the shift amount of each step according to the electrode finger length of each step and the order M of the harmonic becomes significantly severer, and a great deal of effort is required to actually realize the vector sum = 0. However, theoretically, for any high-order harmonic, the advantage that it is possible to efficiently excite only the harmonic that you want to excite and suppress other harmonics, including the fundamental wave, is a practical limitation. There was a problem that there was.

Further, there is a problem that the same problem may occur in the surface acoustic wave reflector. The present invention is to solve such conventional problems.

[0019]

That is, the present invention provides
Set each electrode finger to 3 steps regardless of the harmonic order M.
The above problem can be solved by dividing the problem into groups. Immediately
The present invention according to claim 1 provides a pair of electrodes on the piezoelectric substrate.
Electrode terminals and a plurality of finger-shaped extending electrodes intersecting from the pair of electrode terminals
The electrode fingers are formed and the electrode finger period λ₀A wavelength equal to
Elastic table that excites M-order surface acoustic wave of fundamental wave
It is a surface wave converter, and each electrode finger is divided into 3 steps.
Connect each step by shifting in the propagation direction of the surface acoustic wave,
The deviation amount of the second step from the first step is (N₁/
M) ・ λ₀(N ₁Is a natural number greater than or equal to 1 and less than M), the first step
The deviation amount of the third step with respect to_Two/ M) ・ λ
₀(N_TwoIs N₁Other than 1 and a natural number less than M), and
And the electrode finger lengths of the 1st, 2nd, and 3rd steps are W₁,
W_Two, W_ThreeAnd when

[0020]

[Equation 11] (1)

It is characterized in that the values of N ₁ , N ₂ , W ₁ , W ₂ and W ₃ are selected so as to satisfy When the center of the electrode finger in step 1 of steps 1, 2 and 3 divided into three is used as a reference point, the impulse signal in step 1 is expressed by the following equation.

[0022]

(Equation 12)

Where A₁(F_M) Is the electrode finger from step 1
Frequency f of the Mth harmonic corresponding to long W1_MSAW at
Represents the excitation amplitude of. Next, excite at the center of the electrode finger in step 2.
The amplitude of the generated impulse signal at the reference point is
Harmonic wave number k_MIs M · 2π / λ₀Can be expressed as
The amount of deviation between the center of the electrode finger of₁/ M ・ λ ₀In
Because

[0024]

(Equation 13) It is represented by Similarly, the impulse of step 3 is expressed as follows.

[0025]

[Equation 14]

Therefore, all SAWs from S ₁ to S ₃ are added in phase at the reference point and reinforce each other. Next, considering the case of the fundamental wave, the impulse signal in step 1 is

[0027]

(Equation 15) And for step 2

[0028]

(Equation 16) It is expressed as Similarly, step 3 is expressed as follows.

[0029]

[Equation 17]

SA excited from steps 1, 2, and 3
Since the amplitudes A ₁ (f ₀ ), A ₂ (f ₀ ), and A ₃ (f ₀ ) of W are proportional to the electrode finger lengths W ₁ , W ₂ , and W ₃ of steps 1, 2 and 3, respectively, N ₁ , N ₂ , W ₁ , so as to satisfy the equation (1),
If the values of W ₂ and W ₃ are selected, S _{1 for} the fundamental wave,
The sum of S ₂ and S ₃ becomes zero, and the fundamental wave is not excited. Similarly, for the harmonic components other than the Mth harmonic, the waves excited from each step do not reinforce each other in the same phase at the reference point, and as a result, only the Mth harmonic is efficiently excited. Will be.

The ID, regardless of the order M of the harmonic to be excited,
By dividing the electrode finger of T into three steps and determining the electrode finger length of each step and the amount of deviation between each step so that the sum of the three vectors in the fundamental wave becomes zero,
It is possible to efficiently excite only the harmonic wave to be excited. In the present invention, since it suffices to always divide into three steps irrespective of the order, it is possible to easily realize a harmonic with a large order, which was difficult in the conventional example.

Further, in the invention described in claim 2,
In the invention described above, each electrode finger of the surface acoustic wave converter is a split electrode finger separated into two parallel electrode pieces. The same can be applied to a so-called split electrode finger converter. Also,
According to the third aspect of the present invention, the electrode fingers having the line width of 1 / 4λ ₀ with respect to the fundamental wave of wavelength λ ₀ are formed on the piezoelectric substrate by 1 / 4λ _0.
A surface acoustic wave reflector that is arranged in parallel at intervals of, and reflects the surface acoustic wave of the Mth harmonic (M: odd number) of the fundamental wave at the boundary between the part with electrodes and the part without electrodes. , Each electrode finger is divided into three steps, and each step is shifted and connected in the propagation direction of the surface acoustic wave, and the deviation amount of the second step from the first step is (N ₁ / 2M) · λ ₀ (N ₁ is 1 or more 2
A natural number less than M), the deviation amount of the third step from the first step is (N ₂ / 2M) · λ ₀ (N ₂ is a natural number of 1 or more and less than 2M other than N ₁ ), and further When the electrode finger lengths of 3 steps are W ₁ , W ₂ and W ₃ , respectively,

[0033]

(Equation 18)

It is characterized in that the values of N ₁ , N ₂ , W ₁ , W ₂ and W ₃ are selected so as to satisfy The principle of the invention described in claim 3 will be described with reference to FIG. When the SAW is incident on the electrode finger in step 1 from the left side, a part of the SAW is reflected at the boundary 7a between the portion with the electrode and the portion without the electrode. The SAW that has passed through the boundary 7a is also partially reflected again at the next boundary 7b. The reflected wave by these two boundaries can be represented by one reflected wave from the reflection point placed at the center of the electrode finger, and the reflection coefficient r is then given by the following equation.

[0035]

[Equation 19]

Here, Γ is a coefficient representing the SAW reflection caused by the difference in the speed of the SAW propagating in the part with and without the electrode. The acoustic impedance of the part with the electrode is Zm, and the impedance of the part without the electrode is Zg. And when

[0037]

(Equation 20)

Is defined by Lm represents the line width of the electrode finger. Assuming that the center of the electrode finger in step 1 is zero as the reference point in the x direction, the reflected wave S ₁ reflected by the electrode finger in step 1 has a wave number k _M of the M-th harmonic is M · 2π / λ ₀ .
The point at x = 0 is given by the following equation.

[0039]

(Equation 21)

Here, A ₁ (f _M ) represents the amplitude of the SAW at the frequency f _M of the _Mth harmonic. Similarly, assuming that the reflected wave reflected by the electrode finger in step 2 is S ₂ , the electrode finger in step 2 is displaced from the reference point by N ₁ / 2M · λ _0. expressed.

[0041]

(Equation 22)

This reflected wave also has the same phase at the reference point,
Similarly, the reflected wave of step 3 is added in the same phase, so after all,
In the surface acoustic wave reflector having this structure, the M-th harmonic is strongly reflected. Next, considering the case of the fundamental wave, first, the reflected wave S ₁ of the electrode finger in step ₁ is expressed by the following equation.

[0043]

(Equation 23)

The reflected wave S ₂ of the electrode fingers of the step 2 is expressed by the following equation.

[0045]

(Equation 24)

Similarly, step 3 is expressed as follows.

[0047]

(Equation 25)

SA reflected from each step 1, 2, 3
Since the amplitudes A ₁ (f ₀ ), A ₂ (f ₀ ), and A ₃ (f ₀ ) of W are proportional to the electrode finger lengths W ₁ , W ₂ , and W ₃ of steps 1, 2 and 3, respectively, N ₁ , N ₂ , W ₁ , so that the equation (2) is satisfied,
If the values of W ₂ and W ₃ are selected, S _{1 for} the fundamental wave,
The sum of S ₂ and S ₃ becomes zero, and the fundamental wave is not reflected. Similarly, for the harmonic components other than the M-th harmonic, the waves reflected from each step do not reinforce each other in the same phase at the reference point. As a result, only the M-th harmonic is efficiently reflected. Will be.

[0049]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example in which the surface acoustic wave converter of the present invention is used as a surface acoustic wave converter 2 for transmission (hereinafter referred to as IDT2 for transmission) which excites and transmits a harmonic of a surface acoustic wave.

First, the structure will be described. The transmitting IDT 2
Is a pair of electrode terminals 2, 2 made of a material such as aluminum or gold on the surface of the single crystal piezoelectric substrate 1 and a pair of electrode terminals 2, 2.
A plurality of electrode fingers 4, 4, ... That extend in a crossed finger shape from 2 are formed, and the period of the electrode fingers 4 is the wavelength λ _{0 of the} fundamental wave.
It has become. Each electrode finger 4 is divided into three steps as described later.

The receiving surface acoustic wave converter 3 for receiving the harmonics excited by the IDT 2 (hereinafter referred to as the receiving IDT 3
Is a pair of electrode terminals 2, 2 and a plurality of electrode fingers 5, 5, ... Which extend straight from the pair of electrode terminals 2, 2 in a finger shape on the piezoelectric substrate 1. Is formed, and the period of the electrode finger 5 is a normal IDT having a period equal to the wavelength λ _{0 of the} fundamental wave. IDT2 for transmission and IDT3 for reception
Is the electrode width L so that the harmonics you want to excite can be transmitted and received.
Metallization defined by m and space width Lg
Ratio η

[0052]

(Equation 26)

On the other hand, η is selected based on FIG. 18 showing the excitation efficiency of each harmonic. In this example, M
= 5 is an example configuration with single electrode fingers for exciting the harmonic orders are configured in the vicinity of eta = 0.5, the line width and space width are both the λ _0/4. Each electrode finger 4 of the IDT 2 is divided into three steps 1, 2 and 3.
In as detailed view of one electrode finger 4 2, Step 3 the propagation direction of the deviation amount D ₁ of the surface acoustic wave of Step 2 with respect to Step 1 for D ₂ = 2λ _0/5, Step 1
The shift amount D ₂ is set to D ₂ = 4λ _0/5. In addition, the electrode finger lengths in steps 1, 2 and 3 are set to W ₁ , W ₂ ,
Let's say W ₃ .

Now, assuming that the center of step 1 is the reference point, the signal of the fifth harmonic wave excited at each step is N ₁ = 2, N ₂ = at the reference point in the equations (3)-(5). Four
Is represented by substituting, so SA from S ₁ to S ₃
All Ws are added in phase at the reference point and reinforce each other.
Next, considering the case of the fundamental wave, the signal excited at each step is N ₁ =
2 and N ₂ = 4 are substituted.

SA excited from steps 1, 2, and 3
Since the amplitudes A ₁ (f ₀ ), A ₂ (f ₀ ), and A ₃ (f ₀ ) of W are proportional to the electrode finger lengths W ₁ , W ₂ , and W ₃ of steps 1, 2 and 3, respectively, The electrode finger lengths W ₁ , W ₂ , W ₃ may be determined so that the sum of the signals S ₁ , S ₂ , S ₃ in the case of waves becomes zero. That is,

[0056]

[Equation 27]

In this example, the electrodes of step 1 and step 3
Finger lengths are equal (W₁= W_Three). For simplicity,
Signal S for fundamental wave₁, S_Two, S_ThreeOn the complex plane
It can be expressed as shown in FIG. Three vectors
To make the Le sum zero, S ₁And S_ThreeSynthetic sum S_FourAnd S_Twoof
Must be equal in size. S₁And S_ThreeSynthetic sum S
_FourFor the amplitude of W, use the angle θ in Fig. 3._Two= 2 ・ W₁cosθ
Is required. Where θ = (1/2) · (2π / 5)
is there.

Therefore, the electrode finger length W ₂ in step 2 is set to W ₂ =
If 2 · W ₁ · cos θ, the sum of these three vectors becomes zero at the reference point at the center of the electrode finger in step 1,
The fundamental wave is not excited. Similarly, for the harmonic components other than the 5th harmonic, the waves excited from each step do not strengthen each other in the same phase at the reference point. As a result, only the 5th harmonic is efficiently excited. Will be.

In the embodiment shown in FIG. 1, the transmission ID
T2 is a step electrode finger type IDT, but for receiving
Step electrode finger IDT according to the invention as IDT3
Naturally, a configuration using is also conceivable. Figure 4 shows other
An example of an embodiment will be shown. Fig. 5 shows each stage of Fig. 4 on the complex plane.
Signal S at the reference point of the fundamental wave from the₁, S_Two, S_Three
Shows a vector representation of. In the form example shown in FIG.
Exciting only the 5th harmonic efficiently in 3 steps
In this respect, it is the same as the example shown in FIG.
To make the tor sum zero, go to step 1.
D of the deviation amount of other steps₁= Λ₀/ 5 and D
_Two= 3λ₀Set to / 5 and select three vectors as shown in Fig. 5.
You can also. At this time, the electrode fingers of steps 1 and 2
Long W₁, W_TwoTo W₁= W_TwoAnd then W_ThreeIs W_Three= 2 ・ W ₁cosθ
And Here, θ = (1/2) · (2π / 5).

FIG. 6 shows another embodiment, and FIG. 7 shows a vector representation of the signals S ₁ , S ₂ , S ₃ at the reference point of the fundamental wave from each step of FIG. 6 on the complex plane. Show. The example of the form shown in FIG. 6 aims to efficiently excite only the 7th harmonic in three steps. At this time, the electrode finger lengths W ₁ and W ₃ in step 1 and step ₃
Is set to W ₁ = W _3, and W ₂ is set to W ₂ = 2 · W ₁ · cos θ. Where theta = a (1/2) · (2π / 7 ), and each of the shift amounts D ₁ = 3λ _0/7 and D ₂ = 6λ _0/7. Even when it is desired to excite the 7th harmonic, the electrode finger of the IDT had to be divided into seven in the conventional example, but the same effect can be obtained by simply dividing into three steps.
Compared with the conventional example, the productivity and production yield are dramatically improved, and the accuracy required for the electrode finger length and the amount of displacement is significantly lower than that required for the conventional example.

FIG. 8 shows another embodiment, and FIG. 9 shows a vector representation of the signals S ₁ , S ₂ , S ₃ at the reference point of the fundamental wave from each step of FIG. 8 on the complex plane. Show. The example of the form shown in FIG. 8 is the same as the example of the form of FIG. 6 in that only the 7th harmonic is efficiently excited in three steps, but in order to make the three vector sums zero. Can also select three vectors as shown in FIG. At this time, W ₁ = W ₂ and W ₃ is W ₃ = 2 · W ₁
・ Set to cos θ. Where θ = (1/2) · (2π / 7)
, And the shift amount is set to _{D 1 = λ 0/7,} D 2 = 4λ 0/7.

FIG. 10 shows another embodiment. FIG.
The configuration example shown in (1) is a configuration example of the present invention using the IDT 4 of the split electrode finger. That is, the electrode fingers 6, which extend in a finger-like shape in a cycle λ ₀ from the pair of electrode terminals 2, 2 of the IDT 4.
Each of 6, ... Is separated into two parallel electrode pieces 6a, 6a. In the illustrated example, the line width and space width of the electrode strips 6a are both a lambda _0/8, the metallization ratio eta is a eta = 0.5. Then, each electrode piece 6a is divided into three steps, and the shift amounts D ₁ and D ₂ and the electrode finger lengths W ₁ , W ₂ and W _{3 at} each step are set so as to satisfy the equation (1). There is.

FIG. 19 shows the excitation efficiency of the harmonics excited by the IDT of the split electrode finger. For example, when it is attempted to excite the harmonic of the order of M = 3, the third harmonic cannot be excited in the vicinity of η = 0.5 in the IDT having a single electrode finger as shown in FIG. On the other hand, as shown in FIG. 19, in the IDT of the split electrode finger, the third harmonic can be excited near η = 0.5. Therefore, by selecting an IDT of a single electrode finger or a split electrode finger according to the order M to be excited, it is possible to obtain an IDT of around η = 0.5 which is suitable for manufacturing. Further, by using the split electrode fingers, the reflection of SAW between the electrode fingers can be significantly reduced and the characteristics can be improved.

FIG. 11 shows another embodiment. FIG.
Shows a surface acoustic wave reflector 10 of the present invention. The surface acoustic wave reflector 10 is made of a material such as aluminum or gold for the wavelength λ _{0 of the} fundamental wave on the surface of the single crystal piezoelectric substrate 1. .. are arranged side by side, and the line width and space width of the electrode fingers 7 are both ¼λ ₀ . This example shows a case where a fifth harmonic wave reflector is configured, and each electrode finger 7 of the surface acoustic wave reflector 10 is set to three.
One of the divided step 1,2,3, a shift amount D ₁ of the Step 2 with respect to Step _{1 D 1 = 2λ 0/5} , Step 1
A shift amount D ₂ of Step 3 is set to D ₂ = 4λ _0/5 against. Further, assuming that the electrode finger lengths of steps 1, 2 and 3 are W ₁ , W ₂ and W ₃ , respectively, the values of W ₁ , W ₂ and W ₃ are selected so as to satisfy the equation (2). However, N ₁
= A 4, N ₂ = 8.

FIG. 12 shows another embodiment. FIG.
Is a surface acoustic wave reflector of the fifth harmonic,
Is the same as the example shown in FIG. 11, but each of the shift amounts of the other steps D ₁ = 3 [lambda] _0/10 and D with respect to Step 1
And ₂ = _{6λ 0/10,} it is also possible to choose three vectors as shown in Figure 13. Then steps 1, 2 and 3
If the electrode finger lengths of W are W ₁ , W ₂ , and W ₃ , respectively (2)
The values of W ₁ , W ₂ and W ₃ are selected to satisfy the equation. However, N ₁ = 3 and N ₂ = 6.

FIG. 14 shows an example in which a unidirectional surface acoustic wave converter is constructed by using the IDT of the present invention. Period λ
_The sending IDT 5 and the reflecting IDT 6 having the electrode fingers of ₀ are arranged at a specific distance from each other, and the sending IDT 5 and the reflecting IDT 6 are arranged.
Two signals differing in electrical phase difference by φ are applied to the respective one electrode terminals of 6 and the other electrode terminals of the sending IDT 5 and the reflecting IDT 6 are grounded. The electrode width of the ground terminal between the delivery IDT5 the reflection IDT6 is set to λ _0/2. With such a configuration, if a phase difference of φ = 90 ° is given, SA
W is excited only in the right direction in the drawing shown by the arrow.

Also in the unidirectional surface acoustic wave converter thus constructed, each electrode finger is divided into three steps,
In order to satisfy the equation (1), the step shift amounts D ₁ , D ₂
And electrode finger lengths W ₁ , W ₂ and W _{3 of the 1st} , _2nd , _3rd steps are selected respectively, which allows the unidirectional surface acoustic wave transducer which operates efficiently at the harmonics of the order to be excited. Will be realized.

Further, a surface acoustic wave delay line, a surface acoustic wave filter, or a surface acoustic wave resonator can be constructed by using each IDT or each surface acoustic wave reflector described above.

[0069]

As described above, according to the present invention, the effects listed below can be obtained. (1) The electrode finger of the IDT is divided into three steps regardless of the order of the harmonic to be excited, and the electrode finger length of each step and the deviation amount between the steps are set so that the sum of the three vectors in the fundamental wave becomes zero. By deciding so that, it is possible to efficiently excite only the harmonics to be excited. (2) In the conventional example, according to the order M of the harmonic to be excited,
The electrode fingers of the IDT must be divided and the steps must be staggered, which requires a great deal of effort to implement as the order increases, but the present invention always uses three steps regardless of the order. Since the same effect can be obtained only by dividing and the two shift amounts of these steps and the electrode finger length, it is possible to easily realize a harmonic having a large order, which was substantially difficult in the conventional example. (3) Even in a reflector that reflects high-order harmonics, the electrode fingers are divided into three steps regardless of the order of the harmonics to be reflected, and the electrode finger length at each step and the amount of deviation between each step are calculated. , By determining the sum of the three vectors in the fundamental wave to be zero, it is possible to efficiently reflect only the harmonic wave to be reflected.

[Brief description of the drawings]

FIG. 1 is an example in which the surface acoustic wave converter of the present invention is used as a transmitting IDT 2 which excites and transmits a harmonic of a surface acoustic wave.

2 is a detailed view of one electrode finger of FIG. 1. FIG.

FIG. 3 is a vector representation of the operation of the fundamental wave in the case of FIG. 1 on a complex plane.

FIG. 4 is a detailed view of an electrode finger representing another embodiment.

5 is a diagram in which the operation of the fundamental wave in the case of FIG. 4 is vector-displayed on a complex plane.

FIG. 6 is a detailed view of an electrode finger representing another embodiment.

FIG. 7 is a diagram in which the operation of the fundamental wave in the case of FIG. 6 is vector-displayed on a complex plane.

FIG. 8 is a detailed view of an electrode finger according to another embodiment.

9 is a diagram in which the operation of the fundamental wave in the case of FIG. 8 is vector-displayed on a complex plane.

FIG. 10 is a diagram showing another embodiment.

FIG. 11 is a diagram showing a form example of a surface acoustic wave reflector of the present invention.

FIG. 12 is a view showing another embodiment of the surface acoustic wave reflector of the present invention.

FIG. 13 is a diagram in which the operation of the fundamental wave in the case of FIG. 12 is vector-displayed on a complex plane.

FIG. 14 is an example of a mode in which a unidirectional surface acoustic wave converter is configured using the IDT of the present invention.

FIG. 15 is a plan view showing a conventional surface acoustic wave converter.

16 is a partially enlarged view for explaining the operation of FIG.

17 is a diagram showing the operation of the fundamental wave of FIG. 16 as a vector on a complex plane.

FIG. 18 is a diagram showing relative excitation intensity with respect to metallization ratio η of harmonics excited by a single electrode finger.

FIG. 19 is a diagram showing a relative excitation intensity with respect to a metallization ratio η of a harmonic wave excited by a split electrode finger.

[Explanation of symbols]

IDT2, IDT4, IDT5, IDT6 surface acoustic wave converter 1 piezoelectric substrate 2 electrode terminals 4, 6, 7 electrode fingers 6a electrode piece 10 surface acoustic wave reflector

Claims (3)

[Claims] 1. A pair of electrode terminals and the pair of electrodes on a piezoelectric substrate.
Formed with multiple electrode fingers that extend from the electrode terminals of the
Of the fundamental wave having a wavelength equal to the period λ0 of the electrode finger
A surface acoustic wave converter that excites a surface acoustic wave of the next higher harmonic.
By dividing each electrode finger into 3 steps,
Connect by shifting in the wave propagation direction to the first step
The deviation amount of the second step is (N₁/ M) ・ λ₀(N ₁Is 1 or more
Upper natural number less than M), the third step for the first step
Shift amount (N_Two/ M) ・ λ₀(N_TwoIs N₁Other than 1
A natural number less than M), and the first, second, and third steps
Each electrode finger length is W₁, W_Two, W_ThreeWhen,N to satisfy₁, N_Two, W₁, W_TwoAnd W_ThreeThe value of
A surface acoustic wave converter characterized by being selected. 2. Each of the electrode fingers of the surface acoustic wave transducer has two electrodes.
The surface acoustic wave transducer according to claim 1, wherein the surface acoustic wave transducer is split electrode fingers separated into parallel electrode pieces. To 3. A piezoelectric substrate, are a large number arranged electrode fingers having a line width of 1 / 4.lamda ₀ with respect to the fundamental wave of wavelength lambda ₀ is at intervals of 1 / 4.lamda _0, a part of the electrode A surface acoustic wave reflector that reflects the surface acoustic wave of the Mth harmonic (M: odd number) of the fundamental wave at the boundary with the part without electrodes. Each electrode finger is divided into three steps, and each step is elastic. The connection is performed by shifting in the propagation direction of the surface wave, and the shift amount of the second step with respect to the first step is (N ₁ / 2M) · λ ₀ (N ₁ is 1
The natural amount less than 2M) and the deviation amount of the third step from the first step is (N ₂ / 2M) · λ ₀ (N ₂ is a natural number greater than or equal to 1 and less than 2M other than N ₁ ). , 3
When the electrode finger lengths of the steps are W ₁ , W ₂ , and W ₃ , respectively, A surface acoustic wave reflector characterized in that the values of N ₁ , N ₂ , W ₁ , W ₂ and W ₃ are selected so as to satisfy