JPS5890816A - Ultrasonic wave solid-state delay line - Google Patents

Abstract

PURPOSE:To sufficiently suppress a dispersion mode even if a delay medium having a thickness several times or more the wavelength is used, by polishing the surface coarseness of the major plane of the delay medium and the boundary plane of a transducer to a specific value or below of the propagation wavelength. CONSTITUTION:An input transducer 8 and an output transducer 9 are respectively stuck to end surfaces 3, 4 of a delay medium D having two parallel major planes 1, 2 and 5 end surfaces 3, 4, 5, 6 and 7 intersecting with the major planes, and an ultrasonic wave signal of shear mode propagates in the delay medium D. The input and output transducers 8, 9 have boundary surfaces 10, 11, 12 and 13 coincident with the major planes 1, 2, and the boundary surfaces and the major planes are polished planes having surface coarseness which is <=1/20 of propagation wavelength of ultrasonic waves in the medium D, and the dispersion in the distance between the major planes clipping the propagation signal path in the medium D is <=1/20 of the propagation wavelength.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Portion IF of the Invention) The present invention relates to an ultrasonic solid-state delay line that propagates an ultrasonic signal in an integral delay medium such as glass to obtain a delayed signal.

(Prior Art) The Gates delay line, which is widely used in color televisions, video discs, and video tape recorders◆, has the following structure. #1M shows an example of a conventional glass delay line.

In FIG. 1, in a delay medium having two parallel main surfaces #1.2 and five end surfaces 3.4.5, 6.7 intersecting this main surface, there is a Ultrasonic waves are propagated from the human quadrangle transducer 8 to the output transducer 9 along the reflection path indicated by the arrow. person cadran juicer 8
converts electrical signals into ultrasonic signals and illuminates! It is polarized parallel to the main surface 1.2 of the spreading media and transmits a shear mode ultrasonic signal. On the other hand, the output transducer f9 converts the shear mode super-WI wave signal arriving at the terminal dIJ4 into an electrical signal.

A delay line having such a structure is characterized by its excellent mass productivity and ease of spurious processing. In order to propagate only ultrasonic signals in a non-dispersive mode (zero mode), it is essential to use a transducer with the same thickness as the delay medium. In other words,
The input and output transducers 8.11 are connected to the boundary plane 10 which coincides with the two main planes 1, 2 of the delay medium in figure 11.
, 11°12.13. Furthermore, in order to propagate only this zero mode, it is also an essential requirement that the thickness of the delay medium be five times or less, preferably one-half or less, of the wavelength of the ultrasound propagating therein. There is.

These orders are IRI TRAN8AOTIO
11t8, July 1960 issue, pages 35 to 43
Regarding the spurious removal, Sukyu aB47-27
Each of these is described in Publication No. 574. In particular, the technology described in No. 08F3581247 regarding mass production, in which a transducer is attached to a glass boot switch and then stitched to produce a large number of delay lines at once as shown in Figure 1, has the effect of lowering manufacturing costs. is large, so
This product has been adopted by major manufacturers around the world. and,
The thickness of this glass is generally selected to be approximately twice as strong as the propagation wavelength in terms of its strength.

(Background of the invention) Sate, the above IRI 'I'RAN8AO'l'l0N8
Although the requirement for propagating only the zero mode is that the thickness of the delay medium must be less than half of the propagation wavelength, why does the delay as shown in Figure 1 occur? Regarding the question of whether it is possible to propagate only the zero mode even if the thickness is several times the wavelength, a! I can't find any literature that provides a dramatic explanation.B Moto Inventions etc. analyze this fact as follows.First, starting with Mlmll, the delay line as shown in Figure 1 is due to the delay medium. When the thickness is λ/2 or more, there is a path of the wrinkle number mode according to a certain rule as in the conventional sea. However, the person and the output transducer are in such a configuration that it is impossible to transmit or receive signals in modes other than 0. The key point on Sakaki is the border of the transducer! This is due to the fact that the circle is exactly aligned with the main surface of the delay medium. Then, if the boundary direction of the transducer and the main surface of the delay medium are exactly matched, it will be explained below why a mode other than the 0 mode is not transmitted.

FIG. 3 shows, for example, how an n-3 mode wave propagates through a medium. In the diagram, waves WI, W
l is -. , ej(ky+γx),. 1wt090001
00. ■■ The resultant wave Wl is. This is the mode wave of atrophy-3.

Note that the vertical direction in the figure is the Y direction, the horizontal direction is the X direction, and the direction perpendicular to the plane of the paper is two directions, and all wave cedars indicate displacements in two directions. The media plane is 1,2 and the transducer interface is 12,13. ■If we transform the expression, we get the following.

Wl-0'cos ky-e-j(r” ”'), curve ■Therefore, the wave l is Q'e o s − in the Y direction.
y becomes b It is a mode wave that travels while vibrating 6-j (rx-wt) in the X direction while forming a standing wave.
Figure #4 shows how the standing waves in the Y direction are generated in section 8a. Now the delay medium X-Lf! Mo-B for 6 points
Assume that a transducer -0-D is attached. The wave Wl of ■ is at the interface of the transducer j! Since it coincides with the main surface of the spreading medium, it proceeds through the transducer as it is and is reflected at the point XL. Therefore, the wave Wy in the transducer is 0Wy-0 as shown below.
' COl-2, e-3(yx-wt) + Here, for simplicity, we assume that r is equal to the value in the delay medium.

From the point X-L-T, it becomes r(L-'I')-π. Therefore, from equation 0, #! in the Y direction in the transducer!
6, and in the X direction 5b! A standing wave like J is generated. Due to the shape of this standing wave, the electromotive force on the outside of the transducer cancels out as a whole vibrating bed, and no output is taken out from the output transducer. In other words, a delay line in which the transducer interface (Mu-B, 0-D) coincides with the main plane of the delay medium will not operate in a dispersive mode. However, if the delay medium is made thicker, that is, if the standing wave shown in tlh4 becomes more than several λ (experimentally more than 5 J), an effective standing wave can be obtained. It becomes MIIl and starts working in distributed mode.

Then in the 3'Fj4, A/ n/ Of D
If a transducer of
Only standing waves in the X direction in the figure are generated. That is, this delay line can operate in a distributed mode. Similarly, Mu-A'-0
The same can be said for the transducer '-D.Also, in the case of the transducer I BJF 01D, it is obvious that it works well in the dispersion mode. Although it is disclosed in Japanese Patent Application Laid-Open No. 134350/1989 that the transducer M'-f-0-D is also practical for shared mode, it is clear for the first time from the above theory that this transducer does not operate in distributed mode. can be substantiated.

(Problems with the Prior Art) According to the prior art described in the above-mentioned publications, the thickness of the delay medium is 50% of the wavelength of the ultrasonic signal propagating through it.
It is well known experimentally that it is preferable to have a value of about 2 times or less in order to obtain a practical solid-state delay line. In fact, the center frequency of the color television most commonly used at present is approximately 3.6 MHz, and the thickness of the glass delay medium is selected to be approximately 1 to 1.2 mm thick. The wavelength of the ultrasonic signal in this delay medium is 0.
61111, the thickness of the medium is 1.5 of the wavelength.
This means that approximately twice as many people were selected as

Such a center frequency glass delay line has a transmission band of 2
However, glass delay lines used in video equipment, broadcasting equipment, etc. have a transmission band of around 5Wy.
It is required that the center frequency be as wide as possible from 1 to IOMH, and along with this, the center frequency should be changed from 10MHz to 30MHz!
I have no choice but to choose it highly.

However, when the center and frequency are raised in this manner, the wavelength of the signal in the medium becomes shorter, and for example, in the case of 30 MHg, the maximum stiffness of the medium must be increased to about 0.3-. In practice, when a glass delay medium is used, this is easily damaged and is not practical. When a medium with a thickness of five times the wavelength or more is used, those manufactured by the conventional method have many spurious waves and do not have sufficient characteristics.

Therefore, conventionally, such a high frequency delay line is 55
It was limited to a system using a Baltic wave in which a rectangular or circular transducer was attached to a thick glass retardation medium of 5 g. However, such a delay line is
In addition to the cost of materials, there were drawbacks such as extremely high costs because the method of mass production using slicing described above could not be adopted, and the weight and size of the product could not be reduced.

(Objective of the Invention) The present invention has been made with attention to the above points, and it is possible to achieve a shared mode delay time that sufficiently suppresses the dispersion mode for practical use.
◎The present invention further provides that when the propagation wavelength is a relatively high frequency, even if a delay medium having a thickness several times the wavelength within the medium is used, the dispersion mode The purpose of the present invention is to provide a delay line that can sufficiently suppress the

(Structure of the Invention) The present invention improves the surface roughness within the boundary between the main surface of a delay medium and the transducer connected thereto, as shown in FIG. By polishing the medium to a thickness of 20 times the wavelength or less, the thickness of the medium can be practically reduced to about 20 times the wavelength. This is to prevent the occurrence of dispersion mode.

Furthermore, the present invention provides a transducer such that the propagation wavelength of the ultrasonic waves in the F transducer is longer than that in the delay medium.
The material of the user is selected so that even if the raised surface of the transducer and the main surface of the medium are simultaneously polished under the same conditions, a dispersion mode is unlikely to occur within the transducer.

Here, as shown in FIG. 2, the surface roughness refers to the length (■) between the peaks 14 and 15 of the surface irregularities.

(Embodiments of the Invention) A) Example 1 First, the distance between the main surfaces of a glass delay medium with a propagation signal velocity of 24001 i/s was set to 0.8 m, and the center frequency was 20 MHz.
When the transducer was driven, the amount of attenuation of the dispersion mode changed as shown by the roughness of the main surface of the medium. Note that the wavelength of this signal within the medium is 120X10-
・It is -. Also, transju? ◎ The dispersion mode cannot be suppressed sufficiently in margin comparison tsuba 1 and 2, but as the surface roughness of the medium surface is reduced, the dispersion mode can be suppressed as in the example. Decrease.

Since it is not practical unless the attenuation amount of the dispersion mode is 26 dB or more, it can be seen from the above table that the surface roughness of the main surface of the medium must be about 1/20th of the wavelength or less.

Further, even if the surface roughness of one of the main surfaces of the medium or a part of the main surfaces sandwiching the propagation signal path was increased, the amount of attenuation of the dispersion mode was insufficient as in Comparative Example 1.2.

Furthermore, from the viewpoint of processing accuracy and productivity, the thickness of the medium is preferably 20 times the wavelength and preferably 15 times or less.

Example 2 On the other hand, as an example of the present invention, the surface roughness of the main surface of the delay medium and the interface of the transducer polished at the same time was set to 3.9X.
1G"'1m, and change the material of the transducer.
When a signal with a frequency of 0 MHz was input, the results shown in the table below were obtained.

In any of the above cases, it goes without saying that the wall thickness of the transducer in the signal emitting or receiving direction is half the wavelength of the signal within the transducer.

From this example, we can see that the signal propagation wave in the transducer is also long, and in the case of PZ'I' yarn, it is shorter than that of the medium, so the appearance of the dispersion mode is different. It can also be seen from this table that the properties of the conventional materials are far superior.

Here, some explanation will be added regarding the second embodiment. In FIG. 7, the waves W1 and WH in the delay medium become W(,Wy) in the transgeny.

W1'-0-61('Y+7'X), e3
w tw(-0, *-'("Y-1"),
e j w tw7-σ・coboy, C-j(r'x-
wt) Note that k and 1 are changed to 'r' during transgeny, and the propagation velocity in the medium is V.

The propagation velocity in the transducer is more than “s”.

is getting bigger.

As is clear from 1117m, v'3°>Vs. Therefore, the thickness of the transducer that most efficiently receives this 11-3 mode wave! is larger than 1/2 of the propagation wavelength in the medium. As described above, if the boundary conditions are set correctly in this state, a standing wave in the Y direction will occur, making it impossible to take out the output to the outside of the transducer.

On the other hand, an O-mode signal propagates as shown by W. and can be received with maximum efficiency by a transducer with a thickness of T', which is one-half wavelength thick.

Therefore, the actual thickness of the output delay line is T
◎Here, although a transducer of this thickness cannot receive the previous n-3 mode wave with maximum efficiency, a standing wave is still generated, and the transducer generated by this standing wave is The vibration of Genie is thick! becomes smaller than when .

Therefore, it becomes increasingly difficult to receive the distributed mode.

On the other hand, if the signal propagation speed in the transgenic medium is slower than in the medium as shown in Figure #18, the difference between T and T' becomes 4. This is close to the condition for receiving the mode with maximum efficiency.

Note that the Y-direction standing wave in the transducer becomes as follows if the propagation constant is degraded. From this value, it can be seen that standing waves are formed in the same way regardless of the sound speed of the transducer.

Therefore, by setting VB2 > Vs, even if the main surface of the delay medium and the interface between the transducer and the main surface are made to have the same surface roughness, the ratio of the propagation wavelength to the transducer becomes larger, and the standing wave is most likely to be disturbed. This makes it possible to make the conditions of the transducer part more favorable.

(Effects of the Invention) As explained above, the thickness of the transducer that most efficiently receives a signal propagating through a delay medium is equal to one half of the signal wavelength within the silance dialer. Even if the thickness is thicker than this, the output of the transgenie amount will be small.On the other hand, as explained in Figure 3, even if the thickness of the transgenie is Even if the thickness is set, in a shear mode delay line where the main surface of the medium and the transducer m height match, signals other than 0 mode become standing waves that cancel out the generation of charges on the transducer surface and are output as output. It doesn't come.

The present invention eliminates unevenness larger than the propagation wavelength from the main surface of the medium, and maintains the thickness of the medium in the longitudinal direction with high precision so that the standing wave described above is stably generated. Moreover,
The delay line in Figure 7 is designed to reduce the apparent surface roughness of the medium by transmitting electricity through the material at the transducers, which are located at both ends of the ultrasonic path and where the standing wave is most likely to be disturbed. can also be made smaller.

In addition, the delay line shown in FIG. 7 can make a difference between the thickness of the transducer that most easily receives dispersion mode signals and the optimal thickness of the transducer for receiving zero mode signals, so that the characteristics can be further improved. And, with the above configuration, the ultrasonic solid-state retardation can be achieved that sufficiently suppresses the dispersion mode even when using a medium with a thickness of about 20 degrees or more than 5 times the propagation wavelength in the medium, which was previously unusable due to its characteristics. A line is obtained.

[Brief explanation of drawings]

11th! 1 is a perspective view of a conventional ultrasonic solid state delay line suitable for implementing the present invention, 2nd WJ is a definition of surface roughness, t
s3 to lWJ are explanatory diagrams of waves in the medium of the shear mode delay line, and Figure 7.8 is the i! of the present invention. FIG. 2 is an explanatory diagram of a medium wave plow in an embodiment of one wire extension. D ----------m-delay medium 1, 2-
-------1 main surface of delay medium 3.4, 5, 8, 7--1-- end surface 8 of slow learning medium --------1. input quadrature transducer S --- -------------One output Silance Genie 10.11.12.13 - Transducer interface H--------- One surface roughness 17E ρ 1IIi2Wi 4 71st El Figure 8

Claims (1)

[Claims] 1. A delay medium having two parallel main faces and three or more end faces intersecting the main faces, and a delay medium that is attached to any one of the end faces and polarized in a direction parallel to the main face. It has a manual transmission juicer that manually generates a shear mode ultrasonic signal, and an output juicer that is attached to one of the end faces and converts the ultrasonic signal propagated in the delay medium into an electric signal. In the input and output transducers, the input and output transducers have interface surfaces that coincide with two major surfaces of the delay medium, and the major surfaces and the interface surfaces are both 20 times smaller than the propagation wavelength of the ultrasound in the delay medium. The polished surface has a surface roughness of 1 or less, and the variation in the distance between the main surfaces sandwiching the propagation signal coupling path of the delay medium is 1/20 or less of the propagation wavelength of the ultrasonic wave in the delay medium. Features an ultrasonic solid delay line. 2. The distance between the main surfaces of the delay medium is 1 time or more and 20 times or less, preferably 5 times or more and 15 times or less, the propagation wavelength of the ultrasonic wave in the delay medium, as set forth in claim 1. Ultrasonic solid state delay line. 3. The ultrasonic solid-state delay line according to claim 1 or 2, wherein the delay medium is made of glass. 4. The ultrasonic solid-state delay line according to claims 1 to 3, characterized in that the propagation wavelength of the ultrasonic waves in the transducer is better than that in the delay medium.