JPH0448284B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ultrasonic delay line that delays electrical signals by converting them into sound waves and propagating them through a delay medium.

[Conventional technology]

The ultrasonic delay line described above is widely used in circuits of TV receivers, video tape recorders (VTRs), and the like.

In such an ultrasonic delay line, since the sound waves propagate in paths other than the desired one in the delay medium, the sound waves other than the desired paths are transmitted to an output electromechanical transducer (hereinafter referred to as a "transducer"). ), which becomes so-called spurious noise.
There is a risk that it may have an adverse effect on the playback screen of a VTR, etc. For this reason, a sound absorbing material is provided on the main surface of the delay medium parallel to the sound wave propagation direction or on the side surface perpendicular to the main surface to absorb sound waves other than the desired path,
A method is known in which the main surface and side surfaces are roughened to attenuate sound waves outside the desired path.

In addition, even when a sound wave propagates in a desired path, once it is detected by the output transducer, it propagates again in the desired path and returns to the input transducer for a delay time that is twice the desired delay time τ. have
There are 2τ spurious noises and 3τ spurious noises that are detected by the output transducer after the 2τ spurious noises pass through a desired path again, and in order to remove the 2τ and 3τ spurious noises, the present applicant's own patent application is proposed. As disclosed in Publication No. 52-19942,
A method of attenuating 2τ and 3τ spurious noise by providing a sound absorbing material within a desired passage is also known.

[Problem to be solved by the invention]

In the conventional spurious noise attenuation method described above, consideration was given only to the removal of the fundamental frequency component (hereinafter referred to as "main signal") of the sound wave propagating in the delay medium. In other words, measures have been taken to remove only the fundamental frequency components of spurious signals that follow paths other than the desired path and the fundamental frequency components of 2τ and 3τ spurious signals that travel through the desired path.

However, in general, a sound wave signal propagating in a delay medium has harmonic components, and for example, as shown in the frequency characteristic diagram of Fig. 2, the sound wave signal propagating in a delay medium has harmonic components, for example, as shown in the frequency characteristic diagram of Fig. 2, the central frequency of the main signal passband is ₀ (4.3 MHz in the example shown). The third one has a frequency ₃ to 4 times higher (13 to 16 MHz in the example shown).
Spurious noise of harmonic components is superimposed. The spurious noise of such harmonic components is at a considerable level (in the example in Figure 2, the main signal level is -
If it is superimposed on the main signal at a level of 20 dB, for example, in a video camera, phenomena such as striped noise will occur on the reproduced image, which will impair good image reproduction. .

The present invention was made in order to eliminate such drawbacks of conventional ultrasonic delay lines, and an object of the present invention is to provide an ultrasonic delay element that is free from harmonic spurious noises higher than the third harmonic component. do.

[Means for solving problems]

The ultrasonic delay line of the present invention is an ultrasonic delay line having an ultrasonic delay medium attached with an input/output transducer, in which at least a part of the surface of the delay medium is affected by the sound wave propagating through the delay medium. , a scattering surface is provided that mainly scatters sound waves higher than the third harmonic component of the main signal, and the scattering surface conforms to JIS
B0601 center line average roughness of 0.25μm to 1.50μm
It is characterized by:

Hereinafter, typical examples of the present invention will be explained with reference to the drawings.

FIG. 1 is a side view showing a typical example of an ultrasonic delay line according to the present invention. In the figure, a sound wave 3 emitted from an input transducer 1 into a delay medium 2 is guided to an output transducer 5 through a desired path 4 defined by a sound absorbing material (not shown) for the main signal.

In this example, a scattering surface 6 is formed on the main surface 2a of the delay medium 2 by a method such as a sandblasting method to scatter sound waves having the third harmonic component or higher.

The scattering surface 6 may be provided on the desired path 4 of the sound wave 3 on the main surface 2a, as shown in FIG.
a It may be provided on the entire surface, or as shown in FIG. 3, it may be provided on the side surface. That is, it may be formed on at least a portion of the main surface 2a or side surface of the delay medium 2, which corresponds to the desired path 4 of the sound wave 3.

In addition to the above-mentioned sandblasting method, the scattering surface 6 may be formed by using sandpaper, or by dissolving an abrasive material in a solvent and impregnating it in a cloth or the like and performing a rubbing process.

The roughness of the scattering surface 6 must be such that it hardly attenuates the main signal propagating in the delay medium 2, but mainly attenuates spurious noise of the third harmonic component or higher. For this purpose, the roughness of the scattering surface must be 0.25 μm or more based on the center line average roughness of JIS B0601.
The thickness is preferably 1.50 μm.

As the input/output transducers 1 and 5, piezoelectric elements such as lead zirconate titanate, crystal, thirium niobate, etc. are used, and are fixed to the side surface of the delay medium 2 by adhesive bonding, soldering, etc. be done.

The delay medium 2 is made of a material capable of propagating sound waves, such as isotropic glass, ceramics, or metal.

[Effect]

The sound wave 3 propagating through the delay medium 2 is guided through a desired path 4
Since sound waves propagating in other directions are attenuated by a sound absorbing material (not shown) that attenuates the main signal, they reach the output transducer 5 via the desired path 4.

Since the scattering surface 6 is formed on at least a part of the surface of the delay medium 2 corresponding to the desired path 4,
In the sound wave 3 passing through the desired path 4, components of the third harmonic or higher are scattered and attenuated by the scattering surface 6, and as shown in FIG. 4, spurious components of the third harmonic or higher are attenuated. The frequency characteristics are as follows. That is, by adjusting the roughness of the scattering surface 6, the main signal of the sound wave 3 propagating through the desired path 4 is hardly attenuated, while the spurious components of the third harmonic or higher are attenuated.

〔Example〕

As shown in FIG. 1, two pieces of lead zirconate titanate were adhered to one side of the glass delay medium with adhesive to form an input transducer and an output transducer, respectively.

In a portion of the desired path on the major surface of this retardation medium,
As shown in Figure 1, JIS
A scattering surface with a center line average roughness of 1.0 μm was formed for B0601. Incidentally, epoxy resin was formed to a thickness of 0.2 mm in a portion of the desired passage on the main surface to remove spurious components outside the desired passage.

The center frequency of the main signal is in this ultrasonic delay line.
When a 4.3MHz electrical signal was input, an output signal with extremely good frequency characteristics was obtained, with the signal level of the third harmonic being more than 40dB lower than the signal level of the main signal, as shown in Figure 4. It was done.

〔Effect of the invention〕

In the ultrasonic delay line according to the present invention, at least a part of the surface of the delay medium has a scattering surface that mainly scatters sound waves of the third harmonic component or higher of the main signal among the sound waves propagating in the delay medium. Since we have formed
It is possible to significantly attenuate only the spurious components of the third harmonic and above without attenuating the main signal component, and when used in video cameras, etc., it does not cause striped noise etc. A suitable reproduced image can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a side view showing a typical example of the ultrasonic delay line of the present invention, Fig. 2 is a graph showing the frequency characteristics of the conventional ultrasonic delay line, and Fig. 3 is a graph showing other ultrasonic delay lines of the present invention. FIG. 4 is a graph showing an example of the frequency characteristics of the ultrasonic delay line of the present invention. DESCRIPTION OF SYMBOLS 1... Input transducer, 2... Delay medium, 3... Sound wave, 4... Desired path, 5... Output transducer, 6... Scattering surface.

Claims (1)

[Scope of Claims] 1. In an ultrasonic delay line having an ultrasonic delay medium to which an input/output electromechanical transducer is attached, at least a portion of the surface of the delay medium contains a sound wave propagating through the delay medium. A scattering surface is provided that mainly scatters sound waves higher than the third harmonic component of the main signal,
The scattering surface has a center line average roughness of JIS B0601.
An ultrasonic delay line characterized by a thickness of 0.25 μm to 1.50 μm. 2. The ultrasonic delay line according to claim 1, wherein the scattering surface is provided on the main surface of the delay medium. 3. The ultrasonic delay line according to claim 1, wherein the scattering surface is formed on the side surface of the delay medium.