JPS61251310A - Ultrasonic wave delay line - Google Patents

Abstract

PURPOSE:To eliminate harmonic spurious noise by providing a sound absorbing member absorbing the sound waves of the 3rd harmonics or over in a main signal in the sound waves propagated in a delay medium to the surface of the delay medium. CONSTITUTION:The sound wave 3 irradiated into the delay medium 2 from an input transducer 1 reaches an output transducer 5 via a desired path 4. Since the sound absorbing member 6 is formed at least at a part of the surface of the delay medium 1 at he desired path 4, the 3rd harmonics or over of the sound wave 3 passing through the desired path 4 are absorbed in the sound absorbing member 6 and attenuated. Thus, the frequency characteristic is obtained, where the spurious noise component of the 3rd harmonics or over is attenuated. That is, the spurious noise being the 3rd harmonics or over is attenuated without almost attenuating the main signal of the sound wave 3 propagated through the path 4 by adjusting the type of material and the thickness of the sound absorbing member 6.

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

In such an ultrasonic delay line, since the sound waves propagate in the delay medium in paths other than the desired path, the sound waves in paths other than the desired path are detected by the output transducer and become so-called spurious noise. There is a risk that it will have an adverse effect on the playback screen of a VTR, etc. For this reason, a sound absorbing material that absorbs sound waves other than the desired path may be provided on the main surface of the delay medium parallel to the propagation direction of the sound waves or on the side surfaces perpendicular to the main surface, or the main surface or side surfaces may be roughened. There are known methods of attenuating sound waves outside the desired path.

In addition, even when a sound wave propagates within a desired passage, once it is detected by the output transducer, it propagates within the desired passage again and returns to the human quadrature transducer with a delay time of 2@. There are 2τ spurious noises that have a 2τ spurious noise, and 3τ spurious noises that are detected by the output transducer after the 2τ spurious noises pass through a desired path again. As disclosed in Japanese Publication No. 52-19942, a method is also known in which a sound absorbing material is provided in a desired passage to attenuate 2τ and 3τ spurious noises.

[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. That is,
Measures have been taken to remove only the fundamental frequency components of spurious noises that follow paths other than the desired path and the fundamental frequency components of 2τ and 3τ spurious noises 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. ) is superimposed with spurious noise of a third harmonic component having a frequency f3 (13 to 16 MHz in the illustrated example). If such spurious noise of harmonic components is superimposed on the main signal at a considerable level (in the example in Figure 2, the level is 20 dB below the main signal level), for example, in a video camera, stripes may appear on the reproduced image. This may cause poor image reproduction, such as generation of noise.

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 noise of the third harmonic component or higher. shall be.

[Means for solving problems]

The ultrasonic delay line of the present invention includes an input transducer that generates a sound wave according to an input voltage, a delay medium that propagates the sound wave generated by the input transducer, and an output voltage that is generated by the sound wave propagated in the delay medium. In an ultrasonic delay line equipped with an output transducer, at least a portion of the surface of the delay medium mainly absorbs sound waves having a third harmonic component or higher of the main signal among the sound waves propagating in the delay medium. It is characterized by being provided with a sound absorbing material.

Representative examples of the present invention will be described below 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 sound absorbing material 6 made of epoxy resin is formed on the main surface 2a of the delay medium 2 by a printing method or the like to absorb sound waves higher than the third harmonic component.

The sound absorbing material 6 may be provided on the desired path 4 of the sound wave 3 on the main surface 2a, as shown in FIG. 1, or may be provided on the entire surface of the main surface 2a, or as shown in FIG. It may also be provided on the side. 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.

The sound absorbing material 6 may be any material that can absorb sound waves, such as an elastic resin that absorbs sound waves such as the above-mentioned epoxy resin or silicone resin, metals such as gold or silver, or oxides such as 5i02.

When using an elastic resin as the sound absorbing material 6, in addition to the above-mentioned screen printing method, the elastic resin may be melted in a solvent to form a liquid and the delay medium 2 may be immersed therein. The elastic resin may be adhered onto the surface of the delay medium 2 with an adhesive.

When using a metal or an oxide as the sound absorbing material 6, it may be formed by a vapor deposition method, a sputtering method, or the like.

No matter what kind of material is used and how it is formed as the sound absorbing material 6, its thickness is such that it hardly attenuates the main signal propagating in the delay medium 2 and suppresses spurious waves of the third harmonic component or higher. The thickness must be such that it primarily attenuates noise. For this purpose, when an elastic resin is used as the sound absorbing material 6, the thickness is preferably 500 to 0.05 wm, and when a metal or oxide is used, the thickness is preferably from SOX to 5 μm.

As the input/output transducer 1.5, a piezoelectric element made of lead zirconate titanate, crystal, lithium niobate, etc. is used, and is fixed on the side surface of the delay medium 2 by adhesive bonding, soldering, etc. Ru.

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

[Effect]

The sound waves 3 propagating in the delay medium 2 are transmitted to the output transducer 5 via the desired path 4 because the sound waves propagating in directions other than the desired path 4 are attenuated by a sound absorbing material (not shown) that attenuates the main signal. reach.

Since the sound absorbing material 6 is formed on at least a part of the surface of the delay medium 2 corresponding to the desired passage 4, the sound wave 3 passing through the desired passage 4 has components higher than the third harmonic of the sound absorbing material. 6 and is attenuated, resulting in a frequency characteristic in which spurious noise components higher than the third harmonic are attenuated, as shown in FIG. That is, by adjusting the material and thickness of the sound absorbing material 6, the main signal of the sound wave 3 propagating through the desired path 4 is hardly attenuated, while the spurious noise components of the third harmonic or higher are attenuated.

〔Example〕

On one side of the glass crack retardation medium, as shown in Figure 1 (・ζ,
Two pieces of lead zirconate titanate pieces were attached with adhesive to serve as an input transducer and an output transducer, respectively.

As shown in FIG. 1, epoxy resin is applied to a portion of the desired passage on the main surface of the delay medium by screen printing to a thickness of 1.5 mm.
o o o X was formed. Incidentally, the same epoxy resin was formed in a portion of the desired passage on the main surface to a thickness of α2 to remove spurious components in the main signal pass band.

The center frequency of the main signal in this ultrasonic delay line is 4.5 M)
When the IZ electrical signal is input, as shown in Figure 4,
An output signal was obtained in which the signal level of the fifth harmonic was 40 dB or more lower than the signal level of the main signal, and exhibited extremely good frequency characteristics.

〔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 is provided with a sound absorbing material that mainly absorbs sound waves of the fifth harmonic component or higher of the main signal among the sound waves propagating in the delay medium. Because of this, it is possible to significantly attenuate only the spurious components of the 3rd harmonic and above without attenuating the main signal component, which prevents striped noise etc. from occurring when used in video cameras, etc. Therefore, an extremely 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 side view of a typical example of the ultrasonic delay line of the present invention. FIG. 4 is a perspective view showing another example, and a graph showing an example of the frequency characteristics of the ultrasonic delay line of the present invention. 1... Input transducer, 2... Delay medium, 3
... Sound wave, 4 ... Desired path, 5 ... Output 1st
Figure 3rd Figure 4

Claims (7)

[Claims] (1) An input transducer that generates a sound wave according to an input voltage, a delay medium that propagates the sound wave generated by the input transducer, and an output transducer that generates an output voltage from the sound wave propagated in the delay medium. In the ultrasonic delay line, at least a part of the surface of the delay medium is provided with a sound absorbing material that mainly absorbs sound waves of the fifth harmonic component or higher of the main signal among the sound waves propagating in the delay medium. An ultrasonic delay line characterized by: (2) The ultrasonic delay line according to claim 1, wherein the sound absorbing material is provided on the main surface of the delay medium. (3) The ultrasonic delay line according to claim 1, wherein the sound absorbing material is provided on the side surface of the delay medium. (4) The ultrasonic delay line according to any one of claims 4 to 3, wherein the sound absorbing material is an elastic resin. (5) The ultrasonic delay line according to claim 4, wherein the sound absorbing material has a thickness of 500 Å to 0.05 mm. (6) The ultrasonic delay line according to any one of claims 1 to 5, wherein the sound absorbing material is a metal film. (7) The ultrasonic delay line according to claim 6, wherein the sound absorbing material has a thickness of 50 Å to 5 μm.