JPH0451034B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to an absorbing material that absorbs sound in water without reflecting it, and particularly to the above-mentioned acoustic non-reflective absorbing material characterized in that it is made of silicone rubber having an acoustic impedance equal to that of water. [Technical Background of the Invention] In ultrasonic diagnostic equipment, an ultrasonic transducer converts an electrical signal into an ultrasonic wave and emits the ultrasonic wave into a living body, and also emits the ultrasonic wave reflected from within the living body. Information from within the body is obtained by converting it back into electrical signals. Among such transducers, transducers for mammary ray diagnosis and the like, as shown in the conceptual diagram in Figure 1, place transducer 1 in a water tank and direct it toward subject 2, which is also in the tank. The transducer transmits and receives the ultrasonic waves while emitting the ultrasonic waves 3 while moving the transducer in a direction 4 perpendicular to the emission direction 3.
The water temperature is usually between 25 and 40°C to avoid discomfort to the subject and to ensure constant conditions for measurements.
℃, especially set at a constant temperature around 38℃. [Problems with the background technology] In the case of such ultrasonic examination in the aquarium, the aquarium 5
If it is large enough, there is no problem, but if it is not, not only the reflected sound waves from the subject but also the reflected sound waves from the inner wall of the tank are generated, which causes noise. Furthermore, when performing examinations using ultrasonic waves, there is a limit to the size of the water tank that can be used, and since there is reflection from the walls, the above-mentioned noise problem occurs. For this reason, a sound absorbing material is attached to the inner wall of the aquarium to prevent scattered sound waves from being scattered by the inner wall of the aquarium. However, as shown in the partially enlarged view of the area near the inner wall of the water tank in Figure 2 (the area surrounded by the broken line in Figure 1), conventional commercially available acoustic absorbing materials do not allow the water to reach the water-acoustic absorbing material interface from within the water 6. Although the absorption attenuation rate of the sound wave 9 transmitted through the acoustic absorbing material 8 through the boundary surface 7 is certainly large,
The problem of the sound waves 10 directly reflecting into the water being very large and causing noise has not been solved. Incidentally, reflected waves 9' on the inner wall surface 7' of the water tank (boundary surface between the acoustic absorbing material and the inner wall of the water tank) also pose a problem, but since they pass through the layer of the acoustic absorbing material 8 again, they are attenuated and become smaller. Compared to this, the effect of the reflected sound waves 10 on the water-acoustic absorber interface 7 described above is a particularly serious problem, and countermeasures against this problem are a problem when using this type of transducer. [Object of the Invention] In order to solve the above-mentioned problems, the present invention provides a vulcanized silicone whose acoustic impedance at a measurement temperature is equal to that of water by controlling the type and amount of filler mixed into silicone rubber. By obtaining rubber and using it as a sound absorbing material, the reflectance of sound waves at the water-acoustic absorbing material interface is extremely reduced, and scattering of sound waves by the inner wall of the aquarium is prevented. [Summary of the invention] Acoustic impedance z is determined by the combination of the sound velocity v [m/s] in the material (the sound velocity v is specific to each substance) and the density ρ [Kg/m ³ ] of the material, as shown in the following equation. It is shown as a product. z=v×ρ Acoustic impedance of water z _n is 1.48~ at 20~40℃
1.52×10 ⁶ [Kg/m ²・s], which increases as temperature rises, while the acoustic impedance of general polymeric materials decreases as temperature rises, so the acoustic impedance of water and polymeric acoustic absorbing materials are all combined. It is difficult to match the operating temperature range. In addition, the sound velocity v in plastics such as polystyrene and nylon resin and general organic rubbers such as butyl rubber and fluorocarbon rubber is 1500 to 1900 m/s.
Since the speed of sound v _n in water is much faster than that in water, it is impossible to use these as a base to obtain an absorbing material with an acoustic impedance close to that of water. In contrast, by selecting polydimethylsiloxane as the base polymer, which has a v of 970 to 980 m/s, which has a very low sound velocity compared to other plastics and organic rubbers, and adding silica as a filler to this, water and Equal acoustic impedance can be obtained. As a result of investigating the reflection of sound waves using such materials, the present inventors found that the difference in acoustic impedance between water and acoustic absorbing material was ±0.03×10 ⁶ [Kg/m ²
s], i.e. 1.45 to 1.51× when the acoustic impedance of the acoustic absorbing material is 20℃ depending on the operating temperature.
10 ⁶ [Kg/m ²・s] or 1.49 to 1.55× at 40℃
It has been discovered that an underwater acoustic absorbing material with less reflection of sound waves, which is the object of the present invention, can be obtained if it is in the range of 10 ⁶ [Kg/m ² ·s]. The present invention has been accomplished. That is, the present invention has an acoustic impedance of 1.45 to 1.55×10 ⁶ at a temperature between 20 and 40°C.
This is an underwater acoustic non-reflection-absorbing material characterized by being made of filler-containing silicone rubber of [Kg/m ² ·s]. Such silicone rubber is made by using a base polymer of polydiorganosiloxy, in which most or all of the organic groups are methyl groups, compounding an inorganic filler and curing (vulcanization) using an appropriate method. Forms a shaped elastic body. In other words, millable silicone rubber is produced using polydiorganosiloxane, which has a small amount of vinyl groups bonded to silicon atoms and residual methyl groups, and has an average degree of polymerization exceeding 1000, by the action of an organic peroxide or polyorganohydrodiene siloxane. It is cured by reacting with the metal in the presence of a platinum-based catalyst. In addition, liquid silicone rubber is a polydiorganosiloxane with a reactive group at the end of the molecule and an average degree of polymerization of 100 to 1000, which is cured at room temperature or by heating in the presence of a crosslinking agent and catalyst. Broadly divided into addition type and condensation type. In the present invention, any type of these silicone rubbers can be used. Fillers used to adjust acoustic impedance by filling silicone rubber include silica such as fumed silica, precipitated silica, crushed quartz, and fused silica, as well as diatomaceous earth and calcium carbonate. In order to impart the necessary mechanical properties and stable properties in water to silicone rubber, finely powdered silica is preferred;
Finely powdered silica with an average particle size of 0.5-20 μm is suitable to obtain the loading required to obtain the desired acoustic impedance. If the particle size is smaller than this, it will not be possible to incorporate the amount necessary to obtain the desired acoustic impedance, and if the particle size is larger than this, the surface of the rubber will become rough, and sufficient mechanical strength will not be obtained. I can't do it. Examples of such fine powder silica include crushed quartz and fused silica. The appropriate amount of finely powdered silica to be blended into the silicone rubber is 53 to 65% by weight in the silicone rubber, which is calculated from the respective specific gravity of polydimethylsiloxane and finely powdered silica having the above particle size. Approximately 30-42% by volume. The above-mentioned base polymer and filler are kneaded together with processing aids and other additives as necessary, and then mixed with a crosslinking agent, a crosslinking agent, etc. depending on the curing mechanism.
A rubber-like elastic body can be obtained by blending a catalyst and the like, thoroughly mixing the mixture, forming it into a sheet, and heating it at room temperature to a necessary temperature. During the mixing, either the crosslinking agent or the catalyst may be added during the first stage of kneading. The sheet may be directly molded and vulcanized to desired dimensions as described above, or may be cut to desired dimensions after vulcanization, and the silicone rubber sheet thus obtained may be used as an acoustic absorbing material. By attaching it to the inner wall of the water tank 5, the object of the present invention can be achieved. [Examples of the Invention] The present invention will be explained below with reference to Examples. In Examples and Comparative Examples, all parts represent parts by weight. The magnitude of the reflected wave is expressed in dB compared to a metal plate, which is a perfect reflector. Example 1 0.1 mol% of organic groups bonded to silicon atoms
average degree of polymerization where is a vinyl group and the remainder is a methyl group
160 parts of crushed quartz having an average particle size of 3 μm were sufficiently kneaded with 100 parts of polydiorganosiloxane of 5500 using two rolls to obtain a base conhound. Take 100 parts of this base compound, add 0.3 parts of 2,5-dimethyl-2,5-di-t-butylperoxyhexane, knead it further, put it in a mold with a depth of 10 mm, and press it at 170°C for 30 minutes. A vulcanized silicone rubber sheet was obtained by molding and further heating at 200°C for 4 hours. The amount of filler in this silicone rubber was 61.5% by weight, and the density at 38°C was 1.60. When we measured the acoustic impedance of this silicone rubber at 38°C, it was 1.51×10 ⁶ [Kg/m ²
s]. This silicone rubber was attached to the inner wall of the water tank 5 to form a sound absorbing material 7. Fill this tank with water 6,
Place transducer 1 in it and set the temperature to 38℃.
Set it to generate ultrasonic waves with a frequency of 5MHz,
When the magnitude of the reflected wave was measured, it was -50 dB. Example 2 Having hydroxyl groups bonded to silicon atoms at both ends,
130 parts of crushed quartz having an average particle size of 1 μm was blended with 100 parts of polydimethylsiloxane having a viscosity of 10,000 CP at 25° C. and thoroughly mixed to obtain a base compound. 100 parts of this base compound was placed in a beaker, 1.1 parts of a partial condensate of ethyl silicate was added as a crosslinking agent, and 0.1 part of dimethyltin hydroxide monooleate was added as a catalyst, mixed, and defoamed in a glass vacuum container. The material was injected into a mold with a depth of 10 mm, left at room temperature for one day and night, taken out, and then left for two days and nights to be completely cured to obtain a silicone rubber sheet. The weight ratio of the filler was 56.5%, and the density at 25°C was 1.50. When the same experiment as in Example 1 was conducted using this silicone rubber, the acoustic impedance was 1.50×10 ⁶ [Kg/m ² ·s] and the magnitude of the reflected wave was -38 dB at 25°C. . Comparative Example 1 100 parts of polydiorganosiloxane similar to that used in Example 1, 47 parts of fumed silica with an average particle size of 25 μm that was made hydrophobic by baking with polydimethylsiloxane, and diatoms with an average particle size of 15 μm Saturday 24th part,
A base compound was obtained by blending and kneading 40 parts of crushed quartz with an average particle size of 1 μm and 4 parts of polymethylphenylsiloxane with an average degree of polymerization of 18, both ends of which were blocked with methoxy groups. This base compound was vulcanized in the same manner as in Example 1 to obtain a vulcanized rubber sheet. The amount of filler in this silicone rubber was 48.4% by weight, and the density at 38°C was 1.39. When the same experiment as in Example 1 was conducted using this silicone rubber, the acoustic impedance at 38°C was 1.37×10 ⁶ [Kg/m ² ·s] and the magnitude of the reflected wave was -23 dB. Example 3 Silicone rubber sheets A to E were obtained in the same manner as in Example 1, except that crushed quartz having an average particle size of 2 μm was used and the blending amount was changed as shown in Table 1. However, A and E are comparative samples. For these samples, the density, acoustic impedance, and magnitude of reflected waves at 25°C, 35°C, and 40°C were measured. Regarding Samples C and D, the above characteristics were further measured at 38°C. These results are shown in Table 1. As is clear from Table 1, sample B is at 25°C, sample C is at 35°C and 38°C.
°C, D is 35-40 °C, it is suitable for use as an antireflection agent.

[Table] [Effects of the invention] The present invention achieves an acoustic impedance of 1.46 to 1.55×10 ⁶ [Kg/m ²
s] can be easily obtained. As a result, the amount of reflected ultrasound waves scattered on the inner wall of the aquarium can be significantly reduced, and it is effective for use on the inner wall of the aquarium of an ultrasonic device used for diagnosis of breast rays and the like.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of a scan of a breast ray diagnostic probe, and FIG. 2 is a sectional view of the inner wall of a water tank to which an acoustic absorbing material is pasted. 1... Ultrasonic transducer, 2... Subject, 5... Water tank, 8... Sound absorbing material, 9', 10
...Reflected sound waves.

Claims (1)

[Claims] 1. Acoustic impedance at one temperature between 20 and 40°C is 1.45 to 1.55×10 ⁶ [Kg/m ² ·s]
An underwater acoustic non-reflection absorbing material characterized by being made of filler-containing silicone rubber. 2 As a filler for silicone rubber, the average particle size
The underwater acoustic non-reflection absorbing material according to claim 1, characterized in that silicone rubber is filled with silica of 0.5 to 20 μm in an amount of 53 to 65% by weight.