JP2934970B2 - Underwater acoustic transducer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention includes a piezoelectric rubber made of a piezoelectric composite material in which a piezoelectric ceramic powder is blended with a rubber base material such as a synthetic rubber. The present invention relates to an underwater acoustic transducer for transmitting an ultrasonic wave or receiving a sound wave or ultrasonic wave propagating in water.

[Prior Art] Anisotropic piezoelectric ceramic powder such as lead titanate (PbTiO ₃ ) is a ferroelectric material having a perovskite structure, and is therefore widely used as various piezoelectric materials and pyroelectric materials. However, recently, the piezoelectric constant d _h (d ₃₃ +2
Since d ₃₁ ) and g _h (= d _h / ε) are large, they are attracting attention as piezoelectric materials for underwater acoustic transducers such as hydrophones.

Such a piezoelectric material for underwater acoustic transducers has good acoustic matching with water so that sound waves or ultrasonic waves can be efficiently radiated or received into water, and has sufficient water pressure even when immersed deeply in water. A low-density, highly flexible piezoelectric material is required to have the strength to withstand.

In response to such demands, a composite material in which particles such as lead titanate are prepared and mixed with a rubber base material such as synthetic rubber has been proposed, and in this material, a larger piezoelectric constant d _h , The realization of g _h is desired.

[Problems to be Solved by the Invention] Piezoelectric constants d _h and g of the piezoelectric rubber used in the underwater acoustic transducer
_In order to increase _h , anisotropic piezoelectric ceramics in the rubber substrate, such as PbTiO ₃ , BiFeO ₃ , Bi ₅ TiNbWO ₁₅ (mixed layered composite bismuth oxide), lead titanate / bismuth ferrite solid solution, etc. It is generally known that the volume ratio of the powder may be increased. That is, the dielectric constant ε ₃₃ ^T / ε ₀ with increasing volume fraction as the theoretical curve shown in the graph of Figure 1, is the be expected In the desk of the piezoelectric constant d _h is increased.

Here, as shown in FIG.
A piezoelectric composite material containing only a small particle size such as μm in a rubber base material has a higher piezoelectric size than a material containing only a large particle size such as 31.8 μm in a rubber base material. constant
d _h is said to be low.

Thus a piezoelectric ceramic powder of large particle size, if increasing the volume ratio as possible, and thus capable of increasing the piezoelectric constant d _h.

However, even if the volume ratio is actually increased, the dielectric constant ε ₃₃ ^T / ε ₀ and the piezoelectric constant d _{h are} reduced from about 60% as shown in FIG.
Is on a downtrend and does not always meet the theory. In the case of using only large-diameter piezoelectric ceramic powder,
When the volume ratio to the rubber substrate is increased,
As shown in FIG. 2, the change rate [Delta] d _h / d _h rate of change Δε ₃₃ ^T / ε ₃₃ ^T and the piezoelectric constant of the dielectric constant is increased, the piezoelectric dependency increases. Further, even in a piezoelectric composite material in which only a small particle diameter is contained in a rubber base material, although not as large as that of a large particle diameter, each of the above-mentioned rates of change also increases as the volume ratio increases, and the pressure dependence is increased. Increase.

If the pressure dependency is high in this way, if the underwater acoustic transducer is used at different depths (water pressures), the output will vary, and it will be necessary to correct the output and the signal processing will be complicated. This will cause problems.

Here, each of the above-mentioned rates of change is obtained by taking a change in each characteristic value when the sample of the piezoelectric composite material is immersed in an insulating solution and the hydrostatic pressure is increased from 0.5 MPa to 15 MPa.

The present invention has a low pressure dependency and a piezoelectric constant d _h , g
It is intended to provide an underwater acoustic transducer having a high _h .

[Means for Solving the Problems] The present invention relates to an underwater acoustic transducer provided with a piezoelectric rubber having electrodes formed on the front and back sides and polarized in the thickness direction. ± 3 for diameter
A piezoelectric ceramic particle group having a particle size distribution in the range of σ (σ; standard deviation) and having an average particle size of 5 to 10 μm and a piezoelectric ceramic particle group having an average particle size of 20 μm or more ratio
A small pressure-dependent piezoelectric composite material that is blended in the range of 1: 5 to 5: 1 and mixed so that the volume ratio of the total amount of piezoelectric ceramic particles in the rubber base material is 60% or more It is characterized by having been formed.

[Operation] The reason why the pressure dependency of the piezoelectric composite material used for the piezoelectric rubber of the underwater acoustic transducer having the conventional configuration described above increases with an increase in the volume ratio will be examined.

When the amount of the piezoelectric ceramic powder in the rubber base material is increased, and the powder is constituted by one having a large average particle size, each particle comes into close contact with the increase in the density, and during that time, the relative This creates a large volume gap. For this reason, in the mixing process of the rubber base material and the piezoelectric ceramic powder, air mixed in the material is trapped in the gap, and large pores are easily generated. On the other hand, in the case of particles having a small particle size, the surface area of the piezoelectric ceramic powder is significantly increased, and it is considered that small pores formed at the grain boundary between the piezoelectric ceramic powder and the rubber base material increase as an air layer. Can be

In other words, even if the mechanisms of forming the gaps are different from each other, it is expected that the pore content will increase due to the increase in the blending amount regardless of whether the particle size is too large or too small. And when there are pores like this,
When a piezoelectric composite material is used under high pressure, such as in water, it is compressed and changes its properties.

Therefore, in order to investigate the increase in pores, the measured density ρ _{meas of the} sample and the theoretical density ρ _cal
The change with respect to the volume ratio of the piezoelectric ceramic particles was examined by taking the ratio of As a result, it was found that the density ratio ρ _meas / ρ _{cai at} which the volume ratio becomes 65% or more decreased, and the measured density ρ _meas decreased from the theoretical density ρ _cal . And this density difference is
It can be concluded that the pores increase as the volume fraction increases.

Then, based on such knowledge, the present inventor, if a large particle size and a small particle size are mixed at a predetermined ratio, the small particle size is interposed between the large particle size, Since a rubber-like base material is uniformly mixed between the particles because there is no closed space between the particles, the surface area per unit weight of the particles is reduced, and the generation of pores at the grain boundaries is suppressed. I thought I could do it.

As a result of various tests, piezoelectric ceramic particles having a particle size distribution whose limit value is within ± 3σ (σ; standard deviation) with respect to the average particle size, and having an average particle size of 5 to 10 μm. And a group of piezoelectric ceramic particles having an average particle size of 20 μm or more are blended in a volume ratio of 1: 5 to 5: 1, and the volume ratio of the total volume of the piezoelectric ceramic particles in the rubber base material is 60% or more. It has been confirmed that the piezoelectric composite material formed by mixing so as to have a low pressure dependency and a high piezoelectric constant is a useful material. That is, when a piezoelectric rubber is formed by using such a piezoelectric composite material and a hydroacoustic transducer is formed by using the piezoelectric rubber, excellent characteristics can be realized.

[Example] A piezoelectric composite material for forming the piezoelectric rubbers 1a and 1b according to the present invention will be described.

First, a lead titanate particle group (PT) having an average particle size of 7.3 μm and 31.8 μm was prepared, and was blended in a ratio of 1: 5, 1: 2, 1: 1, 2: 1 and 5: 1. Is mixed with chloroprene rubber, and the compounding ratio is such that the volume ratio of lead titanate particles is 50%, 55%, 62.5%.
%, 65%, 70%, 72.5%, 75%, 77.5% and 80% of 50 mixed samples were prepared. Here, the average particle size is 7.3 μm and 31.8
The μm lead titanate particle group has the particle size distribution shown in FIG. 7B and FIG. 7C, and the limit value of the particle size distribution is within ± 3σ (σ; standard deviation) with respect to the average particle size.

Then, a vulcanizing agent is added to the mixture having the above-mentioned compounding ratio, and after kneading, vulcanization molding is performed to form a flat plate of 80 mm (0.5 mm in thickness) while applying pressure in the plane direction. The piezoelectric rubbers 1a and 1b thus formed are cut out into a disc of φ30 as shown in FIG. 3, and the two pieces are bonded together such that the center becomes the anode and the outer surface becomes the negative electrode. The cables 2a and 2b were connected to the respective poles, which were further attached to a damping material 3, and resin-molded with a polyurethane resin 4 to form an underwater acoustic transducer having piezoelectric rubbers 1a and 1b.
And each characteristic was measured.

Similarly, as compared with this, the PT powder alone having an average particle diameter of 3.3 μm, 7.3 μm, and 31.8 μm of lead titanate powder was used in a volume ratio of 30%, 40%, 50%, 60%, 65%, 7
A total of 27 types of piezoelectric composite materials mixed with a rubber base material so as to be 0%, 75%, and 80% were prepared. Here, the average grain size is 3.3 μm
Are particle groups having a particle size distribution shown in FIG. 7A, and the limit value of the particle size distribution is within a range of ± 3σ (σ; standard deviation) with respect to the average particle size.

Similarly, a piezoelectric composite material in which a single PT powder having an average particle size of 15.2 μm was mixed with a rubber base material such that the volume ratio was 70% was prepared as a comparative sample.

Further, as an example of another material of the present invention, an average particle size of 6.9 μm
m and 35.0 μm of lead zirconate titanate (PZT) porcelain powder were blended at a volume ratio of 1: 1 and blended in chloroprene rubber so as to have a volume ratio of 80%. Then, an underwater acoustic transducer made of piezoelectric rubber having the same structure was constituted by each piezoelectric composite material, and each characteristic was measured and compared.

As a result, the respective relationships shown in FIGS. 1 to 6 could be obtained. Also, the values shown in the following table were obtained. Here, the following table shows each measured value when the volume ratio of PT is 70% and its vicinity.

As shown in the above table, in each of the volume ratios, the density ratio ρ _meas / ρ _cal is 90% or more. Then, as shown in FIG. 2, the average particle size is 3.3 μm, 7.3 μm or 31.8 μm.
When only the lead titanate particles are mixed with the rubber base material, the volume ratio rapidly decreases when the volume ratio is 60% or more, and as shown in the preceding table, when the volume ratio is about 70%, the density ratio is 96.7% (average particle size).
7.3 μm), 96,9% (average particle size 31.8 μm) and 96.2% (average particle size 15.2 μm), whereas the PT-based composite material of the present invention also has a density ratio of about 70% by volume. 97.2%, indicating that the decrease was small and the pores were reduced as compared with the conventional configuration.

On the other hand, the sound velocity c did not change much, and did not change the acoustic impedance, so that the usefulness as a piezoelectric material for an underwater acoustic transducer could be maintained.

Further, the dielectric constant ε ₃₃ ^T / ε ₀ , the wave receiving sensitivity and the piezoelectric constants d _h , d ₃₃ were also improved, and it was confirmed that they had good characteristics.

Further, the piezoelectric constant d ₃₁ in the radial direction was calculated from the relationship d _h = d ₃₃ + 2d _{31 using} the piezoelectric constants d _h and d ₃₃ .
The absolute value of the piezoelectric constant d ₃₁ Remarkably becomes extremely small value, it was confirmed that the volume ratio of the mixed particles to chloroprene rubber may be assumed to approximate to zero at 77.5 percent or more.

When the piezoelectric constant d ₃₁ is close zero, the vibration in the radial direction is applied to the piezoelectric transducer, but is intended to generate a normal noise, generation of the output according to the radial vibration is suppressed,
There is an advantage that the wave receiving characteristics are improved.

Furthermore the conventional piezoelectric composites using PZT ceramic powder, the piezoelectric constant d ₃₃ compared with the lead titanate particles have good characteristics of high piezoelectric constant d ₃₁ in the other hand
Absolute value was also high, and its usefulness had been diminished. However, PZT-based composite material of the present invention obtained by mixing piezoelectric ceramic particles having an average particle diameter of the two kinds of large and small as the previous table piezoelectric constant d ₃₁ is -
1.5 and small. As induction from this experiment, even in the PZT-based composite material, by applying the present invention it is possible to improve the piezoelectric constant d _33, can also reduce the absolute value of piezoelectric constant d _31, the It turns out that usefulness can be further extracted.

Looking at the pressure dependence, the rate of change of the dielectric constant Δε ₃₃ ^T / ε ₃₃ ^T and the rate of change of the piezoelectric constant Δd _h when the sample was immersed in an insulating solution and the hydrostatic pressure was increased from 0.5 MPa to 15 MPa /
d _h is observed to be small. Therefore, it can be seen that the present invention can reduce the pressure dependency as compared with the conventional configuration.

Here, large materials commonly piezoelectric constant d _h is the rate of change Δ
d _h / d _h also have been greater, the front Comparing the comparative sample consisting of a single PT Composites what percentage by volume of 70% as shown in Table, the piezoelectric constant d _h is 30.2 despite it indicates a large value, the change rate [Delta] d _h / d _h was observed to be much smaller than the comparative sample.

Thus, it is confirmed that the piezoelectric composite material having such a configuration is extremely useful.

[Reason for limiting the numerical values] Mixed particles were prepared by mixing lead titanate particles having an average particle size of 31.8 μm and 7.3 μm at various compounding ratios, and the particles were mixed at various volume ratios with respect to the rubber base material. The pressure dependence of each was investigated.

Here, FIG. 4 shows the average particle size of 31.8 μm and 7.3 μm on the horizontal axis.
Taking the ratio of the vertical axis represents the piezoelectric constant d _h, yet in which examined the pressure dependency by changing the hydrostatic pressure in the material.

As a result, the difference between when the hydrostatic pressure is applied (15 MPa) and when the pressure is released (0.5 MPa) as the volume ratio to the rubber substrate increases or as the mixing ratio of the average particle size increases to 31.8 μm. Was increased, and the pressure dependence was confirmed to increase.

By the way, as described above, the pressure dependency is closely related to the content of air in the piezoelectric composite material. That is, it can be understood that the smaller the density ratio ρ _meas / ρ _cal , the larger the proportion of air. It can be said that the higher the ratio of the average particle diameter is 31.8 μm, or the higher the volume ratio of the mixed particles to the rubber base material, the larger the air content and the smaller the density ratio ρ _meas / ρ _cal . That is, by using the density ratio ρ _meas / ρ _cal as a reference, the mixing ratio, the volume ratio, and other factors can be dealt with on the same basis and handled as similar factors.

Therefore, in FIG. 5, showing the density ratio ρ _meas / ρ _cal, the relationship between the reduction rate of the piezoelectric constant d _h.

Examining this relationship, each sample was roughly composed of three groups I, I
It can be classified into I and III. That is, even by changing the hydrostatic unchanged piezoelectric constant d _h is almost the pressure dependency is small group I, group II, and the rate of change and the density ratio of the piezoelectric constant changes a linear function manner, and random value And the rate of change is relatively stable. Group II
It can be divided into a group IIa having a small change rate by approximating the group I, a group IIb having a similar change rate to the group III, and a group IIc having a larger change rate.

This time, the average particle size is 31.8μ on the horizontal axis in FIG.
The relationship between each group was examined by taking the ratio of m to 7.3 μm, and taking the volume ratio of the mixed particles on the vertical axis.

As a result, it is interesting that group IIa, which has relatively small pressure dependence, penetrates into the higher volume fraction of the mixed particles at its center (in the range of 1: 5 to 5: 1), In such a range, even if a large amount of piezoelectric ceramic particles were mixed into the rubber substrate, the pressure dependency was good. However it if the volume fraction of the piezoelectric ceramic is larger dielectric constant ε ₃₃ ^T / ε _0, and the piezoelectric constant d _h is improved is apparent even in the first FIG. Therefore, from such analysis, the average particle size of 31.8μm and 7.3μm
The volume ratio of m is 1: 5 to 5: 1 in the range, the pressure dependency is relatively small and it is determined a material capable of obtaining a high dielectric constant ε ₃₃ ^T / ε _0, and the piezoelectric constant d _h Can be done.

And the average particle diameters 31.8 μm and 7.3 μm shown in the previous table
Even when the volume ratio is 1: 1, predetermined characteristics are generated in the above range.

On the other hand, the average particle size of the piezoelectric ceramic powder having a small average particle size is 5 to 10 μm.
m. This is because those in this range are excellent in terms of ease of preparation and realistic. The average particle size of the piezoelectric ceramic powder having a large average particle size is considered to be in a range of 20 μm or more. Although the difference from the small average particle size is 10 μm, there is an eight-fold difference in the volume ratio of the particles, and if there is such a difference in the average particle size, the limit value is ± 3σ with respect to the average particle size.
(Σ; standard deviation), having a particle size distribution in the range, each particle size is less likely to overlap,
This is because the required operation and effect can be obtained.

As a result, the piezoelectric composite material used in the present invention has the above-mentioned particle size distribution, and the average particle size has a difference of two times or more from each other. It can be defined as a mixture of a plurality of groups of piezoelectric ceramic powders having different average particle diameters which can be substantially avoided from being wrapped and mixed with a rubber base material. For example, a piezoelectric ceramic powder having an average particle size of 5 to 10 μm and a piezoelectric ceramic powder having an average particle size of 20 μm or more have a volume ratio of 1: 5.
It can be grasped as what was blended in a range of from 5: 1 to 5: 1 by mixing them in a rubber base material such that the volume ratio of the total amount of piezoelectric ceramic particles was 60% or more.

In each of the examples, test values for lead titanate particles were shown. However, since the present invention relies on mutual physical behaviors having different average particle sizes, other piezoelectric materials such as PZT are used. The same effect can be obtained with the porcelain powder, and is not limited to lead titanate particles.

[Effects of the Invention] The piezoelectric composite material used in the underwater acoustic transducer of the present invention is obtained by mixing two or more types of piezoelectric ceramic particles having a predetermined relationship between a large average particle and a small average particle diameter, thereby forming pores. The content is reduced as much as possible, which results in good properties such that the piezoelectric constant d _h is sufficiently large and the pressure dependence is small. Therefore, the underwater acoustic transducer of the present invention including the piezoelectric rubber formed of the piezoelectric composite material has a small pressure dependency,
Even when used at different depths (water pressure), a stable output can be obtained.

[Brief description of the drawings]

FIG. 1 shows the volume ratio of the piezoelectric ceramic powder and the dielectric constant ε ₃₃ ^T / ε _0.
And a graph showing the relationship between the piezoelectric constant d _h, the graph FIG. 2 showing the volume fraction of piezoelectric ceramic powders, the relationship between the change rate and the density ratio of the dielectric constant epsilon ₃₃ ^T and the piezoelectric constant d _h, Fig. 3 graph showing the vertical sectional side view showing a configuration of the underwater acoustic transducer of the present invention, the relation between the mixing ratio and the piezoelectric constant d _h in Fig. 4 mixed particles,
Figure 5 is a graph showing the reduction rate of the density ratio and the piezoelectric constant d _h, graph Figure 6 is showing a relationship between the mixing ratio of the mixed particles and their volume fraction, seventh stamen, b, c are each present invention 10 is a graph showing the particle size distribution of the lead titanate particles having an average particle size of 3.3 μm, 7.3 μm, and 31.8 μm used in the example of FIG.

Claims (1)

(57) [Claims] 1. An underwater acoustic transducer comprising a piezoelectric rubber having electrodes formed on both sides thereof and polarized in a thickness direction, wherein the piezoelectric rubber has a limit value of ± 3σ with respect to an average particle diameter.
(Σ; standard deviation), a volume ratio between a piezoelectric ceramic particle group having an average particle size of 5 to 10 μm and a piezoelectric ceramic particle group having an average particle size of 20 μm or more. 1:
It is formed of a small pressure-dependent piezoelectric composite material that is blended in a range of 5 to 5: 1 and mixed in a rubber base material so that the volume ratio of the total amount of piezoelectric ceramic particles is 60% or more. An underwater acoustic transducer.