JPH047880B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a piezoelectric transducer capable of transmitting high-power ultrasonic waves underwater. (Prior Art) Conventionally, a bolt-tight lunge van transducer as shown in Fig. 3 has been used as a high-efficiency ultrasonic transducer capable of transmitting high-power waves in the frequency band of several KHz to several tens of KHz underwater. It has been known. As shown in Fig. 3, this bolt-tight lunge transducer is made of Al-alloy, Ti-alloy,
A front mass 31 made of a highly rigid material such as steel,
A ring-shaped piezoelectric ceramic 32 disposed between the front mass 31 and the rear mass 33 is made of a highly rigid material such as stainless steel like the front mass 31, and has the function of applying compressive stress to the rear mass 33 and the ring-shaped piezoelectric ceramic 32. Has Cr
- It is composed of bolts 34 and nuts 35 made of high tensile strength steel such as Mo steel, and has the great feature of being capable of high power driving.
Here, the ring-shaped piezoelectric ceramic 32 uses a longitudinal effect longitudinal vibration mode (33 mode) which can obtain a much larger electromechanical coupling coefficient than a transverse effect longitudinal vibration mode (31 mode). Adjacent piezoelectric ceramic rings 32 are polarized in opposite directions as shown by the arrows in the figure, and matched with the power amplifier by electrically connecting them in parallel. In addition, since piezoelectric ceramics are generally more vulnerable to tensile stress than compressive stress, a static bias stress is applied in advance by the bolt 34 and nut 35, making it suitable for use even at high power. It has a durable structure. Incidentally, as is well known, the bolt-tightening lunge transducer with this structure is 1/2
A wavelength resonance mode is used. (Problem to be Solved by the Invention) Since the above-mentioned bolted lunge van transducer uses half wavelength resonance, the resonant frequency and the length of the transducer are inversely proportional if the shapes are the same. The relationship is that if the frequency is halved, the length will be twice as long. Furthermore, these transducers are usually arranged in large numbers in order to obtain the desired directivity, and arrays in which many transducers are arranged in this way inevitably become larger and heavier as they are used at lower frequencies. Become. For this reason, in recent years there has been a strong demand for bolt-tight lunge transducers to be smaller and lighter. In order to reduce the size of this transducer, it is better to make the cross-sectional area of the front mass larger than the cross-sectional area of the piezoelectric ceramic, or to make the front mass as thin as possible. However, when the front mass is made thinner, the front mass itself tends to bend, making it difficult to efficiently radiate sound. On the other hand, in order to reduce the deflection of this front mass, it is conceivable to make the bolt diameter sufficiently small. That is, by reducing the diameter of the bolt, the shearing force acting on the front mass can be reduced. This shear force is
When a piezoelectric ceramic ring expands and contracts piezoelectrically,
This occurs because the bolts try to prevent the expansion and contraction of the piezoelectric ceramics. However, when the diameter of the bolt is reduced, it becomes difficult to apply sufficient bias stress to the ring-shaped piezoelectric ceramic, as is well known. Further, the bolted lunge transducer is typically designed and manufactured so that the acoustic radiating surface causes the piston to vibrate. Most of the vibration stress acting on a conventional bolt-tightening lunge transducer is applied to the ring-shaped piezoelectric ceramic and the bolt portion, and the front mass 31 and rear mass 33 only perform translational displacement of the piston. In other words, the front mass that emits acoustics is displaced by the same amount as the displacement generated in the piezoelectric ceramics, and this displacement is generally small, and the mechanical impedance when looking at the transducer from the acoustic radiation surface is similar to that of water as a medium. It is considerably large compared to the acoustic radiation impedance. This creates an acoustic impedance mismatch between the water and the transducer.
This had the disadvantage that the transducer bandwidth was limited. Therefore, it has been difficult to reduce the underwater Q value (reciprocal of 3 dB specific bandwidth) of a bolted lunge van transducer to 5 or less. As described above, there are certain limitations when trying to make the transducer smaller, lighter, and wider with the conventional bolt-tight lunge van transducer. An object of the present invention is to realize a broadband transducer that is small, lightweight, and has high electroacoustic conversion efficiency. (Means for Solving the Problem) The present invention includes a piezoelectric ceramic laminate having a through hole inside thereof arranged between a bending front mass and a rear mass, and a piezoelectric ceramic laminate having a through hole provided in the piezoelectric ceramic laminate. A bolt that applies compressive stress to the body is provided, a slit or groove is formed in the bent front mass portion from the outer edge to the center portion, and an acoustic radiation front mass is further provided from near the outer edge of the bent front mass via a hinge. This is an underwater ultrasonic transducer featuring: (Function) Contrary to the conventional bolt-tight lunge transducer, the present invention actively utilizes the shearing force generated between the piezoelectric ceramic laminate and the bolt.
Excite bending vibration accompanied by rigid body rotation of a bending front mass in which slits have been formed in advance. At this time, an expanded displacement several times that of the piezoelectric ceramic laminate occurs at the outer edge of the bent front mass, and the expanded displacement is transferred from the outer edge of the bent front mass to the acoustic radiation front mass via the hinge. It is characterized by efficient acoustic radiation over a wide band by transmission. An underwater ultrasound transducer according to the invention is shown in FIG. In FIG. 1, 11 is a bent front mass, 12 is a rear mass, 13 is a piezoelectric ceramic laminate, 14 is a bolt, and 14' is a bolt head.
15 is a nut; 17 is a neck that transmits the displacement generated in the piezoelectric ceramic laminate to the bending front mass 11;
18 is an acoustic radiation front mass, and 19 is a hinge that transmits the displacement of the bending front mass to the acoustic front mass 18. Further, FIG. 2 shows a front view of the front mass portion 11. In FIG. 2, 16 indicates a slit or groove. The principle of operation of the transducer according to the present invention will be explained based on FIG.
The bending front mass 11 is extended forward when the piezoelectric ceramic laminate 13 is piezoelectrically extended. However, since the bolt 14 is not piezoelectrically stretched, when the piezoelectric ceramic laminate 13 is stretched, the piezoelectric ceramic laminate 1 is inserted into the bolt 14.
A force is generated that tries to prevent the elongation of 3. This pressure increases as the diameter of the bolt 14 increases. In this way, the bent front mass 1
When a shearing force is generated in the neck portion 1 and the bending front mass 11 is bent, the phases of the bending front mass portion outside the neck portion 17 and the bending front mass portion inside the neck portion 17 become opposite to each other. In the transducer according to the present invention, even if the phase of the vibration displacement is opposite between the central part and the outer edge of the bent front mass, it is sufficient that a large displacement can be obtained at the outer edge. Due to the addition of rigid body translational displacement due to the elongation of the piezoelectric ceramic laminate, the final result is the broken line a-
The vibration displacement of the outer edge of the bent front mass is caused by the piezoelectric ceramic laminate 1.
It reaches several times the displacement of 3. This expanded displacement at the outer edge of the bent front mass is transmitted to the acoustic radiation front mass 18 via the hinge 19, and a large amount of medium displacement is obtained, making extremely effective acoustic radiation possible. The principle of operation of the transducer according to the present invention has been described above. When the slit shown in FIG. 2 is provided with the groove 16 in the bent front mass 11, effective medium removal becomes possible. By providing such a slit or groove 16, the contact point between the bolt and the front mass, the contact point between the neck 17 protruding from the piezoelectric ceramic laminate and the front mass, that is, the contact point between these two contact points can be used as a lever arm. This principle allows the vibration displacement to be significantly expanded at the outer edge of the front mass. In conventional bolt-tight lunge transducers, the front mass only undergoes rigid translational displacement, so the amount of medium displacement is small and the bandwidth is not very wide. On the other hand, in the transducer of the present invention, since the bending front mass has a function of expanding the displacement, the piston displacement is magnified in the acoustic radiation front mass via the hinge. Therefore, it is possible to reduce the input mechanical impedance when looking at the transducer from the acoustic radiation due to its small size and light weight, and it is possible to achieve high efficiency and wide band. (Example) As an example of the present invention, an underwater ultrasonic transducer shown in FIG. 1 will be described. The transducer shown in Figure 1 has a resonant frequency of 7KHz.
The acoustic radiation surface is a square with a side length of 11.3 cm.
The piezoelectric ceramic of the piezoelectric ceramic laminate has an electromechanical coupling coefficient K ₃₃ of 0.61 and a relative dielectric constant ε ₃₃ T/
Lead zircon titanate piezoelectric ceramics with ε ₀ of 1080 were used. Al alloy for bent front mass 11, stainless steel for rear mass 12, bolt 1
4 and the nut 15, stainless steel for the neck 17, high-strength steel for the hinge 19, and honeycomb-structured Al alloy for the acoustic radiation front mass 18. Further, a slit 16 with a width of 0.5 mm was formed in the bent front mass 11. The transducer of this example had a length of 13.1 mm and a weight of 1660 g. This transducer is then mounted in a watertight housing to improve the electroacoustic conversion efficiency.
The 3 dB specific bandwidth in water (the reciprocal of the Q value in water) was measured. The results are shown in Table 1 in comparison with a conventional bolt-tight lunge transducer that resonates at 7kHz.

[Table] Therefore, this transducer is advantageous in terms of weight reduction compared to conventional bolt-on lunge transducers, and has excellent acoustic impedance matching with water in water. Sound conversion efficiency is also high. Note that the same effect can be obtained even if a groove is formed instead of the slit 16. It is desirable that the resonance frequency of the front mass's bending vibration is about 0.5 to 1.5 times the resonance frequency of its translational vibration. Also, the diameter of the front mass should be approximately 3 times or more the diameter of the neck.
It is desirable to have a circle that is approximately 10 times larger or less, or a shape that has an area equal to this circle. (Effects of the Invention) As described above, the transducer of the present invention expands the displacement with the bent front mass and transmits the expanded displacement to the front mass that emits sound through the hinge, so it is lightweight. A highly efficient broadband underwater ultrasound transducer can be obtained.

[Brief explanation of drawings]

FIG. 1 shows an underwater ultrasonic transducer according to the present invention, in which 11 is a bent front mass, 12 is a rear mass, 13 is a piezoelectric ceramic laminate, 14 is a bolt, 14' is a bolt head,
15 is a nut, 17 is a neck, 18 is an acoustic radiation front mass, 19 is a hinge, broken lines a-a' and b-
b′ indicates the vibration displacement of the front mass. FIG. 2 is a front view of the bent front mass, with 16 indicating the slits or grooves. FIG. 3 is a diagram showing a conventional bolt-tight lunge transducer, and in the figure,
31 is a front mass, 32 is a piezoelectric ceramic ring, 33 is a rear mass, 34 is a bolt, and 35 is a nut.

Claims (1)

[Claims] 1 A piezoelectric ceramic laminate with a through hole inside is arranged between the bent front mass and the rear mass,
A bolt that applies compressive stress to the piezoelectric ceramic laminate is provided in a through hole provided in the piezoelectric ceramic laminate, and a slit or groove is formed in the bent front mass portion from the outer edge to the center portion, and a slit or groove is formed in the bent front mass portion. An underwater ultrasonic transducer characterized in that an acoustic radiation front mass is provided via a hinge from the vicinity of the underwater ultrasonic transducer.