JPH0511717B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a high power underwater ultrasonic transducer having broadband and high efficiency characteristics.

(Prior Art) Conventionally, among underwater ultrasonic transducers, a transducer is used on the acoustic side of a piezoelectric ceramic transducer 71 as shown in FIG. A transducer is known in which an acoustic matching plate 72 with a quarter wavelength is provided for a resonant frequency of 71 (I.E.
IEEE
PROCEEDIHGS, Vol.131, PartF, No.3,
June 1984)). This matching plate 72 has an impedance intermediate between that of the piezoelectric ceramic transducer and the load medium of water, and has an impedance of 3.2×10 ⁶ to 4.5×10 ⁶ MKS Rayls.
An impedance match with water is just achieved at an acoustic impedance density (defined as the product of the speed of sound and the density) of approximately The matching layer material having such an acoustic impedance density is usually a composite material in which inorganic fine particles such as glass are uniformly dispersed in epoxy resin, and the desired acoustic impedance can be achieved by adjusting the blending ratio of the inorganic fine particles. density can be obtained.

(Problems to be Solved by the Invention) Although the conventional underwater ultrasonic transducer equipped with an acoustic matching plate has excellent characteristics such as high efficiency over a wide band, it is difficult to use the acoustic matching plate and ceramics. Adhesion to the vibrator had to be carried out exclusively using epoxy adhesive, and as a result, there was a risk that the acoustic matching plate would peel off from the ceramic vibrator during high-power wave transmission. In addition, the acoustic matching layer itself made of such a material easily reaches a nonlinear region during high-power transmission, which causes distortion of the transmitted waveform and deterioration of the linearity of the acoustic radiation power with respect to the input power. It was hot. Furthermore, simply changing the acoustic matching plate to a material with higher strength does not work, and even if the acoustic matching layers are multiplexed, the design becomes extremely difficult, making it impossible to achieve high power and high bandwidth. Therefore, the use of such transducers is limited to small or medium power transmission, and is unsuitable for high power transmission (eg, parametric arrays).

An object of the present invention is to realize a transducer that has wide-band, highly efficient acoustic radiation characteristics and is capable of high-power transmission.

(Means for Solving the Problems) The underwater ultrasonic transducer according to the present invention includes a one-half wavelength resonant bolt-tight Lange-van transducer and a half-wave resonant bolt-tight Lange-van transducer on the sound field side. The underwater ultrasonic transducer is characterized in that a wavelength resonator is provided, and the bolted LangueVant resonator and the half-wavelength resonator are firmly coupled by a longitudinal coupler.

(Function) A typical example of the high power underwater ultrasonic transducer of the present invention is shown in FIG. 1a. In FIG. 1a, 11 is a hollow piezoelectric ceramic vibrator;
2 and 13 are metal masses, 14 is a bolt, 15 is 2
1/1 wavelength resonator, 16 is a longitudinal coupler. Further, 17 is a nut, and in the case of the transducer shown in FIG.
Even with the nut 17, the piezoelectric ceramic vibrator 11
It is now possible to apply a static stress bias to the part. As is well known, the strength of piezoelectric ceramics against tension is only a fraction of the strength against pressure, so a bolt-fastened lunge resonator with means for applying such static compressive stress can be excited with high power and force. This is particularly good in cases where The bolted Languevin resonator consisting of the constituent elements 11, 12, 13, 14, and 17 as shown in FIG. 1 operates in a half wavelength resonance mode. In addition, 15 is a half-wavelength resonator made of a lightweight and high-strength metal material such as Al alloy, Ti alloy, or Mg alloy;
6 is a vertical connector made of a high-strength metal material (for example, Cr-Mo steel).

As is clear from Figure 1a, all important parts of this transducer are constructed from high-strength metal materials or fiber-reinforced materials, and there is no need to rely on organic adhesives for connections between mechanical parts. Therefore, mechanical strength several times that of a conventional transducer with an alignment plate can be easily achieved.

The vibration mode of the multi-mechanical transducer shown in FIG. 1a is shown in FIG. 1b. This transducer has two resonance modes with resonance frequencies ₁ and ₂ . The operating range of this transducer is between resonance frequency ₁ and ₂ . In the case of this transducer, by increasing the thickness of the vertical coupler 16, the interval between ₁ and _f2 increases, and a wider band can be achieved. Therefore, if a transducer is made to have a wider band, the longitudinal coupling becomes thicker, which increases the mechanical strength.

One end surface 18 of the half wavelength resonator 15 serves as an acoustic radiation end, and plays an important role in impedance matching with water, which is a load.

When achieving a wide band in the transducer based on the present invention, it is advantageous to use a material with a small acoustic impedance density as the material for the half-wavelength resonator 15, and therefore impedance matching with respect to water is advantageous. Light and high strength materials such as alloys, Al alloys, CFRP (carbon fiber reinforced plastics) or FRM (fiber reinforced metals) are preferred.

The operation of the transducer according to the present invention can be understood using a lumped constant approximation equivalent circuit. Figure 2 shows the lumped constant approximation equivalent circuit. Second
In the figure, Cd is the damping capacity, -Cd is the one that appears when a longitudinal effect ceramic vibrator is used, and -Cd does not appear in the transverse effect vibrator.
A is the force coefficient, m and c are each the equivalent mass of the Langillevin resonator, m ₂ and c ₂ are the equivalent mass and equivalent compliance of the 1/2 wavelength resonator viewed from the longitudinal coupler side, and n is 1/2. Mechanical transformation ratio that represents the degree of asymmetry of a wavelength resonator; n for a uniform rod
= 1, and n≠1 in the case of a non-uniform rod (for example, an exponelsial horn). Sa is the radiation cross section and Za is the radiation impedance of water in the acoustic system. In this transducer, bolts are tightened by making full use of the asymmetric operating parameter method or transformer filter theory, as well as transducers with equal mass and resonance frequency with small left and right resonances across the longitudinal coupler. Needless to say, it is possible to construct an asymmetric underwater ultrasonic transducer in which the resonant frequency and equivalent mass of the Langevin oscillator and the 1/2 wavelength resonator are different.

Furthermore, since all of the components of the transducer based on the present invention are made only of piezoelectric ceramics and metal materials or fiber reinforced materials, it is possible to achieve more stable high-power wave transmission than conventional transducers with matching layers. can be achieved.

(Embodiment 1) An embodiment of the transducer of the present invention is shown in FIG. In Fig. 3, 11 is a ring made of piezoelectric ceramics polarized in the longitudinal direction, and adjacent rings are arranged so that the polarization directions are opposite to each other, and each ring is electrically driven in parallel. . Reference numerals 12 and 13 denote metal masses made of stainless steel, of which metal mass 13 is threaded and has the function of applying a static pressure bias to the piezoelectric ceramics together with the nut 17 and bolt 14. 15a, 15b, and 15c form a 1/2 wavelength resonator, 15a is made of Al alloy, and 15b is also made of Al alloy, but as shown in the cross-sectional view in Fig. 4, a cavity is provided inside. ing. This cavity has a characteristic mechanical impedance (density x
It is effective to improve the impedance matching with water as a broadband transducer by reducing the speed (defined as the speed of sound multiplied by the cross-sectional area). 1
5c acts as an acoustic radiation surface, and has the appearance of covering the cavity of section 15b. In this case, the thickness of the portion 15c is determined to such an extent that the acoustic radiation surface does not cause radial vibration in water so that the added mass effect is as small as possible. 16 indicates a vertical connector, but in this example, 15a, 15
The parts b, 15c, 16b and 14 are made of Al alloy and are integrated. Incidentally, when the transducer of this embodiment is used in deep sea, a liquid such as oil may be filled in the cavity portion 15b to improve water pressure resistance.

The transducer of this example uses a material with high strength such as Al alloy, and furthermore, in order to improve the acoustic matching with water, a cavity is formed in the part 15b, so that the effective Reduces mechanical impedance. For this reason
High-power wave transmission of 200 dBre 1 μPa or higher can be performed extremely easily, and high-efficiency wave transmission of 80% or higher is possible due to its broadband characteristics and excellent acoustic matching with water.

In this embodiment, the 1/2 wavelength resonator portion 15b has a structure in which a cavity is provided, but this portion may have a honeycomb structure or a porous structure.

(Embodiment 2) Another embodiment of the transducer based on the present invention is shown in FIG. Components 11, 12, 13, and 17 of the bolted lunge resonator are those of Example 1.
It is the same as that of the transducer. The bolt 14, the longitudinal coupler 16, and a portion 15d of the 1/2 wavelength resonator are made of Cr-Mo steel and are integrated. 15e is a GFRP in which glass fibers are arranged in the length direction, and a cavity is formed in the same way as the part 15b in FIG. Fixed.

Further, 15f is firmly adhered to part 15e, and a GFRP plate in which carbon fibers are arranged in a satin weave pattern forms an acoustic radiation surface for radial vibration. In this embodiment 2, half wavelength resonators 15d, 15e, 15f
Although they are not integrated, the connection points are all close to the vibrating membrane, so even during high-power operation, vibration stress is not concentrated and stable acoustic power can be extracted. Furthermore, in the transducer of Example 2, the main part of the 1/2 wavelength resonator is made of a material that has a smaller acoustic impedance density than metal materials, so the 50% It has the advantage of being able to realize an ultra-wideband transducer that exceeds .

(Embodiment 3) Another embodiment of the transducer based on the present invention is shown in FIG. The bolted lunge van oscillator part and the vertical coupler part are the same as those in Examples 1 and 2, but a two-part structure consisting of a horn 15g and a honeycomb structured acoustic radiator 15h (both made of Al alloy) is used. A single wavelength resonator is used. With a resonator having such a structure, a lightweight and highly rigid acoustic radiator can be realized, and due to the action of the horn, a displacement several times the tip displacement of the bolt-fastened Lange-Van vibrator, which is the driving source, is generated at the acoustic radiating end. A broadband high-power transducer with perfect acoustic matching with water can be constructed.

(Effects of the Invention) As detailed above, according to the present invention, it is possible to provide an underwater ultrasonic transducer having a wide band, high efficiency, and excellent high power characteristics.

[Brief explanation of the drawing]

1a and 1b are diagrams showing an example of an underwater ultrasonic transducer based on the present invention, FIG. 2 is an equivalent circuit diagram of an underwater ultrasonic transducer based on the present invention, FIGS. 3, 5, Fig. 6 is a diagram showing an embodiment of an underwater ultrasonic transducer based on the present invention, Fig. 4 is a cross-sectional view of a 1/2 wavelength resonator, and Fig. 7 is a diagram showing a conventional underwater ultrasonic transducer with a matching plate. A diagram showing a user. In the figure, 11 is a piezoelectric ceramic vibrator;
2 and 13 are metal masses, 14 and 19 are bolts, 15
are half wavelength resonators 15a, 15b, 15
c, 15d, 15e, 15f, 15g, 15h are its constituent elements, 16 is a vertical connector, 17 is a nut,
18 is an acoustic radiation surface, 71 is a piezoelectric ceramic vibrator, and 72 is an acoustic matching layer.

Claims (1)

[Claims] 1. An underwater ultrasonic transducer characterized by a 1/2 wavelength resonant bolted Langevan transducer and a 1/2 wavelength resonator provided on the sound field side of the bolted Langevan oscillator via a coupler. .