JPH0475720B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a bolted lunge transducer used in an underwater ultrasonic transducer,
The purpose is to reduce the weight of the bolt-tight lunge van oscillator and at the same time increase its power. Conventionally, a bolt-tight lunge resonator has a front mass 11 made of a high-steel material such as aluminum alloy, titanium alloy, or steel, and a ring-shaped resonator disposed between the front mass 11 and the rear mass 13, as shown in FIG. A piezoelectric ceramic 12, a rear mass 13 made of a high steel material such as stainless steel like the front mass, and a bolt 14 and a nut made of a high tensile strength alloy such as Cr-Mo steel that has the function of applying compressive stress to the ring-shaped piezoelectric ceramic 12. 15, and has the great feature of being capable of high power driving. Here, the ring-shaped piezoelectric ceramic 12 has a transverse effect longitudinal vibration mode (31
The longitudinal effect longitudinal vibration mode (33 modes) is used, which provides a much larger electromechanical coupling coefficient than the 33rd mode. Adjacent ring-shaped piezoelectric ceramics 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 ceramics are generally weaker against tensile stress than compressive stress, the bolt 14,
A static bias compressive stress is applied in advance by the nut 15, and the structure is strong enough to withstand use even at high power. As is well known, in the bolt-tight Languevan oscillator having such a structure, a half wavelength resonance mode is used, and there is a vibration node in the piezoelectric ceramic 12.
The stress acts concentratedly on the piezoelectric ceramic 12 and the bolt 14. The bolt-fastened lunge transducers used in the above-mentioned underwater ultrasonic transducer are usually arranged in large numbers in order to obtain the desired directivity, and such a large number of transducer arrays are inevitably Because it is large and extremely heavy,
Recently, there has been a strong demand for smaller and lighter bolt-tight lunge resonators. However, conventionally,
A resonator shape that is compatible with both size and weight reduction and high power generation has not yet been obtained. The present invention was made in order to reduce the weight of a bolt-tight lunge transducer and simultaneously increase its power.The purpose of the present invention is to provide a vibrator having an optimal shape that achieves both weight reduction and high power. It is something to do. That is, in the present invention, in a half-wavelength resonant bolt-tight Languevan vibrator consisting of a front mass part, a piezoelectric ceramic part, and a rear mass part, the acoustic radiation cross-sectional area of the front mass part is _S1 , and the cross-sectional area of the piezoelectric ceramic part is _S2. , the cross-sectional area of the bolt part is S ₃ , the cross-sectional area of the rear mass part is S ₄ , the length of the front mass part is l ₁ , and the length from the acoustic radiation end of the front mass part to the vibration node is l ₀ Sometimes, the cross-sectional area _S3 of the bolt part is set considerably smaller than the cross-sectional area _S2 of the piezoelectric ceramic part, and the first half from the acoustic radiation end of the front mass part to the vibration node is _0.03S2 /
This is a bolted lunge van oscillator characterized in that S ₁ 0.1, 0.1<l ₁ /l ₀ 0.3, and S ₂ /S ₄ >0.2 in the rear half from the vibration node to the end of the rear mass. In order to obtain a bolt-fastened Lange-Van vibrator having an optimal shape, which is the object of the present invention, it is divided into a quarter-wavelength part, the first half from the front mass to the vibration node, and a second half, from the vibration node to the rear mass. First, we will consider the mechanical system of a bolt-tight Languevin oscillator using an equivalent composite transmission line.
Here, due to the balance between the standardized vibrator mass, which is a guideline for weight reduction, and the stress applied to the bolts and piezoelectric ceramic parts when operated underwater, it is lightweight and has excellent mechanical strength at high power. The shape of the resonator is clarified. Furthermore, we performed an analysis that included the electrical system, and determined the relationship between the capacitance ratio (the smaller the capacitance ratio, the higher the energy conversion rate) and the resonator shape, which are closely related to the electromechanical conversion efficiency.Finally, we analyzed the mechanical and electrical systems. Taking both into consideration, we found the optimal transducer shape that reduces weight and increases power at the same time. In order to obtain a lightweight and high-power vibrator, we first conduct a theoretical study on the half section of the vibrator from the acoustic radiation end to the vibration node, as shown in Figure 2. In Fig. 2, part 11 is the front mass part, part 12 is the piezoelectric ceramic part, and part 14 is the front mass part.
is the bolt part, l ₁ is the length of the front mass, l ₂ is the length of the piezoelectric ceramic part (= length of the bolt part,
l ₀ (=l ₁ +l ₂ ) indicates an effective quarter wavelength. FIG. 3 shows an equivalent composite transmission line for the half-section model shown in FIG. 2. In FIG. 3, the i-th part (i=1, 2, 3)
The density of is ρ _i , the longitudinal wave velocity is c _i , the cross-sectional area is S _i , the phase constant is β _i (=ω/c _i , ω; angular frequency, ω=2πf), and the characteristic impedance density is Z _pi (= ρ _i c _i ), the characteristic impedance is Z _pi (=z _pi S _i ), and R _a is the acoustic radiation impedance, which is expressed by the following equation. R _a = ρ ₀ c ₀ S ₁ (1) where ρ ₀ ; density of water c ₀ ; sound speed of water S ₁ ; radiation cross section However, the effective longitudinal wave velocity for the piezoelectric ceramic part is c _2e (=√1 _{2 33} ^E , s ₃₃ ^E ; elastic conformance when electric field is constant), and the effective phase constant, characteristic impedance density, and characteristic impedance are respectively β _2e , Z _02e , and Z _02e . The resonance equation of the equivalent composite transmission line shown in FIG. 3 can be obtained by setting the sum of the impedances of the respective transmission lines as seen from 1-1' to the left and right to zero. (R _a = 0 since it is the resonant frequency of the vibrator itself) That is, Z ₀₁ tan (β ₁ l ₁ ) − Z _02e cot (β _2e l ₂ )
−Z ₀₃ cotβ ₃ l ₂ = 0(2) Here, as the ratio of characteristic impedance, K _12e = Z _02e /Z ₀₁ (3) K ₁₃ = Z ₀₃ /Z ₀₁ (4) Also, the quarter wavelength is used as the standard. As the normative constant α ₁ ,
Introducing α ₂ , β ₁ l ₁ =ωl ₁ /C ₁ =π/2α ₁ (5) β _2e l ₂ =ωl ₂ /C _2e =π/2α ₂ (6) β ₃ l ₃ =ωl ₂ /c ₃ =π/2(c _2e /c ₃ ) α ₂ (7) Then, equation (2) becomes as follows. tanπ/2α ₁ −K _12e cotπ/2α ₂ −K ₁₃ cotπ
/2(c _2e /c ₃ )α ₂ =0(8) Determine the material of each part of the vibrator, and then calculate the cross-sectional area ratio S ₁ /
When S ₁ and S ₃ /S ₁ are given, equation (8) becomes an equation consisting of two variables α ₁ and α ₂ . That is, when α ₁ is given, α ₂ corresponding to α ₁ is found, and the relationship between the size ratio l ₁ /l ₂ and the resonant frequency is found. The total mass M of the half-section oscillator shown in FIG _{. 2} is given by M=ρ ₁ l ₁ S ₁ +ρ ₂ l ₂ S ₂ +ρ ₃ l ₃ S ₃ (9). Since the resonant frequency is inversely proportional to the length, the optimum shape for weight reduction per unit acoustic radiation area normalized by the resonant frequency is given by Mfr/S ₁ . Further, when this is normalized by the characteristic acoustic impedance density z ₀₂ (ρ ₂ c _2e ) of the piezoelectric ceramic part, the normalized resonator mass M _o is M _o = Mf _r /z _02e S ₁ = (Z ₀₁ /z _02e ) {α ₁ /4
+K _12e α ₂ /4 + K ₁₃ (c _2e /c ₃ ) α ₂ /4}(10). Prior to the calculation, Table 1 shows the density and longitudinal wave velocity of the materials normally used for each part of the bolt-tight LangueVan transducer.

[Table] Using the materials shown in Table 1 and assuming that the ratio of the bolt cross-sectional area to the acoustic radiation area is constant S ₃ /S ₁ = 0.006, the piezoelectric ceramic cross-sectional area to the acoustic radiation area S ₂ /S ₁ is set as a parameter. Then, the ratio of the front mass length to the effective quarter wavelength
FIG. 4 shows the relationship between l ₁ /l ₀ and the normalized mass M _o of the first half of the vibrator. From Figure 4, l ₁ /l ₀ is 0 to 0.4
In the range of , M _o increases slowly as l ₁ /l ₀ increases, but when l ₁ /l ₀ becomes larger than 0.3, M _o increases rapidly, which is due to the weight reduction of the resonator. It can be seen that it is better to proceed in the direction of decreasing S ₂ /S ₁ and l ₁ /l ₀ . In addition, the cross-sectional area of the bolt
_S3 is usually designed to be much smaller than the cross-sectional area _S2 of the piezoelectric ceramic portion, as shown in FIG.
This is due to the negative effect that electromechanical conversion efficiency decreases as S ₃ approaches S ₂ . In the range where S ₃ is much smaller than S ₂ , M _o is hardly affected by S ₃ /S ₁ . At this time, if the cross-sectional areas S ₂ and S ₃ of the piezoelectric ceramic part and the bolt part are set smaller than the acoustic radiation area S ₁ , the weight can be reduced accordingly, but stress will be concentrated on the bolt part and the piezoelectric ceramic part. Therefore, simply the cross-sectional area S ₂ ,
It can be inferred that it would be difficult to reduce weight while taking high power into consideration just by making the S ₃ smaller. Next, we will theoretically examine the vibration stress applied to the piezoelectric ceramic part and the bolt part of the bolted lunge van oscillator. Normally, when transmitting waves underwater, the stress acting inside the vibrator is different from the state of vibration in the air, and a reaction due to the acoustic radiation impedance of the water is further added to the acoustic radiation end face. Here, when the acoustic radiation surface resonates at a unit speed (1 m/sec) under water load, the stress applied to the piezoelectric ceramic part and the bolt part is determined from the equivalent circuit shown in Figure 3, and the oscillator of these stresses is calculated. Calculate shape dependence. Regarding the stress in the piezoelectric ceramic part, the part receiving the maximum stress is the vibration node shown in FIG. 3-2-2', and the stress there is T _pn . Dimensional ratio when S ₂ /S ₁ is used as a parameter when S ₃ /S ₁ = 0.006 constant as in Figure 4
The relationship of |T _pn to l ₁ /l ₀ is shown in Figure 5.
The smaller S ₂ /S ₁ , the larger l ₁ /l ₀ |T _pn |
It can be seen that is increasing. Next, in exactly the same manner, the relationship between the stress acting on the bolt portion and the shape of the vibrator is determined. The vibration stress acting on the bolt at the joint with the front mass is T _bc , and the vibration stress acting on the bolt at the vibration node is T _bn . The relationship between |T _bc |, |T _bn and the vibrator shape is shown in FIG. 6 in the same manner as in FIG. 5. In FIG. 6, the solid line indicates the characteristic of |T _bc |, and the dotted line indicates the characteristic of |T _bn |. When l ₁ /l ₀ > 0.2, there is not much difference between |T _bc | and |T _bn |, but |T _bc | < |T _bn
｜and as l ₁ /l ₀ increases, ｜T _bc ｜, ｜
T _bn | also increases, and at the same time, |T _bc | and |T _bn | approach each other. However, when l ₁ /l ₀ <0.1, l ₁ /l ₀ decreases, that is, the shorter the front mass length, the more |
When T _bc | and |T _bn | increase, the following behavior occurs. This is because when the front mass becomes extremely thin, stress is concentrated at the joint between the bolt and the front mass due to the reaction of the acoustic radiation impedance of water. The parts with the weakest mechanical strength in a bolted lunge resonator are the joint between the front mass and the bolt and the ceramic center part. In order to reduce the weight of the vibrator and increase its power at the same time, it is desirable to have a vibrator shape that prevents stress from concentrating on a portion with weak mechanical strength for a constant vibration velocity at the acoustic radiation end. Therefore, we give FMM _n = 1/M ₂ |T _bc |・|T _pn | (11) as a figure of merit regarding the mass of the oscillator. This is closely related to the maximum acoustic power that can be extracted per unit mass of the vibrator.
The larger the FMM _n, the better the shape of the resonator. Next, the capacity ratio γ, which is a guideline for electromechanical conversion efficiency, is
The equivalent transmission line of the piezoelectric ceramic part shown in Fig. 3 is transformed into Martin's equivalent circuit (GEMaytin:
“Vibrations of Caaxially Segmented,
Longitudinally Polarized Ferroelectric
Tubes”, Journal of Acoust.Soc.Am.Vol.36,
No. 8, pp. 1496-1506, (1964)), it can be easily obtained from the relationship between resonance and anti-resonance frequencies. The smaller γ is, the better the electromechanical change efficiency is.
The figure of merit FM _n for weight reduction including the electrical system of the resonator in the wavelength section is expressed by the following equation. FM _n = FFM _n / γ (12) Using the materials shown in Table 1 as the materials for each part of the vibrator, the electromechanical coupling coefficient of piezoelectric ceramic k ₃₃ =
Figure 7 shows the FM _n characteristics when set to 0.50. It is well known that when the front mass becomes thinner and l ₁ /l ₀ becomes less than 0.1, the front mass itself undergoes bending vibration and is no longer able to perform pure piston motion, resulting in a decrease in sound radiation efficiency. . Therefore, in FIG. 7, the range of l ₁ /l ₀ >0.1 is of practical use. When S ₂ /S ₁ is extremely small and becomes less than 0.03, the capacity ratio γ increases even though FMM _n does not increase much, and as a result, FM _n decreases. In addition, the cross-sectional area ratio of the front half wavelength part from the acoustic radiation end of the front mass to the vibration node is
If S ₂ /S ₁ is smaller than 0.03, the piezoelectric ceramic ring will not have sufficient radial strength against the static stress when the bolt is tightened, which is not preferred in practice. In Fig. 7, when piezoelectric ceramics with k ₃₃ = 0.50 and Al alloy are used for the front mass, the value of FM _n is the desired value of 1.5 in the conventional vibrator shape.
×10 ^-7 m ² /N has not been achieved. Also, if S ₂ /S ₁ is about 0.12 or more or l ₁ /l ₀ is
If it is larger than 0.3, it becomes difficult for FM _n to exceed 1.5×10 ⁻⁷ m ² /N. That is, the shape of a vibrator that increases FM _n , in other words, the shape of a vibrator that is lightweight and has high power, has a cross-sectional area of 0.03≦S ₂ /S ₁ ≦0.1 and a length of 0.1l ₁ /l ₀ 0.30. It is discovered that
Next, Figure 8 shows the FM _n characteristics when using carbon fiber reinforced resin (C-FRP), which has the same or higher rigidity as the Al alloy and has a lower density than the Al alloy, as the front mass material. . From Fig. 8, the FM _n value is generally larger than that when the Al alloy shown in Fig. 7 is used for the front mass, but the tendency of the vibrator shape to increase the FM _n is as follows.
It is clear that although the front mass materials are different, they are exactly the same. Next, we will discuss the shape of the oscillator that can reduce weight and increase power at the same time regarding the quarter-wavelength portion in the latter half from the vibration node to the rear mass. 1st
FIG. 9 shows a physical model of the vibrator section from the vibration node to the rear mass end of the bolted lunge van vibrator shown in the figure. In Figure 9, 12', 1
4' is a piezoelectric ceramic part and a bolt part, respectively, and 13 is a rear mass part. l ₀ ' is the effective quarter wavelength, l ₂ ' is the length of the piezoelectric ceramic part (= bolt part), and l ₄ is the length of the rear mass part. 12' and 14' are mechanically continuous with the piezoelectric ceramic part and bolt part 14 from the front mass to the vibration node shown in FIG.
It is assumed that the material of 2' and the material of 14 and 14' are the same, and the cross-sectional areas of the portions 12 and 12' are the same. Here, in order to find the optimal shape of the vibrator, the vibrator is divided into two halves, the front half and the back half, but in reality, 12 and 12', and 14 and 14' are integrated. When the acoustic radiating end of the front mass vibrates at a certain speed, the vibration contacts in the front and rear halves of the transducer are common, and the stress acting thereon is, of course, equal. At this vibrating contact point, the maximum stress occurs unless the length of the front mass becomes extremely short. Vibration stress in this part
T _pn and T _bn have already been determined. The density of the rear mass part is ρ ₄ , the speed of sound is c ₄ , and the cross-sectional area is S ₄
shall be. _{The characteristic} acoustic impedance Z ₀₄ and phase constant β4 _are Z ₀₄ =ρ ₄ c ₄ S ₄ =z _{04 S 4} ( ₁₃ ) becomes. Total mass of the second half of the vibrator shown in Figure 9
Let it be M′. Regarding the mass of the second half of the vibrator, the common frequency and length are inversely proportional, and the cross-sectional shape of the piezoelectric ceramic part is the same in the front half and the rear half, so the characteristic acoustic impedance of the piezoelectric ceramic part is Z _02e . Can be standardized.
If the normalized mass is M′ _o , then M′ _o is M′ _o = M′f _r /Z _02e = 1/K _42e {α ₄ /
4+K _42e α' ₂ /4+K ₄₃ c _2e /c ₃ α' ₂ }(15) However, π/2α' ₂ = β _2e l' ₂ (16) K _42e =Z _02e /Z ₀₄ (17) K ₄₃ = Z ₀₃ /Z ₀₄ (18). Since the stress at the vibrating contact point is determined by the first half of the vibrator, the smaller the standardized mass M′ _o and the smaller the capacitance ratio γ′ of the latter half of the vibrator, the smaller the
Of Merit is superior. in the second half
Figure of Merit FM′m is given by the following equation. FM′m=1/M′ _o γ′ (19) Vibrator shape regarding FM′ _n when using Al alloy and stainless steel (ρ=7.91Kg/m ³ , c=5.00m/sec) as the rear mass The dependent characteristics are shown in FIG. 10 and FIG. 11, respectively. both
As S ₂ /S ₄ increases, FM′ _n also increases, and when it becomes 0.20 or more, it tends to become saturated. 1/2 of the rear half from the vibration contact to the rear mass end
Regarding the four-wavelength portion, the value of FM′ _n is required to be 0.8 or more in order to be lightweight and obtain the required sound pressure. In order to achieve this, as shown in Figure 11,
If S ₂ /S ₄ is about 0.15, it is extremely difficult to make the value of FM′ _n greater than 0.8, and S ₂ /S ₄ of 0.20 is necessary. Furthermore, FM'm tends to increase as S ₂ /S ₄ increases, but when S ₃ /S ₄ exceeds 0.70, it becomes difficult to hold the bolts 14 and nuts 15 as shown in Figure 1. It becomes impractical. Above is the theoretically considered Figure of Merit.
Regarding FM _n and FM′ _n , the larger FM _n is, the better the electroacoustic conversion efficiency is, and if the vibration applied to the piezoelectric ceramic and the bolt part is the same, the vibration velocity u of the acoustic radiation end face per vibrator mass can be increased. I can do it. The vibration velocity u is proportional to the square root of the acoustic radiation energy Pa. Furthermore, the larger FM′ _n is, the better the electroacoustic conversion efficiency is, and a lightweight vibrator can be realized. In other words, if the acoustic radiation cross section S ₁ and the resonant frequency f _r are the same, the larger FM _n and FM' _n are, the Figure of Merit FM=√Pa/M _t (√/Kg) (20) where M _t ;The value of the total mass of the vibrator can be increased. In recent years, the depth sensing distance of sonar transducers has increased, and at the same time, there has been a demand for lighter weight and higher power. For a 10KHz band vibrator, the square root of the acoustic output per kg, or the value of FM′ _n in equation (20), is 100.
√/Kg or more is required. Next, as an embodiment of the present invention, four types of underwater ultrasonic waves A, B, C, and D having a resonant frequency in the 10 KHz band, the same radiation area, and different shapes as shown in Table 2 are used. We prototyped a bolt-tight lunge van oscillator for wave instruments and evaluated its figure of merit. The vibrators A, B, C, and D are all piezoelectric ceramics made of zircon with k ₃₃ =0.50.
Lead titanate ceramics are used, Al alloy is used as the front mass material, stainless steel is used as the rear mass material, and Cr-Mo steel is used as the bolt and nut material.

[Table] The values of FM _n and FM' _n calculated from the vibrators having the four shapes A, B, C, and D shown in Table 2 are plotted in FIGS. 7 and 11. figure of
Regarding the experimental evaluation of Merit, we drove the vibrator electrically, found the relationship between the acoustic output power and the electrical input power, and calculated the acoustic output power (Pa) when the linearity of the acoustic output power with respect to the electrical input power suddenly deteriorated. FM was calculated according to equation (20).
The results are shown in Table 3.

[Table] Oscillator A satisfies FM' _n >0.8, but FM _n is small. Oscillator B satisfies FM _n > 1.5×10 ^-7 m ² /N, but FM' _n is small. Also, the vibrator C is
Both FM _n and FM′ _n are small. The oscillator D is FM _n ,
Both FM′ _n are designed to be large. It is clear that the vibrator with larger values of FM _n and FM′ _n shown in FIGS. 7 and 11 is actually a vibrator that is lighter and has a larger output sound pressure. especially,
The oscillator D with large values of both FM _n and FM′ _n is
It can be seen that it is lightweight and has excellent high power characteristics. As detailed above, according to the present invention, a bolted lunge transducer for an underwater ultrasonic transducer that is lightweight and has excellent high power characteristics can be obtained.
It also has great industrial value.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of a bolted Languevan transducer used in underwater ultrasound transducers, Figure 2 is a model of the first half of the transducer from the acoustic radiation end to the vibration node, and Figure 3 is the equivalent circuit. Figure 4 shows the relationship between the normalized mass M _o of the front half of the vibrator and the vibrator shape, and Figure 5 shows the relationship between the stress T _pn at the vibration node of the piezoelectric ceramic part and the vibrator shape. Figure 6 shows the relationship between the stress T _bc acting on the bolt at the joint with the front mass, the stress T _bn acting on the vibration node of the bolt and the shape of the vibrator, and Figure 7 shows the relationship between the vibrator shape. Figure of Merit A diagram showing the relationship between FM _n and the resonator shape for weight reduction including the electrical system of the part. Figure 8 shows the FM _n and the resonator shape when C-FRP is used as the front mass material. Figure 9 is a physical model diagram of the half section of the vibrator from the vibration node to the rear mass end of the bolted lunge van oscillator, Figures 10 and 11
The figures show the rear half of the vibrator when Al and stainless steel are used as the rear mass materials, respectively.
Figure of Merit FM′ _n characteristic diagram is shown. In the figure, 11 is the front mass, 12, 1
2' is a piezoelectric ceramic ring, 13 is a rear mass,
14 and 14' are bolts, 15 is a nut, _l1 is the length of the front mass, _l2 , _l2 ' is the length of the piezoelectric ceramic part, _l4 is the length of the rear mass, _l0 , _l0 ' are the effective 4
1/1 wavelength, S ₁ is the cross-sectional area of the front mass, S ₂ is the cross-sectional area of the piezoelectric ceramic ring, S ₃ is the cross-sectional area of the bolt, S ₄ is the cross-sectional area of the rear mass, K ₃₃ is the electromechanical coupling coefficient, and Ra is Acoustic radiation impedance, Z ₀₁ , Z _02e ,
Z ₀₃ is the characteristic acoustic impedance, β ₁ , β _2e , and β ₃ are the phase constants.

Claims (1)

[Claims] 1. In a half-wavelength resonant bolt-tight Languevan vibrator consisting of a front mass part, a piezoelectric ceramic part, and a rear mass part, the acoustic radiation cross-sectional area of the front mass part is S ₁ , and the cross-sectional area of the piezoelectric ceramic part is S 1 .
S ₂ , the cross-sectional area of the bolt part is S ₃ , the cross-sectional area of the rear mass part is S ₄ , the length of the front mass part is l ₁ , and the length from the acoustic radiation end of the front mass part to the vibration node is l ₀ When, the cross-sectional area of the piezoelectric ceramic part S ₂
The cross-sectional area S ₃ of the bolt part is set quite small compared to that, and for the first half from the acoustic radiation end of the front mass part to the vibration node, 0.03S ₂ /S ₁ 0.1, 0.1
A bolted lunge van oscillator characterized in that _{S 2 /} S _{4 >} 0.2 in the rear half from the vibration node to the rear mass end.