JP7182783B2 - Bolt-clamped Langevin transducers, ultrasonic measurement equipment - Google Patents

Description

The present invention relates to a bolt-clamped Langevin transducer and an ultrasonic measuring device using the same.

Conventionally, a bolt-clamped Langevin type vibrator 51 as shown in FIG. 6(a) is well known. In this bolt-clamped Langevin vibrator 51 , a drive unit 56 is sandwiched between a front mass 52 and a back mass 53 by stacking two piezoelectric elements 54 and two electrode plates 55 . A tightening bolt (not shown) is inserted through a hole penetrating the driving portion 56, and by tightening the tightening bolt, the front mass 52 and the back mass 53 are fastened and each member is integrated. Note that a structure similar to that of the vibrator 51 is disclosed, for example, in Japanese Patent Laid-Open No. 2002-300000.

In the conventional bolted Langevin vibrator 51, the front mass 52 and the back mass 53 are generally made of a metal material such as aluminum. The piezoelectric element 54 is generally made of a ceramic piezoelectric material containing lead such as lead zirconate titanate (PZT). In recent years, from the viewpoint of improving environmental friendliness, there is an increasing demand for the piezoelectric element 54 using a lead-free ceramic piezoelectric material.

JP-A-8-89893

However, although lead-free ceramic piezoelectric materials are preferable in that they have little impact on the environment, they are inferior to lead-containing ceramic piezoelectric materials represented by PZT in terms of piezoelectric characteristics. Therefore, even if the vibrator 51 having the above structure is constructed using the piezoelectric element 54 formed of a lead-free ceramic piezoelectric material, the performance is equivalent to that of the conventional one constructed using the piezoelectric element 54 formed of PZT. is difficult to achieve. Therefore, some measure is conventionally desired to achieve such performance.

In addition, since the bolt-tightened Langevin oscillator 51 has a relatively large power, it is usually used for machining applications. It is also desired to use in

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a piezoelectric element having a performance equal to or better than that of a lead-containing piezoelectric material even though the piezoelectric element is formed using a lead-free piezoelectric material. An object of the present invention is to provide a bolt-clamped Langevin transducer and an ultrasonic measuring device that can be realized.

In view of the above problems, the inventors of the present application conducted extensive research, and based on the prediction that alkali niobate-based ceramic piezoelectric materials would be preferable among many lead-free ceramic piezoelectric materials, When two piezoelectric elements were used in the conventional manner to form a drive unit, the desired performance could not be obtained. Therefore, the inventors of the present application conducted further trial and error and found that desired and suitable performance can be obtained by increasing the number of piezoelectric elements to more than two and by making the back mass heavier than the front mass. They made new discoveries and finally came up with the following invention.

In order to solve the above-mentioned problems, the invention according to claim 1 has a driving part formed by stacking a plurality of piezoelectric elements and electrode plates each made of a lead-free material and sandwiched between a front mass and a back mass. and the front mass and the back mass are fastened by a tightening bolt inserted through a hole penetrating the driving portion, wherein the driving portion is made of alkaline niobate-based ceramics. The piezoelectric element includes four or more piezoelectric elements formed using a piezoelectric material, the front mass is formed using a first metal material, and the back mass has a higher specific gravity than the first metal material. The vibrator is formed using a second metal material, the total length of the vibrator corresponds to the length of half the wavelength of the resonance frequency, the thickness of the drive section is less than ⅓ of the total length of the vibrator, and the front mass The gist thereof is a bolted Langevin type vibrator characterized in that the thickness of the vibrator exceeds 1/3 of the total length of the vibrator .

Therefore, according to the first aspect of the invention, the front mass is formed using the first metal material having a relatively low specific gravity, and the back mass is formed using the second metal material having a relatively high specific gravity. By forming it, the front mass can be lightened, and the amplitude on the front mass side can be increased. Among lead-free ceramic piezoelectric materials, alkali niobate-based ceramic piezoelectric materials have relatively excellent piezoelectric characteristics. By constructing the driving section including four or more piezoelectric elements formed using such materials, it is possible to generate greater vibration energy than in the conventional structure. As a result, although the piezoelectric element is formed using a lead-free piezoelectric material, it is possible to achieve performance equal to or better than that of a lead-containing piezoelectric material. In addition, according to the present invention, since the piezoelectric element is formed using an alkali niobate-based ceramic piezoelectric material, environmental friendliness is improved and the weight of the entire device can be easily reduced.

According to a second aspect of the present invention, in the first aspect, the piezoelectric element is formed using a ceramic piezoelectric material based on sodium potassium niobate.

Therefore, according to the second aspect of the present invention, the drive unit is configured using sodium potassium niobate (KNN) ceramics, which has particularly favorable piezoelectric characteristics among alkali niobate ceramics. Therefore, it is possible to reliably generate larger vibration energy.

A third aspect of the invention is the first or second aspect, wherein the specific gravity of the second metal material is at least twice the specific gravity of the first metal material.

Therefore, according to the third aspect of the invention, since the difference in specific gravity between the first metal material and the second metal material is sufficiently large, the front mass and the back mass are not changed much in size and shape. , the front mass can be lightened, and the amplitude on the front mass side can be increased.

The invention according to claim 4 is based on claim 3, wherein the specific gravity of the first metal material is 2.5 or more and 3.5 or less, and the specific gravity of the second metal material is 7.0 or more and 9.0. The gist of it is as follows.

Therefore, according to the fourth aspect of the invention, it is possible to relatively easily select suitable materials for the first metal material and the second metal material within the respective ranges of specific gravities.

In addition, in the invention described in claim 1, etc., the thickness of the driving portion is suppressed to less than 1/3 of the total length of the vibrator when the total length of the vibrator corresponds to the length of half the wavelength of the resonance frequency. Therefore, it becomes easy to dispose the entire driving section near the vibration nodes. Therefore, the amplitude in the drive section can be suppressed, and peeling or the like is less likely to occur at the joint interface between the piezoelectric element and the electrode plate. In addition, since the thickness of each piezoelectric element constituting the drive section is reduced, the electric field is increased, and as a result, the vibration displacement is increased and the transmitted sound pressure is increased. In addition, by increasing the ratio of the thickness of the front mass to the total length of the vibrator, even if the back mass is relatively heavy, it becomes easier to balance the vibration, and the amplitude on the front mass side is more reliable. You can make it bigger.

According to a fifth aspect of the present invention, there is provided a device for measuring a physical quantity by transmitting and receiving ultrasonic waves, comprising one or more of the bolted Langevin transducers according to any one of the first to fourth aspects. The gist of the present invention is a configured ultrasonic measurement device.

The invention according to claim 6 is the ultrasonic measuring device according to claim 5 , wherein the ultrasonic measuring device is a fish finder sensor having a structure in which a plurality of the bolt-tightened Langevin transducers are oriented in the same direction and rubber-molded. is the gist of it.

As described in detail above, according to the inventions described in claims 1 to 6 , although the piezoelectric element is formed using a lead-free piezoelectric material, the performance is equal to or better than that using a lead-containing piezoelectric material. It is possible to provide a bolt-clamped Langevin transducer and an ultrasonic measuring device that can be realized.

1 is a front view showing a bolt-clamped Langevin transducer of an embodiment embodying the present invention; FIG. FIG. 2 is a plan view showing the bolt-clamped Langevin transducer of the embodiment; FIG. 3 is a cross-sectional view taken along line AA of FIG. 2; 1 is a schematic vertical cross-sectional view of a fish finder sensor configured using a bolt-clamped Langevin transducer according to an embodiment; FIG. 5 is a schematic cross-sectional view along line BB of FIG. 4; FIG. (a) is a schematic diagram of a conventional bolt-clamped Langevin transducer of Comparative Example 1, (b) is a schematic diagram of a bolt-clamped Langevin transducer of Comparative Example 2, and (c) is a bolt-clamped Langevin transducer of an embodiment. Schematic of a type transducer. Graph comparing the relationship between input voltage and radiation plane amplitude. A graph comparing the transmitted wave sound pressure and the received wave sensitivity. A graph comparing directional characteristics.

A bolt-clamped Langevin transducer 11 and a fish finder sensor 41 according to an embodiment of the present invention will be described in detail below with reference to FIGS. 1 to 9. FIG.

As shown in FIGS. 1 to 3, the bolted Langevin vibrator 11 of this embodiment includes a front mass 21, a back mass 22, a driving portion 31, and a tightening bolt 25. As shown in FIGS.

The front mass 21 (front plate) is arranged on the front end side of the bolted Langevin transducer 11 and emits ultrasonic waves from its front surface 26 . The back mass 22 (backing plate) is arranged on the rear end side of the bolted Langevin type vibrator 11 . In the present embodiment, the front mass 21 is formed to have a rectangular cross section of 25 mm square, while the back mass 22 is formed to have a circular cross section of 25 mm in diameter (see FIG. 2).

The drive unit 31 is formed by stacking a plurality of piezoelectric elements 32 and electrode plates 33 (four in this embodiment), and is sandwiched between the front mass 21 and the back mass 22 . Since the piezoelectric element 32 has an annular shape and the electrode plate 33 has a substantially annular shape with a tab portion in part, the driving portion 31 has a bolt insertion hole 34 passing through the center thereof. . Each piezoelectric element 32 is polarized in the thickness direction, and the directions of the polarization are indicated by arrows in FIG. Female threaded holes 24 and 23 are formed in the front mass 21 and the back mass 22, respectively, coaxially with the center axis C1 of the vibrator 11. As shown in FIG. The female screw hole 23 on the back mass 22 side is a through hole, while the female screw hole 24 on the front mass 21 side is a non-through hole that does not penetrate the front surface 26 . A tightening bolt 25 having a male thread formed on its outer peripheral surface is inserted from the back mass 22 side, and its tip reaches the female thread hole 24 on the front mass 21 side through the female screw hole 23 and the bolt insertion hole 34 . The tightening bolts 25 are screwed into the female threaded holes 23 and 24, and by tightening them, the front mass 21, the driving portion 31 and the back mass 22 are fixed and integrated with each other.

In the bolt-clamped Langevin vibrator 11 of the present embodiment, the front mass 21 is formed using a first metal material having a specific gravity of 2.5 or more and 3.5 or less, and the back mass 22 has a specific gravity higher than that of the first metal material. and a second metal material having a specific gravity of 7.0 or more and 9.0 or less. Specifically, the front mass 21 is formed using aluminum (specific gravity 2.7) as the first metal material, and the back mass 22 is made of stainless steel such as SUS304 (specific gravity 7.70 to 8.0) as the second metal material. 00) is used to form the back mass 22 . That is, the specific gravity of the metal material used for the back mass 22 is approximately 2.9 times the specific gravity of the metal material used for the front mass 21 . Although any metal material can be used to form the tightening bolt 25, stainless steel is used here.

In the bolt-clamped Langevin vibrator 11 of the present embodiment, the piezoelectric elements 32 constituting the drive unit 31 are all formed using a lead-free ceramic piezoelectric material. formed by

Suitable examples of alkali niobate-based ceramic piezoelectric materials include potassium-sodium niobate-based (KNN-based) ceramic piezoelectric materials that have a perovskite structure and are a solid solution of potassium niobate and sodium niobate. A KNN-based ceramic piezoelectric material is one that contains at least K (potassium), Na (sodium), and Nb (niobium) as main metal components, and contains other elements such as Pb (lead) in its composition. Contains little or no toxic and harmful elements. Such a KNN-based ceramic piezoelectric material may contain alkali metals such as Li (lithium) in addition to K (potassium) and Na (sodium), and in addition to Nb (niobium), Ca ( calcium), Sr (strontium), Ba (barium), Ta (tantalum), and Sb (antimony). Further, the KNN-based ceramic piezoelectric material may contain small amounts of Bi (bismuth), Fe (iron), Al (aluminum), Mn (manganese), Co (cobalt), Ni (nickel), and the like.

In particular, in this embodiment, a KNN-based ceramic piezoelectric material represented by the following compositional formula (1), which contains a small amount of Bi (bismuth) and Fe (iron) as metal elements as additives, is used. to form the piezoelectric element 32 .
{Li _x (K _1-y Na _y ) _1-x }(Nb _1-z Sb _z )O ₃ (1)

Here, when the added amount (molar ratio) of Bi is v and the added amount (molar ratio) of Fe is w, 0.03≤x≤0.045, 0.5≤y≤0.58, 0.03≤x≤0.045, 0.5≤y≤0.58. It has a composition satisfying the ranges of 03≦z≦0.045 and 0.006≦v<w≦0.010. When a KNN-based ceramic piezoelectric material satisfying such a composition range is used, good piezoelectric characteristics (for example, piezoelectric constant _d33 of 250 pC/N or more and Curie temperature Tc of 330° C. or more) and good electrical properties are obtained. Characteristics (for example, a radial electromechanical coupling coefficient Kp of 0.44 or more, a dielectric constant ε ₃₃ ^T /ε ₀ of 1390 or more, and a dielectric loss tan δ of 0.03 or less) can be easily obtained. Furthermore, when the composition range of 0.007 ≤ v < w ≤ 0.009 is satisfied, the piezoelectric constant _d33 is 270 pC/N or more, the Curie temperature is 340 ° C. or more, and the radial electromechanical coupling coefficient Kp is 0.47 or more, relative dielectric constant ε ₃₃ ^T /ε ₀ is 1450 or more, and dielectric loss tan δ is 0.25 or less.

As shown in FIG. 1, the bolt-clamped Langevin vibrator 11 of this embodiment has a resonance frequency of 50 kHz and a total vibrator length L1 of about 42 mm. That is, the vibrator total length L1 corresponds to the half wavelength length (λ/2) of the resonance frequency.

The thickness T3 of the front mass 21 preferably exceeds 1/3 of the total length L1 of the transducer, more preferably 34% to 44% of the total length L1 of the transducer. about 38% of the total length L1).

The thickness T1 of the back mass 22 is preferably about 1/3 of the total length L1 of the transducer, more preferably 30% to 40% of the total length L1 of the transducer. about 36% of The thickness T1 of the back mass 22 is preferably slightly smaller than the thickness T3 of the front mass 21 as described above.

Further, the thickness T2 of the driving portion 31, which is the sum of the thicknesses of the four piezoelectric elements 32 and the four electrode plates 33, is preferably less than ⅓ of the total length L1 of the vibrator. More preferably, it is 21% to 31% of the total length L1, and here it is about 11 mm (about 26% of the total length L1 of the vibrator). Incidentally, each piezoelectric element 32 has a thickness of about 2.5 mm, and each electrode plate 33 has a considerably thinner thickness of about 0.2 mm.

As shown in FIG. 1, in the case of the bolt-clamped Langevin type vibrator 11 of the present embodiment, the central portion of the driving section 31, which is the midpoint in the length direction of the vibrator, more specifically, the second piezoelectric layer. It is designed so that the node F1 of the ultrasonic vibration comes to the interface between the element 32 and the electrode plate 33 and the piezoelectric element 32 and the electrode plate 33 of the third layer. Moreover, it is designed so that the abdomen H1 of the ultrasonic vibration comes to both end portions (the end surfaces of the front mass 21 and the back mass 22) of the vibrator.

4 and 5 show a fish finder sensor 41 configured using the bolt-clamped Langevin transducer 11 of the embodiment. This fish finder sensor 41 has a structure in which a plurality of bolted Langevin transducers 11 are oriented in the same direction and molded with rubber. More specifically, the container (rubber molded portion) in this fish finder sensor 41 includes a container body 42 and a lid portion 43 . A bottom portion 45 of the container body 42 also serves as an acoustic matching layer, and four bolted Langevin transducers 11 are joined and fixed on the bottom portion 45 so that the front mass 21 faces downward. An electric wire (not shown) is electrically connected to the tab portion of the electrode plate 33 in each bolt-clamped Langevin vibrator 11 . These electric wires are drawn out of the sensor via a cable 44 and electrically connected to a drive control device including an oscillator and the like and a power supply device (both not shown). According to the fish finder sensor 41 having such a structure, the four bolt-tightened Langevin-type vibrators 11 are simultaneously driven and start vibrating based on the drive signal from the drive control device. Then, the ultrasonic waves emitted from each bolt-tightened Langevin transducer 11 are transmitted to the bottom portion 45 of the container body 42 and radiated to the outside from the bottom surface of the container. A reflected wave of the previously emitted ultrasonic wave is transmitted to each bolt-tightened Langevin transducer 11 via the bottom portion 45 of the container body 42, and is output as a detection signal to the drive control device.

Examples that embody the present embodiment more concretely will be described below.

In this example, the following three types of bolted Langevin vibrators were produced. FIG. 6(c) is basically the bolt-clamped Langevin transducer 11 of the above-described embodiment. ), and has a structure in which a drive unit 31 is sandwiched by stacking four piezoelectric elements 32 and four electrode plates 33 each made of a KNN ceramic piezoelectric material. The direction of polarization is also indicated by arrows in FIGS. 6(a) to 6(c).

A method for manufacturing the piezoelectric element 32 used here will be described in detail. First, raw material powders _{( purity of} 99% or more) _{of K2CO3 , Na2CO3} , _{Li2CO3 , Nb2O5} , _{Sb2O3 , Bi2O3} , and _Fe2O3 were prepared. Raw material powders containing the respective metal elements were weighed so as to satisfy the composition represented by the above composition formula (1), and mixed in alcohol by a ball mill for 24 hours to obtain a mixed slurry. The type of raw material powder (compound) containing each metal element is not particularly limited, but oxides, carbonates, and the like of each metal element can be used. Next, the obtained mixed slurry was dried, calcined at 900° C. for 3 hours, and then pulverized by a ball mill for 24 hours. Further, an aqueous solution of polyvinyl alcohol was added as a binder and granulated. Then, the powder after granulation is pressure-molded into an annular shape having a diameter of 24 mm and a thickness of about 2.5 mm at a pressure of 200 MPa, and the compact is fired at 1000 to 1200 ° C. for 2.5 hours and fired. made the body. The sintering temperature at this time was selected between 1000 and 1200° C. so that the sintered body has the maximum density. After that, the piezoelectric element 32 made of a KNN-based ceramic piezoelectric material was obtained through double-sided polishing, polarization, and the like.

On the other hand, FIG. 6B shows a bolt-clamped Langevin oscillator 11A of Comparative Example 2, in which a KNN ceramic represented by the composition formula (1) is placed between the front mass 21 and the back mass 22. It is common to the embodiment in that a piezoelectric element 32 and an electrode plate 33 formed of a piezoelectric material are sandwiched to hold a drive section 31 . However, both the front mass 21 and the back mass 22 are made of aluminum, two piezoelectric elements 32 and two electrode plates 33 are used to form the driving unit 31, and the piezoelectric element 32 is thick. This is different from the embodiment in that respect.

FIG. 6A shows a bolt-clamped Langevin vibrator 51 of Comparative Example 1 (conventional example). And the fact that the drive unit 56 formed by stacking the electrode plates 55 is sandwiched is common to the embodiment. However, both the front mass 52 and the back mass 53 are made of aluminum, two piezoelectric elements 54 and two electrode plates 55 are used to form the drive unit 56, and the piezoelectric element 54 is thick. The difference from the embodiment is that the piezoelectric element 54 is made of PZT (that is, a leaded ceramic piezoelectric material).

In order to compare the performance of the embodiment, Comparative Examples 1 and 2, the relationship between the input power and the radiation surface amplitude was investigated. The results are shown in the graph of FIG. In this graph, the data curve of the embodiment is represented by connecting the points indicated by ♦, the data curve of Comparative Example 1 is represented by connecting the points indicated by ▪, and the data of Comparative Example 2 The curve is represented as connecting the points indicated by ●.

In the case of Comparative Example 1, it was found that the radiation surface amplitude tended to increase linearly when the input power was in the range of about 10 W or less, but when the input power exceeded about 10 W, the linearity was lost and the waveform was distorted. all right. Therefore, the results suggest that the bolted Langevin vibrator 51 of Comparative Example 1 cannot be stably used in a range exceeding about 10 W.

In the case of Comparative Example 2, the curve was drawn at a position lower than that of Comparative Example 1 in the graph, and the radiation surface amplitude with respect to the input voltage was generally small. In addition, it was found that the radiation surface amplitude tended to increase linearly in the range of input power of about 5 W or less, but that the linearity was lost and the waveform was distorted in the range of more than about 5 W. Therefore, it was found that the bolted Langevin transducer 11A of Comparative Example 2 has a narrower range of electric power that can be stably used compared to Comparative Example 1. From the above, although Comparative Example 2 is preferable in that it has a small impact on the environment, it cannot generate large vibration energy on the front mass 21 side as compared with Comparative Example 1 configured using PZT. all right. Therefore, it was concluded that Comparative Example 2 could not achieve the same piezoelectric performance as Comparative Example 1.

On the other hand, in the case of the embodiment, the curve was drawn at a position higher than that of Comparative Example 1 in the graph, and the radiation surface amplitude with respect to the input voltage was generally large. Also, a tendency was recognized that the radiation surface amplitude increased linearly until the input power reached about 15W. Therefore, it was found that the bolted Langevin transducer 11 of the embodiment has a wider range of electric power that can be stably used compared to the first comparative example. From the above, it was found that the embodiment can generate a large vibration energy on the front mass 21 side compared to Comparative Example 1 configured using PZT, in addition to having a small impact on the environment. Therefore, it was concluded that the embodiment can achieve piezoelectric performance superior to that of Comparative Example 1.

Next, using the bolt-clamped Langevin-type transducer 11 of the embodiment and the bolt-clamped Langevin-type transducer 51 of Comparative Example 1, fish finder sensors 41 as shown in FIGS. We actually used them and compared their performance. The upper part of FIG. 8 is a graph for comparing both transmission sound pressures, and the lower part of FIG. 8 is a graph for comparing both reception sensitivities. In both cases, the horizontal axis indicates frequency, and the vertical axis indicates sound pressure (sensitivity). In the graph of FIG. 8, the data curve of the embodiment is represented by connecting points indicated by ♦, and the data curve of Comparative Example 1 is represented by connecting points indicated by ▪. According to this result, it can be said that the embodiment has substantially the same transmission/reception sensitivity as the first comparative example. 9 is a graph showing the directional characteristics of the embodiment, and the lower part of FIG. 9 is a graph showing the directional characteristics of the first comparative example. According to this, the half-life angle of Comparative Example 1 was 48°, whereas the half-life angle of the embodiment was 30°. Therefore, it was found that a narrow directivity angle can be achieved according to the embodiment.

And according to this embodiment, the following effects can be acquired.

(1) In the bolt-clamped Langevin transducer 11 of the present embodiment, the front mass 21 is formed using aluminum (first metal material) with a relatively low specific gravity, and stainless steel (second metal material) with a relatively high specific gravity is used. metal material) is used to form the back mass 22 . As a result, the weight of the front mass 21 can be reduced, and the amplitude on the side of the front mass 21 can be increased. Among lead-free ceramic piezoelectric materials, alkali niobate-based ceramic piezoelectric materials have relatively excellent piezoelectric characteristics. By constructing the driving section 31 including four or more piezoelectric elements 32 formed using such materials, it is possible to generate large vibration energy compared to the conventional structure. As a result, although the piezoelectric element 32 is formed using a lead-free piezoelectric material, it is possible to achieve performance equal to or better than that using PZT. Further, according to the present embodiment, since the piezoelectric element 32 is formed using an alkali niobate-based ceramic piezoelectric material, the environment is improved and the weight of the entire device can be easily reduced.

(2) In the present embodiment, the drive unit 31 is made of KNN-based ceramics having a characteristic composition, which has particularly favorable piezoelectric properties among alkali niobate-based ceramics. Therefore, it is possible to reliably generate a larger vibration energy, and it is possible to relatively easily achieve performance equivalent to or better than that using PZT.

(3) In the present embodiment, the difference in specific gravity between aluminum, which is the first metal material, and stainless steel, which is the second metal material, is twice or more, which is sufficiently large. Therefore, the front mass 21 can be made lighter without changing the dimensions and shapes of the front mass 21 and the back mass 22, and the amplitude on the front mass 21 side can be increased.

(4) In the present embodiment, the thickness T2 of the drive section 31 is suppressed to less than ⅓ of the total length L1 of the vibrator when the total length L1 of the vibrator corresponds to the half wavelength λ/2 of the resonance frequency. Therefore, it becomes easy to dispose the entire drive unit 31 near the vibration node F1. Therefore, the amplitude in the driving portion 31 can be suppressed, and peeling or the like is less likely to occur at the bonding interface between the piezoelectric element 32 and the electrode plate 33 . In addition, since the thickness of each piezoelectric element 32 constituting the drive unit 31 is reduced, the electric field is increased, and as a result, the vibration displacement is increased and the transmitted sound pressure is increased. In addition, since the ratio of the thickness of the front mass 21 to the total length L1 of the vibrator becomes large, even if the back mass 22 is made relatively heavy, it becomes easy to balance the vibration, and the amplitude of the front mass 21 side is increased. can be increased more reliably.

(5) By the way, the KNN-based ceramic piezoelectric material used in this embodiment is superior to PZT in high voltage resistance, so the piezoelectric element 32 is thinner and the electric field during driving is about doubled. Also, the deterioration of the piezoelectric characteristics can be suppressed. Therefore, by using a KNN-based ceramic piezoelectric material, it becomes easy to form a thin piezoelectric element 32, and by stacking a plurality of piezoelectric elements 32, it is possible to fabricate the drive unit 31 with a reduced overall thickness.

Each embodiment of the present invention may be modified as follows.

In the above-described embodiment, the piezoelectric element 32 is formed using a KNN-based ceramic piezoelectric material as the alkaline niobate-based ceramic piezoelectric material, but it is of course possible to use an alkaline niobate-based ceramic piezoelectric material other than the KNN-based ceramic piezoelectric material. .

In the above-described embodiment, the driving unit 31 including four piezoelectric elements 32 was illustrated, but the driving unit 31 including more piezoelectric elements 32 (for example, six or eight) may be used. good too.

In the above-described embodiment, the bolt-clamped Langevin oscillator 11 having a resonant frequency of 50 kHz and a total oscillator length L1 corresponding to half the wavelength λ/2 of the resonant frequency was illustrated. It is not limited to 50 kHz, and may be any frequency in the range of 25 kHz to 50 kHz, for example. Further, the vibrator total length L1 is not limited to the length corresponding to the half wavelength λ/2 of the resonance frequency, and may correspond to the wavelength λ, for example.

In the above embodiment, the front mass 21 is formed using aluminum, which is the first metal material, and the back mass 22 is formed using stainless steel, which is the second metal material having a higher specific gravity than the first metal material. However, it is not limited to this. For example, metal materials other than aluminum, such as aluminum alloys such as duralumin (specific gravity 2.80), magnesium (specific gravity 1.74), magnesium alloys, titanium (specific gravity 4.51), titanium alloys (6-4) (specific gravity 4) .43) or the like may be used as the first metal material to form the front mass 21 . Metal materials other than stainless steel, such as copper (specific gravity 8.96), copper alloys such as brass (specific gravity 8.50-8.70), steel materials such as carbon steel and nickel steel (specific gravity 7.70-9. 00), nickel (specific gravity 8.90), nickel alloy (specific gravity 8.50 to 9.30), chromium (specific gravity 7.19), chromium alloy, cobalt (specific gravity 8.85), cobalt alloy, etc. as the second It may be used as a metal material to form the back mass 22 .

- In the above-described embodiment, the front mass 21 has a rectangular cross-section and the back mass 22 has a circular cross-section, but the present invention is not limited to this. For example, both the front mass 21 and the back mass 22 may have a rectangular cross-section, or both the front mass 21 and the back mass 22 may have a circular cross-section. Furthermore, at least one of the front mass 21 and the back mass 22 may have a polygonal cross-section (for example, a hexagonal cross-section) other than a rectangular cross-section.

- In the above-described embodiment, the front mass 21 has a greater length (thickness) than the back mass 22, but this size relationship may be reversed. Moreover, both lengths (thicknesses) may be equal.

In the above embodiment, the first metal material is used to form the front mass 21, and the second metal material having a higher specific gravity than the first metal material is used to form the back mass 22, but the specific gravities are equal. The front mass 21 and the back mass 22 may be formed using a metal material, in which case the back mass 22 should be heavier than the front mass 21 . In addition, as the above-mentioned "metal material having the same specific gravity", metal materials having the same specific gravity may be selected, or different metals having the same specific gravity may be selected.

In the above-described embodiment, an example in which the fish finder sensor 41 is configured using the bolt-clamped Langevin transducer 11 is given. Devices (for example, an ultrasonic air sensor, an ultrasonic level meter, an ultrasonic flow meter, an ultrasonic concentration meter, an ultrasonic air bubble detection sensor, an ultrasonic knocking sensor, etc.) may be configured.

REFERENCE SIGNS LIST 11: Bolt-clamped Langevin transducer 21: Front mass 22: Back mass 25: Tightening bolt 31: Drive unit 32: Piezoelectric element 33: Electrode plate 34: Hole 41: Fish finder sensor L1: Full length of transducer T2: Drive Part thickness T3: Back mass thickness λ/2: Half wavelength of resonance frequency

Claims (6)

Between the front mass and the back mass, a drive unit comprising a plurality of laminated piezoelectric elements and electrode plates made of lead-free material is sandwiched. A Langevin oscillator having a structure in which the front mass and the back mass are fastened,
The drive unit includes four or more piezoelectric elements formed using an alkali niobate-based ceramic piezoelectric material,
The front mass is formed using a first metal material, the back mass is formed using a second metal material having a higher specific gravity than the first metal material ,
The total length of the vibrator corresponds to half the wavelength of the resonance frequency, the thickness of the driving portion is less than 1/3 of the total length of the vibrator, and the thickness of the front mass is 1/1 of the total length of the vibrator. is greater than 3
A bolt-clamped Langevin transducer characterized by: 2. A bolt-clamped Langevin vibrator according to claim 1, wherein said piezoelectric element is formed using a sodium-potassium niobate-based ceramic piezoelectric material. 3. The bolt-clamped Langevin vibrator according to claim 1, wherein the specific gravity of said second metal material is at least twice the specific gravity of said first metal material. 4. The method according to claim 3, wherein the first metal material has a specific gravity of 2.5 or more and 3.5 or less, and the second metal material has a specific gravity of 7.0 or more and 9.0 or less. Bolted Langevin transducer. 5. An ultrasonic measurement device for measuring a physical quantity by transmitting and receiving ultrasonic waves, comprising one or a plurality of the bolted Langevin transducers according to any one of claims 1 to 4 . 6. The ultrasonic measurement device according to claim 5 , wherein the ultrasonic measurement device is a fish finder sensor having a structure in which a plurality of the bolt-tightened Langevin transducers are oriented in the same direction and rubber-molded. machine.

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