WO1993009641A1 - Shell for flextensional transmitter - Google Patents

Shell for flextensional transmitter Download PDF

Info

Publication number
WO1993009641A1
WO1993009641A1 PCT/SE1992/000666 SE9200666W WO9309641A1 WO 1993009641 A1 WO1993009641 A1 WO 1993009641A1 SE 9200666 W SE9200666 W SE 9200666W WO 9309641 A1 WO9309641 A1 WO 9309641A1
Authority
WO
WIPO (PCT)
Prior art keywords
shell
regions
flextensional
bendable
transmitter
Prior art date
Application number
PCT/SE1992/000666
Other languages
French (fr)
Inventor
Göran Engdahl
Gunnar Molund
Rune Tenghamn
Original Assignee
Abb Atom Ab
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Abb Atom Ab filed Critical Abb Atom Ab
Publication of WO1993009641A1 publication Critical patent/WO1993009641A1/en

Links

Classifications

    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K9/00—Devices in which sound is produced by vibrating a diaphragm or analogous element, e.g. fog horns, vehicle hooters or buzzers
    • G10K9/12—Devices in which sound is produced by vibrating a diaphragm or analogous element, e.g. fog horns, vehicle hooters or buzzers electrically operated
    • G10K9/121—Flextensional transducers

Definitions

  • the invention relates to a special embodiment of shells for flextensional transmitters, that is, devices which serve as
  • a typical application of such a transmitter is as a so-called Sonar, that is, a trans ⁇ mitter which sends out sound waves under water which, after 10 reflection, may be monitored by hydrophones of various kinds. With the aid of the reflected waves, objects within a wide circumference may be detected, and knowledge about the composition of the earth crust below the sea bed may be obtained.
  • Sonar that is, a trans ⁇ mitter which sends out sound waves under water which, after 10 reflection, may be monitored by hydrophones of various kinds. With the aid of the reflected waves, objects within a wide circumference may be detected, and knowledge about the composition of the earth crust below the sea bed may be obtained.
  • the shell has a cylindrical shape with a largely elliptical cross section.
  • the driving elements of the transmitter are always centred around the major axis of the elliptical cross section. For the attachment of the driving elements to the
  • the shell at the ends of the major axis in most designs, is formed with a plane surface perpendicular to the major axis. What distinguishes the various shell designs from each other to a certain extent is the shape of the outer contour of the shell at the end regions of the major
  • a primary object for these transmitters is to achieve as great an amplitude or as great a displacement as possible of the oscillations of the shell when the driving elements are activated.
  • the choice of the shape of the elliptical cross section area is of great importance in that connection. It can be noted that the ratio of the major axis to the minor axis of the ellipse is often chosen as 2:1. If a certain change of length of the major axis is obtained with the aid of the driving elements, the change of length of the minor axis will be 2-4 times as great, all according to the properties of the shell with uniform thickness and the shape of other features.
  • the invention comprises a special embodiment of the shell between the two end portions at the major axis of the elliptical cross section.
  • the embodiment gives a more even frequency response in that the second oscillation mode is displaced upwards in frequency and in that the destructive interference between the first and second fundamental oscillation modes is mitigated.
  • the principle of operation of the shell according to the invention is that its freedom to be bent is limited to small bending regions on each side of the end regions and in the middle of the belly of the shell, that is, at the minor axis of the elliptical cross section. This causes the basic appearance of the second fundamental oscillation mode to be changed in such a way that the corresponding displacement has the same signs in the first and second fundamental oscillation modes . This means that the radiated sound effect will not be reduced so markedly within the mentioned frequency band between the frequencies corresponding to the first and second fundamen ⁇ tal oscillation modes as in a shell with uniform thickness between the end regions.
  • the simplest way is to stiffen a shell, with otherwise uniform thickness, along its bellies with the exception of those points where it is desired that it should be bent.
  • One suitable way of obtaining such stiffened regions may be to provide the shell with thickened regions in the form of ' grooves along the shell and perpendicular to its above- mentioned end portions.
  • the grooves may, for example, be realized by embedding reinforcement strips or by winding the shell onto a templet provided with a suitable pattern.
  • the stiffened regions may also be obtained by a suitable use of materials with different stiffness properties.
  • Figure 1 shows the fundamental oscillation mode for a shell of uniform thickness and for a shell formed according to the invention.
  • Figure 2 shows the second fundamental oscillation mode for a shell of uniform thickness and the same for a shell according to the invention.
  • Figure 3 shows the division of a shell into different regions.
  • Figures 1 and 2 are mainly drawn to show the first and second fundamental oscillation modes of a flextensional transmitter designed with a cylindrical shell with a near elliptical cross section.
  • the fundamental oscillation mode of a shell 1 with end regions 2 and 3 when the shell is subjected to a force in the direction of the major axis is clear from Figure 1.
  • the shell then oscillates between the unbroken and the broken line.
  • the shape itself is the same for a shell with uniform thickness as for a shell which in the regions at the bellies of the second oscillation mode, at each side of the end regions, is provided with stiffened regions. A marginal bending of the resonance frequency of the fundamental oscillation mode can be noted when the shell is provided with these stiffened regions.
  • the increased net displacement which is a result of the invention, is clear from Figure 2.
  • the second fundamental oscillation mode for a shell with uniform thickness is clear from the unbroken line whereas the same for a shell with stiffened regions in a region at the bellies on each side of the end regions is clear from the unbroken line between the end regions.
  • This second fundamental oscillation mode is superimposed on the fundamental oscillation mode in the usual manner. Also for the second fundamental oscillation mode a certain increase of the resonance frequency occurs at the transition from a shell with uniform thickness to a shell with stiffened bellies.
  • Figure 3 can be made the starting-point, this figure showing how the periphery of the shell can be divided into a number of regions with different functions.
  • the above-mentioned end regions "a" are situated.
  • End beams 4 and 5 are fixed to the inside of the shell at the end regions, and drive units (not shown) are connected to these end beams.
  • the shell changes from the end regions into bending regions "b” with relatively great flexibility. These regions then change into stiffened regions "c” with a relatively stiff shell centred around the belly of the second fundamental oscillation mode.
  • stiffened regions "c” with a relatively stiff shell centred around the belly of the second fundamental oscillation mode.
  • bending regions "d” with relatively great flexibility are also provided. This means that the circumference S of the shell can be described as
  • R constitutes one half of the movable part of the shell.
  • the bellies of the second oscillation mode, and hence also the mid-point of the thickened parts, will thus be located on the shell at a distance corresponding to F/4 from the minor axis of the near elliptical cross section.
  • the transitions are bevelled.

Landscapes

  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Multimedia (AREA)
  • Transducers For Ultrasonic Waves (AREA)
  • Arrangements For Transmission Of Measured Signals (AREA)
  • Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)
  • Vibration Prevention Devices (AREA)

Abstract

Shell (1) for a flextensional transmitter wherein the shell has a cylindrical shape with a near elliptical cross section and wherein the driving elements of the flextensional transmitter, which are centred around the major axis of the elliptical cross section, are connected to end beams (4, 5) fixed to the inside of the end regions (2, 3) of the shell and wherein the shell between the end regions is formed with both bendable (b, d) and stiffened (c) regions.

Description

Shell for flextensional transmitter
TECHNICAL FIELD
ψ 5 The invention relates to a special embodiment of shells for flextensional transmitters, that is, devices which serve as
* high intensity sound sources. A typical application of such a transmitter is as a so-called Sonar, that is, a trans¬ mitter which sends out sound waves under water which, after 10 reflection, may be monitored by hydrophones of various kinds. With the aid of the reflected waves, objects within a wide circumference may be detected, and knowledge about the composition of the earth crust below the sea bed may be obtained.
15
BACKGROUND ART, THE PROBLEMS
Flextensional transmitters are described in a large number of publications of various kinds, among other things in the
20 form of patent specifications, articles, catalogues, etc. Examples of such publications are US 4,420,826, US 4,764,907, WO 86/03888, WO 87/05772 and others, and, for example, DEFENCE SYSTEM REVIEW, Nov. 1984, pp. 50-54 and in EDO CORPORATION'S catalogue (Salt Lake City, Utah) . A
25 recurring theme in all of these publications is that the shell has a cylindrical shape with a largely elliptical cross section. The driving elements of the transmitter are always centred around the major axis of the elliptical cross section. For the attachment of the driving elements to the
30 shell, the shell at the ends of the major axis, in most designs, is formed with a plane surface perpendicular to the major axis. What distinguishes the various shell designs from each other to a certain extent is the shape of the outer contour of the shell at the end regions of the major
35 axis. However, the most common feature in accordance with WO 86/03888 is that "The ends of the flextensional shell associated with the shell major axis have a full radius curvature" . However, what is common to all shell designs according to the state of the art is that the wall thickness of the shell between the end regions is constant.
A primary object for these transmitters is to achieve as great an amplitude or as great a displacement as possible of the oscillations of the shell when the driving elements are activated. The choice of the shape of the elliptical cross section area is of great importance in that connection. It can be noted that the ratio of the major axis to the minor axis of the ellipse is often chosen as 2:1. If a certain change of length of the major axis is obtained with the aid of the driving elements, the change of length of the minor axis will be 2-4 times as great, all according to the properties of the shell with uniform thickness and the shape of other features.
SUMMARY OF THE INVENTION, ADVANTAGES
With a smooth shell of uniform thickness in a flextensional transmitter in underwater operation, it can be demonstrated that the resonances corresponding to the first and second fundamental oscillation modes appear very clearly. For frequencies between these resonances these two oscillation modes are excited simultaneously. It can also be demon¬ strated that, since these oscillations are displaced in phase 180° in relation to each other, a destructive inter¬ ference occurs in a frequency band between the frequencies corresponding to the two fundamental modes. This means that the radiating sound effect within this band is relatively low.
The invention comprises a special embodiment of the shell between the two end portions at the major axis of the elliptical cross section. The embodiment gives a more even frequency response in that the second oscillation mode is displaced upwards in frequency and in that the destructive interference between the first and second fundamental oscillation modes is mitigated. The principle of operation of the shell according to the invention is that its freedom to be bent is limited to small bending regions on each side of the end regions and in the middle of the belly of the shell, that is, at the minor axis of the elliptical cross section. This causes the basic appearance of the second fundamental oscillation mode to be changed in such a way that the corresponding displacement has the same signs in the first and second fundamental oscillation modes . This means that the radiated sound effect will not be reduced so markedly within the mentioned frequency band between the frequencies corresponding to the first and second fundamen¬ tal oscillation modes as in a shell with uniform thickness between the end regions.
There are several different methods for limiting the oscillations of the shell to the above-mentioned regions. The simplest way is to stiffen a shell, with otherwise uniform thickness, along its bellies with the exception of those points where it is desired that it should be bent. One suitable way of obtaining such stiffened regions may be to provide the shell with thickened regions in the form of ' grooves along the shell and perpendicular to its above- mentioned end portions. The grooves may, for example, be realized by embedding reinforcement strips or by winding the shell onto a templet provided with a suitable pattern. The stiffened regions may also be obtained by a suitable use of materials with different stiffness properties.
The same effect as above can also be obtained if the bending regions are made very short and easily bendable. In practice, this could be realized by forming the bending regions with the aid of discrete components in the form of hinges, a mechanical bearing such as a slide bearing, or the like. BRIEF DESCRIPTION OF THE DRAWING
Figure 1 shows the fundamental oscillation mode for a shell of uniform thickness and for a shell formed according to the invention.
Figure 2 shows the second fundamental oscillation mode for a shell of uniform thickness and the same for a shell according to the invention.
Figure 3 shows the division of a shell into different regions.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figures 1 and 2 are mainly drawn to show the first and second fundamental oscillation modes of a flextensional transmitter designed with a cylindrical shell with a near elliptical cross section.
The fundamental oscillation mode of a shell 1 with end regions 2 and 3 when the shell is subjected to a force in the direction of the major axis is clear from Figure 1. The shell then oscillates between the unbroken and the broken line. The shape itself is the same for a shell with uniform thickness as for a shell which in the regions at the bellies of the second oscillation mode, at each side of the end regions, is provided with stiffened regions. A marginal bending of the resonance frequency of the fundamental oscillation mode can be noted when the shell is provided with these stiffened regions.
The increased net displacement, which is a result of the invention, is clear from Figure 2. The second fundamental oscillation mode for a shell with uniform thickness is clear from the unbroken line whereas the same for a shell with stiffened regions in a region at the bellies on each side of the end regions is clear from the unbroken line between the end regions. This second fundamental oscillation mode is superimposed on the fundamental oscillation mode in the usual manner. Also for the second fundamental oscillation mode a certain increase of the resonance frequency occurs at the transition from a shell with uniform thickness to a shell with stiffened bellies.
To define the invention more in detail, Figure 3 can be made the starting-point, this figure showing how the periphery of the shell can be divided into a number of regions with different functions. At the ends of the major axis, the above-mentioned end regions "a" are situated. End beams 4 and 5 are fixed to the inside of the shell at the end regions, and drive units (not shown) are connected to these end beams. The shell changes from the end regions into bending regions "b" with relatively great flexibility. These regions then change into stiffened regions "c" with a relatively stiff shell centred around the belly of the second fundamental oscillation mode. Between two and two of the two "c" regions, at the minor axis of the near elliptical cross section, bending regions "d" with relatively great flexibility are also provided. This means that the circumference S of the shell can be described as
S = 2a + 4b + 4c + 2d = 2a + 2R
where R constitutes one half of the movable part of the shell.
In order to obtain the desired oscillation properties, the following differences should be maintained
0 < b < 0.25 R
0.005 R < c < 0.5 R
0 < d < 0.25 R Another way of exactly defining the invention is also clear from Figure 3. The length of the major axis of the elliptical cross section is designated "L". Since the end regions of the shell are fixed to the end beams, the projection on the major axis of that part of the shell which is able to move freely, F, will be "L" minus twice the projection new on the major axis of the end beams, that is,
F = L - 2 e
The bellies of the second oscillation mode, and hence also the mid-point of the thickened parts, will thus be located on the shell at a distance corresponding to F/4 from the minor axis of the near elliptical cross section.
To prevent the transition between the flexural regions and the thickened regions from serving as indications of fracture, the transitions are bevelled.

Claims

1. Shell (1) for a flextensional transmitter, wherein the shell has a cylindrical shape with a near elliptical cross section and wherein the driving elements of the flexten¬ sional transmitter, which are centred around the major axis of the elliptical cross section, are connected to end beams (4, 5) fixed to the inside of the end regions (2, 3) of the shell, characterized in that the shell between the end regions are formed with both bendable (b, d) and stiffened (c) regions.
2. Shell (1) for a flextensional transmitter according to claim 1, characterized in that the shell is formed such that that part of the shell between the end regions which adjoins the end regions (c) and that part of the shell which within a region is centred around the minor axis (d) of the near elliptical cross section are formed as bendable regions and that those parts of the shell (c) between the end regions which lie between the bendable regions are formed as stiff regions.
3. Shell (1) for a flextensional transmitter according to claim 1, characterized in that the bendable regions (b, d) are formed with a smaller shell thickness than the stiffened regions (c) .
4. Shell (1) for a flextensional transmitter according to claim 1, characterized in that the material of the shell in the bendable regions is formed with softer stiffness properties than the material in the stiffened regions.
5. Shell (1) for a flextensional transmitter according to claim 1, characterized in that bendable regions are formed with the aid of hinges .
6. Shell (1) for a flextensional transmitter according to claim 1, characterized in that the bendable regions are formed with the aid of a mechanical bearing.
7. Shell (1) for a flextensional transmitter according to claim 1, characterized in that with a given shell length "R" between the end regions the bendable regions (b, d) shall have a shell length according to
0<b,c<0.25 R
and that the stiffened regions (c) shall have a shell length according to
0.05S<c<0.5 R
8. Shell (1) for a flextensional transmitter according to claim 1, characterized in that the mid-point for the stiffened regions (c) lies at a distance from the minor axis of the near elliptical cross section corresponding to one- fourth of that part of the shell between the end regions which is projected on the major axis.
PCT/SE1992/000666 1991-10-28 1992-09-25 Shell for flextensional transmitter WO1993009641A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE9103134-4 1991-10-28
SE9103134A SE469309B (en) 1991-10-28 1991-10-28 MUST HAVE FLEXTENSIONAL SENDERS

Publications (1)

Publication Number Publication Date
WO1993009641A1 true WO1993009641A1 (en) 1993-05-13

Family

ID=20384123

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/SE1992/000666 WO1993009641A1 (en) 1991-10-28 1992-09-25 Shell for flextensional transmitter

Country Status (3)

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CN (1) CN1073568A (en)
SE (1) SE469309B (en)
WO (1) WO1993009641A1 (en)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1995032601A1 (en) * 1994-05-19 1995-11-30 Staahl Lars A surface element and a device for generating sound
WO1996027863A1 (en) * 1995-03-07 1996-09-12 Staahl Lars A device for generating sound
WO2004057911A1 (en) * 2002-12-19 2004-07-08 Abb Ab Method and device for converting energy between membranes
WO2015103244A3 (en) * 2013-12-30 2015-09-11 Photosonix Medical, Inc. Flextensional transducers and related methods

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1986003888A1 (en) * 1984-12-19 1986-07-03 Gould Inc. A rare earth flextensional transducer
WO1987005773A1 (en) * 1986-03-19 1987-09-24 The Secretary Of State For Defence In Her Britanni Flextensional transducers

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1986003888A1 (en) * 1984-12-19 1986-07-03 Gould Inc. A rare earth flextensional transducer
WO1987005773A1 (en) * 1986-03-19 1987-09-24 The Secretary Of State For Defence In Her Britanni Flextensional transducers

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1995032601A1 (en) * 1994-05-19 1995-11-30 Staahl Lars A surface element and a device for generating sound
US5706254A (en) * 1994-05-19 1998-01-06 Stahl; Lars Surface element and a device for generating sound
WO1996027863A1 (en) * 1995-03-07 1996-09-12 Staahl Lars A device for generating sound
WO2004057911A1 (en) * 2002-12-19 2004-07-08 Abb Ab Method and device for converting energy between membranes
WO2015103244A3 (en) * 2013-12-30 2015-09-11 Photosonix Medical, Inc. Flextensional transducers and related methods
US9919344B2 (en) 2013-12-30 2018-03-20 Photosonix Medical, Inc. Flextensional transducers and related methods
US11110489B2 (en) 2013-12-30 2021-09-07 Photosonix Medical, Inc. Flextensional transducers and related methods
US11717854B2 (en) 2013-12-30 2023-08-08 Photosonix Medical, Inc. Flextensional transducers and related methods

Also Published As

Publication number Publication date
SE469309B (en) 1993-06-14
SE9103134D0 (en) 1991-10-28
CN1073568A (en) 1993-06-23
SE9103134L (en) 1993-04-29

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