CN1188548A - Electrodynamic driving means for acoustic emitters - Google Patents

Abstract

An excitation assembly of a sonic source, in particular an excitation assembly of a sonic source applied in the study of the seismic research, has a vibration surface (1) which can vibrate, and includes a framework (4), which contains at least an excitation component (3,13) preferably located in the center. This excitation assembly also includes: two or more fastening devices (2) installed relative to the acoustic emitting surface (1), and placed on the reverse side of the framework (4); two or more flexible transmission components (5) linking the fastening devices (2) with one another, and extending on both sides of the axis between the two fastening devices; two or more second excitation components (6,7,16,17) connected with the transmission component (5), and combining with the first excitation components (3,13) to form an electromagnetic apparatus; and each of electromagnetic actuators is suitable to guarantee that the related excitation components (3,6,7, 16, 17) carry out a controlled vibration relative movement.

Description

Electric Actuator for Sonic Transmitters

The present invention relates to an excitation assembly for an acoustic wave source having an acoustic wave emitting surface which can be excited to vibrate, and more particularly to an excitation assembly for an acoustic wave source used in seismic exploration. technical field

Sources for generating sound waves in water may be such as sonar sources, flexural extension sources, and seismic transmitters or sources. The invention can be well used in these types of sources, ie for emitting sound waves underwater. When reflected from the seabed and underlying geological structures, the resulting echo signals can be detected by various types of oceanophones or geophones.

It is known that low frequency sound waves can be transmitted over longer distances through underwater and geological structures than high frequency sound waves. There has long been a need for powerful low-frequency sound sources capable of operating underwater in military applications and in the marine sector of the oil and gas industry. Sources of various structures and designs for these purposes and domains have also existed for a long time. These acoustic sources are described, for example, in Seismic Energy 1968 Handbook, Bendix, Union Geophysical Union 1968, and in the Proceedings of the Second International Conference on High-Power Acoustic and Ultrasonic Transmitters held in France on June 12-13, 1990, Transmit Transducers require the sound wave source described in Low Frequency Sonar.

Most acoustic sources in use today are of the pulsed type, in which the effort is focused on delivering as much energy as possible in the shortest possible time. The frequency components of this type of source can only be corrected within a very small range, so different sources need to be selected for different exploration problems.

Recently seismic energy sources in the form of vibrators have been developed which vibrate in various frequency bands called "frequency sweeps". Among such seismic energy sources are vibrators operating with hydraulic means and sources using piezoelectric or magnetostrictive materials. In a hydraulic vibrator, the piston is controlled by a valve device so that it achieves high vibration amplitude. The piezoelectric effect is known to involve changes in length when a voltage is applied to the outer surface of a crystalline material, and conversely, a voltage is generated when the material is subjected to physical deformation. Magnetostriction means that the length of a magnetic material changes when subjected to a change in a magnetic field, and conversely, a change in the length of the material produces a change in the magnetic field.

The construction of the sound wave source is various. For low frequency applications, it is common to designate the source as having a circular surface (in the shape of a piston) when hydraulic principles are used, while when applying piezoelectric or magnetostrictive materials, it is common to have the source as a cylinder with a circular or elliptical cross-section shaped shape.

The concept of applying a hydraulic piston source is described in Marine Vibrator Sources, First Interval Volume 6, Issue 9 September 1988/285.

The biggest problem with this type of controllable source is to get a reasonably accurate and sufficiently large amplitude. For this, either a large source surface or a small source surface with high amplitude is required.

Vibrators based on hydraulic principles (eg in marine seismic surveying) provide high amplitudes at low frequencies. The movement of the piston is controlled by a valve device. However, there is a limit to the degree of control over the amplitude as well as frequency of these hydraulic piston sources.

Another type of sound source works on the same principle as an electrodynamic loudspeaker, with a conductive coil that generates a controllable magnetic field and a permanent magnet. When a varying current is applied to the coil, the two parts move relative to each other. These in turn set the pistons into motion, transmitting vibrations to the surrounding water. The diameter of the piston is approximately the same as the diameter of the coil. Examples of these sources can be found in the US Navy series J-9, J-11 and J-15 produced by Marine Resources Corporation of Florida, USA.

These sources come in many different sizes. They have a relatively flat frequency response, but are inefficient. Larger sources are more efficient but have less bandwidth.

Norwegian patent 176457 describes an excitation assembly for an acoustic wave source, the basic structure of which consists of a cylindrical elastic jacket with an elliptical cross-section. The source has two columns near the ends of the main axis between which the drive assembly is placed.

A curved extensional source with various embodiments of acoustic emitting surfaces is described in Norwegian Patent Application No. 941708 (International Patent Application No. PCT/NO95/00071).

The object of the invention is to propose an excitation assembly capable of transmitting signals over a wide frequency range. In addition to seismic surveying, this excitation assembly can be used in many different situations, such as those related to submarine acoustics, sources and sonar. The shape of the sound emitting surface can be changed according to the application, and all the different embodiments described above are applicable.

To achieve this object, an actuation assembly is proposed, which is characterized by what is stated in claim 1 .

The present invention will be described in detail below in conjunction with accompanying drawing:

Fig. 1 is a sectional view of an embodiment of the present invention viewed from one side;

Fig. 2 represents the details of this electromagnetic exciter;

Figure 3 shows a section corresponding to that shown in Figure 1, but with a different embodiment of the electromagnetic actuator;

Fig. 4 shows the electromagnetic exciter among Fig. 3;

Fig. 5 shows an alternative embodiment of the conveying member;

FIG. 6 shows a front view of the frame 4 of FIGS. 1 and 3 .

An embodiment of the present invention is shown in FIG. 1, wherein the transmission part 5 has a slightly arched shape, and the electromagnetic parts 3, 6 are installed in the center of the frame 4 and the transmission part 5, respectively. The transfer member 5 can be formed as a resilient plate or rod and is preferably rotatably fastened to the fastening device 2 . The distance from the central part of the transfer part 5 to the axis between the fastening means 2 is much smaller than the distance from the central part to the fastening means 2 . Thereby a transfer method is provided in which a large movement of the activation part 6 on the transfer member 5 with a relatively small force results in a small movement of the fastening device 2 with a correspondingly high force. This delivery will vary according to the curvature of the delivery part 5 . Provided that the transfer element is substantially straight, a frequency doubling is obtained compared to the motion of the exciter.

The fastening means 2 shown in the figures are posts, but the fastening of the transmitting part 5 on the sound-wave emitting surface can also be made directly to the sound-wave emitting surface.

The sound emitting surface in Fig. 1 is elliptical. When the transfer member 5 pulls the fastening device 2 inwards, the ellipse widens, creating a pressure wave in the surrounding ring cycle. The motion of the electromagnetic actuator will propagate outward in this way, causing sound waves in the water. By changing the eccentricity of the ellipse, the transmission rate in the excitation assembly can be adapted to different situations.

In other embodiments of the acoustic wave emitting surface, other solutions can also be chosen. As an example of fastening means, they may be fastened directly to the piston, where a relatively large movement of the actuator will result in a small movement of the piston. In this embodiment, the frame can also extend at least partially outside the conveying part 5, so that said first activation element is placed outside the other activation elements 6,7.

FIG. 2 shows the electromagnetic actuator in FIG. 1. FIG. This actuator consists of two parts, where the first excitation part 3 is fastened to the frame 4 and consists of a permanent magnetic material, while the second excitation part is fastened to one of the transmission parts 5 and consists of a coil . When current is fed through the coil, a magnetic field is generated. This magnetic field will interact with the magnetic field of the magnetic part, producing relative motion of the part. The resultant force can be expressed as:

F=I·L·B where I is the current in the coil, L is the length of the conductor, and B is the magnetic flux density.

Depending on the force required, either the size of the electromagnetic actuators can be changed, or the number of actuators on each transfer element 5 can be varied. It is also possible to place multiple transmission parts along the axis of the excitation assembly, and to place one or more exciters on each transmission part 5 . However, it is best if the resultant forces on each side of the frame are symmetrical about the frame axis to minimize stress on the structure. In the configuration shown in FIG. 1 it is also good if the resulting force vector is perpendicular to the main axis of the elliptical sound emitting surface 1 .

Figure 3 shows an acoustic wave source comparable to Figure 1, but with an alternative electromagnetic exciter. Details of this actuator are shown in Figure 4. At this time, the exciter is composed of a first excitation part 13 and two second excitation parts 16, 17, the coil is placed in the first excitation part 13 on the frame, and the second excitation parts 16, 17 are passive magnetic components . In this way, it is relatively easy to obtain a symmetrical movement of the two second actuating parts. A coil 13 surrounds a core of magnetic material, such as an iron core, which directs the magnetic field outwards towards second magnetically actuating parts 16, 17, for example also made of iron, so that the force F acting on these parts can be expressed as: $f=\frac{N^2{I}^2}{{\mathrm{\&gamma;}}_{\mathrm{<figure-callout\; id="2"\; label="tot"\; filenames="A9619499300091.png"\; state="\{\{state\}\}">tot</figure-callout>}}^2{\mathrm{\&mu;}}_{\mathrm{gap}}{\mathrm{\&mu;}}_{0}A}$ Here N is the number of windings, I is the current, γ _tot is the reluctance, μ _gap is the magnetic permeability, μ _o is the vacuum magnetic permeability, and A is the area.

Fig. 5 shows another embodiment of the transfer member, which consists of relatively rigid rods, each rod being rotatably fastened at one end to the second actuating part 6 and rotatably fastened at the other end. onto the fastening device 2. When the energizing part 6 moves outwards, the other end of the rod is pulled inwards at the above-mentioned transmission rate. The ratio between these movements is in this case equal to b/a.

Figure 5 shows yet another embodiment of the actuating part of Figure 2, here again it is made of a control rod placed through the center of the coil 6 and the magnet 3 to ensure a smooth movement.

Figure 6 shows a front view of the frame 4 with several centrally arranged holes 8 for mounting the first excitation parts 3, 13 and bolts for fastening the corresponding fastening means to the acoustic wave source (not shown) 9. When more than one electromagnetic actuator is applied, the frame can be equipped with more holes for fastening these parts.

Claims (11)

1, the Drive assembly of acoustic wave source, the Drive assembly of the acoustic wave source of using during particularly seismic method is studied, this Drive assembly has the vibration surface (1) that can vibrate, and comprise a framework (4), this framework (4) comprises a preferably excitation part (3 of centering at least, 13), it is characterized in that described Drive assembly also comprises:

Two or more relative sound wave emissions surfaces (1) and install and be placed on fastener (2) on the another side of framework (4);

The elasticity transfer member (5) that two or more are interconnected fastener (2) and extend the axis both sides between two fasteners;

It is that two or more are connected with transfer member (5) and be provided with described first excitation part (3, the 13) combination constituting the second excitation part (6,7,16,17) of electromagnetic driver,

And each electromagnetic driver is suitable for all guaranteeing that relevant excitation part (3,6,7,16,17) carries out the controlled vibration relative motion betwixt.

2, Drive assembly as claimed in claim 1 is characterized in that, has at least a transfer member (5) preferably to be made up of elastic plate.

3, Drive assembly as claimed in claim 1 is characterized in that, has at least a transfer member (5) to be made up of elastic rod.

4, the described Drive assembly of one of claim as described above is characterized in that transfer member (5) has curve shape.

5, the described Drive assembly of one of claim as described above is characterized in that one or more electromagnetic drivers are installed with respect to each transfer member (5).

6, the described Drive assembly of one of claim as described above, it is characterized in that, have at least one to be made of bar in the transfer member, an end of every bar is fastened on the described second excitation part rotationally, and the other end then is fastened on the described fastener (2) rotationally.

7, the described Drive assembly of one of claim as described above is characterized in that, each electromagnetic driver (3,6,7,13,16,17) is made of a current coil (6,7,13) and one or two magnetic material part (3,16,17).

8, the described Drive assembly of one of claim as described above is characterized in that, is arranged on the excitation part (some encourage part) (3 on the framework (4), 13) position is than the described second excitation part (6,7,16,17) axis between the more close fastener (2).

9, the described Drive assembly of one of claim as described above is characterized in that electromagnetic driver (3,6,7,13,16,17) is provided with symmetrically with respect to the axis between the fastener (2).

10, Drive assembly as claimed in claim 9 is characterized in that, described first (3,13) and second (6,7,16,17) excitation part and two fasteners (2) the identical distance of being separated by, be installed in respectively on framework (4) and the transfer member, and first (3,13) and second (6,7,16,17) axis normal between the basic and fastener (2) of the direction of the relative oscillating movement of excitation between the part.

11, the described Drive assembly of one of claim as described above, it is characterized in that the distance between the fastener (2) will be much larger than the described second excitation part (6,7,16,17) two ones of the tie point on the transfer member (5) to the distance of axis between the fastener (2).

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