Acoustics – Geophysical or subsurface exploration – Seismic source and detector
Patent
1995-11-20
1997-07-08
Eldred, J. Woodrow
Acoustics
Geophysical or subsurface exploration
Seismic source and detector
367142, G01V 100
Patent
active
056463804
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a drive assembly for acoustic sources having sound emitting surfaces adapted to be excited into vibrational movement, in particular for use in seismic prospecting.
Sources employed for generating sound waves in water can for example be sonar sources, flextensional sources or seismic transmitters or energy sources. Advantageously the invention can be employed for such types of sources, i.e. for emitting sound waves under water. Upon reflection from the sea bed and underlying geological formations resulting echo signals can be detected by means of hydrophones or geophones of various types.
It is well known that low frequency sound waves can be transmitted over longer distances through water and geological structures than high frequency sound waves can. Within military applications as well as within the marine sector of oil and gas industry there has for a long time been a need for powerful low frequency sound sources which can operate under water. Sources of various constructions and designs for these purposes and fields of use, have been available for a long time. Such acoustic sources are for example described in Seismic Energy Sources 1968 Handbook, Bendix, United Geophysical Corporation 1968, and in Transducer Needs for Low-Frequency Sonar, Proceedings of the Second International Workshop on Power Transducers for Sonic and Ultrasonics, France, June 12-13, 1990.
Most of the acoustic sources employed today are of the impulsive type, in which efforts are made to have the sources emit as much energy as possible during as short time as possible. The frequency contents of such a source can be modified only to a very small degree, and different sources are selected for different surveying problems.
In recent time there have been developed seismic energy sources in the form of vibrators which can vibrate within various frequency bands, so-called "frequency sweep". To this group there belong vibrators which operate by employing hydraulic means and sources employing piezoelectric or magnetostrictive materials. In hydraulic vibrators a piston is controlled by a valve arrangement, and thereby it is possible to obtain large oscillation amplitudes. The piezo-electrical effect as known involves a change of length of a crystalline material when an electrical voltage is applied to the outer surfaces thereof, and conversely that an electrical voltage is generated when the material is subjected to a physical deformation. Magnetostriction means that a magnetic material being subjected to a magnetic field change will undergo a length change, and conversely that an applied length change of the material will give rise to a change of the magnetic field.
There are various different manners of designing acoustic sources. For low frequency uses it is common to let the sources have a circular surface (in the form of a piston) when the hydraulic principle is employed, and a cylindrical shape with either a circular or elliptic cross-section when piezoelectric and magnetostrictive materials are used.
A concept where a hydraulic piston source is employed, is described in The Marine Vibrator Source, First Break Vol. 6 No. 9, September 1988/285.
The greatest problem with this type of controllable sources is to obtain a well defined and sufficiently high amplitude of the oscillations. In order to obtain this there will be a need for either a large source surface or a small source surface having high oscillation amplitudes.
Vibrators based on the hydraulic principle (for example within marine seismic exploration) provide high amplitudes at low frequencies. The piston movements are controlled by a valve arrangement. The degree of control of these hydraulic piston sources as regards amplitude combined with frequency, is limited, however.
The availability of so-called high-magnetostrictive magnetic materials has improved the possibilities of manufacturing good acoustic sources. By using this type of materials as drive elements it is possible to obtain amplitude changes which can be up to 20 times larger than the corr
REFERENCES:
patent: 4332017 (1982-05-01), Massa
patent: 4514834 (1985-04-01), Hanson et al.
patent: 4845688 (1989-07-01), Butler
patent: 4941202 (1990-07-01), Upton
patent: 5070486 (1991-12-01), Boucher
patent: 5237543 (1993-08-01), Erickson et al.
patent: 5276657 (1994-01-01), Newnham et al.
patent: 5291461 (1994-03-01), Boeglin et al.
patent: 5329499 (1994-07-01), Molund et al.
LandOfFree
Drive assembly for acoustic sources does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Drive assembly for acoustic sources, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Drive assembly for acoustic sources will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2410003