Electroacoustic transducer with mechanical impedance transformer

Details Electroacoustic transducer with mechanical impedance transformer Electroacoustic transducer with mechanical impedance transformer

1995-08-10

1997-06-03

Dang, Khanh

Acoustics

Geophysical or subsurface exploration

Well logging

367912, G01V 140

Patent

active

056356854

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to an electroacoustic transducer provided with a mechanical impedance transformer, capable of emitting powerful acoustic waves in a liquid environment.
2. Description of the Prior Art
French Patent applications FR-A-2,667,518 and 2,678,390 describe electrohydraulic vibrating sources suited for working notably in wells where the vibrations generated by a piling of piezoelectric disks are applied to pads coupled with an underground formation by means of hydraulic jacks and connecting circuits. Selection of the sections of the jacks allows the obtaining of a mechanical amplitude impedance matching and an amplification of the amplitude of the vibrations applied to the ground by the pads.
U.S. Pat No.5,069,308 describes a source of acoustic waves suited for working in a well, which comprises a tubular body, an electromechanical generator consisting of one or two pilings of piezoelectric disks, coupled with a mechanical impedance transformer which lowers the acoustic impedance of the generator. The transformer comprises several flexible elongated blades arranged symmetrically around the central axis of the body. The central part of each blade has an elliptical curvature in a radial plane and it is connected at its opposite ends to two plates substantially perpendicular to the axis of the source, which rest on vibrating faces of the generator.


SUMMARY OF THE INVENTION

The electroacoustic transducer according to the invention comprises at least a vibration generator (comprising for example a piling of piezoelectric disks or of a magnetostrictive type motor, connected to a voltage source) arranged in an elongated body and an impedance transformer coupled mechanically with the generator.
On account of its dimensions, the transducer according to the invention is particularly well-suited for being used in wells of relatively small section such as petroleum or gas wells.
The impedance transformer comprises a tubular part or shell having at least a curved and flexible central part and at least a tubular part, the curved part at least being provided with openings (such as slits oriented along generating lines of the shell), the inner volume of the tubular part being selected for reinforcing the lowest frequencies generated by the vibration generator.
The vibration generator comprises for example a piling of sensitive elements that is extended at both ends by two end pieces or ferrules resting against end faces thereof and coupled therewith by a coupling means.
According to another embodiment, the transducer comprises a flexible housing arranged around the shell, for insulating the inner volume thereof from the outside environment, at least one ferrule being provided with openings allowing the volume to be filled with a fluid.
According to another embodiment, the tubular part is kept under stress with respect to the ferrules by two end caps secured respectively to the two ferrules.
According to another embodiment, the transducer comprises two sleeves extending on either side of the vibration generator and the shell, and connected by means of elastic decoupling elements (elastomer block, spring, etc).
According to another embodiment, each of the two sleeves comprises an inner wall and a plate secured to the wall by means of the elastic element, the plate being fastened against the end cap.
One of the two sleeves may comprise an end wall provided with sealed electric ducts and channels allowing passage of electric conductors connecting each of the sealed ducts to the generator.
The transducer can be used at depths in a well and comprises linking means allowing connection to a surface installation outside the well or on the water surface.
According to another embodiment, the transducer comprises static compensation means allowing a static compensation of the variations in the static pressure of the outside environment in which it is used.
The transducer can be connected for example to a surface installation (onshore or offshore for exampl

REFERENCES:
patent: 3205970 (1965-09-01), Holmes et al.
patent: 4960181 (1990-10-01), Marin et al.
patent: 5069308 (1991-12-01), Yin et al.
patent: 5109946 (1992-05-01), Sorrells

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