Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Electrostrictive – magnetostrictive – or piezoelectric
Reexamination Certificate
2001-02-26
2003-12-30
Kuntz, Curtis (Department: 2643)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Electrostrictive, magnetostrictive, or piezoelectric
C310S367000
Reexamination Certificate
active
06671380
ABSTRACT:
TECHNICAL FIELD
The present invention relates to apparatus and methods for acoustic transducer technology for oil field and underwater applications, and more particularly to improvements in piezoelectric transmitters and receivers for oil field acoustic logging applications.
BACKGROUND OF THE INVENTION
Modern oil field acoustic logging involves sonic imaging of objects outside the borehole. This is accomplished by transmitting an acoustic signal along the borehole and detecting signals reflected back from objects outside the borehole. The reflected signal is subject to severe attenuation in this process and is typically very weak compared to the signal transmitted down the borehole.
Traditional sonic logging acquisition systems typically measure guided borehole waves that do not suffer such severe attenuation. Detecting the much weaker reflected signals from reflectors outside the borehole requires a more sensitive receiver, or a more powerful transmitter, or both.
Larger receivers or multiple receiving elements (e.g., stacked piezoelectric plates) of the prior art can be used to increase sensitivity and improve low-frequency response. However, for oil field logging application, particularly for acoustic receivers used in wireline and LWD acoustic logging, available space is limited. Available space is further limited by the need to place receivers in an azimuthal array for azimuthal resolution.
There is a large mismatch in acoustic impedance between borehole fluid and piezoelectric ceramics. Both the shape and the packaging of the piezoelectric ceramics affect the severity and frequency characteristics of the acoustic disturbance introduced by the mismatch. Receivers having larger surface area can be used to reduce the effects of mismatch. However, larger surface area in prior art receiver designs is only achievable at the expense of larger size. Also, receivers used for oil field logging must be designed to withstand the extremely high pressures experienced near the bottom of a borehole.
The prior art hydrophone best suitable for use as a receiver in wireline and LWD acoustic logging is the traditional cylindrical shape hydrophone disclosed in U.S. Pat. No. 3,327,023, “Piezoelectric Transducer Having Good Sensitivity Over A Wide Range Of Temperature And Pressure”, issued Jul. 30, 1974, to Henriquez, et al. Another cylindrical shape hydrophone is disclosed in U.S. Pat. No. 5,122,992, “Transducer Assembly”, issued Jun. 16, 1992, to Kompanek.
Other prior art acoustic receivers known as “benders” offer higher sensitivity, but lack the omni-directional capability of the hydrophone.
Available prior art acoustic transmitters most suitable for use in wireline and LWD acoustic logging are phased array transmitters, but these are inherently large for a given power output. More powerful transmitters of a given size would facilitate improvements in system sensitivity of wireline and LWD acoustic logging systems. In particular, there is a need for a high-power, pressure-balanced, acoustic transmitter small enough to fit in a logging tool.
There is a need to improve signal to noise ratio of downhole acoustic detection, and to improve low-frequency response. Thus, the need exists for more powerful transmitters and smaller, more sensitive, receivers with improved low-frequency response, both transmitters and receivers having higher capacitance and being better matched to the impedance of downhole borehole fluid.
SUMMARY OF THE INVENTION
The invention provides an acoustic transducer including a polarized piezoelectric shell having a spiral-shaped surface. The acoustic transducer may be used in a receiver or a transmitter. In one embodiment, the shell is a solid spiral having outer and inner spiral-shaped surfaces. In a preferred bender-type receiver embodiment, the shell defines an exterior, spiral-shaped, closed-loop surface and a spiral slot. The spiral slot defines a closed cavity with an interior, spiral-shaped, closed-loop surface.
REFERENCES:
patent: 3781955 (1974-01-01), Lavrinenko et al.
patent: 3827023 (1974-07-01), Henriquez et al.
patent: 4376302 (1983-03-01), Miller
patent: 4435667 (1984-03-01), Kolm et al.
patent: 4500377 (1985-02-01), Broussoux et al.
patent: 5122992 (1992-06-01), Kompanek
patent: 5631040 (1997-05-01), Takuchi et al.
patent: 60121899 (1985-06-01), None
patent: 60264200 (1985-12-01), None
Basic Designs of Piezoelectric Positioning Elements located at http://www.physikinstrumente.com/tutorial/4_41.html (Feb. 15, 2001).
Chang Chung
Hori Hiroshi
Batzer William B.
DeStefanis Jody Lynn
Ensey Brian
Kuntz Curtis
Lee John L.
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