Patent US4079309A successfully refreshed from Google Patents.
US4079309A
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Method for determining changes in earth resistivity by measuring phase difference between magnetic field components
Assignee: United States Department of the Navy
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Filing: 1976-09-03
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Granted: 1978-03-14
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Expires: 1996-09-03
Abstract
Abstract Method and apparatus for detecting tunnels beneath an area of the earth's rface wherein an oscillator couples a current into a linear conductor at the earth's surface to generate a magnetic field in the earth beneath the area. Phase angle measuring means measures phase difference between the vertical and horizontal components of the magnetic field at selected points along a line parallel to the linear conductor to detect abrupt changes in earth resistivity, changes in resistivity indicating the presence and horizontal position of a tunnel.
Inventors
- 👤 Elwin W. Seeley
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-28 12:10
CPC Classifications
G; G01; G01V; G01V3/00; G01V3/08
Claims Analysis
Total Claims: 2
Claim 1
Independent Claim
165 words
A method for determining the presence of a tunnel beneath the earth surface which comprises the following steps: a. generating a magnetic field having a first component and a second component at the earth surface in the general area above which a tunnel is known or suspected to be; b. measuring the phase difference between said first component and said second component at selected points along a line parallel to the radiating element of the magnetic field generating means; c. observing the measured phase difference as inferring the presence of a tunnel when there is an abrupt change in the measured phase difference; and d. varying the frequency of said magnetic field inversely proportional to tunnel depth whereby sensitivity to tunnel detection is kept constant by decreasing the frequency of said magnetic field as the distance between the earth surface and the detected tunnel increases and by increasing the frequency of said magnetic field as the distance between earth surface and the detected tunnel decreases.
Claim 2
Independent Claim
165 words
A method for determining the presence of a tunnel beneath the earth surface which comprises the following steps: a. generating a magnetic field having a first component and a second component at the earth surface in the general area above which a tunnel is known or suspected to be; b. measuring the phase difference between said first component and said second component at selected points along a line parallel to the radiating element of the magnetic field generating means; c. observing the measured phase difference as inferring the presence of a tunnel when there is an abrupt change in the measured phase difference; and d. varying the frequency of said magnetic field inversely proportional to tunnel depth whereby sensitivity to tunnel detection is kept constant by decreasing the frequency of said magnetic field as the distance between the earth surface and the detected tunnel increases and by increasing the frequency of said magnetic field as the distance between earth surface and the detected tunnel decreases.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1981-03-13 | 1981-09-12 | 1982-03-14 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1985-03-13 | 1985-09-12 | 1986-03-14 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1989-03-13 | 1989-09-12 | 1990-03-14 | $7700.00 | Window Closed / Lapsed |