Superconductive quantum interference device for the non-destructive evaluation of metals

• US 5,004,724 A
• Filed: 03/09/1989
• Issued: 04/02/1991
• Est. Priority Date: 03/09/1989
• Status: Expired due to Fees

• Current Assignee: International Superconductor Corp.
• Original Assignee: International Superconductor Corp.
• Inventors: De, Dilip K.
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): EDMONDS, WARREN
• Application Number:
  US07/321,263
• Time in Patent Office: 754 Days
• Field of Search: 324/248, 324/239-243, 324/234, 324/236, 324/238, 324/237, 505/702, 505/849, 505/843, 505/845, 505/846, 505/701, 505/705, 428/930
• US Class Current: 505/162
• CPC Class Codes: G01N 27/9006 Details, e.g. in the structure or functioning of sensors
• CPC Class Codes: G01R 33/0358 coupling the flux to the SQUID gradiometer coils G01R33/022; coils with superconductive winding H01F6/06
• CPC Class Codes: G01R 33/1238 Measuring superconductive properties
• CPC Class Codes: Y10S 505/702 Josephson junction present

Abstract

High-T_c superconductor quantum interference devices (SQUIDs) for noise-free, accurate measurements of defects and flaws in metal shapes and forms by measuring changes in the secondary magnetic field intensity around any point which is excited by a primary excitation current or by measuring changes in the impedance of the exciting coils. These measured changes are correlated to defects and flaws present in the metal.

Claims

1. A method of nondestructive evaluation of locations of flaws in a metal body, comprising the steps of:

(a) positioning a high-critical-temperature superconductive quantum interference device having a pair of insulated junctions in a superconductor loop in a flux-sensing relationship to a location adjoining said body;

(b) relatively displacing said body and said location;

(c) while said body and said location are relatively displaced, exciting said body with a modulated alternating current and detecting with said device flux irregularities representing flaws in said body;

(d) establishing locations of said flaws by the relative positions of said location and said body upon the detection of said flux irregularities, a plurality of said devices being connected in series are juxtaposed with said body;

(e) demodulating a signal generated by the series-connected devices to form an output; and

(f) connecting respective modulating coils inductively coupled to the respective high-critical-temperature superconductive quantum interference devices and connected to said output in a feedback path to form a flux-locked loop with said high-critical-temperature superconductive quantum interference devices.

2. The method defined in claim 1 wherein said body is excited in step (c) by passing an alternating current through two series-connected coil wound in opposite senses around said body, said alternating current having a frequency between substantially 1 kHz and 1 MHz and being modulated with a modulating frequency which is a fraction thereof.

3. The method defined in claim 2, further comprising the step of energizing said modulation coils with a square-wave signal of a frequency of 10 kHz to 500 kHz modulated with a frequency of 1/2 to 1/20 of the frequency of the square-wave signal.

4. The method defined in claim 3 wherein said square-wave signal is modulated with a frequency which is 1/2 of the frequency of the square-wave signal.

5. The method defined in claim 2 wherein said body is composed of a ferromagnetic material, further comprising the step of applying a constant unidirectional magnetic field to said body as a bias magnetic field during nondestructive evaluation of the body.

6. The method defined in claim 2 wherein four of said high-critical-temperature superconductive quantum interference devices are juxtaposed with said body and constitute two parallel-connected pairs of series-connected high-critical-temperature superconductive quantum interference devices.

7. A method of nondestructive evaluation of locations of flaws in a metal body, comprising the steps of:

(a) positioning a high-critical-temperature superconductive quantum interference device having a pair of insulated junctions in a superconductor loop in a flux-sensing relationship to a location adjoining said body;

(b) relatively displacing said body and said location;

(c) while said body and said location are relatively displaced, exciting said body with a modulated alternating current and detecting with said device flux irregularities representing flaws in said body; and

(d) establishing locations of said flaws by the relative positions of said location and said body upon the detection of said flux irregularities, said location being defined by a coil juxtaposed with said body and connected in series with a coil located remote from said body, said high-critical-temperature superconductive quantum interference device being juxtaposed with said coil located remote from said body.

8. A method of nondestructive evaluation of locations of flaws in a metal body, comprising the steps of:

(a) positioning a high-critical-temperature superconductive quantum interference device having a pair of insulated junctions in a superconductor loop in a flux-sensing relationship to a location adjoining said body;

(b) relatively displacing said body and said location;

(c) while said body and said location are relatively displaced, exciting said body with a modulated alternating current and detecting with said device flux irregularities representing flaws in said body;

(d) establishing locations of said flaws by the relative positions of said location and said body upon the detection of said flux irregularities, said location being defined by a coil juxtaposed with said body and connected in series with a coil located remote from said body; and

(e) inductively coupling said coil located remote from said body with said high-critical-temperature superconductive quantum interference device.

9. An apparatus for nondestructive location of flaws in a metal body, comprising:

a high-critical-temperature superconductive quantum interference device having a pair of insulated junctions in a superconductor loop disposed in flux-sensing relationship to a location adjoining said body;

means for relatively displacing said body and said location;

means for exciting said body with a modulated alternating current while said body and said location are relatively displaced, whereby said device detects flux irregularities representing flaws in said body;

means for establishing locations of said flaws by the relative positions of said location and said body upon the detection of said flux irregularities, a plurality of said devices connected in series being juxtaposed with said body,

means for demodulating a signal generated by the series-connected devices to form an output; and

respective modulating coils inductively coupled to the respective high-critical-temperature superconductive quantum interference devices and connected to said output in a feedback path to form a flux-locked loop with said high-critical-temperature superconductive quantum interference devices.

10. The apparatus defined in claim 9 wherein said body is excited in step (c) by passing an alternating current through two series-connected coils wound in opposite senses around said body, said alternating current having a frequency between substantially 1 kHz and 1 MHz and being modulated with a modulating frequency which is a fraction thereof.

11. The apparatus defined in claim 10, further comprising means for energizing said modulation coils with a square-wave signal of a frequency of 10 kHz to 500 kHz modulated with a frequency of 1/2 to 1/20 of the frequency of the square-wave signal.

12. The apparatus defined in claim 9 wherein said body is composed of a ferromagnetic material, further comprising means for applying a constant unidirectional magnetic field to said body as a bias magnetic field during nondestructive evaluation of the body.

13. The apparatus defined in claim 9 wherein four of said high-critical-temperature superconductive quantum interference devices are juxtaposed with said body and constitute two parallel-connected pairs of series-connected high-critical-temperature superconductive quantum interference devices.

14. An apparatus for nondestructive location of flaws in a metal body, comprising:

a high-critical-temperature superconductive quantum interference device having a pair of insulated junctions in a superconductor loop disposed in flux-sensing relationship to a location adjoining said body;

means for relatively displacing said body and said location;

means for exciting said body with a modulated alternating current while said body and said location are relatively displaced, whereby said device detects flux irregularities representing flaws in said body; and

means for establishing locations of said flaws by the relative positions of said location and said body upon the detection of said flux irregularities, said location being defined by a coil juxtaposed with said body and connected in series with a coil located remote from said body, said high-critical-temperature superconductive quantum interference device being juxtaposed with said coil located remote from said body.

15. An apparatus for nondestructive location of flaws in a metal body, comprising:

a high-critical-temperature superconductive quantum interference device having a pair of insulated junctions in a superconductor loop disposed in flux-sensing relationship to a location adjoining said body;

means for relatively displacing said body and said location;

means for exciting said body with a modulated alternating current while said body and said location are relatively displaced, whereby said device detects flux irregularities representing flaws in said body;

means for establishing locations of said flaws by the relative positions of said location and said body upon the detection of said flux irregularities, said location being defined by a coil juxtaposed with said body and connected in series with a coil located remote from said body; and

means for inductively coupling said coil located remote from said body with said high-critical-temperature superconductive quantum interference device.