This invention relates to a method for tuning the resonance frequencies of two or more coupled high temperature superconductor (“HTS”) self-resonant coils by mechanically displacing the two or more coils with respect to one another. This invention also relates to a detection system containing such coupled coils.
The use of HTS coils in obtaining nuclear magnetic resonance spectra and in magnetic resonance imaging has resulted in substantial gains in signal-to-noise ratios. See, for example, Wong et al, Advances in Cryogenic Engineering, 42B, pages 953-959 (1997); and Miller et al, Mag. Reson. Med., 41, pages 72-79 (1999). For many applications it is advantageous to be able to tune the self-resonance frequency of these coils.
An object of the present invention is to provide method and apparatus related to tuning the resonant frequencies of high temperature superconductor (HTS) coils.
This invention provides a method for tuning the resonance frequencies of two or more coupled high temperature superconductor self-resonant coils, comprising varying the distance between the centers of the two or more coils. In particular, the resonance frequency of the fundamental symmetric mode increases as the distance between the centers of the two or more coils increases and the resonance frequency of the fundamental symmetric mode decreases as the distance between the centers decreases.
The two or more coils are preferably essentially identical, and most preferably, they are identical. The two or more coils are preferably parallel, and they are preferably surface or planar coils.
This invention also provides a frequency detection system, e.g. a nuclear quadrupole resonance detection system, comprised of two or more coupled high temperature superconductor coils and means to vary the distance between the coils.
a-1c show a cross-sectional drawing of two coupled HTS coils in various configurations.
The resonance frequency of the fundamental symmetric mode of two or more coupled HTS self-resonant coils can be used to detect the presence of signals of that frequency. It has now been observed that when the distance between the centers of two or more HTS coils is sufficiently small the resonance frequency of the fundamental symmetric mode can be readily tuned, and having been thus tuned can be used to detect the presence of signals.
This invention provides a method for tuning the resonance frequency of the fundamental symmetric mode by varying the distance between the centers of the two or more coils. As the distance between the centers of the two or more coils is increased, the resonance frequency is increased. As the distance between the centers of the two or more coils is decreased, the resonance frequency is decreased. This tuning is accomplished with little degradation or reduction, i.e. less than a 20% change, in the quality factor (“Q”) of the coil.
The two or more HTS coils are essentially identical if they are not actually identical. Coils are essentially identical when they are, if not actually identical, as nearly alike in every respect as possible. In essentially identical coils, the materials from which they have been fabricated, the process by which they have been fabricated, and the properties they exhibit are as nearly alike as possible. Preferably, however, the coils are actually identical.
The coil preferred for use in this invention is a planar or surface coil that has an HTS coil configuration on only one side of a substrate or, more preferably, has identical, or essentially identical, HTS coil configurations on both sides of the substrate. The coils used in the examples have essentially identical, if not identical, HTS coil configurations on both sides of the substrate. The plane of a coil is the plane of the substrate supporting the HTS coil configuration.
A schematic cross-sectional drawing of two coupled HTS coils is shown in
Distance d can be increased, thereby increasing the fundamental frequency, by increasing the separation between planes 2 and 7; by moving second coil 4 up or down vertically in plane 7 in the plane of
b is a cross-sectional drawing of two HTS coils when they are parallel, i.e. when plane 5 has been rotated into plane 7, and coaxial, i.e. the line connecting their centers is perpendicular to the planes of the coils (planes 2 and 5). The first coil 1 again lies in plane 2, which is perpendicular to the plane of the drawing, and has a coil center 3 that lies in plane 2. The second coil 4 lies in plane 5, which is now parallel to plane 2. Second coil 4 has a coil center 6 that lies in plane 5. The distance d is the separation between coil center 3 and coil center 6. Distance d can be increased, thereby increasing the frequency of the fundamental symmetric mode, by increasing the separation between planes 2 and 5; by moving second coil 4 up or down vertically in plane 5 in the plane of the drawing; by moving second coil 4 horizontally in plane 5, i.e. perpendicular to the plane of
In one embodiment, a case, for example, when the two coils are parallel, the method of the invention for tuning the frequency of the fundamental symmetric mode is useful when the distance between the planes of the coils, i.e. plane 2 and plane 5 of
In this embodiment, when the two coils are not only parallel but are in the coaxial configuration as shown in
c is a cross-sectional drawing of two HTS coils when they are parallel, i.e. when plane 2 is parallel to plane 5, but the coils are not coaxial, i.e. the line connecting the centers of the coils is not perpendicular to the plane of each coil. The first coil 1 again lies in plane 2, which is perpendicular to the plane of the drawing and has a coil center 3 that lies in plane 2. The second coil 4 lies in plane 5, which is parallel to plane 2 and is perpendicular to the plane of the drawing. Second coil 4 has a coil center 6 that lies in plane 5. The distance d is the separation between coil center 3 and coil center 6. However, as shown in
In this embodiment, when the two coils are parallel but are not in a coaxial configuration (as shown in the configuration in
In this embodiment, lateral displacements and other off-axis displacements in any other direction within the plane of the second coil will have the same effect as, and are equivalent to, the vertical off-axis displacement described above as long as the planes of the coils are parallel and the distance between the planes is the same.
To decrease resonance frequency, the distance between coils can be decreased by performing the reverse of the movements described above by which the distance was increased.
It is preferred that the coils be parallel, but the coils may be non-parallel, i.e. the plane of one coil may be rotated with respect to the plane of another coil by a small angle. As a result, in yet another embodiment, when the coils are not exactly parallel, such as the result of imperfections in the alignment process, the same magnitudes of change in the resonance frequency occur when the two or more coils are subjected to any of the types of movements described above.
No matter how many coils are coupled, the distance between adjacent coils can be changed by varying the distance between the planes of the coils, i.e., lateral displacement of coaxial coils, or by adjusting the off-axis displacement of one or more coils with respect to an adjacent coil.
The distance between the centers of the coils can be changed by any convenient means. Means to vary the distance between coils include changing both x and y, or changing the distance in any other direction, using micropositioners in order to be able to make a continuous variation in distance between the centers of the two or more coils and therefore make a continuous tuning of the resonance frequency of the fundamental symmetric mode.
The frequency of the fundamental symmetric mode of the coupled high temperature superconductor coils is lower than the resonance frequency of a single coil. The reduction in the frequency of the fundamental symmetric mode of the coupled high temperature superconductor coils relative to the resonance frequency of a single coil is greater the larger the number of coils used. Two coupled coils will provide a fundamental symmetric mode frequency reduced by a certain percentage from the resonance frequency of a single coil. The use of three such coils provides a fundamental symmetric mode frequency reduced by a greater percentage and the use of four such coils provides a fundamental symmetric mode frequency reduced by a still greater percentage. These greater reductions are important. The frequency tuning range of the coupled coils is set at the upper end by the resonance frequency of a single coil and at the lower end by the fundamental symmetric mode frequency of the coupled coils with essentially no separation between the coils. Thus the use of two coupled coils provides a certain frequency tuning range and the use of three, four or more coupled coils provides increased frequency tuning ranges. The range is increased as the number of coils used is increased.
The method of this invention for tuning the resonance frequency of the fundamental symmetric mode of two or more coupled high temperature superconductor self-resonant coils is useful when the coupled coils are used in a detection system for detecting frequencies. The ability to tune frequencies is especially valuable in a nuclear quadrupole resonance (NQR) detection system that is being used to detect the presence of a particular chemical compound where there is a specificity of NQR frequencies as to the particular compound.
An NQR detection system comprised of two or more coupled high temperature superconductor self-resonant coils, and means to vary the distance between them, can be used to detect the presence of chemical compounds for any purpose, but is particularly useful for detecting the presence of controlled substances such as explosives, drugs or contraband of any kind. Such an NQR detection system could be usefully incorporated into a safety system, a security system, or a law enforcement screening system. For example, these systems can be used to scan persons and their clothing, carry-on articles, luggage, cargo, mail and/or vehicles. They can also be used to monitor quality control, to monitor air or water quality, and to detect biological materials.
In the detection system of the invention, the two or more coupled high temperature superconductor self-resonant coils can be used to both transmit and receive signals, so that in an NQR detection system the two or more coupled high temperature superconductor self-resonant coils can be used to both excite the NQR as well as to detect the resulting NQR frequency. Preferably, the two or more coupled high temperature superconductor self-resonant coils are used solely as sensors, i.e., to detect the NQR frequency, and one or more other coils are used to transmit the RF signal and excite the NQR.
High temperature superconductors are superconducting above about 77K, or at temperatures that may be reached by cooling with liquid nitrogen. The high temperature superconductor used to form the HTS coils is preferably selected from the group consisting of YBa2Cu3O7, Tl2Ba2CaCu2O8, TlBa2Ca2Cu3O9, (TlPb)Sr2CaCu2O7 and (TlPb)Sr2Ca2Cu3O9. Most preferably, the high temperature superconductor is Tl2Ba2CaCu2O8.
The coils could, for example, be constructed from a single crystal sapphire substrate with a CeO2 buffer layer and a high temperature superconductor pattern of the configuration shown in
The advantageous effects of this invention are demonstrated by a series of examples, as described below. The embodiments of the invention on which the examples are based are illustrative only, and do not limit the scope of the invention.
This example uses two HTS Tl2Ba2CaCu2O8 coils that are essentially identical, if not actually identical, on sapphire (Al2O3) substrates, each with the coil design configuration shown in
A clean, polished single crystal sapphire substrate with a radius of 2 inches (5.1 cm) and an approximate thickness of 0.018 inches (0.46 mm) was obtained from Union Carbide Corp. An epitaxial CeO2 buffer layer was grown on both sides of the substrate by off-axis sputter deposition with the substrate temperature held in the range of about 700-800° C. Off-axis magnetron sputtering of a Ba:Ca:Cu oxide target was used to deposit, at room temperature (about 20° C.), an amorphous precursor Ba:Ca:Cu oxide film on the CeO2 buffer layer on both sides of the substrate. This amorphous Ba:Ca:Cu oxide film was about 550 nm thick and had a stoichiometry of about 2:1:2. The precursor film was then thallinated by annealing it in air for about 45 minutes at 850° C. in the presence of a powder mixture of Tl2Ba2Ca2Cu3O10 and Tl2O3. When this powder mixture is heated, Tl2O evolves from the powder mixture, diffuses to the precursor film and reacts with it to form the Tl2Ba2CaCu2O8 phase.
The sample was then coated with photoresist on both sides and baked. A coil design mask with the design shown in
The two coils were placed with the planes of the coils parallel and as close together as possible in a co-axial configuration, i.e., with the line connecting the centers perpendicular to the two planes of the coils. The coils were immersed in liquid nitrogen held in a Nalgene® dewar. A pick-up coil comprised of a loop of copper wire was placed about 1 inch (2.5 cm) away from the coils with the plane of the pick-up coil parallel to the planes of the coils. The pick-up coil was formed by removing the outer jacket and dielectric spacer from a piece of 0.080 inch (2 mm) coax cable. The loop was formed by bending the inner conductor into a circle and soldering it to the outer jacket of the coax cable just outside the point where the jacket and dielectric were removed. The pick-up coil is connected to an Agilent 8753 Vector Network Analyzer (Agilent Technologies, Palo Alto, Calif.). The frequency was swept and the resonance frequency and Q measured as the distance between the centers of the coils was increased from essentially zero, i.e., the two coils were placed as close to one another as possible, to 6.1 mm while maintaining the co-axial configuration. Referring to the configuration of
The two coils were then placed with the planes of the coils parallel in a co-axial configuration, i.e., with the line connecting the centers perpendicular to the two planes of the coils. Again referring to
These results demonstrate the method for tuning the fundamental symmetric mode resonance frequency of two essentially identical coupled high temperature superconductor self-resonant coils by mechanically displacing one coil with respect to the other.
This example uses two HTS Tl2Ba2CaCu2O8 coils that are essentially identical, if not actually identical, on sapphire (Al2O3) substrates, each with the coil design configuration shown in
The two coils were then placed with the planes of the coils parallel in a co-axial configuration, i.e., with the line connecting the centers perpendicular to the two planes of the coils. Again referring to
These results demonstrate the method for tuning the fundamental symmetric mode resonance frequency of two coupled essentially identical high temperature superconductor self-resonant coils by mechanically displacing one coil with respect to the other.
This example uses two HTS Tl2Ba2CaCu2O8 coils that are essentially identical, if not actually identical, on LaAlO3 substrates, each with the coil design configuration shown in
The two coils were placed with the planes of the coils parallel in a co-axial configuration, i.e., with the line connecting the centers perpendicular to the two planes of the coils. Again referring to
These results demonstrate the method for tuning the fundamental symmetric mode resonance frequency of two coupled essentially identical high temperature superconductor self-resonant coils by mechanically displacing one coil with respect to the other.
Sonnet EM Software, obtained from Sonnet Software, Inc., Liverpool, N.Y. 13088, was used to simulate the performance of coupled coils to further demonstrate the advantages of using 2, 3 or 4 coupled coils as well as to further demonstrate the frequency tuning afforded by the use of two or more coupled coils. The following model was used. The substrate had a thickness of 0.5 mm and a dielectric constant ∈=24. The substrate had a front side and a back side. A 36 mm×36 mm square coil, with outermost turn 2 mm wide, innermost turn 3.25 mm wide and all other turns and spacings 0.25 mm wide was simulated on both sides of the substrate.
The resonance frequency of one such square coil was 4.95 MHz. Two, three and four such coils were coupled in a coaxial configuration with the planes of the coils parallel and the fundamental symmetric mode frequency determined for various separations between the coils. When two coupled coils were used the separation was the distance between the substrates of the two coils. When three or four coupled coils were used the separation was the distance between the substrates of adjacent coils. The results obtained are shown in Table I. “FSM frequency” is the fundamental symmetric mode frequency. “FSM Frequency Reduction” is the fractional reduction in the FSM frequency relative to the single coil resonance frequency. For example, the FSM frequency of two coupled coils separated by 0.05 mm is 3.29 MHz. This is 34% lower than the single coil resonance frequency 4.95 MHz and the FSM Frequency Reduction is listed as the fractional reduction, i.e., 0.34.
The FSM Frequency Reduction is plotted in
The FSM Frequency Reduction is plotted in
This example uses three HTS Tl2Ba2CaCu2O8 coils that are essentially identical on single crystal LaAlO3 substrates to demonstrate the greater reduction in the fundamental symmetric mode resonance frequency achieved with three coupled coils compared to that achieved with two coupled coils.
The three coils were prepared essentially as described in Example 3 except that the coil design configuration was altered so that the inner radius was about 3.5 mm. The outer radius was about 22.5 mm as before. The outermost HTS ring of the coil was 1.88 mm wide and the innermost HTS ring was 3.38 mm wide. The 19 intermediate HTS rings were about 250 μm wide with about 250 μm gaps between the rings. In addition, each coil was coated with a thin protective layer of Teflon™ AF.
The resonance frequency of each of the three coils was 2.43 MHz. When two of the coils were placed with no deliberate separation between them, except for the Teflon™ AF layers, the fundamental symmetric mode frequency was 1.50 MHz, 38% lower than the single coil resonance frequency. When all three coils were placed with no deliberate separation between them, except for the Teflon™ AF layers, the fundamental symmetric mode frequency was 1.02 MHz, 58% lower than the single coil resonance frequency.
This demonstrates the greater reduction in the fundamental symmetric mode resonance frequency achieved with three coupled coils compared to that achieved with two coupled coils. The frequency tuning range is increased accordingly.
This application claims the benefit of U.S. Provisional Applications No. 60/468,220, filed May 6, 2003; 60/498,045, filed Aug. 27, 2003; and 60/541,144, filed Feb. 2, 2004; each of which is incorporated in its entirety as a part hereof for all purposes.
Number | Name | Date | Kind |
---|---|---|---|
3373348 | Vanier et al. | Mar 1968 | A |
3530374 | Waugh et al. | Sep 1970 | A |
3764892 | Rollwitz | Oct 1973 | A |
4072768 | Fraser et al. | Feb 1978 | A |
4514691 | De Los Santos et al. | Apr 1985 | A |
5036279 | Jonsen | Jul 1991 | A |
5135908 | Yang et al. | Aug 1992 | A |
5206592 | Buess et al. | Apr 1993 | A |
5233300 | Buess et al. | Aug 1993 | A |
5258710 | Black et al. | Nov 1993 | A |
5262394 | Wu et al. | Nov 1993 | A |
5276398 | Withers et al. | Jan 1994 | A |
5351007 | Withers et al. | Sep 1994 | A |
5418213 | Tanaka et al. | May 1995 | A |
5457385 | Sydney et al. | Oct 1995 | A |
5565778 | Brey et al. | Oct 1996 | A |
5583437 | Smith et al. | Dec 1996 | A |
5585723 | Withers | Dec 1996 | A |
5592083 | Magnuson et al. | Jan 1997 | A |
5594338 | Magnuson | Jan 1997 | A |
5656937 | Cantor | Aug 1997 | A |
5661400 | Plies et al. | Aug 1997 | A |
5750473 | Shen | May 1998 | A |
5751146 | Hrovat | May 1998 | A |
5804967 | Miller et al. | Sep 1998 | A |
5814987 | Smith et al. | Sep 1998 | A |
5814989 | Smith et al. | Sep 1998 | A |
5814992 | Busse-Gravitz et al. | Sep 1998 | A |
5872080 | Arendt et al. | Feb 1999 | A |
5952269 | Ma et al. | Sep 1999 | A |
5973495 | Mansfield | Oct 1999 | A |
5986455 | Magnuson | Nov 1999 | A |
5999000 | Srinivasan | Dec 1999 | A |
6025719 | Anderson | Feb 2000 | A |
6054856 | Garroway et al. | Apr 2000 | A |
6088423 | Krug et al. | Jul 2000 | A |
6091240 | Smith et al. | Jul 2000 | A |
6104190 | Buess et al. | Aug 2000 | A |
6108569 | Shen | Aug 2000 | A |
6150816 | Srinivansan | Nov 2000 | A |
6166541 | Smith et al. | Dec 2000 | A |
6169399 | Zhang et al. | Jan 2001 | B1 |
6194898 | Magnuson et al. | Feb 2001 | B1 |
6201392 | Anderson et al. | Mar 2001 | B1 |
6218943 | Ellenbogen | Apr 2001 | B1 |
6242918 | Miller et al. | Jun 2001 | B1 |
6291994 | Kim et al. | Sep 2001 | B1 |
6335622 | James et al. | Jan 2002 | B1 |
6370404 | Shen | Apr 2002 | B1 |
D459245 | Power | Jun 2002 | S |
6420872 | Garroway et al. | Jul 2002 | B1 |
6478434 | Streetman et al. | Nov 2002 | B1 |
6486838 | Smith et al. | Nov 2002 | B1 |
6503831 | Speakman | Jan 2003 | B2 |
6538445 | James et al. | Mar 2003 | B2 |
6541966 | Keene | Apr 2003 | B1 |
6556013 | Withers | Apr 2003 | B2 |
6566873 | Smith et al. | May 2003 | B1 |
6590394 | Wong et al. | Jul 2003 | B2 |
6617591 | Simonson et al. | Sep 2003 | B1 |
6653917 | Kang et al. | Nov 2003 | B2 |
6751489 | Shen | Jun 2004 | B2 |
6751847 | Brey et al. | Jun 2004 | B1 |
6777937 | Miller et al. | Aug 2004 | B1 |
6822444 | Lai | Oct 2004 | B2 |
6819109 | Sowers et al. | Nov 2004 | B2 |
6847208 | Crowley et al. | Jan 2005 | B1 |
6952163 | Muey et al. | Oct 2005 | B2 |
6956476 | Buess et al. | Oct 2005 | B2 |
6958608 | Takagi et al. | Oct 2005 | B2 |
7049814 | Mann | May 2006 | B2 |
7106058 | Wilker et al. | Sep 2006 | B2 |
7148684 | Laubacher et al. | Dec 2006 | B2 |
7196454 | Baur et al. | Mar 2007 | B2 |
7265550 | Laubacher et al. | Sep 2007 | B2 |
7279896 | Alvarez et al. | Oct 2007 | B2 |
7279897 | Alvarez et al. | Oct 2007 | B2 |
7332910 | Laubacher et al. | Feb 2008 | B2 |
20020068682 | Shen | Jun 2002 | A1 |
20020153891 | Smith et al. | Oct 2002 | A1 |
20020156362 | Bock et al. | Oct 2002 | A1 |
20020169374 | Jevtic | Nov 2002 | A1 |
20020190715 | Marek | Dec 2002 | A1 |
20030020553 | Gao et al. | Jan 2003 | A1 |
20030062896 | Wong et al. | Apr 2003 | A1 |
20030071619 | Sauer et al. | Apr 2003 | A1 |
20030119677 | Qiyan et al. | Jun 2003 | A1 |
20030136920 | Flores et al. | Jul 2003 | A1 |
20040124840 | Reykowski | Jul 2004 | A1 |
20040222790 | Karmi et al. | Nov 2004 | A1 |
20040251902 | Takagi et al. | Dec 2004 | A1 |
20050104593 | Laubacher et al. | May 2005 | A1 |
20050122109 | Wilker et al. | Jun 2005 | A1 |
20050140371 | Alvarez et al. | Jun 2005 | A1 |
20050146331 | Flexman et al. | Jul 2005 | A1 |
20050206382 | Laubacher et al. | Sep 2005 | A1 |
20050248345 | Alvarez | Nov 2005 | A1 |
20050258831 | Alvarez | Nov 2005 | A1 |
20050264289 | Alvarez | Dec 2005 | A1 |
20050270028 | Alvarez et al. | Dec 2005 | A1 |
20060012371 | Laubacher et al. | Jan 2006 | A1 |
20060038563 | Cisholm et al. | Feb 2006 | A1 |
20060082368 | McCambridge | Apr 2006 | A1 |
20060119360 | Yamamoto et al. | Jun 2006 | A1 |
Number | Date | Country |
---|---|---|
0 426 851 | May 1991 | EP |
1 122 550 | Aug 2001 | EP |
1 168 483 | Jan 2002 | EP |
1 416 291 | May 2004 | EP |
1 477 823 | Nov 2004 | EP |
2 286 248 | Aug 1995 | GB |
2 289 344 | Nov 1995 | GB |
05 269 108 | Oct 1993 | JP |
07 265 278 | Oct 1995 | JP |
WO 9217793 | Oct 1992 | WO |
WO 9217794 | Oct 1992 | WO |
WO 9219978 | Nov 1992 | WO |
WO 9221989 | Dec 1992 | WO |
WO 9405022 | Mar 1994 | WO |
WO 9534096 | Dec 1995 | WO |
WO 9639636 | Dec 1996 | WO |
WO 9639638 | Dec 1996 | WO |
WO 9837438 | Aug 1998 | WO |
WO 9854590 | Dec 1998 | WO |
WO 9945409 | Sep 1999 | WO |
WO 9950689 | Oct 1999 | WO |
WO 0070356 | Nov 2000 | WO |
WO 02082115 | Oct 2002 | WO |
WO 02098364 | Dec 2002 | WO |
WO 03014700 | Feb 2003 | WO |
WO 03040761 | May 2003 | WO |
WO 03096041 | Nov 2003 | WO |
WO 2004001454 | Dec 2003 | WO |
WO 2004102596 | Nov 2004 | WO |
WO 2005059582 | Jun 2005 | WO |
Number | Date | Country | |
---|---|---|---|
20050046420 A1 | Mar 2005 | US |
Number | Date | Country | |
---|---|---|---|
60468220 | May 2003 | US | |
60498045 | Aug 2003 | US | |
60541144 | Feb 2004 | US |