Magnetic Mine Sweeping

Description

GOVERNMENT RIGHTS

This invention was made with U.S. Government support under contract HR001121C0063 and HR001122C0149 awarded by the Defense Advanced Research Projects Agency (DARPA) The government has certain rights in this invention.

FIELD

This disclosure relates to the field of magnetic mine sweeping (M-MS) or magnetic mine countermeasures (M-MCM). More particularly, this invention relates to the use of permanent type magnets and high temperature superconducting (HTS) trapped flux magnets to generate both AC and DC magnetic signatures used in magnetic mine sweeping devices.

Introduction

Magnetic Mine Sweeping, sometimes referred to as Magnetic Mine Countermeasures (M-MCM), is useful in applications where both steady-state magnetic fields (here on B-field) and time-changing magnetic fields (here on AC B-fields or dB/dt) are used to trigger magnetic influence mines (MIM). For the purposes of clarity, brevity, and enablement of the embodiments described in this disclosure, the terms steady-state, static, fixed, stationary, time independent, and direct current (DC) generally have the same meaning, and are used interchangeably throughout this disclosure. Likewise, for the purposes of clarity, brevity, and enablement of the embodiments described in this disclosure, the terms time-dependent, time-varying, dB/dt, and alternating current (AC) B-fields, have the same general meaning and are used interchangeably throughout this disclosure.

M-MCM devices can be mounted on a wide variety of naval platforms, including but not limited to manned surface vessels (MSV), unmanned surface vessels (USV), unmanned underwater vessels (UUV), towable arrays, and other types of mine sweeping vessels.

Traditional M-MCM devices from the prior art typically involve one of two magnetic mine sweeping approaches: 1) long-length, high current cables dragged behind a MSV, or 2) large diameter electro-magnets mounted on board an MSV or USV. For the former, long-length, high ampacity cables are typically dragged behind surface vessels and perform sweep patterns over the specified area to be cleared of MIMs. These long-length, high ampacity cables are typically made of heavy gauge copper wire or aluminum wire, and are quite heavy and cumbersome to handle.

During mine sweeping operations, the heavy cables are first uncoiled from their storage spool, mounted to the rear of the MSV, into the surrounding sea water. The cables are then energized with high currents to generate a corresponding B-field in the nearby vicinity of the cable. The B-field emanating from the cable falls off in magnitude as 1/r, where r is the radius of the cable. In this approach to magnetic mine sweeping, the electrically conductive sea water is used as a return path to the negative polarity (−) side of the power supply that is energizing the cable. The B-field emanating from the cable is used to detonate MIMs near the cable as the MSV performs its sweep patterns. After the magnetic sweep operation is performed, the long length cables are wound back up on a large-diameter spool, and stored on the mine sweeping vessel.

The second approach is to mount a large electro-magnet on the deck of an MSV. For this type of M-MCM operation, typically a superconducting electro-magnet is used instead of a normal-resistive copper magnet, because the superconducting magnet, wound with its zero or near zero electrical resistance superconducting wire, has a much higher current density (J in A/m²), and hence would be far lighter and require less electrical power consumption than an equivalent resistive copper electro-magnet possessing the same magnetic dipole moment.

In this approach to magnetic mine sweeping, once the superconducting electro-magnet is energized, the MSV performs its sweep pattern over the area to be cleared of MIM. When an MIM is magnetically influenced by the B-field emanating from the surface-mounted superconducting electro-magnet, the MIM detonates. Due to the large spatial magnetic signature (i.e., the effective range) of the superconducting electro-magnet, the detonation typically occurs at a distance far enough away as not to severely damage the MSV.

While not bound by theory, the magnetic dipole moment (m) in units of A-m² of this type of electro-magnet is given by:

m = N * I * A eff [ 1 ]

where N is the number of turns in the electro-magnet, I is magnet's current (in Amps (A), and A_eff is the effective cross sectional area of the electro-magnet. Thus, the larger the diameter of the electro-magnet, the larger the magnetic dipole moment (M), and hence the larger the effective range of the MSV, which translates to fewer sweeps per unit area. Similarly, the larger the number of turns (N), or the larger the current (I) flowing in the conductor of the electro-magnet, or both, the larger the dipole magnetic moment.

To increase the current (I) flowing in the electro-magnetic, superconducting wire is typically used because of its higher current density (J) and zero or nearly zero electrical resistivity (ρ=0), which results in a significantly lighter, more energy efficient electro-magnet. With the discovery of high temperature superconductivity (HTS), HTS wire is available in long enough lengths to fabricate HTS magnets of sufficient size for surface mounted M-MCM devices.

For the purposes of clarity, brevity, and enablement of the embodiments described in this disclosure, the terms wire, tape, and conductor generally have the same meaning and are used interchangeably throughout this disclosure. Likewise for the purposes of clarity, brevity, and enablement of the embodiments described in this disclosure, the terms magnetic signature, magnetic moment, dipole moment, and magnetic dipole moment generally have the same meaning and are used interchangeably. The term magnetization (M) is specifically reserved for the magnetic moment per unit volume (V) of the M-MCM device.

The two traditional approaches to M-MCM described above have several disadvantages. First, both approaches are extremely large, heavy, and require complex shipboard operations to deploy from surface ships. Second, large surface mounted superconducting electro-magnets are extremely expensive to fabricate and have high operating and maintenance costs. These high costs limit the number of mine sweeping vessels that can be deployed for a sweeping operation. Fewer mine sweeping vessels result in longer sweep times for a given area. Third, both approaches require large, heavy, and expensive electrical power sources, which consume large quantities of electrical power.

Fourth, the generation of both DC and AC magnetic signatures is beneficial during mine sweeping operations, as MIM can be triggered by DC B-fields, AC B-fields, or combinations of both DC and AC B-fields. The generation of an AC magnetic signature for these two traditional M-MCM approaches is particularly challenging for a variety of reasons. First, it requires a large and expensive power supply that requires a high voltage to overcome the inductance of the coil. Second, there is significant unwanted heating from the AC losses that must be removed from the superconducting coil by the cryogenic refrigeration system.

Finally, surface mounted superconducting electro-magnets by definition are located at some physical distance above the water's surface, away from the underwater mine threat. Thus, as MIMs are located deeper and deeper under water, eventually a surface mounted electro-magnets dipole moment becomes too weak to trigger the MIM, rendering these surface mount superconducting electro-magnets ineffective below a certain water depth.

What is needed, therefore, is an M-MCM device that tends to reduce issues such as those described above, at least in part.

SUMMARY

The above and other needs are met by a magnetic mine countermeasure payload device with a non-magnetic plate, and magnetic elements, each having a north magnetic pole and a south magnetic pole, affixed to the plate in a magnetic array. A rotational shaft is coupled to the plate, with a motor coupled to the shaft, and an electrical power source electrically connected to the motor. The motor is configured to at least one of selectively rotate the magnetic array, thereby creating an AC magnetic moment in the magnetic mine countermeasure payload device, and not rotate the magnetic array, thereby enabling a DC magnetic moment in the magnetic mine countermeasure payload device.

In some embodiments according to this aspect of the disclosure, the magnetic elements include at least one of a permanent magnet, and a superconducting trapped flux magnet. In some embodiments, the permanent magnet is formed of at least one of Nd—Fe—B, Sm—Co, and Al—Ni—Co. In some embodiments, the superconducting trapped flux magnet is formed of at least one of Bi—Sr—Ca—Cu—O, Re—Ba—Cu—O, Tl—Ba—Ca—Cu—O, Hg—Ca—Ba—Cu—O, Mg—B, Nb—Ti, Nb—Sn, N—N, and Nb—Ge.

In some embodiments, a gearbox is mechanically coupled between the motor and the shaft. In some embodiments, the device generates at least one of a steady state magnetic moment, and a time varying magnetic moment. In some embodiments, multiple plates are rotated at at least one of a constant angular velocity, and variable angular velocity. In some embodiments, the plates are aligned in at least one of a parallel configuration, and an anti-parallel configuration. In some embodiments, a hermetic water-tight container is configured to house the magnetic mine countermeasure payload. In some embodiments, the payload is mounted to at least one of an unmanned surface vessel, an unmanned underwater vessel, a manned surface vessel, and a towable array.

In some embodiments, the rotational shaft is rotated at at least one of a fixed AC frequency, and a variable AC frequency. In some embodiments, the motor is at least one of an electric motor, a magnetic motor, a pneumatic motor, a hydraulic motor, and a wax motor. In some embodiments, the power source is at least one of a battery, an AC power source, and a DC power source. In some embodiments, the plates are at least one of round, square, rectangular, hexagonal, and multi-polygonal. In some embodiments, the device is fixed in a vessel and the vessel is rotated in at least one of a fixed angular rotation, and a variable angular rotation, thereby creating an AC magnetic signature of the array.

According to another aspect of the disclosure, there is described a magnetic mine countermeasure payload device with a non-magnetic plate, and magnetic elements, each having a north magnetic pole and a south magnetic pole. The magnetic elements are affixed to the plate in a magnetic array, wherein when the array is rotated, an AC magnetic moment in the magnetic mine countermeasure payload device is generated, and when the array is not rotated, a DC magnetic moment in the device is generated.

In various embodiments according to this aspect of the disclosure, the magnetic elements include at least one of a permanent magnet, and a superconducting trapped flux magnet. In some embodiments, the array is rotated at at least one of a constant angular velocity, and variable angular velocity. In some embodiments, multiple plates are aligned in at least one of a parallel configuration, and an anti-parallel configuration. In some embodiments, a hermetic water-tight container is configured to house the magnetic mine countermeasure payload.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages of the invention are apparent by reference to the detailed description when considered in conjunction with the figures, which are not to scale so as to more clearly show the details, wherein like reference numbers indicate like elements throughout the several views, and wherein:

FIG. 1 depicts a simple schematic of twelve separate PMs equally spaced on a single plate, with all twelve of the N/S poles of the PMs facing outward in the radial (r) direction, according to an embodiment of the present disclosure.

FIG. 2 depicts a simple schematic of twelve separate PMs equally spaced on a single plate, but with all twelve of the N/S poles of the PMs facing in tangential (θ) directions, according to an embodiment of the present disclosure.

FIG. 3 depicts a simple schematic of twelve separate PMs equally spaced on a single plate, but with all twelve of the N/S poles of the PMs facing in a common axial (z) direction, according to an embodiment of the present disclosure.

FIG. 4 depicts a simple schematic of twelve separate PMs equally spaced on a single plate, but with all twelve of the N/S poles of the PMs facing in a common vertical (y) direction, according to an embodiment of the present disclosure.

FIG. 5 depicts a simple schematic of multiple non-magnetic plates, housing multiple PMs located along a central axis of a single rotational shaft, according to an embodiment of the present disclosure.

FIG. 6 depicts a magnetic payload, including multiple non-magnetic plates, housing multiple PMs located along a central axis of a single rotational shaft, where the magnetic payload is hermetically sealed in a water-tight container, which can then be mounted inside a UUV, according to an embodiment of the present disclosure.

FIG. 7 depicts a simple schematic of a four-plate magnetic array used for storage, launch, and retrieval operations, where every other plate is rotated by 180° (i.e., anti-aligned) relative to its adjacent neighbor, according to an embodiment of the present disclosure,

FIG. 8 depicts a two-dimensional B-field plot, showing the magnitude of the B-field vector in the x-z plane, according to an embodiment of the present disclosure.

FIG. 9 depicts a simple schematic of a four-plate magnetic array used for mine sweeping operations, where every other plate is aligned in the same direction to its adjacent neighbor, according to an embodiment of the present disclosure.

FIG. 10 depicts a two-dimensional B-field plot, showing the magnitude of the B-field vector in the x-z plane, according to an embodiment of the present disclosure.

DESCRIPTION

With reference now to the drawings, there are depicted all of the claimed elements of the various embodiments, although all claimed embodiments might not be depicted in a single drawing. Thus, it is appreciated that not all embodiments include all of the elements as depicted, and that some embodiments include different combinations of the depicted elements. It is further appreciated that the various elements can all have many different configurations, and are not limited to just the configuration of a given element as depicted. As indicated above, the elements of the drawings as depicted are not to scale, even with respect one to another, and relative size or thickness of one element cannot be determined by the aspect ratios of that element or with reference to any dimension of another element.

Definitions

The terms, acronyms, and explanations listed below are provided for convenience and are not to be taken as binding for claim construction.

Depicted Embodiments

FIG. 1 depicts a magnetic payload embodiment that includes PMs (20) arranged in a circular array (30) with a mid-line diameter and mechanically confined within a non-magnetic plate (40). Although circular PMs (20) embedded in a circular magnetic array (30) are depicted in FIG. 1 for simplicity purposes, it is understood by one skilled in the art that there are many other shaped PMs (20) (e.g. square, rectangular, etc.) and other magnetic arrangements that that could be used in the magnetic array (30), depending upon the application and function, and this disclosure does limit the applicability of these embodiments to the shape or placement of the PMs in other alternate arrays, patterns, arrangements, shapes, packing factor, or configurations. Similarly, although the thickness of the magnetic element is not specified, one skilled in the art can optimize the thickness geometric dimension to best suit the given application.

In this embodiment, the multiple PMs (20) in the magnetic array (30) have their N/S poles (50) facing in the radial or (r) direction (60). When the magnetic array (30) or plate (40) is stationary or fixed, the PMs (20) of the array (30) create a steady state magnetic signature or DC magnetization (not shown). When the plate (40) is rotated about its central axis via a shaft (80) at an angular velocity ω (90), the rotating array (30) creates a time varying B-field (dB/dt) or AC magnetization (not shown).

FIG. 2 depicts another magnetic payload embodiment that includes multiple PMs (20) arranged in a circular magnetic array (30) with a mid-line diameter, and mechanically confined within a non-magnetic plate (40). In this embodiment, the PMs (20) of the magnetic array (30) have their N/S poles (50) facing in the tangential or (θ) direction (110). When the non-magnetic plates (40) are fixed or stationary, the multiple PMs (20) of the magnetic array (30) create a steady state magnetic signature or DC magnetization (not shown). When the non-magnetic plate (40) is rotated about its central axis (80) at an angular velocity ω (90), the magnetic array (30) creates a time varying B-field or AC magnetization (not shown).

FIG. 3 depicts another magnetic payload embodiment that includes multiple PMs (20) arranged in a circular magnetic array (30) with a mid-line diameter, and mechanically confined within a non-magnetic plate (40). The PMs (20) of the array (30) have their N/S poles (50) facing in the axial or (z) direction (120). When the plate (40) is stationary the PMs (20) of the array (30) create a steady state magnetic signature or DC magnetization (not shown). When the plate (40) is rotated about its central axis (80) and at angular velocity ω (90), the array (30) creates a time varying B-field or AC magnetization (not shown).

FIG. 4 depicts yet another magnetic payload embodiment (4) that includes multiple PMs (20) arranged in a circular magnetic array (30) with a mid-line diameter, and mechanically confined within a non-magnetic plate (40). In this embodiment, the PMs (20) of the array (30) have their N/S poles (50) facing in the vertical or (y) direction (125). When the plate (40) is stationary the PMs (20) of the array (30) create a steady state magnetic signature or DC magnetization (not shown). When the plate (40) is rotated about its central axis (80) and at angular velocity ω (90), the array (30) creates a time varying B-field or AC magnetization (not shown)

FIG. 5 depicts yet another magnetic payload embodiment that includes multiple non-magnetic plates (40) aligned along a shaft (80), located at their central axis of rotation. Located at the end of the shaft (80) is a motor (130) and a power source (140). The motor (130) is electrically connected to the power source (140). The power source (140) in one embodiment is a rechargeable battery. The shaft (80) is mechanically coupled to both the motor (130) and the plates (40) that house the multiple PMs as described above.

The motor (130) in one embodiment is coupled to a gearbox (not shown), which increases the torque on the shaft (80). The motor (130) and gear box rotate the multiple plates (40) about their central axis at an angular velocity (90), and the power source (140) powers the motor (130). When the plates (40) are stationary, the PMs of the arrays create a steady state magnetic signature or DC magnetization. When the plates (40) are rotated by the shaft (80) by the motor (130) and gearbox at angular velocity ω (90), the multiple arrays create a time varying B-field or AC magnetization.

FIG. 6 depicts a magnetic payload, such as depicted in FIG. 5, disposed in a hermetically sealed water-tight container (150). The water-tight container (150) has hermetic feedthroughs (160) that allow electrical power to pass through the water-tight container (150) to signal the motor (130) to turn on and off. The hermetic feedthroughs (160) can also be used to recharge the power source (140) as necessary or desirable.

FIG. 7 depicts a simple schematic of the magnetic payload with four plates (40). In this embodiment, every other non-magnetic plate (40) is rotated by substantially 180° along its shaft (80) relative to its adjacent neighbors. This is referred to as the anti-aligned or anti-parallel plate configuration (170). In this configuration, the N/S poles (50) of each of the PMs (20) are rotated in the substantially opposite direction as the N/S pole (50) of its nearest neighbor.

When the multiple non-magnetic plates (40) are arranged with their N/S poles (50) in the opposite orientation as its nearest neighbor, it reduces the net magnetic signature of the magnetic payload. FIG. 8 graphically depicts the reduced magnetic signature enabled by the anti-aligned configuration. This arrangement is advantageous for the storage and launch functions during M-MCM operations, where it is desired to have the B-field minimized. FIG. 8 depicts a 2-dimensional B-field plot showing the spatial extent of the B-field when every other non-magnetic plate (40) is anti-parallel (170) along the central axis (80).

FIG. 9 depicts a simple schematic of the magnetic payload with four non-magnetic plates (40). In this embodiment, every other plate (40) is aligned (i.e., not rotated) along the shaft (80) relative to its nearest neighbor. This is referred to as the aligned or parallel plate configuration (180). In this aligned configuration (180), the N/S poles (50) of each of the PMs (20) is rotated in the same direction as the N/S pole (50) of its nearest neighbor.

When the multiple plates (40) are arranged with their N/S/ poles (50) with the same orientation as its nearest neighbor, it increases the net magnetic signature of the magnetic payload. The aligned configuration (180) is advantageous for the sweeping function during M-MCM operations. FIG. 10 is a 2-dimensional B-field plot depicting the spatial extent of the B-field when all the plates (40) are aligned along the shaft (80).

Further Embodiments

The present disclosure describes an apparatus or device that includes a magnetic payload as used in M-MCM operations. The magnetic payload includes at least one of permanent magnets and multiple HTS trapped flux magnets. HTS trapped flux magnets are also sometimes referred to as HTS induced field magnets. For the purposes of clarity, brevity, and enablement of the embodiments described in this disclosure, the terms HTS trapped flux magnet and HTS induced field magnet generally have the same meaning and are used interchangeably. Likewise, for the purposes of simplicity, clarity, brevity, and enablement of the embodiments described in this disclosure, most descriptions of the embodiments in this disclosure are made using only PMs operating at ambient or near ambient temperatures, and not HTS trapped flux magnets operating at cryogenic temperatures, unless specific differences between the two are noted. It is understood by one skilled in the art, however, that a similar (though not identical) description could be used for the HTS trapped flux magnets, provided the trapped flux magnets remained at cold cryogenic temperatures below their superconducting critical temperature (T_c).

One of the many advantages of the invention described in this disclosure over prior art is that the PMs (or HTS trapped flux magnets) do not require the use of any electrical power source to initially generate and maintain a static B-field or its resulting static magnetic moment (m). Once the PMs (or HTS trapped flux magnets) are initially magnetized, these PMs will retain their magnetic moments indefinitely, so long as they remain below a critical threshold temperature. Above that critical temperature, both PMs (and HTS trapped flux magnets lose their net internal magnetization and can become either non-magnetic, weakly diamagnetic, or weakly paramagnetic. If this critical threshold temperature is reached and the PMs or HTS trapped flux magnets become non-magnetic, they might no longer be useful in M-MCM devices.

For HTS trapped flux magnets, that critical temperature is typically referred to as the superconducting transition temperature (T_c). The T_c's of HTS material vary widely depending upon many factors, including applied pressure and applied B-field, but in general, range from about 38 K up to about 162K for most known practical HTS materials. For PMs, the threshold temperature at which the PMs lose their internal magnetic moment is known as the Curie temperature (T_curie). Curie temperatures in PMs vary widely among various types of PMs, but for the rare-earth PM Nd—Fe—B magnets, one of the preferred embodiments for the PMs described in this disclosure, values typically range from about 410-500 K.

Another noteworthy difference between a PM and an HTS trapped flux magnet is the difference in magnitude of the remnant magnetic flux density B_r. HTS tapped flux magnets typically have a much higher B_r than PMs, depending upon the operating temperature of the HTS trapped flux magnet. As the operating temperature of the HTS tapped flux magnet approaches T_c from below, the amount of trapped B-field decreases, eventually disappearing above T_c. Similarly, as the operating temperature of the HTS trapped flux magnet is lowered from T_c, the amount of trapped flux can similarly be increased.

It is advantageous in magnetic mine sweeping to have a large B_r since it can extend the effective range of the magnetic signature of the magnetic payload. The larger the magnetic signature (i.e., effective area) of the magnetic payload, the larger its effective range to trigger MIMs. However, HTS trapped flux magnets require cryogenic cooling whereas PMs do not, and PMs can operate at room temperature and higher. The need for cryogenic cooling in HTS trapped flux magnets versus PMs presents logistical and operational challenges as well as additional costs, which must be considered when selecting the magnets for the magnetic payloads as described in this disclosure.

Another advantage of the embodiments as described in this disclosure over the prior art, is the substantially lower cost of PMs when compared to surface mounted HTS electro-magnets. When comparing material costs of PMs to HTS electro-magnets of equivalent size (e.g. 0.01 m to 0.1 m diameter), a rare-earth PM (e.g. Nd—Fe—B, Sm—Co, Al—Ni—Co, etc.) tends to be significantly lower in cost per unit mass or unit volume than that of an equivalent size and magnetic moment HTS electro-magnet. Furthermore, the non-superconducting PM would not require either cryogenic cooling to keep it cold and below its T_c, nor a thermally insulating vacuum cryostat to minimize heat load to the cryogenic coolant, further lowering costs.

As mentioned previously, PMs, after the initial magnetization, do not require a power source to maintain the static B-field and its corresponding static magnetic moment. Most PMs are initially magnetized in the factory where they are fabricated, thereby eliminating the need to magnetize them once installed in the magnetic payload. The cost of PMs when compared to current state of the art HTS electro-magnets is so low by comparison that the PMs could be considered expendable in some limited circumstances, if they were accidentally damaged, such as by mine detonation during mine sweeping operations. The substantially lower cost of the embodiments described herein over prior art allows for a much greater number of UUVs and expendable UUVs to be deployed in MCM operations.

The PM-MCM embodiments described in this disclosure overcome many of the disadvantages of prior art configurations. In a traditional PM, once initially magnetized there is no simple or practical method to turn off its internal magnetization (M) barring raising its temperature above T_curie Raising a PM above its T_curie not only requires an external heat source, but it is typically an irreversible process in which the PM may no longer retain its original internal magnetization when once again cooled below its T_curie, unless it is again re-magnetized with an external magnet.

For a PM based M MCM device, the apparent inability to turn off (or at least reduce in part) its internal magnetization when not performing its mine sweeping function creates a practical logistical problem for using PMs in mine sweeping. For example, during storage and launch of the magnetic payload, the B-field emanating from the magnetic payload may interfere with nearby electrical equipment, magnetic tools, instrumentation, or even a person's heart pacemaker. This inability to turn off or even reduce its internal magnetization can create an unwanted hazard or nuisance.

From Eq. [1], the magnetic moment m=N*I*A (A−m²) is directly proportional to the area (A) of the M-MCM device. The physical size of many PMs can vary substantially, with typical sizes ranging from as small as 0.0001 m up to about 0.1 m. However, even at its largest single unit size, PMs are still significantly smaller than a typical large diameter, surface mounted HTS electro-magnet (˜e.g., 1-2 m). Thus, a PM would have a corresponding smaller magnetic moment and hence its effective range is reduced relative to the surface mounted HTS electro-magnet. Since the effective range of most PMs is somewhat smaller due to its smaller physical size, when compared to its surface mounted HTS electro-magnet counterpart, more sweeps or passes are required by the mine sweeping vessel to cover an equivalent area of ocean. More sweeps/passes take longer to cover the same area to be cleared of mines.

For the embodiments described in this disclosure, the smaller physical size of the PM, and hence its smaller magnetic moment, can be somewhat compensated in part by using two approaches: 1) adding more PMs to an array of PMs to increase its physical size and extend its effective range of influence, and 2) using more (lower cost) mine sweeping vessels to perform the mine sweeping operation. Due to the substantially lower cost of an equivalent size and magnetic moment PM when compared to an HTS electro-magnet, multiple PMs can be spread out in an array to help extend the effective range or magnetic signature of the embodiments described in this disclosure. This, coupled with the absence of an electrical power source, makes mine sweeping operations less costly and less complex.

Second, since there is no expensive HTS wire to purchase, nor a cryogenic coolant or cryogenic refrigerator to maintain the system's temperature, nor a costly thermally insulating cryostat, nor an electrical power source, it makes adding multiple mine sweeping vessels a superior cost-effective solution when compared to a single expensive surface mounted HTS electro-magnet.

There are a wide variety of naval vessels where magnetic payload devices described in this disclosure could be used, including but not limited to submarines, USV, UUV, MSV, and other types of naval vessels. A particularly advantageous naval vessel is the UUV, where multiple UUVs, with their corresponding low cost, and possibly expendable, PM magnetic payloads can be used in a so-called “swarm” technique to sweep a given area.

In one embodiment, the magnetic payload device includes multiple PMs mounted onto a single plate or disk. The physical size and shape of the plate or disk include, but is not limited to, round, square, rectangular, hexagonal, multi-polygonal, among other shapes that might best suit the application and geometry of the mine sweeping vessel. To increase the effective range (i.e., magnetic signature) of the magnetic payload, multiple plates, combined with these multiple PMs per plate, can then form the magnetic payload. Furthermore, the arrangement of the PMs within each plate, combined with the orientation of the north/south poles of the PM, can be optimized to obtain the largest magnetic signature with the largest spatial extent. For the embodiments described in this disclosure, determining the optimal magnetic signature with the greatest spatial range is best accomplished by performing electro-magnetic optimization calculations prior to the fabrication thereof, and then confirming those calculations with B-field measurements once fabricated.

Thus, the total magnetic moment of the magnetic payload described in this disclosure is thus determined by several factors including, but not limited to, 1) type of PM material selected (e.g. Nd—Fe—B, Sm—Co, Al—Ni—Co, etc.), 2) the total number of PMs mounted on each individual plate, 3) the total number of plates in the magnetic payload, 4) the geometrical arrangement of the PMs on each plate, and 5) the orientation of the N/S poles of the PMs among other factors.

In this disclosure, three common types of PMs (Nd—Fe—B, Sm—Co, and Al—Ni—Co) are used to describe the embodiments. However, it is recognized one skilled in the art that there are many types of PMs that could be used for mounting on the plates of the magnetic payload, and nothing in the descriptions in this disclosure limit the type of PMs selected for use. For the purposes of clarity, brevity, and enablement of the embodiments described in this disclosure, the terms plates and disks generally have the same meaning, and are used interchangeably.

In one embodiment, the magnetic payload device described in this disclosure generates a DC magnetic signature or steady state magnetic moment. This DC magnetic moment can be used in mine sweeping operations. In this embodiment, no power source is needed to create the DC magnetic moment once the PM has been initially magnetized. Different types of PM materials possess different B_r. There are many magnetic materials that could be used for the PMs described in this disclosure including, but not limited to, Nd—Fe—B, Sm—Co, Al—Ni—Co, and other types of PMs. Likewise, there are a plethora of superconducting materials that could be used for the superconducting trapped flux magnets described in this disclosure including, but not limited to, Bi—S—Ca—Cu—O, Re—Ba—Cu—O, Tl—Ba—Ca—Cu—O, Mg—B, Nb—Ti, Nb—Sn, Nb—Al, Nb—N, Nb—Ge, and other types of superconducting materials.

In one embodiment, the magnetic payload device described in this disclosure generates a dB/dt or an AC magnetic signature. To generate an AC magnetic signature, at least one of the individual PMs and the plates containing the multiple PMs are rotated about an axis to create a dB/dt, resulting in an AC magnetic signature. For the purposes of clarity, brevity, and enablement of the embodiments described in this disclosure, the term axis of rotation or simply axis refers to the shaft that is mechanically coupled to both the motor and the plates that house the PMs. The shaft can be made of metal, composite, high strength plastic, and other types of materials.

The AC frequency at which the magnetic payload operates can be adjusted or tuned as needed to obtain the most effective mine sweeping frequency. The AC frequency (o) at which the individual PMs or the plates containing the array of multiple PMs are rotated can be at a constant/fixed frequency, a variable frequency, or a combination of constant and variable rotational frequencies. Rotating the individual PMs or the plates containing the array of multiple PMs requires, in some embodiments, a motor and a power source such as a battery.

There are many motor types that could be used to rotate the individual PMs or the array of multiple PMs including, but not limited to, electric motors, wax motors, pneumatic motors, hydraulic motors, and other types of motors. To increase the amount of torque applied by the motor to rotate the shaft containing the magnetic plates, a gearbox mechanically coupled to the motor could also be used in combination with the motor and power source, in some embodiments.

In another embodiment, the magnetic payload device described in this disclosure includes a combination of both DC and AC magnetic signatures.

In yet another embodiment, an AC magnetic signature or time varying B-field can be created by the mine sweeping vessel without the use of a motor and battery power source located in the magnetic payload. In this embodiment, the mine sweeping vessel, having a fixed array of multiple PMs, is rotated about is central axis at a desired frequency or multiple frequencies. In this embodiment, the preferred mine sweeping vessel is a UUV that can be remotely guided or controlled. In this embodiment, the magnetic payload remains fixed while the UUV itself provides both the forward propulsion and the ability to spin/rotate about its axis.

In one embodiment, all of the magnetic plates of the magnetic payload are aligned in a parallel arrangement so that their corresponding N/S poles vectorially add, thus creating the largest possible magnetic moment. This embodiment is useful during the sweep function of M-MCM operations. For the purposes of clarity, brevity, and enablement for the embodiments described in this disclosure, this arrangement is referred to as the “parallel” or “aligned” configuration.

In another embodiment, every other magnetic plate of the magnetic payload is rotated by substantially 180°. In this configuration, the plates are aligned in a so-called “anti-parallel” or “anti-aligned” arrangement with its nearest neighbor, so that their corresponding N/S poles vectorially cancel, thus creating the smallest possible magnetic moment. This embodiment is most useful during the storage and launch function of M-MCM operations, For the purposes of clarity, brevity, and enablement for the embodiments described in this disclosure, this arrangement is referred to as the anti-parallel or anti-aligned configuration.

As used herein, the phrase “at least one of A, B, and C” means all possible combinations of none or multiple instances of each of A, B, and C, but at least one A, or one B, or one C. For example, and without limitation: A×1, A×2+B×1, C×2, A×1+B×1+C×1, A×7+B×12+C×113. It does not mean A×0+B×0+C×0.

The foregoing description of embodiments for this invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments are chosen and described in an effort to provide illustrations of the principles of the invention and its practical application, and to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.