WO2018055150A1

WO2018055150A1 - Device for generating a magnetic field

Info

Publication number: WO2018055150A1
Application number: PCT/EP2017/074179
Authority: WO
Inventors: Nicolás CASSINELLI
Original assignee: Nanoscale Biomagnetics SL
Current assignee: Nanoscale Biomagnetics SL
Priority date: 2016-09-26
Filing date: 2017-09-25
Publication date: 2018-03-29
Anticipated expiration: 2019-03-26

Abstract

The invention is characterized by the combination of at least four coils and an electromotive source such that a region on which an oscillating magnetic field is generated is established such that, outside the device, the magnetic field is minimal without requiring magnetic field shielding elements.

Description

DEVICE FOR GENERATING A MAGNETIC FIELD

Object of the Invention

The present invention is a device for generating a magnetic field particularly suitable for use in methods of heating by means of magnetic field coupling (HMC) in general, and magnetic hyperthermia coupling in particular.

Background of the Invention

One of the most intensively developing fields of the art is the field of heating nanomaterials by magnetic coupling. At present, its most relevant applications are magnetic hyperthermia and controlled drug release.

Magnetic hyperthermia (MHT) is a therapeutic technique that uses heat generated by magnetic nanomaterials when being exposed to an alternating magnetic field (AMF) to reduce the size of certain tumors, improve their response to radiotherapy, and even completely eliminate the tumor.

In the technique for controlled drug release (CL) by means of magnetic field, magnetic nanomaterials are used in combination with drugs and other chemical entities to construct nanosystems which, when exposed to AMF, are capable of releasing their drug load, with the subsequent therapeutic effect on the patient .

These studies require specific devices that allow generating different volumes of alternating magnetic fields, the most extreme case being applicators for human beings that must be capable of generating a magnetic field in the entire body or in significant sections of the body of a patient.

Alternating magnetic fields usually operate at frequencies less than 1 MHz and intensities in the order of 10⁴ Amperes/meter (hundreds of Oersted) . Focusing this type of electromagnetic radiation on the region under study is of interest mainly due to factors that include energy efficiency, safety in use and compatibility with regulations in force.

Due to the frequency ranges used in HMC and particularly the fields used for clinical applications, the large wavelengths involved do not allow focusing the radiation with the same "optical" techniques allowed by high frequencies; in other words, using interference and diffraction phenomena, for example .

Solenoid inductor is the simplest and most widely used field radiator. By means of this geometry, the highest energy density available is located in the cylindrical space surrounded by turns. Given that the magnetic flux lines are closed, the scattered flux in the rest of the space decreases with distance and is particularly intense in the axial direction.

When field generating devices are scaled to sizes for clinical application, the scattered flux becomes highly relevant due to compatibility with regulations in force. Devices known today usually solve this problem by means of two strategies: using magnetic cores which contain most of the magnetic flux and lead it to a gap (the application area) ; or, using magnetic shields .

Both approaches, however, involve significant energy expenditure due to the magnetic losses occurring in the materials interposed in the path of the magnetic flux.

It is also known in the prior art the application N° WO 2010/125510 Al that discloses an arrangement and a method for influencing and/or detecting magnetic particles and for magnetic resonance imaging.

The present invention solves the problem with a particular combination of coils without requiring shields.

Description of the Invention

The present invention relates to a device for generating a magnetic field configured such that it does not require a shield for shielding the generated magnetic flux. Said device comprises :

a first set of two coils, a first coil and a second coil, essentially the same, coaxial and spaced from one another by a pre-established distance d ;

a second set of two coils, a third coil and a fourth coil, essentially the same, coaxial and spaced from one another by a second pre-established distance d₂ , with d₂ > d₁ ,

at least one alternating electromotive source for the excitation of the four coils where each coil is powered at the same frequency and phase.

The first set of coils formed by the first coil and the second coil is intended for generating the magnetic field which will have great contribution in the region of interest. This region of interest is located at the intermediate point between both coils and according to the axial position. In this region, the magnetic field is very uniform, as if it were formed by a single very large solenoid, and allows accessing the region of interest from directions perpendicular to the axial direction. The samples that are subjected to the alternating magnetic field will be located in this region of interest.

The second set of coils is constructed with a larger distance between the coils such that the first set of coils is housed in the separation existing between both. This second set of coils has the function of attenuating the resulting magnetic flux in the region outside the device by establishing a magnetic field having similar magnitude and direction virtually opposite the direction generated by the first set at each point of the space outside the device. To demonstrate this function, the four coils furthermore demonstrate that:

the first set of coils and the second set of coils are coaxial ;

the first set of two coils is located between the third coil and the fourth coil of the second set;

the geometric midpoint of the first set coincides with the geometric midpoint of the second set; the at least one electromotive source as well as the first coil and the second coil of the first set are adapted for generating a magnetic field with the same direction ; and, the at least one electromotive source as well as the third coil and the fourth coil of the second set are adapted for generating a magnetic field with the same direction but with direction opposite the direction of the coils of the first group .

The direction defined by the geometric axis of the coil is identified as axial direction. The coils can have a flat, square or rectangular configuration, although the preferred configuration is that of a solenoid having a circular section.

When a coil is powered by an electromotive source, the direction of the magnetic flux created by the coil depends on the orientation of the turns of the coil and on the polarization of the electromotive source. In other words, if the winding direction is changed, going around the coil 180°, the direction of the magnetic field also changes. If the winding direction is maintained but the polarization of the electromotive source is changed, the magnetic field also changes direction. Finally, if the winding direction is changed, going around the coil 180°, and the polarization of the electromotive source is changed then the direction of the magnetic field generated does not change.

For that reason, when characterizing the direction of the magnetic field it is understood that the direction of the turns and the polarization of the electromotive source is such that the generated field is in the desired direction.

Likewise, the electromotive source is an alternating electromotive source, so all the coils must be powered at the same frequency and phase. Although a coil powered by an alternating electromotive source generates an also alternating magnetic field, when it is established that a coil generates a magnetic field in a specific direction and another coil in an opposite direction, it shall be interpreted that said condition applies when both coils are observed at the same time instant.

A simple way to power the two frequency- and phase- synchronized coils is to establish a serial electrical connection of both coils by connecting a terminal of one coil with another terminal of the other coil and, to power the free terminals of both coils by means of the electromotive source.

Several particular configurations of the device are described with the help of the drawings.

Description of the Drawings

The foregoing and other features and advantages of the invention will be more clearly understood based on the following detailed description of a preferred embodiment, given only by way of illustrative and non-limiting example in reference to the attached drawings.

Figure 1 shows a schematic depiction of an example of the invention in which an electromotive source is used for the excitation of the coils.

Figure 2 shows a schematic depiction of another embodiment of the invention in which two electromotive sources are used separately powering the pairs of coils of the first group and second group.

Figure 3 shows a schematic depiction of another embodiment of the invention in which two electromotive sources are used separately powering the pairs of adjacent coils.

Detailed Description of the Invention

According to the first inventive aspect, the present invention relates to a device for generating a magnetic field without requiring magnetic shielding.

Figure 1 shows a schematic depiction of a first embodiment. Four coils are shown in this embodiment. A first set is formed by two coils, a first coil (CI) and a second coil (C2) . In this example, both coils (CI, C2 ) are the same because they have the same number of turns and the same configuration, and are spaced from one another by a pre-established distance identified as d . The two coils (CI, C2 ) are coaxial and define a space between them which allows establishing a working region in which the magnetic field is highly uniform.

This first set of two coils (CI, C2 ) is located centered between a second set of two same, coaxial coils, a third coil (C3) a fourth coil (C4), sufficiently spaced from one another so as to allow housing the first set of coils (CI, C2) .

The distance between the two coils of the second group (C3, C4) is the pre-established distance identified as d₂ where d₂ > d is demonstrated.

The four coils (CI, C2 , C3, C4) are powered by an alternating electromotive source (E) which, in an operative mode, powers them with the same frequency and phase. Figure 1 schematically shows a single line electrically communicating the electromotive source (E) and each coil (CI, C2 , C3, C4) graphically representing several alternative ways of supplying power :

supplying power in parallel in which the line represents the two conductors which originate from the electromotive source (E) and directly power the two terminals of the coil or,

supplying power in series in which the powered coils are connected to one another in series and the conductors which originate from the electromotive source (E) directly power the free terminals of the end coils of the serial configuration or,

a combination of the foregoing such that the coils can be connected to one another in series in twos and both pairs of coils can be powered in parallel.

This same interpretation applies to other drawings unless a specific configuration is explicitly indicated.

The coils of the second group (C3, C4) are adapted, along with the electromotive source (E) powering them, for generating a magnetic field oriented in the direction opposite the magnetic field generated by the coils of the first group (CI, C2) . The magnetic field generated by the coils of the first group therefore serves, in the central part thereof, for establishing the field in the working region; and the field that comes out containing the flux lines are counteracted by the flux created by the coils (C3, C4) of the second group, preventing the need to shield the entire device.

Each of the coils can be powered, for example, by an independent alternating electromotive source (E) , provided that all the electromotive sources are frequency- and phase- synchronized.

According to the embodiment shown in Figure 2, it is possible to use two separate electromotive sources, a first electromotive source (E) powering the coils (CI, C2 ) of the first group of coils, and a second electromotive source (E) powering the coils (C3, C4) of the second group of coils. Therefore, the first electromotive source (E) is intended for generating the magnetic field which extends through the working region and the second electromotive source (E) is intended for generating the magnetic field which serves for shielding the device and efficiently attenuating the resulting magnetic field in an area away from the device.

Figure 3 shows a preferred embodiment which also uses two separate alternating electromotive sources, a first electromotive source (E) powering the first coil (CI) and the third (C3) coil and a second electromotive source (E) powering the second coil (C2) and the fourth (C4) coil. Each electromotive source (E) therefore powers a pair of adjacent coils, which generates on one hand the field for the working region and also the coil externally shielding the magnetic field.

This configuration is preferred because it has been observed surprisingly in experiments that the overall consumption resulting from the sum of the consumptions of the first electromotive source (E) and of the second electromotive source (E) are considerably lower.

The three embodiments show a support (S) intended for keeping an object (0) in place in the working region, so that said object is subjected to the uniform alternating magnetic field in the operative mode. This support (S) is configured such that the object (0) is located centered between the first coil (CI) and the second coil (C2), according to the axial axis of symmetry of the coils (CI, C2) .

It is possible to use a smaller number of electromotive sources by connecting two or more coils in series. In the case of the first coil (CI) and the second coil (C2) both connected in series, only one electromotive source (E) is required. If connection is carried out between the adjacent coils of the first and second group of coils, for example, either between the first coil (CI) and the third coil (C3), or between the second coil (C2) and the fourth coil (C4), the connection must be in series but with the polarization of one of them being reverse so that magnetic fields with opposite directions are generated with the same electromotive source (E) .

In the embodiments shown in the drawings, the diameter D of all the coils is the same, the support is located according to the axial direction in a position located in an interval 0.5 < d /D < 1.5 and additionally the supporting means (S) are adapted so that the physical object (0) to be subjected to the magnetic field is located according to the axial direction in a position centered in the geometric center of the first set of coils. This position centered according to the axial direction is interpreted as the position being able to be at any point of the transverse plane (P) transverse to the axial direction provided that the transverse plane (P) is centered in the geometric center of the first set of coils. Nevertheless, a preferred example is when the centered position coincides with the axis of the coils (CI, C2); i.e., in the intersection of the transverse plane (P) and the axis of the coils (CI, C2) .

In a preferred example of the invention, the coils (CI, C2 , C3, C4) are configured in the form of a solenoid having a length I .

In a preferred example of the invention, the distance between adjacent coils of the first set of coils and the second set of coils is the same and takes the value A = (d₂— d₁)/2 .

In another more specific embodiment, the length of the solenoid I satisfies the condition I < A/2 .

According to another embodiment, one or more coils (CI, C2 , C3, C4) is formed from conductive tube to allow the passage of a coolant which allows discharging the heat generated in the coil.

Claims

1. A device for generating a magnetic field comprising:

- a first set of two coils, a first coil (CI) and a second coil (C2), essentially the same, coaxial and spaced from one another by a pre-established distance d ;

- a second set of two coils, a third coil (C3) and a fourth coil (C4), essentially the same, coaxial and spaced from one another by a second pre-established distance d₂ , with d₂ > d_{l r} - at least one alternating electromotive source (E) for the excitation of the four coils (CI, C2 , C3, C4) where each coil is powered at the same frequency and phase,

characterized in that

- the first set of coils (CI, C2 ) and the second set of coils (C3, C4) are coaxial;

- the first set of two coils (CI, C2 ) is located between the third coil (C3) and the fourth coil (C4) of the second set;

- the geometric midpoint of the first set coincides with the geometric midpoint of the second set;

- the at least one electromotive source (E) as well as the first coil (CI) and the second coil (C2) of the first set are adapted for generating a magnetic field with the same direction; and,

- the at least one electromotive source (E) as well as the third coil (C3) and the fourth coil (C4) of the second set are adapted for generating a magnetic field with the same direction but with direction opposite the direction of the coils of the first group.

2. The device according to claim 1, at least comprising two electromotive sources, a first electromotive source (E) adapted for the excitation of two of the adjacent coils (CI, C3) of the first set and second set of two coils; and a second electromotive source (E) adapted for the excitation of the other two adjacent coils (C2, C4) of the first set and second set of two coils, respectively, wherein the first electromotive source (E) and the second electromotive source (E) are adapted for generating the same current and, with the same frequency and phase .

3. The device according to claim 1, comprising a first alternating electromotive source (E) for the excitation of the first set of two coils (CI, C2 ) and a second alternating electromotive source (E) for the excitation of the second set of two coils (C3, C4) wherein the first electromotive source (E) and the second electromotive source (E) are adapted for generating the same current and, with the same frequency and phase .

4. The device according to claim 1 or 2, wherein the first and the second coil of the second set of two coils are connected in series such that the magnetic field generated in an operative mode has the same direction.

5. The device according to claim 1, wherein the adjacent coils between the first set of two coils and the second set of two coils (CI and C3 as well as C2 and C4) are connected in series such that the magnetic field generated in an operative mode by the adjacent coils has the opposite direction.

6. The device according to any of the preceding claims, where the diameter D of the coils of the first set of coils and the diameter of coils of the second set of coils is the same.

7. The device according to any of the preceding claims, comprising supporting means (S) for supporting a physical object

(0) to be subjected to the magnetic field generated by the first set of coils (CI, C2 ) , these supporting means (S) are adapted so that said physical object (0) is located between the coils (CI, C2) of the first set of coils.

8. The device according to claims 6 and 7, wherein the supporting means (S) are located according to the axial direction in a position located in an interval of 0.5 < d /D < 1.5

9. The device according to claim 8, wherein the supporting means (S) are adapted so that the physical object (0) to be subjected to the magnetic field is located according to the axial direction in a position centered in the geometric center of the first set of coils (CI, C2 ) .

10. The device according to claim 9, wherein the supporting means (S) are adapted so that the physical object (0) to be subjected to the magnetic field is located in the axis of the coils (CI, C2) .

11. The device according to any of the preceding claims, wherein the coils (CI, C2 , C3, C4) are configured in the form of a solenoid having a length I .

12. The device according to any of the preceding claims, wherein the distance between adjacent coils of the first set of coils and the second set of coils is the same and takes the value A = (d₂ ^~

.

13. The device according to claims 11 and 12, wherein the length of the solenoid I satisfies the condition I < A/2 .

14. The device according to any of the preceding claims, wherein one or more coils (CI, C2, C3, C4) is formed from conductive tube to allow the passage of a coolant which allows discharging the heat generated in the coil.