WO2017142476A1

WO2017142476A1 - Electric circuits for providing motive force, drive module and methods of operation thereof

Info

Publication number: WO2017142476A1
Application number: PCT/SG2016/050235
Authority: WO
Inventors: Giulio Manzoni
Original assignee: Microspace Rapid Pte Ltd
Priority date: 2016-02-16
Filing date: 2016-05-18
Publication date: 2017-08-24

Abstract

An electric circuit (200) configured to provide motive force comprises a first circuit portion (204) and a corresponding second circuit portion (206). The first circuit portion is configured, when the electric circuit is disposed in a magnetic field (B) and powered by a power supply, for a first Lorentz force component (F_AB) acting in the first circuit portion to be less than a second Lorentz force component (F_CD) acting in the corresponding second circuit portion. An electric circuit (200) configured to provide motive force is configured, when the electric circuit is disposed in a magnetic field (B) and powered by a power supply, for a net Lorentz force (F_tot) to be non-zero.

Description

ELECTRIC CIRCUITS FOR PROVIDING MOTIVE FORCE, DRIVE MODULE AND METHODS

OF OPERATION THEREOF

The invention relates to electric circuits configured to provide motive force. The invention also relates to a drive module for a vehicle incorporating a plurality of electric circuits configured to provide motive force. The invention also relates to methods of providing motive force. The invention also relates to a method of operating a drive module. The techniques as disclosed herein have particular, but not exclusive, use in vehicle propulsion, propellant-less aerospace propulsion and in electric machines not having a reactive element.

Propulsion systems are by necessity based on the action-reaction principle stated in Newton's Third Law or equivalently in the Law of Conservation of Momentum. All such vehicles have therefore traditionally worked by expelling some sort of material or producing a force against the material of the vehicle's surrounding environment. Jet and rocket propulsion vehicles are of the first kind, propeller-driven or wheel- driven vehicles in air, sea or land are of the second kind. The only propulsion available and routinely used in space is so far rocket propulsion which requires the vehicle to carry in it the propellant material to be expelled to generate thrust and hence has only an available limited total momentum therefore limiting the time that the propulsion can be operated. One other propulsion method is that of Electrodynamic Tethers whereby a conductor allows only one way current flow and the charges arriving at one end of the tether are emitted and released in Space. In such way a spacecraft attached to such conductor will experience a thrust due to the interaction between the current and the Earth's magnetic field. Such thrust can be used to deorbit a satellite or to vary the orbit depending on the direction of the current. The length of such a tether is usually much larger than the spacecraft and its deployment is not a simple manoeuvre. Thus far, the technology has been attempted with only limited success.

The invention is defined in the independent claims. Some optional features of the invention are defined in the dependent claims.

Implementation of the techniques disclosed herein may provide significant technical benefits. An electric circuit may be provided in which at least one portion is prevented from interacting with the surrounding magnetic field. As a consequence of this, charge carriers moving in this portion of the circuit are subjected to a reduced Lorentz force which would otherwise be the case where the carriers not prevented from interacting with the magnetic field. As a result, the net Lorentz force acting on the charge carriers moving in the circuit as a whole is non-zero and this force in turn acts on the conducting material of the circuit. The resultant force can be used to provide motive force for, for example, as a propulsion force for a vehicle. Concerning Newton's Third Law and the principle of action and reaction, it will be evident from the following discussion that here reaction is produced on the body generating the magnetic field (e.g. the Earth) via the interaction with the magnetic field itself.

In one arrangement, the circuit portion is prevented from interacting with the surrounding magnetic field by being surrounded, at least in part, by a magnetic shield. As a consequence, the Lorentz force acting on the conductor(s) in this part of the circuit is significantly reduced, and reduced to zero if the shielding is perfect in this portion of the circuit. Additionally or alternatively, a circuit interruption is provided where the voltage applied across the gap between conductors is sufficiently large for charge carriers still to move across the medium between the conductors and close the circuit to provide current flow. While the magnetic field still acts in these charge carriers as they move across the gap between the conductors, the charge carriers are not flowing through a conductor per se and, therefore, there is no conductor to which the Lorentz force acting on the charge carriers can be transferred. As such, the Lorentz force component acting in this circuit portion is less than in other portions of the circuit. Therefore, this results in an imbalance in the overall net Lorentz force which can be used to provide motive force.

The techniques disclosed herein overcome the disadvantages of the cumbersome tether conductor as described above, if the environment in which the electric circuit is disposed presents a magnetic field, allowing production of a reaction by a current flowing in a conducting circuit. If the electric circuit is disposed on, say, a vehicle, this can be translated into motive force for moving and/or orienting the vehicle.

Provided one portion of the circuit is magnetically isolated from the magnetic field, and so being prevented to interact with the magnetic field and/or having the circuit interruption described above, this will leave only the rest of the circuit free to interact with the field and hence to produce a net non-zero force that can be used for propulsion. By means of known electrical generators or batteries, eventually supplied by Solar Energy for example, the current can be kept flowing for an unlimited time hence producing a useful thrust effect even if the net force available is very small.

The invention will now be described, by way of example only, and with reference to the accompanying drawings in which:

Figure 1 is a schematic diagram illustrating the Lorentz force effect for a straight conductor, also called the Laplace force in this example;

Figure 2 is a schematic diagram illustrating an electric circuit configured to provide motive force;

Figure 3 is a schematic diagram illustrating the forces generated in or by the electric circuit of Figure 2.

Figure 4 is a schematic diagram illustrating another electric circuit configured to provide motive force; Figure 5 is a schematic diagram illustrating another electric circuit configured to provide motive force;

Figure 6 is a schematic diagram illustrating another electric circuit configured to provide motive force;

Figure 7 is a schematic diagram illustrating another electric circuit configured to provide motive force;

Figure 8 provides a series of schematic diagrams illustrating electric circuits configured to provide motive force;

Figure 9 is a schematic diagram illustrating another electric circuit configured to provide motive force;

Figure 10 is a schematic diagram illustrating another electric circuit configured to provide motive force;

Figure 11 is a schematic diagram illustrating a plurality of electric circuits configured to provide motive force, as may be disposed within, for example, a drive module for a vehicle or in a motor;

Figure 12 is a schematic diagram illustrating the Lorentz force components acting in the plurality of electric circuits of Figure 4;

Figure 13 is a schematic diagram illustrating the force components from each active wire in the plurality of electric circuits of Figure 11; and

Figure 14 is a series of traces illustrating measured angular deflection according to different configurations.

Referring first to Figure 1, this diagram provides a useful reminder of the Lorentz force effect. Circuit 100 is energised by a power supply (not illustrated) so that charge carriers 102 flow as an electrical current I in the conductor of the circuit in the direction indicated by the arrow. In the example of Figure 1, this illustrates conventional current flow and, thus, the charge carriers which are illustrated moving in the circuit are holes. It will of course be appreciated, that the principles described herein apply equally to electrons. It is known that an electric charge q moving in a magnetic field B and an electric field E is subjected to a force F proportional to its velocity v_q and the component of the magnetic field perpendicular to the velocity as stated by the Lorentz formula (Formula 1):

F = q[E + (v_q x B)] [l]

A plurality of charge carriers moving in the conductor as an electric current are subject to the same forces which sum is transferred to the atoms of the material and eventually to the body of the conductor and all objects attached to it as shown in Figure 1.

It is also known that the electric current I in a conductor comprises flow of electrons, negative charge carriers -e and it is conventionally indicated by "holes", nominally positive charge carriers, moving in the opposite direction. Hence the negative charge and its actual velocity v_e opposite the velocity v_q of the charge carriers of the conventionally indicated current cancel their negative signs and result in the same force direction that can be still evaluated with the right hand rule, as indicated by hand 104.

F = e[E + (v_e x B)]

F = e[E + (-v_q x B)]

F = e[E + (v, x B)] [1.1] It is therefore known that for a straight conductor of length I and current i interacting with uniform magnetic field B the force (also known as the Laplace force) can be simply expressed as in Formula 2:

F = / i x Bdl = i x Bl [2]

In a closed electric circuit, hence characterised by a uniform current i, interacting with a uniform magnetic field B the total resultant of such forces can only be a torque and a net zero force. If the interaction between current and magnetic field is uniform on the whole circuit, as in all classic applications of electromagnetic circuits, the sum is zero as shown in Formula 3:

F = i x Bdl [3] If B(l) is uniform over any dl this can be considered to be equal to B , then F=0 since the current is obviously and by necessity the same along the whole circuit as dictated by the Continuity and Conservation laws.

Now, the Applicant has devised new and useful techniques in light of the above.

Any non-uniformity of such interaction may result in a net force as non-zero sum of essentially two terms obtained from the integration over the circuit of the Formula 2 as represented by Formula 4:

F = φ ϊ x Bdl = J_A ^B i x B_ABdl + f i x Bdl [4]

If BAB < B, then the net resultant force is non-zero, with the first part of the expression (the integral from A to B) relating to a first circuit portion A to B now described in more detail with reference to Fig. 2, while the second part of the expression (the integral from B to E = A) relating to the remainder of the circuit. The remainder of the circuit may be divided into a second circuit portion C to D which produces a Lorentz force component which at least partially cancels the Lorentz force component produced by the circuit portion A to B. The circuit may also have third and fourth portions B to C and D to E.

Figure 2 illustrates an electric circuit 200 disposed in a magnetic field B and configured to provide motive force. Circuit 200 is formed by a conductor 202 having plural circuit portions, and has terminals A and E for connection thereto of a DC power supply (not shown in Figure 2). Note that the DC supply power may be a pulse width modulated supply to provide an averaged DC waveform to provide the motive force. First circuit portion 204 is formed between terminal A and circuit point B. Opposite this first circuit portion, is "corresponding" second circuit portion 206, formed between circuit points C and D. Third circuit portion 208 is formed between circuit points B and C, while fourth circuit portion 210 is formed between circuit point D and terminal E.

Note that the electric circuit is illustrated schematically in Figure 2 and it is not a requirement that each of the circuit portions be physically the same length, or physically arranged in a regular shape such as the square shape shown in the figure.

Second circuit portion 206 is "corresponding" in that it corresponds to first circuit portion 204, as will be described shortly. In a similar manner, third and fourth circuit portions 208, 210 may correspond with one another. First circuit portion 204 is provided with a magnetic shield 212 formed preferably from high magnetic permeability material, or any other material that can at least attenuate the strength of the field present in the region enveloped by it. For example, any material which may concentrate the magnetic field in itself so that the field is at least partially prevented from interacting with the conductor disposed within it will likely be useful. Thus, at least part of the circuit conductor 202 in first circuit portion 204 is at least partially shielded from the magnetic field B, and the Lorentz force acting on the charge carriers in the first circuit portion 204 is correspondingly reduced. As a further consequence, the amount of force imparted to the circuit conductor from this reduced Lorentz force is correspondingly reduced. The first Lorentz force component acting in the first circuit portion 204 is therefore represented by the Lorentz force component FAB. (It will be appreciated that the term "Lorentz force component" includes a force component which is itself a vector, as will be appreciated from, say, Figure 2, and the fact this refers to the force component FAB which can be seen to be made up of components in the X, Y and Z axes. This is also evident from Figure 13, described below, which shows how a

Lorentz force component acting in a circuit (or sub-circuit) may be the vector sum of two vector force components, each of which is made up of components in the X, Y and Z axes.) The second Lorentz force component FCD acting as normal - i.e. in an unimpeded way - in the second circuit portion 206 is also illustrated. Third and fourth Lorentz force components FBC and FDE respectively are also illustrated.

However, it will be appreciated that these third and fourth Lorentz force components are equal and opposite to one another, thereby cancelling each other out. This means that the net Lorentz force is determined by the difference between the first Lorentz force component FAB and the second Lorentz force component FCD. This is illustrated schematically in Figure 3 which illustrates the summation of all forces produced in the circuit elements. It is evident that the vector forces in the portions BC and DE, when summed together, are balanced, and do not produce any net force. If the shielding in the first circuit portion AB is perfect, then the portion CD is subjected to the only unbalanced force in the circuit, hence providing the net force that is acting in the whole circuit. Thus, in this respect, even if the first Lorentz force component is zero or non-existent, this still means that the first Lorentz force component acting in this first circuit portion is still "less" than the second Lorentz force component acting in the corresponding second circuit portion in the context of this application. In practice, it is expected that some residual magnetic field will act upon the first circuit portion, resulting in a first Lorentz force component which has a non-zero magnitude which is smaller/lesser than the second Lorentz force component acting in the corresponding circuit portion CD. Regardless, as long as there is a difference in magnitude between the first and second Lorentz force components, this will result in a net vector differential force FTOT as shown in Figure 3, which is non-zero.

Therefore, it will be appreciated that Figure 2 illustrates an electric circuit 200 configured to provide motive force FTOT, the electric circuit 200 comprising a first circuit portion 204 and a corresponding second circuit portion 206, wherein the first circuit portion 204 is configured, when the electric circuit 200 is disposed in a magnetic field B and powered by a power supply (not shown, but connected between terminals A and E), for a first Lorentz force component FAB acting in the first circuit portion 204 to be less than a second Lorentz force component FCD acting in the corresponding second circuit portion 206. A corresponding method is also described.

As an alternative expression, it may be considered that Figure 2 illustrates an electric circuit 200 configured to provide motive force, electric circuit 200 being configured, when the electric circuit is disposed in a magnetic field B and powered by a power supply (not illustrated in Figure 2, but connected between terminals A and E), for a net Lorentz force acting in the electric circuit to be non-zero. A corresponding method is also described. In this respect, the net Lorentz force is the sum vector total of the Lorentz force components acting in each of the circuit portions 204, 206, 208, 210 of the circuit 200.

The shield 212 may be realised by, for example, folding and/or wrapping around the conductor in at least part of the first circuit portion 204, a high permeability material such as soft iron or a "mu-metal" alloy. Other suitable materials include one or more of Co-Netic, supermalloy, supermumetal, nilomag, sanbold, molybdenum permalloy, Sendust, M-1040, Hipernom, HyMu-80, Amumetal and others with similar properties.

Thus, electric circuit 200 comprises a magnetic shield 212 for shielding the first circuit portion 204 from the magnetic field B, with the magnetic shield 212 preferably comprising high-permeability material.

As noted, the circuit portions BC and DE do not make any contribution to the net resultant vector force. As such, it may be preferable that these circuit portions are each as short as possible to minimise on resource wastage. For instance, the amount of conductor required for these circuit portions can be reduced, along with the circuit footprint, likely to be an important consideration in some applications.

Further, the shorter the length of these circuit conductor portions, the less the "ohmic losses" - loss through heat generated in the circuit when current flows therethrough - will be.

Figure 4 illustrates one such arrangement. The electrical circuit 400 comprises first circuit portion 404 between terminal A and circuit point B, second circuit portion 408 between circuit point C and circuit point D, third circuit portion 406 between circuit point B and circuit point C, and fourth circuit portion 410 between circuit point D and terminal E. Each of the circuit portions has a corresponding length. For instance, first circuit portion 404 has a first physical length 412, second circuit portion 408 has a second physical length 416, third circuit portion 406 has a third physical length 414, and fourth circuit portion 410 has a fourth physical length 418. In the example of Figure 4, the lengths 414, 418 of third and fourth circuit portions 406, 410 are shorter than the lengths 412, 416 of the first and second circuit portions 404, 408.

It will be appreciated that Figure 4 illustrates an electric circuit 400, wherein the first circuit portion 404 has a first physical length 412 and the corresponding second circuit portion 408 has a second physical length 416, and wherein the electric circuit comprises a third circuit portion 406 having a third physical length 414 and a fourth circuit portion 410 having a fourth physical length 418, where each of the third physical length 414 and the fourth physical length 414 are less than the first physical length 412 and the second physical length 416.

As noted above, it is preferable that the third and fourth circuit portions are as short as possible. This may be realised by arranging the conductor of second circuit portion 408 so that it - or, rather, an external surface of the conductor insulator (not shown) - lies in contact with the external surface of the shield along at least a part of its length, and along the full length of the shield. Alternatively, it may not be necessary for there to be contact between the conductor insulator and the shield, but a minimal gap therebetween of a few millimetres. The gap may be, say, 1 mm or less, between 1 mm and 2 mm, between 2 mm and 3 mm, between 3 mm and 4 mm or between 4 mm and 5 mm, is maintained. The gap may be between 1 mm and 5 mm, or between, say, 1 mm and 10 mm. Therefore, there is no need for the circuit lengths 414, 418 to be any greater than is required for this arrangement. In some realisations, it may be that the lengths 414, 418 are determined by the minimum bending radius of the conductor forming the circuit. As noted above, physical characteristics of the circuit are not to be inferred from the schematic arrangement of Figure 2. In fact, it is found that the circuit can be arranged in practically any physical shape, by controlling the current flowing through the circuit in order to achieve the desired effect of different force directions depending on needs. Figure 5, 6 and 7 show different circuit arrangements.

Figure 5 illustrates a generic circuit shape with a magnetic shield portion, although the portion which is shielded is of an irregular shape, comprising bends in the circuit and in the shield, whereas the remainder of the circuit is in a relatively regular loop arrangement. Figure 6 provides an example of a circuit were the second circuit portion comprises a plurality of conductors. Thus, circuit 600 has an electrical conductor 604 in the first circuit portion and a plurality of return conductors 606 as the corresponding second circuit portion. As can be seen, the first circuit portion is provided centrally to the second circuit portion conductors 606, with the second circuit portion conductors 606 arranged around the first circuit portion. The first circuit portion is shielded by magnetic shield 612 which may take the form described above.

Figure 7 illustrates a co-axial arrangement. The circuit 700 comprises a first circuit portion having an electrical conductor 704, with the corresponding second circuit portion comprising a conductor 706 arranged coaxially around the first circuit portion/conductor 704. In at least one arrangement, the conductor 706 is also arranged around the magnetic shield 712. That is, the magnetic shield 712 is disposed in the coaxial arrangement between the first conductor 704 and the second conductor 706, with both the magnetic shield 712 and the second conductor 706 being disposed coaxially around conductor 704.

Therefore, Figure 7 illustrates an electric circuit 700 which is arranged in a coaxial configuration, with the first circuit portion 704 shielded by the magnetic shield 712, and the second circuit portion 706 comprising a second circuit conductor arranged coaxially around the shield.

Note that it may not be necessary for the magnetic shield 712 to surround completely first conductor 704. Additionally, it may not be necessary for second conductor 706 to surround completely the magnetic shield 712.

Figure 8 provides a series of views of exemplary electrical circuits were the electric circuit comprises a plurality of first circuit portions and a plurality of corresponding second circuit portions. Figure 8 (a) illustrates plural sub-circuits comprising respective first circuit portions 804a, 804b, 804c, plural corresponding second circuit portions 806a, 806b, 806c and plural shields 812a, 812b, 812c, surrounding, at least in part, the respective first circuit portions 804a, 804b, 804c. Each of the sub-circuits terminate in terminations so that they may be connected as required. Figure 8(b) illustrates the sub-circuits of Figure 8 (a) connected in series. In this arrangement, the plurality of first circuit portions are interspersed with the plurality of corresponding second circuit portions. That is, the plurality of first circuit portions and a plurality of corresponding second circuit portions are connected such that these are connected in series with the first circuit portions alternating with the corresponding second circuit portions. That is, and to give just one example, first circuit portion 804a is connected in series with second circuit portion 806a which is, in turn, connected in series with first circuit portion 804b of the second sub- circuit, and so on. Figure 8(c) illustrates an arrangement where a shield is provided to shield more than one first circuit portion. In this example, one shield 812 is provided as a common shield for the plural first circuit portions 804a, 804b, 804c, with the plural sub- circuits connected in series in a manner similar to that illustrated in Figure 8(b) (notwithstanding the difference in the shielding arrangement between the two figures).

Figure 8 illustrates a series of electric circuits comprising a plurality of first circuit portions 804a, 804b, 804c and a plurality of corresponding second circuit portions 806a, 806b, 806c, where the electric circuit is configured for respective first Lorentz force components for each of the first circuit portions to be less than respective second Lorentz force components for each of the corresponding second circuit portions. Indeed, Figure 8 (b) illustrates an electric circuit in which the plurality of first circuit portions 804a, 804b, 804c and the plurality of corresponding second circuit portions are connected in series 806a, 806b, 806c, with the plurality of first circuit portions being interspersed with the plurality of corresponding second circuit portions.

Another technique may be used to reduce the Lorentz force component acting in a first circuit portion as an additional or alternative technique to those described above with respect to Figures 2 to 7. In this arrangement, an interruption in the circuit is created, although the voltage applied across the interruption in the circuit is sufficiently large so that charge carriers may still cross the gap across the interruption when a power supply is applied to the circuit terminals. In a preferred arrangement, a vacuum exists in the interruption, between the terminal points of the conductors. Thus, circuit 900 includes an interruption in the first circuit portion 904 and a normal circuit connection (i.e. one or more conductors) in the

corresponding second circuit portion 906. Charge carriers 910 are illustrated crossing the gap when the circuit is energised by a power supply (not shown) connected to the terminals, but the trajectory of the charge carriers is curved because the Lorentz force is active on the charge carriers as presented in Formula 1 given above.

However, given the fact that the charge carriers are crossing a gap in the interruption, and not flowing in an electrical conductor in this circuit portion, the Lorentz force component in this first circuit portion 904 is not transmitted to the conductor - indeed, there is no conductor in this gap for the force to be transmitted to - thereby reducing the action of the Lorentz force in the first circuit portion and resulting in an imbalance, a non-zero vector result, of the overall Lorentz forces in the complete circuit. Therefore, Figure 9 illustrates an electric circuit 900 wherein the first circuit portion 904 comprises an interruption arranged for charge carriers flowing in the circuit when powered by a power supply to cross the interruption.

The curvature of the path of the free electrons may produce an unequal length of the circuit elements causing unwanted or unnecessary unbalanced force as well but the effect of this can be mitigated/balanced by reversing the polarity of a second free path by means of, for example, two twisted conductors which are producing themselves a balanced force as shown in Figure 10. Thus, in Figure 10, circuit portion 1006 having an interruption therein allows charge carriers 1010 to cross the gap on a curved trajectory 1008 as described above with reference to Figure 9. That is, Figure 10 illustrates an electric circuit 1000 having a first interruption 1004 as described above with respect to Figure 9 and further comprising a second interruption 1006 arranged for charge carriers to cross the second interruption, the second interruption being connected in parallel with the first interruption. The part of the circuit responsible for the generation of the unbalanced force is the part between the circuit points C and D which carries the total current 2i that is then flowing in the two separate circuits with interruption. In at least one arrangement, over and above having the first and second interruptions connected electrically in parallel to each other, the physical arrangement is such that the polarities of the potential differences across the respective gaps are the reverse of each other. For instance, and taking the example of Figure 10, this indicates the orientation of the circuit portions 1004, 1006 with respect to each other. First interruption 1004 has a first termination point at the same potential as circuit point B (negative potential) and a second termination point at the same potential as circuit point A'(positive potential), with the potential difference from positive to negative being from A' to B. In this example, second interruption 1006 has a first termination point at the same potential as circuit point B" (negative potential) and a second termination point at the same potential as circuit point A" (positive potential), with the potential difference from positive to negative being from A" to B". With such an arrangement, any effects by the overall increase in the circuit length caused by the curved trajectory 1008 of the negatively-charged charge carriers 1010 may be mitigated.

In any case, whatever is the chosen shape for the circuit and its interruption, an unbalanced force will be generated and, once its direction is defined by design a calibrated by experiments, it can be used for the purpose of propulsion. Exemplary operational arrangements of these techniques will now be described.

It is likely that the resultant propulsive force, as generated using one or more of the techniques described above, is required in a particular direction with respect to an attitude of the body on or in which the circuit is disposed and to a reference system external to the body, for example, the Earth Centred Inertial ECl. For this purpose, at least two operational modes are contemplated: single actuator mode and multiple actuator motor. In the case of the single actuator mode, the direction of the portion of circuit that is able to produce force may be not aligned to the desired direction of the force and hence some other system may be used to rotate the body accordingly. The amount of current and direction may be then calculated from the desired force and magnetic field intensities applied according to the Formula 2. For maximum efficiency it may be preferred to have the force producing portion of circuit perpendicular to both the desired force direction and magnetic field.

If multiple actuators are used, as illustrated in Figure 11 with three circuits perpendicular to each other, then each contributing circuit portion will produce a component of force perpendicular to the respective conductor. This allows avoiding the need to the circuits in a specific position for any desired total force, so attitude actuators may not be needed. The knowledge of the body and each circuit attitude with respect to the external magnetic field may allow calculating the current direction and intensity on each circuit to produce the necessary force components for each desired total force. It is clear from Figure 11 that for a given magnetic field B, the two components perpendicular to each one of the force-contributing circuit wires (e.g. B_y and B_z for i_x) will define the magnetic field portion (e.g. B_yz) that is interacting with the current (i_x) flowing in the wire to produce its force component contribution (F_yz). Figure 12 illustrates the same concept using circuit portions according to the arrangement of Figure 4.

Several algorithms and strategies can be implemented to determine how much electric current should flow in each wire, and the energisation sequence. One possible algorithm may use the following steps by using as reference the Figure 13:

The "active wire" of each circuit may be defined as the unshielded part that produces the unbalanced force, for practical purposes it is preferred that this is made as a straight wire;

Three such "active wires" may be assembled aligned to three perpendicular coordinate axes X, Y and Z so that the currents ix, iy, iz running in each of them will be also parallel to such axes directions;

A desired total force F to be produced is decomposed in the 3 components Fx, Fy and Fz parallel to the 3 axes X,Y and Z;

The magnetic field B present in the area of the 3 wires is decomposed in the 3 components Bx, By and Bz parallel to the 3 axes X,Y and Z;

Each component of force on a given direction is produced by the current and magnetic field that are both perpendicular to it; the current intensity shall be calculated according to the desired force and magnetic field component intensities and signs.

Fx F_xi + F_x2 lyB_z iz^y

F_z = F_zl + F_z2 iyB_x

Fx F_xi F_x2 iyB_z i_∑ByFy Fyi Fy2 ί∑Βχ ~ i-xB_zF_z ⁼ F_z\— F_z2 = i_xB_y i_yB_xor

Where [B], an odd and skew matrix, is known to be singular and hence cannot be inverted, in fact a system with three active wires is redundant as two active wires would be enough to create a force in any direction as any wire already produces two independent components of force F as can be appreciate by Figure 13. (Figure 13 also illustrates the manner in which the circuits in the incorporated into a drive module, generally referred to by 1300, which further comprises a processor 1302 as described below.) A possible strategy to calculate the current intensity to be applied on each circuity may involve the condition that the total current shall be minimum and this may be obtained by calculating the current on each circuit while one of the circuits is assumed having zero current.

i HtxoO ~ ~ i₇

_ . . _ Fx Fy and then by selecting the case which gives the smallest total current among the three options. Thus, in this arrangement of Figure 13, processor 1302 calculates multiple scenarios of currents required to flow in each of the first electric circuit and the second electric circuit (and the third electric circuit, where provided) in order to achieve a desired motive force, and to identify one of the multiple scenarios in which an optimum operating condition will be realised. In this example, the optimum operating condition which is to be realised is minimum power/current consumption. Other more complex algorithms may be used for the same purpose.

The necessary current intensity shall then be generated by an appropriate controlling device such as a Pulse Width Modulation circuit or equivalent. The controlling device shall operate based on measurements of the magnetic field B in the reference system of the active wires and calculation of the desired force F in the same reference system which may come from other dynamic control algorithms that may produce the desired motion of the overall system in which the active wires are installed. As can be seen, a Lorentz force component acting in a circuit - or, as is the case in Figure 13 in a sub- circuit - maybe the vector sum of two force components, each of which is made up of components in the X, Y and Z axes. For instance, the sub- circuit 1306 comprises two Lorentz force components acting therein: F_y2 and F_zi, each of which are vector components. The net resultant sum of the two components is a vector force having a direction not lying in any of the principal X, Y or Z axes.

The techniques described herein may be implemented in a broad range of applications. For example, they may be implemented in spacecraft propulsion, in the presence of a magnetic field produced by one or more planets, asteroids stars/star systems, or present in space due to other phenomena as well as artificially produced by other devices. The techniques may have particular application in, for example, microsatellite systems. The techniques may be applied in ground (for example Earth) based vehicles, or air-based vehicles flying in the atmosphere of a planet having a magnetic field, and being sufficient to generate enough force intensity to overcome friction and drag. The techniques may be applied to deorbit a satellite or to accelerate and bring a vehicle from, say, a low altitude at the limits of the atmosphere up to an altitude high enough where the atmospheric drag may be negligible and the vehicle becomes an orbiting satellite or the techniques may be applied to keep moving the vehicle at any intermediate altitude, trajectory and velocity where gravity and inertial forces are not perfectly balanced. The techniques may be applied to parts of moving machinery in which the external magnetic field may be a planetary field, or artificially generated by other means.

Thus it will be appreciated that the drive module for a vehicle has been disclosed, the drive module comprising a first electric circuit and a second electric circuit, each of which is in accordance with the techniques described above, wherein the first electric circuit is disposed in a first orientation, and the second electric circuit is disposed in a second orientation, where the first orientation is different from the second orientation. In this example, the first electric circuit 1102 (or at least an unbalanced force generating portion thereof, in this case the circuit portion which is shielded) is in an orientation which is orthogonal to the second electric circuit (or at least an unbalanced force generating portion thereof, in this case the circuit portion which is shielded) 1104, 1106. For instance, the first electric circuit (or portion thereof) may be disposed in, say, a z-axis and the second electric circuit (or portion thereof) may be disposed in the x-axis or the y-axis. A corresponding method of operating the drive module is disclosed, in which power is selectively applied to the first electric circuit and/or the second electric circuit to provide motive force in a desired orientation. Preferably, the first and second orientations are orthogonal to each other.

Optionally, a third electric circuit may also be provided, and disposed in a third orientation which is orthogonal to both the first orientation and the second orientation. For example, the first, second and third orientations may be disposed according to the X, Y and Z axes.

In an experimental setup, a first proof of concept was to demonstrate that an unbalanced force can be produced by partial shielding of an electromagnetic coil. The first simple experimental set up has been based on an already existing Magnetic Coil, originally designed and made to generate a magnetic field for testing magnetometer sensors. Such a coil has been suspended by the same two copper wires that are used to supply the current. The copper wires are thereby acting as torsional spring with an elastic constant that can be estimated to give a rough sizing of the testing parameters. The coil was of square size with 0.5m side and 130 turns of copper wire with 0.5mm diameter, thereby a maximum current of 0.6A is recommended for constant safe operation. The coil was immersed in the local Earth magnetic field which can be considered uniform for a first approximation experiment. When a current is passed through the coil, a rotation around the suspension axis is expected due to two opposite forces generated on the vertical sides of the coil, resulting in a pure torque on the coil.

If part of the coil is shielded as prescribed by the above-described techniques, then a smaller rotation is expected because only one of the two sides producing useful torqueing force is active. If the shield is perfect then exactly half the rotation is expected, if the shielding is not perfect due to insufficient thickness of the material or to incomplete wrapping, then a rotation larger than half and smaller than the unshielded one is expected. Such rotation smaller than the one obtained in the unshielded case, proves that an unbalanced force is present on the coil and such force would also propel the coil if it was let free to act as in for example free space. Since the coil is constrained around a vertical suspension, only a rotation can happen and the acting force may only result in a pendulum oscillation which could be detected by a finer instrument.

For this first approximation experiment, the deflection was manually measured with a goniometer and verified by two operators at the same time.

A first series of tests was conducted and repeated to observe the deflection of the unshielded coil. It was found convenient to set the power supply limit at 0.4A and the actual current supplied was of 0.37A as indicated at the power supply. This setting was maintained constant through all the experiments and used as reference. A deflection of about 52degrees at equilibrium has been measured.

One of the sides of the coil was shielded with a single layer of 0.5mm mu-metal foil wrapped on it and also on the corners of the side. A second series of tests was conducted at the same supplied current and a deflection of about 47degrees has been measured, smaller than detected when not using the shield, but larger than theoretically expected with the perfect shield.

The ideal case would have required a deflection of 26degrees, a completely negative test would have recorded the same 52 degrees as the unshielded test, and hence a measure of the system efficiency can be calculated as

Experiment efficiency = (Unshielded deflection - Shielded deflection)/expected deflection

= (52 - 47)/26 = 19%

If the test had no result the efficiency would be zero, if it was perfect it would be one (100%).

It must be noted that such an experiment at constant current is obviously characterized by damped oscillations because the forces on the coil are constant while the elastic reaction of the suspension wires is proportional to the rotation angle and hence an acceleration results at the start, where there is an excess of forces applied to the coil with respect to the elastic reaction, which produces a double deflection as the excess initial kinetic energy transforms in potential elastic energy. Only after the excess energy is dissipated by frictions and the oscillations are fully damped, the final position indicates the balance between forces and the elastic reaction.

The profile of the oscillations envelope is theoretically of exponential shape but due to the presence of surrounding air and turbulence in the testing area some irregularities appear overlapped to the exponential trend which is eventually confirmed with the oscillations reaching a very small value around the asymptotic position. In an experiment, the arrangement of Fig. 8(c) was used, and Figure 14 provides a series of traces illustrating measured angular deflection according to different configurations produced with the arrangement of Figure 8. This arrangement is found to be particularly beneficial, since it is of a relatively simple construction. It will be useful here to mention some dimensions of practical use on, for example, a satellite propulsion application. A typical modest value of the Earth magnetic field in Low Orbit is assumed to be 31mG = 31000 nT and the size of the spacecraft, which limits the maximum linear extension of the circuit, is assumed to be 0.5m. Several options of current and number of circuit coils in series are possible; one useful configuration has 65 coils with a current of 1A which can produce a force of 31E- 6*0.5*65*1=1E-3N= lmN if perfect shielding is realized as described here. An imperfect shielding may require up to 100 or 200 coils to produce the same force of lmN. Such configurations can be produced with copper wire of 0.2mm diameter with a typical linear resistance of 0.5 Ohm/m as the skilled person will know and total resistance of 0.5*2*32.5=32.5 Ohm requiring 32.5*1=32.5V to produce the current of 1A and a total power dissipation of 32.5*1=32.5W which is achievable by such small spacecraft by using high efficiency (30%) photovoltaic solar panels of about 0.1m² surface. To avoid any confusion and misunderstanding, it is stated that these techniques are in conformity with the Laws of Momentum Conservation, which are still valid on the full system of both the body producing the magnetic field (for example, a plan) and a body hosting the circuit describe. It is also very clear that no energy will be produced and the system will necessitate supply with electric power from an external source in order to perform its function.

It will be appreciated that the invention has been described by way of example only and that various modifications may be made to the techniques described above without departing from the spirit and scope of the appended claims.

Claims

1. An electric circuit configured to provide motive force, the electric circuit comprising a first circuit portion and a corresponding second circuit portion, wherein the first circuit portion is configured, when the electric circuit is disposed in a magnetic field and powered by a power supply, for a first Lorentz force component acting in the first circuit portion to be less than a second Lorentz force component acting in the corresponding second circuit portion.

2. The electric circuit of claim 1, wherein the electric circuit comprises a magnetic shield for shielding the first circuit portion from the magnetic field.

3. The electric circuit of claim 2, wherein the electric circuit is arranged in a coaxial configuration, with the first circuit portion shielded by the magnetic shield, and the second circuit portion comprising a second circuit conductor arranged coaxially around the shield.

4. The electric circuit of any preceding claim, wherein the second circuit portion comprises a plurality of conductors.

5. The electric circuit of any preceding claim, wherein the electric circuit comprises a plurality of first circuit portions and a plurality of corresponding second circuit portions, where the electric circuit is configured for respective first Lorentz force components for each of the first circuit portions to be less than respective second Lorentz force components for each of the corresponding second circuit portions.

6. The electric circuit of claim 5, wherein the plurality of first circuit portions and the plurality of corresponding second circuit portions are connected in series, with the plurality of first circuit portions being interspersed with the plurality of corresponding second circuit portions.

7. The electric circuit of any preceding claim, wherein the first circuit portion has a first physical length and the corresponding second circuit portion has a second physical length, and wherein the electric circuit comprises a third circuit portion having a third physical length and a fourth circuit portion having a fourth physical length, where each of the third physical length and the fourth physical length are less than the first physical length and the second physical length.

8. The electric circuit of claim 7, wherein the electric circuit is arranged for a conductor of the second circuit portion to contact with an external surface of the shield.

9. The electric circuit of any preceding claim, wherein the first circuit portion comprises an interruption arranged for charge carriers flowing in the circuit when powered by a power supply to cross the interruption.

10. The electric circuit of claim 9, wherein the electric circuit further comprises a second interruption arranged for charge carriers to cross the second interruption, the second interruption being connected in parallel with the first interruption.

11. An electric circuit configured to provide motive force, the electric circuit being configured, when the electric circuit is disposed in a magnetic field and powered by a power supply, for a net Lorentz force acting in the electric circuit to be non-zero.

12. A drive module for a vehicle, the drive module comprising a first electric circuit and a second electric circuit, each of the first electric circuit and the second electric circuit being in accordance with any preceding claim, wherein the first electric circuit is disposed in a first orientation and the second electric circuit is disposed in a second orientation, where the first orientation is different from the second orientation.

13. The drive module of claim 12 further comprising a processor, the processor being configured to calculate multiple scenarios of currents required to flow in each of the first electric circuit and the second electric circuit in order to achieve a desired motive force, and to identify one of the multiple scenarios in which an optimum operating condition will be realised.

14. A method of providing motive force comprising operating the electric circuit of any of claims 1 to 10.

15. A method of providing motive force comprising operating the electric circuit of claim 11.

16. A method of operating the drive module of claim 12 or claim 13 and selectively applying power to the first electric circuit and/or the second electric circuit to provide motive force in a desired orientation.