Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B5/00—Near-field transmission systems, e.g. inductive or capacitive transmission systems
  • H04B5/70—Near-field transmission systems, e.g. inductive or capacitive transmission systems specially adapted for specific purposes
  • H04B5/79—Near-field transmission systems, e.g. inductive or capacitive transmission systems specially adapted for specific purposes for data transfer in combination with power transfer
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J50/00—Circuit arrangements or systems for wireless supply or distribution of electric power
  • H02J50/10—Circuit arrangements or systems for wireless supply or distribution of electric power using inductive coupling
  • H02J50/12—Circuit arrangements or systems for wireless supply or distribution of electric power using inductive coupling of the resonant type
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J50/00—Circuit arrangements or systems for wireless supply or distribution of electric power
  • H02J50/90—Circuit arrangements or systems for wireless supply or distribution of electric power involving detection or optimisation of position, e.g. alignment
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B5/00—Near-field transmission systems, e.g. inductive or capacitive transmission systems
  • H04B5/20—Near-field transmission systems, e.g. inductive or capacitive transmission systems characterised by the transmission technique; characterised by the transmission medium
  • H04B5/24—Inductive coupling
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J50/00—Circuit arrangements or systems for wireless supply or distribution of electric power
  • H02J50/70—Circuit arrangements or systems for wireless supply or distribution of electric power involving the reduction of electric, magnetic or electromagnetic leakage fields

Definitions

• Previous applications by Nigel Power LLC have described a wireless powering and/or charging system using a transmitter that sends a magnetic signal with a substantially unmodulated carrier.
• a receiver extracts energy from the radiated field of the transmitter. The energy that is extracted can be rectified and used to power a load or charge a battery.
• Non-radiative means that both the receive and transmit antennas are "small” compared to the wavelength, and therefore have a low radiation efficiency with respect to Hertzian waves. High efficiency can be obtained between the transmit antenna and a receive antenna that is located within the near field of the transmit antenna.
• the present application describes techniques for capturing wireless power based on a magnetic transmission.
• Figure 1 shows a block diagram of induction between transmit and receive loops
• Figure 2 shows an elemental torsion pendulum
• Figure 3 shows a dynamo receiver
• Figures 4A and 4B show flux and field strength within a sphere
• Figure 5 shows an integrated embodiment
• Figure 6 shows a disc shaped array
• Figure 7 illustrates how a coil can be wound around the disc shaped array.
• a transmitter forms a primary and a receiver forms a secondary separated by a transmission distance.
• the primary represents the transmit antenna generating an alternating magnetic field.
• the secondary represents the receive antenna that extracts electrical power from the alternating magnetic field using Faraday's induction law.
• the efficiency of the transmission can decrease.
• larger loops, and/or larger Q factors may be used to improve the efficiency.
• the size of the loop may be limited by the parameters of the portable device.
• Efficiency can be improved by reducing antenna losses. At low frequencies such as less than 1 MHz, losses can be attributed to imperfectly conducting materials, and eddy currents in the proximity of the loop.
• Flux magnification materials such as ferrite materials can be used to artificially increase the size of the antenna. Eddy current losses are inherently reduced by concentrating the magnetic field.
• Special kinds of wire can also be used to lower the resistance, such as stranded or litz wire at low frequencies to mitigate skin effect.
• magneto mechanical system as described in our co-pending application number 12/210,200, filed September 14, 2008. This picks up energy from the magnetic field, converts it to mechanical energy, and then reconverts to electrical energy using Faraday's induction law.
• the magneto mechanical system may be part of an energy receiving system that receives energy from an alternating magnetic field.
• the magneto mechanical system is formed of a magnet, e.g. a permanent magnet, which is mounted in a way that allows it to oscillate under the force of an external alternating magnetic field. This transforms energy from the magnetic field into mechanical energy .
• this oscillation uses rotational moment around an axis perpendicular to the vector of the magnetic dipole moment m, and is also positioned in the center of gravity of the magnet. This allows equilibrium and thus minimizes the effect of the gravitational force.
• a magnetic field applied to this system produces a torque of
• This torque aligns the magnetic dipole moment of the elementary magnet along the direction of the field vector.
• the torque accelerates the moving magnet (s), thereby transforming the oscillating magnetic energy into mechanical energy.
• the basic system is shown in figure 2.
• the magnet 200 is held in place by a torsion spring 210.
• Magnetic torque causes the magnet 200 to move against the force of the spring, to the position 202, against the force of the spring with spring constant K R .
• the movement forms an inertial moment I that creates a torsion pendulum that exhibits a resonance at a frequency proportional to K R and
• some or all of the torsion spring is replaced by an additional static magnetic field H DC .
• This static magnetic field is oriented to provide the torque
• Another embodiment may use both the spring and a static magnetic field to hold the device.
• the mechanical energy is reconverted into electrical energy using ordinary Faraday induction e.g. the Dynamo principle.
• This can be used for example an induction coil 305 wound around the magneto electrical system 200 as shown in figure 3.
• a load such as 310 can be connected across the coil 305. This load appears as a mechanical resonance. The load dampens the system and lowers the Q factor of the mechanical oscillator.
• the eddy currents in the magnets may increase. These eddy currents will also contribute to system losses.
• the Eddy currents are produced by the alternating magnetic field that results from the coil current. Smaller magnets in the magneto system may reduce the eddy currents. According to an embodiment, an array of smaller magnets is used in order to minimize this eddy current effect.
• a magneto mechanical system will exhibit saturation if the angular displacement of the magnet reaches a peak value. This peak value can be determined from the direction of the external H field or by the presence of a displacement stopper such as 315 to protect the torsion spring against plastic deformation. This may also be limited by the packaging, such as the limited available space for a magnet element.
• optimum matching is obtained when the loaded Q becomes half of the unloaded Q.
• the induction coil is designed to fulfill that condition to maximize the amount of output power.
• the magnets can be radially symmetrical, e.g., spheroids, either regular or prolate, as shown in figures 4A and 4B.
• Figure 4A shows the parallel flux lines of a magnetized sphere. This shows the magnetic flux density B.
• Figure 4B shows the magnetic field strength in a magnetized sphere. From these figures that can be seen that there is effectively zero displacement between magnets in a spheroid shaped three-dimensional array.
• the magnets are preferably in-line with the axis of the spheroid shown as 400. This causes the internal forces to vanish for angular displacement of the magnets. This causes the resonance frequency to be solely defined by the mechanical system parameters.
• a sphere has these advantageous factors, but may also have a demagnetization factor is low as 1/3, where an optimum demagnetization factor is one. Assuming equal orientation of axes in all directions, a disc shaped array can also be used. Discs have a magnetization factor that is very high, for example closer to 1.
• Magnetization factor of a disc will depend on the width to diameter ratio.
• the shaped elements also have a form factor that is more suitable for integration into a device, since spheroids have a flat part that may be more easily used without increasing the thickness of the structure
• the following is a comparison of magneto-mechanical systems with classical ferrimagnetic materials (ferrites) .
• Ferrimagnetic materials or ferrites may be modeled as a magneto-mechanical system or conversely, magneto-mechanical systems may be considered as ferrites with special properties that may not be achievable with the classical ferrite materials.
• ferrimagnetic materials known as ferrites
• ferrites have a low electrical conductivity. This makes these materials useful in the cores of AC inductors and transformers since induced eddy currents are lower.
• a low electrical conductivity can also be found in a magneto-mechanical system composed of a multitude of small elementary magnets that are mutually electrically isolated so that eddy currents are attenuated.
• the crystalline Ferromagnetic and ferrimagnetic materials are typically structured in magnetic domains also called Weiss domains. Atoms in a domain are aligned so that a net magnetic moment results. These domains may be considered as the magnets of a magneto-mechanical system.
• the domain magnetization tends to align itself along one of the main crystal directions. This direction is called the easy direction of magnetization and represents a state of minimum energy.
• the directions of crystal domains may be considered randomly oriented so that there is complete cancellation and the resultant net magnetic moment at macroscopic level is zero, if no external magnetic field is applied. This is in contrast to the magneto-mechanical systems where the "elementary" magnets are equally oriented.
• a certain force and work is required depending on the angle of rotation. Such work is performed if the ferrimagnetic material is subjected to an external magnetic field.
• the underlying physical phenomenon is Lorentz force applied to the magnetic moment, as described above .
• the torsion spring (mechanical or magnetic) of a magneto-mechanical system sets the magnetic orientation of domains back to their state of minimum energy, if the external field is removed, may be considered as the torsion spring of a magneto-mechanical system. Since crystal domains in ferrites have different shapes and sizes, they appear as different spring constants. Another embodiment uses elementary oscillators which all have an equal spring constant. [0051] Stronger external fields cause more domains to be aligned or better aligned to the direction given by the external magnetic field. This effect is called magnetic polarization. This may be mathematically expressed as
• J is the magnetic polarization
• M is the magnetization
• ⁇ r the relative permeabilty.
• the magnetization effect may be considered as a magnification of the magnetic flux density at the receive location by the factor ⁇ r using rotatable magnetic moments. This principle of local magnification of magnetic flux density is inherent to the magneto-mechanical system described above. Thus a relative permeability may be attributed to a magneto- mechanical system. In a resonant system, this relative permeability will be a function of frequency and reaches a maximum close to the resonance frequency.
• This kind of magnetisation process differs from that of a magneto-mechanical system as described above. If the external magnetic field is continuously increased, the ferrite material will be progressively magnetized until a point of saturation is reached. Saturation is a state where net magnetic moments of domains are maximally aligned to the external magnetic field.
• Magneto-mechanical systems as described above, saturate when the angular displacement of elementary magnets reaches the maximum peak angular displacement.
• the dynamic behavior when an alternating external magnetic field is applied is different.
• the magnetization process of a bulk ferrite material can be considered.
• M as a function of the external field H
• three major regions can be identified in which the ferrite shows different dynamic behavior .
• the second region of the magnetization curve is one in which the slope of magnetization (M vs. H) is greater and in which irreversible domain wall motion occurs .
• the third section of the curve is one of irreversible domain rotations.
• the slope is very flat indicating the high field strength that is required to rotate the remaining domain magnetization in line with the external magnetic field.
• Irreversible domain wall motion or domain rotation explains the well known hysteresis in the magnetization curve that is presented by all ferrites in a more or less pronounced manner.
• Hysteresis means that the magnetization or the induction B lags relative to the external magnetic field. As a consequence, the induction B at at a given field H cannot be specified without knowledge of the previous magnetic history of the ferrite sample. Thus hysteresis may be considered as memory inherent to the material.
• the area included in a hysteresis loop is a measure of the magnetic losses incurred in a cyclic magnetization process e.g. as resulting from an alternating external magnetic field.
• a ferrite With respect to the application of wireless energy transfer, there will be a requirement to drive a ferrite at least into the second region of magnetization where hysteresis losses typically become significant. This requirement is different e.g. for a communication receiver antenna. This is, however, not further shown here.
• Hysteresis losses due to irreversible domain changes; and -eddy current losses due to residual conductivity in the ferrite.
• Hysteresis losses increase proportionally with frequency as the energy to cycle once around the hysteresis loop is independent of the speed. Eddy current losses have the effect of broadening the hysteresis loop.
• Magneto-mechanical systems using a torsion spring as described above are largely hysteresis-free, where irreversible effects are concerned. At higher frequencies eddy current losses must be expected too. At lower frequencies ( « 1 MHz) a magneto-mechanical system has the potential to provide high Q-factors at levels close to saturation.
• a ferrite core material may be characterised by its complex permeability
• the real and imaginary part represent the permeability with the magnetization in phase and in quadrature to the external field, respectively.
• the two permeabilities can often be found plotted in data sheets for ferrite materials.
• the real component is fairly constant with frequency, rises slightly, then falls rapidly at higher frequencies.
• the imaginary component on the other hand first rises slowly and then increases quite abruptly where the real component is falling sharply .
• ferrimagnetic resonance is an intrinsic property of a ferrite material and may be considered as the upper frequency at which the material can be used. It is also observed that the higher the permeability p' of the material, the lower the frequency of the ferrimagnetic resonance. This phenomenon of resonance indicates domain rotation, a counter torque (spring), and a certain intertial moment. It can be shown that the resonance frequency depends on the so-called gyromagnetic ratio.
• Ferrites show a resonance similar to a magneto- mechanical system however with a too low Q-factor so that this effect cannot be technically exploited to get materials with high permeability p' at a specified frequency.
• Gyromagnetic resonance with high Q-factors up to 10,000 can be observed at microwave frequencies (> 1 GHz) in certain ferrite materials (e.g. Yttrium Iron Garnets) if the material is subjected to strong static magnetic fields. This effect, which is based on electron spin precession, can be exploited to build microwave components such as circulators, isolators, high-Q filters and oscillators. Non-radiative energy transfer using coupled magnetic resonance in the microwave range would however be limited to extremely short range .
• Gyromagnetic resonance may be considered as a magneto- mechanical system at the atomic level. A difference is however that magnetic moments are precessing around the field lines of the static magnetic field rather than oscillating axially. In both cases there is, however, a moving magnetic moment and an angular displacement.
• a magneto-mechanical system may be formed of a single permanent magnet or of a multitude (an array) of elementary magnets. Theoretical analyses shows that: the ratio of magnetic moment-to-inertial moment increases with the number of elementary magnets. This ratio is similar to the gyromagnetic ratio known from ferromagnetism. the performance of the magneto-mechanical system increases with this ratio of moments A figure of merit for the performance of a magneto-mechanical system
• H AC is the external alternating magnetic field strength
• V the volume required by the magneto-mechanical system. This figure of merit, which is called the specific power conversion factor, is indicative of how much power per unit system volume can be extracted from an alternating magnetic field, H AC ' if penduli are perpendicularly oriented to the direction of the exciting magnetic field.
• FIG. 5 shows one embodiment of forming an array of magneto mechanical oscillators using MEMS technology.
• An array 500 may be formed of a number of magnet elements such as 502.
• Each magnet elements 502 is formed of two U-shaped slots 512, 514 that are micro-machined into a silicon substrate.
• a permanent rod magnet 504, 506 of similar size is formed within the slots.
• the magnet may be 10 ⁇ m or smaller.
• crystalline materials may behave differently than larger sizes. Hence, this system can provide considerable angular displacement e.g. as high as 10°. This may provide the ability to increase the Q factor of such a system.
• the magnet itself may be on the order of 10 ⁇ m or smaller. These devices may be formed in a single bulk material such as silicon.
• the magnets 504, 506 can have a high magnetization e.g. higher than 1 Tesla.
• the magnet itself is composed of two half pieces, one piece attached to the upper side and the other piece attached to the lower side. Preferably these devices are mounted so that the center of gravity coincides with the rotational axes.
• the device may be covered with a low friction material, or may have a vacuum located in the area between the tongue and bulk material in order to reduce type the friction.
• Figure 6 shows a cut through area of a three- dimensional array of magnets.
• the array itself is formed of a radial symmetric shape, such as disc shaped.
• the disc shaped array of figure 6, 600 may provide a virtually constant demagnetization factor at virtually all displacement angles.
• an induction coil may be wound around the disc to pick up the dynamic component of the oscillating induction field generated by the MEMS-magneto mechanical system. The resulting dynamic component of the system may be expressed as
• Figure 7 illustrates how the induction coil can be wound around the disc.
• Equations for the maximum available power are determined under the constraints of a limited angular displacement and Q-factor of the magneto-mechanical oscillator .
• a primary system parameter is a parameter that is independent of any other parameter of the set and thus cannot be expressed as a function of another parameter.
• Vs Volume of magneto mechanical system [m 3 ] .
• Pe m Specific volume of elementary magnet in [m 3 /kg]
• QUL Unloaded Q-factor of mechanical resonator (s) .
• Opeak Maximum peak displacement angle of magnet rod supported by the mechanical resonator [rad] .
• fo Resonance frequency [Hz]
• HAc Externally applied alternating magnetic field
• Pav_mech Available mechanical power, (maximum power into load)
• Secondary system parameters and physical quantities include :
• the magnetic moment of an elementary magnet may be expressed as:
• This equation may also be expressed in terms of the total magnetic moment m tot of the magneto-mechanical system and the external magnetic induction BAC as follows:
• a system may be designed for a high k c , compromising with a lower saturation level.
• a system may be designed for a higher saturation level compromising with a lower kc.
• a system using rod magnets of 20 ⁇ m length saturates at approximately 2.5 W while a system using 10 ⁇ m rod length saturates at a lower value of about 600 mW.
• the 10 ⁇ m system however is more sensitive (higher specific power conversion factor) than the one that uses 20 urn rods. This can be checked at a field strength of 5 A/m.
• a disc shaped system with 4 cm diameter 3 cm thickness can extract up to 260 mW from a magnetic field of 5 amps per meter at 135 kHz.

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Power Engineering (AREA)
• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Micromachines (AREA)
• Soft Magnetic Materials (AREA)
• Hall/Mr Elements (AREA)
• Dynamo-Electric Clutches, Dynamo-Electric Brakes (AREA)
• General Electrical Machinery Utilizing Piezoelectricity, Electrostriction Or Magnetostriction (AREA)
• Near-Field Transmission Systems (AREA)
• Transceivers (AREA)

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• 2008
  • 2008-10-13 JP JP2010529136A patent/JP5362733B2/ja not_active Expired - Fee Related
  • 2008-10-13 KR KR1020137032687A patent/KR101507265B1/ko not_active Expired - Fee Related
  • 2008-10-13 KR KR1020127030514A patent/KR101414404B1/ko not_active Expired - Fee Related
  • 2008-10-13 KR KR1020147022324A patent/KR101606664B1/ko not_active Expired - Fee Related
  • 2008-10-13 US US12/250,015 patent/US8373514B2/en not_active Expired - Fee Related
  • 2008-10-13 WO PCT/US2008/079681 patent/WO2009049281A2/en not_active Ceased
  • 2008-10-13 CN CN200880114332.5A patent/CN101842963B/zh not_active Expired - Fee Related
  • 2008-10-13 KR KR1020107010397A patent/KR101312215B1/ko not_active Expired - Fee Related
  • 2008-10-13 EP EP08836964.0A patent/EP2208279A4/en not_active Withdrawn
  • 2008-10-13 CN CN201410161890.4A patent/CN103904787B/zh not_active Expired - Fee Related
• 2013
  • 2013-09-04 JP JP2013183454A patent/JP5694469B2/ja not_active Expired - Fee Related

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