Hybrid EM-LC resonator

Abstract

A hybrid EM-LC resonator for a wireless power transfer (WPT) system includes a plurality of capacitive loops and LC circuits each having mutual inductance in a non-resonant mode of operation. The resonator is useful in a wireless energy transfer system. The system comprises a transmitter antenna assembly and a receiver antenna assembly, wherein each antenna assembly comprises at least two circuits isolated from each other. One way of isolating circuits is to place them at a pre-selected distance from each other, as shown below. It is required to sufficiently separate the circuits to allow for a relatively loose coupling between them.

Description

SUMMARY

[0001] One of the invention is a hybrid EM-LC resonator for a wireless power transfer (WPT) system, the resonator comprising a mutual inductance of LC circuits in a capacitive loop and a non-resonant mode of operation. The resonator is usable in a wireless energy transfer system. The system comprises a transmitter antenna assembly and a receiver antenna assembly, each of which comprises at least two circuits isolated from each other. One way to isolate the circuits is to place them at a pre-selected distance from each other, as shown in the following figure. The requirement is to separate the circuits sufficiently to allow a relatively loose coupling between them.

[0002] Each of the circuits is an LC circuit with the same resonant frequency, and each circuit is powered by the same power-frequency source via a parallel or series connection to the power-frequency generator. Because of the electromagnetic interaction between the LC circuits, the resonant frequency of the system is relatively low, and those LC circuits share inductance and capacitance, which results in a reduction of the effective reactive impedance of the antennas. DETAILED DESCRIPTION

[0003] In one version of the system, the operating frequency is 120 kHz, and the self-resonant frequency of each LC circuit is 200 kHz. Circuit 1 has inductance LI and capacitance CI, and circuit 2 has inductance L2 and capacitance C2. Each LC circuit operates at a frequency substantially lower than its resonant frequency, which makes each LC circuit have a capacitive impedance, i.e., each LC circuit is a capacitive loop itself during system operation. The inductance of the system is the mutual inductance of the LC circuits, which means that the system inductance is not associated with the wires, but instead with the EM interaction of the wires. The construction of this system also results in a significant increase in the density of the EM field generated by the system, almost twice the density of a conventional system. The increased density is due to the loose coupling and the anti-damping. The anti-damping occurs because: the circuits generate EM fields of the same phase, which increases the total density of the EM field. In other words, the self-resonant frequency of a single circuit is much higher than the resulting operating frequency. The system produces a voltage step-up effect because it results in an increase in the induced voltage without the need for a conventional step-up transformer.

[0004]

[0005] The system is a hybrid EM-LC resonator, rather than a simple LC resonator or EM resonator, because of the capacitive behavior of each individual LC circuit, and because the resonant frequency of the system is much lower than the resonant frequency of each individual LC circuit. To achieve this system functionality, the LC circuits are positioned at a pre-selected distance to achieve non-resonant, relatively loose coupling between the circuits at a frequency that is significantly lower than the self-resonant frequency. The pre-selected distance is 5%-25% of the size of the LC circuits, with each LC circuit preferably formed as a circle or loop. For example, a system with multiple transmitters, each formed as a circular or loop shape with a 3m diameter, spaced apart at a distance of 30cm between the planes containing the loops in a coaxial configuration, with the first loop positioned above the second loop, and so on for as many transmitters in the system. The typical range of frequencies associated with the loose coupling is 1.3 to 1.8 times lower than the self-resonant frequency.

[0006] Unlike the invention in the systems described in this application, conventional wireless energy transfer systems utilize resonant coupling of resonant LC circuits, where the transmitting LC resonator and the receiving LC resonator have the same resonant frequency. Unlike those conventional systems, the hybrid EM-LC resonator invention has a resonant frequency associated with each LC circuit that is significantly greater than the operating frequency (the frequency associated with the system). The hybrid EM-LC resonator invention can function as a transmitter or receiver, and it includes multiple LC circuits, with no galvanic connections between them. Each LC circuit has its own resonant frequency, and each LC circuit in the system has the same resonant frequency. The resonant frequency of each LC circuit is higher than the operating frequency. Through EM interaction between the LC circuits, those LC circuits share impedance, which results in a reduction of the operating frequency, which is then lower than the resonant frequency of each LC circuit.

[0007] In addition to utilizing a capacitive load loop conducted by a wire, the systems described in this application achieve their functionality by utilizing the specific three-dimensional structure of the loops and their associated capacitive behavior.

[0008] In operation, each LC circuit of the system has a capacitive impedance. Unlike conventional systems that use inductive loops, the EM-LC resonator of the system includes the capacitive loop and mutual inductance of the LC circuits.

[0009] The hybrid EM-LC resonator described above can function as a transmitting antenna and / or a receiving antenna, and its advantages over conventional systems that use resonant circuit coupling or inductive loops include:

[0010] 1. The density of the EM field generated by the EM-LC resonator is higher than those associated with a conventional LC resonator having the same voltage on the capacitor of the resonator. For one version of the system invention comprising two LC circuits, each having a diameter of 3 meters and being 30 cm apart from each other, the EM field is generated 1.8 times higher density. For another version comprising three LC circuits placed 20 cm apart from each other, the system invention generates an EM field 2.6 times higher density, keeping the same voltage at the capacitor of each circuit. The system invention causes a step-up effect in the induced EM field without increasing the voltage or the capacitance / inductance of each LC circuit.

[0011] 2. The magnetic field density in the space between the wires of the LC circuit is reduced because of the opposite direction of the magnetic field generated by each wire. As a result is that the total inductive voltage associated with the wires of the LC circuit is reduced (for the same current) due to the actual reduction of the inductance of each wire related to the reduction of the density of the magnetic field near the wires, while at the same time the density of the EM field associated with the system operation is not affected. When the system operates, the current in the LC circuit produces the same density of the EM field and at the same time, the generation of such current / EM field density requires a reduction of the voltage on the capacitance / inductance of the LC circuit.

[0012] Hybrid EM-LC resonator increasing the stepping-up effect and reducing the EM noise

[0013] The structure of the hybrid EM-LC resonator requires a relatively high voltage to be applied to the capacitance of each LC loop. In order to further reduce the voltage applied to the reactance of the LC circuit, the capacitance and the inductance of each loop can be split and distributed along the wires of the loop, as follows. The reactance of the LC circuit means the reactive impedance (including both capacitive impedance or inductive impedance).

[0014]

[0015] In the above illustration, each capacitor must be changed so that the total capacitance remains unchanged. For example, in the case of three equal capacitors placed along the wire of the loop, each capacitor must be three times the initial (unsegmented) capacitance so that the total capacitance remains unchanged, as shown: C1 = 1 / (1 / C11 + 1 / C12 + 1 / C13). In another example of a parallel connection of a power-frequency generator and an LC circuit, each capacitor must be inversely proportional to the voltage driving that capacitor. In general, the capacitors must be driven by an AC source that is galvanically isolated from each other. However, in a version of equal capacitors placed along the wire of the loop at equal distances from each other, all capacitors can be driven in parallel from the same source, i.e., without galvanic isolation. In this version, the loop can be made of smaller LC resonators of the same impedance / frequency connected in series. Due to the symmetry of the system, this will allow driving all LC resonators of a single loop from the same voltage / current source, which also makes this version of the system easier to implement from an engineering perspective.

[0016] The system described in this application will also result in a reduction of any parasitic (i.e., unusable) EM fields associated with the alternating charges on the wires of the loop. The focus of the system is on the eddy current electric field (E-field) induced in the volume around the loop system. However, there is also an unused parasitic electric field generated by each loop. For example, if there is one capacitor and one wire in the loop, the AC surface charge on the loop will create an electric dipole EM field of the main power frequency. If there are three loop segments, an AC hexapole will be created, as shown below:

[0017]

[0018] In the above example, the field of the hexapole decreases much faster with distance, and for the same AC current amplitude in the loop, the voltage on each capacitor of the loop will be three times lower (for equal capacitors), which also induces a threefold decrease in the density of the parasitic EM field produced by the system. An additional reduction of the unwanted parasitic multipole electric field can be achieved by rotating the loops to each other by a certain degree. For example, rotating one of the loops (in a double loop structure) consisting of one capacitor and one inductor by 180 degrees will create a quadrupole configuration of the parasitic electric field instead of the dipole configuration shown below, and rotating one of the loops (in a double loop structure) consisting of three capacitors and three inductors by 60 degrees will change the hexapole configuration to a 12-pole configuration, and so on.

[0019]

[0020]

[0021] The above described method can be applied to any desired number of divisions per loop, including different numbers of divisions for different loops, different capacitances spaced apart at different distances along a loop. It can also be applied to any desired number of loops to obtain a higher multipole configuration, which will significantly reduce the parasitic electric field over a certain distance (which is associated with the alternating surface charge of the wire).

[0022] Hybrid EM-LC resonator for reducing the density of EM fields for biosafety reasons

[0023] The above described method results in a reduction of the voltage over the reactance of the loop, and also reduces the parasitic electric field associated with the alternating surface charge of the wire. However, the density of the main EM field (the eddy EM field in the area around the antenna) is high. To reduce the density of the EM field in the area where a human is present, active field suppression is used. To implement active field suppression in the system described in this application, additional "damping" loops of current can be added to the system. These loops typically have a diameter that is 2-3 times smaller than the other loops, and are placed coaxially with the antenna loops at a pre-selected distance from the plane that passes through the antenna loops, typically at a distance of 1-2 diameters of the damping loops. The current in the damping loops flows in the opposite direction to the current in the antenna primary loops. As a result, the damping loop current produces the same EM field at the same frequency, but with a 180 degree phase shift compared to the main loop current. This means that the field produced by the damping loops and the field produced by the antenna loops will cancel each other out or at least partially suppress each other.

[0024] By selecting the appropriate current level in the damping loops and the appropriate geometry and placement of the damping loops, a significant reduction of any resulting EM field in the area where a human is present can be achieved. For example, one version of the system has a transmitting antenna with a diameter of three meters, and includes two loops spaced apart from each other by 30 cm, which are divided into three equal parts using the technique described in the above paragraph. Two damping loops, each with a diameter of 1.5 meters, are positioned 1.5 meters below the plane containing the lower loop of the transmitting antenna, and are spaced apart from each other by 30 cm. The distance between the plane containing the lower loop of the transmitting antenna and the mounting surface (the ground) is five meters. For this version, the optimal current in the damping loops is 120% of the current in the loops of the transmitting antenna, which results in a tenfold decrease in the density of the EM field at a height of one meter above the ground. A schematic diagram of this version is shown below.

[0025]

[0026] The benefits of actively suppressing the EM field generated by the antenna of the system described in this application due to biosafety reasons include:

[0027] 1. The density of the suppressed EM field at ground level and adjacent to the antenna is low enough to be safe for humans.

[0028] 2. There is an increase in the efficiency of the wireless energy transfer / reception of the system because the relatively low density of the EM field at ground level also results in lower parasitic energy losses in the ground itself (caused by lower currents induced in the ground).

[0029] 3. There is an increase in the power level / distance / efficiency of the system because of the increased density of the EM field above the antenna. While the EM field of the damping loop will reduce the density of the resulting EM field above the transmitting antenna (typically by 5-15%), it will also reduce the density of the EM field at ground level (by 5-10 times). Thus, there is a significant increase in the current in the presence antenna, which results in a corresponding increase in the density of the EM field above the antenna, but also maintains a safe density of the EM field at ground level.

[0030] For different diameters / positions (heights) of the antenna loop and the damping loop, appropriate current levels can be established in the damping loop to minimize the EM field density to achieve bio-safety, such as making the area safe for human presence.

[0031] The above methods and systems can encompass a number of distinct inventions with independent utility. While each of these inventions has been disclosed in its preferred form, the specific embodiments disclosed and illustrated herein are not to be considered in a limiting sense as numerous variations are possible. The subject matter of the present invention includes all novel and nonobvious combinations and subcombinations of the various elements, features, functions and / or properties disclosed herein. The following claims particularly point out certain combinations and subcombinations that are regarded as novel and nonobvious. Other combinations and subcombinations of features, functions, elements and / or properties can be claimed through amendment of the following claims or presentation of additional claims in the application. Such amended claims, whether they are directed to distinctly different inventions or directed to the same invention as any other claim, are to be considered within the scope of the present disclosure.

Claims

1. A hybrid EM-LC resonator for a wireless power transfer (WPT) system, comprising: a plurality of capacitive loops; and LC circuits, each of the LC circuits having mutual inductance in a non-resonant mode of operation.

2. The hybrid EM-LC resonator of claim 1, wherein the plurality of capacitive loops are arranged in a circular pattern.

3. The hybrid EM-LC resonator of claim 1, wherein the plurality of capacitive loops are arranged in a square pattern.

4. The hybrid EM-LC resonator of claim 1,

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