Embodiments of the present disclosure relate to an inductive power and data transmission system and, more particularly, to an improved power and data transmission system that uses hyper resonance.
Inductive power transmission links that utilize a pair of mutually coupled coils have been in use for decades to, for example, power radio frequency identification (RFID) transponders and cochlear implants. These components typically have with power consumption in the range of microwatts (μW) to milliwatts (mW). The use of this technique to wirelessly transfer energy across a short distance is expected to see an explosive growth over the next decade in a much broader range of applications from advanced implantable microelectronic devices (IMD), such as, for example and not limitation, retinal implants and brain computer interfaces (BCI), contactless smartcards, and wireless microelectromechanical systems (MEMS). This technology can also be used to obviate the power cord in charging mobile gadgets, operating small home appliances, and energizing electric vehicles, which have higher levels of power consumptions on the order of hundreds of milliwatts (mW) to kilowatts (kW).
An inductive link between two magnetically-coupled coils (L2 and L3 in FIG. 1A) is one of the most common methods for wireless power transmission. The coupling coefficient between the two coils, L2 and L3, is represented by k23, which can be found from k23=M23/(L2×L3)^0.5, where M23 is the mutual coupling between the two coils, which is proportional to d−3, where d is the center-to-center spacing between the coils when they are in parallel planes and perfectly aligned. Capacitors, C2 and C3, are added in parallel or series to the coupled coils to form resonant LC tank circuits. By tuning these LC tank circuits at the wireless link carrier frequency (f=½π(L2×C2)^0.5=½π(L3×C3)^0.5), the amplitude of the received signal on the receiver (Rx) side (i.e. across L3) can be significantly increased, while attenuating the out of band interference.
A key requirement in all of the above applications, however, is delivering sufficient power to the load with high power transfer efficiency (PTE) when the distance, d, between L2 and L3, is relatively large or the coils are misaligned, i.e. when M is very small. An increase in PTE reduces heat dissipation within the coils, exposure to AC magnetic field, size of the main energy source (e.g. battery), and interference with nearby electronics to satisfy regulatory requirements. Therefore, design, theoretical analysis, and geometrical optimization of the conventional 2-coil inductive link has been extensively studied over the last few decades. More recently, a 4-coil power transmission link, which operates based on coupled-mode magnetic-resonance, was proposed to further increase the PTE, particularly at large d. In the 4-coil arrangement, as shown schematically in FIG. 1B, a pair of coils is used on the transmitter (Tx) side, which are referred to as the driver, L1, and primary, L2, coils. A second pair of coils is used on the Rx side, which is referred to as the secondary, L3, and load, L4, coils. Conventionally, all of these coils are tuned at the same resonance frequency, f, using capacitors C1-C4 (f=½π(L1-4×C1-4)^0.5). The coils' parasitic resistances are also represented by lumped components, R1-R4. Utilizing the 4-coil method, however, increases the PTE at large d at the cost of a significant reduction in the power delivered to the load (PDL). It has also been demonstrated that a 3-coil inductive power transfer link (FIG. 1C) that uses one coil at the primary, L2, and two coils at the secondary, L3 and L4, all tuned to the same frequency, provides as high PTE as the 4-coil method and also offers a PDL that is significantly higher than both 2- and 4-coil links at large d.
The reason for small PTE at large d is the significant reduction in the magnetic coupling between the coils, M, which is proportional to d−3. One way to compensate for small M is to reduce the loss of the coils. This involves using very high quality-factor (Q) coils, which is the equivalent of reducing the wire conductor losses and loading effects of the source and load resistances. Placing intermediate resonators, which are also called repeaters, between the Tx and Rx coils to receive the magnetic field from Tx and then relay the field to Rx, has shown considerable increase in the magnetic coupling and, therefore, PTE at large d. Such repeaters are also tuned to the same frequency as the Tx and Rx coils. Although such intermediate field repeaters increase the PTE, they reduce the effective distance between the Tx and Rx and their use is limited in most applications such as, for example, IMDs and RFID.
Metamaterials, which are artificial composites with engineered electromagnetic properties to achieve positive or negative effective permittivity and permeability, have recently been used to increase the PTE of the inductive link Metamaterials are fabricated by repeating a 3D resonant element to constitute a periodic structure. Although metamaterials have been studied and have shown significant benefits in many fields, such as microwaves, optics, and acoustics, the design of such 3D structures is quite complicated. Moreover, the metamaterials are suited for short wavelength or high frequency application, whereas the wireless power transfer systems generally utilize low frequencies. Therefore, conventional methods of using metamaterials are generally not feasible.
High-frequency electromagnetic waves have also been considered for wireless power transmission. Although the high-frequency link can offer reliable communication, the received power by the high-frequency antenna is still small (on the order of microwatts) for most aforementioned applications. Furthermore, the significant electromagnetic-field absorption in human tissue increases the losses of the tissue and, therefore, increases the tissue temperature. This can cause safety issues in biomedical implant applications. Moreover, since far field electromagnetic waves attenuate at a rate of 1/d2, there is a high degree of interference with other nearby electronic appliances.
It has also been shown that different resonance frequencies or different distances between Tx, repeater, and Rx coils would result in higher performance. In such a system, the repeater is located close to the Tx coil, which results in a strong coupling between these coils and a lower effective resonance frequency due to frequency splitting. In this configuration, the Tx and repeater can be tuned at a higher frequency to operate the whole link at the same resonance frequency as the driver switching frequency (f) to achieve the maximum voltage gain.
Embodiments of the present disclosure are related to an inductive link comprising two or more resonators on the Tx side as shown in FIG. 2. The additional resonators enhance the magnetic resonance and the overall PTE. Unlike conventional designs, the resonance frequency of the additional resonators can be higher than the operating frequency. By adjusting the resonance frequencies of the additional resonators within the Tx, the degree of magnetic resonance between Tx and Rx coils can be controlled.
The transmitter and repeaters, which can be placed in close proximity to the Tx coil, can effectively be regarded as one transmitter with two or more resonators. The resonance frequencies of the repeaters can also be designed to be higher than the operating frequency of the link. The selected frequency of conventional repeaters, however, was fixed to a specific value which was generally determined by the coupling between the Tx resonators. Because of this, the coupling increase was previously limited to a factor of two. Although doubling the coupling is the limit if the Q-factors of the original Tx coil and the additional coil are the same, in practice, the Q-factors of different coils are usually not the same. The Tx is driven by a power amplifier (PA), for example, which has finite output resistance. The output resistance of power amplifier is connected in series with the Tx coil, and significantly reduces the overall Q-factor of the original Tx coil. In such cases, the degree of resonance enhancement can be further increased. Unfortunately, conventional methods are limited to doubling the degree of coupling.
One attempt to address performance degradation in wireless energy transfer is described in PCT/KR2012/007735 (“the '735 PCT”) filed by Ahn et al (now published as WO2013118954). The '735 PCT adjusts the resonance frequency of the transmitter and the enhancing resonator such that the effective resonance frequency is either the same as the excitation frequency or the receiver resonance frequency. As a result, the level of resonance enhancement is fixed. Embodiments according to the present disclosure address this limitation by allowing the resonance enhancement to be controlled and set to a desired level.
In contrast to the '735 PCT and others, the present disclosure provides a generalized method which can control the degree of resonance enhancement to a desired value. Moreover, a method is provided to achieve improved resonance enhancement to yield the higher efficiency based on the given coils' Q-factors. The resonance frequencies of the additional resonators can be adjusted to control and improve the resonance enhancement.
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