Lateral Misalignment Research Articles

Design and Performance Analysis of Misalignment Tolerant Charging Coils for Wireless Electric Vehicle Charging Systems

In order to design a high efficiency Wireless Electric Vehicle Charging (WEVC) system, the design of the different system components needs to be optimized, particularly the design of a high-coupling, misalignment-tolerant inductive link (IL), comprising primary and secondary charging coils. Different coil geometries can be utilized for the primary and the secondary sides, each with a set of advantages and drawbacks in terms of weight, cost, coupling at perfect alignment and coupling at lateral misalignments. In this work, a Finite Element Method (FEM)-based systematic approach for the design of double-D (DD) charging coils is presented in detail. In particular, this paper studies the effect of different coil parameters, namely the number of turns and the turn-to-turn spacing, on the coupling performance of the IL at perfect alignment and at ±200 mm lateral misalignment, given a set of space constraints. The proposed design is verified by an experimental prototype to validate the accuracy of the FEM model and the simulation results. Accordingly, FEM simulations are utilized to compare the performance of rectangular, DD and DDQ coils. The FEM results prove the importance of utilizing an additional quadrature coil on the secondary side, despite the added weight and cost, to further improve the misalignment tolerance of the proposed inductive link design.

Dental cross-bite: The paradigm of interception in orthodontics

Crossbite is a form of malocclusion in which a tooth (or teeth) in the upper or lower dental arch is more buccal or lingual (that is, closer to the cheek or tongue) than its corresponding antagonist tooth. Crossbite, to put it another way, is a lateral misalignment of the dental arches. Crossbite should be corrected as soon as a child's cooperation is obtained. Early treatment may prevent or slow the progression of abnormal alveolar processes and jaws.

TSV Based Orthogonal Coils With High Misalignment Tolerance for Inductive Power Transfer in Biomedical Implants

To improve the misalignment tolerance for inductive power transfer (IPT) systems in implantable medical devices, like retinal prosthesis, a 3-D through silicon via (TSV) based orthogonal receiving coil is proposed in this brief. The mutual inductance between the receiving coil and the transmitting coil is calculated, analyzed, and compared. Results obtained from the analytical model and finite element method show the proposed coil structure significantly enhances the inductive coupling between coils under misalignment. Furthermore, we present receiving circuits with current summing techniques to enhance the energy transfer between the receiving coil to the load. The prototype of the inductive power transfer system is developed and the experimental results demonstrate that the proposed coil structure can provide a good misalignment tolerance. A maximum variation of the power transfer efficiency (PTE) is only 18.0% under angular misalignment of 90° and 23.4% under lateral misalignment of 37.5% of the transmitting coil's diameter, which indicates the proposed coil structure can meet the demand of IPT systems in retinal prosthesis applications.

Lateral stability of CWR tracks in transition zones of open-deck steel bridges

Relative displacements are introduced between steel bridges and continuously welded rail (CWR) tracks as the bridge girders expand and contract due to thermal effects. Depending on the fastening profile between the CWRs and steel bridge girders, additional forces are transmitted between the two, and when rail compression forces are introduced at the transition zones of the bridge, the risk of track buckling increases. The aim of this paper is to study CWR track buckling in the transition zones of open-deck steel bridges. In order to do so, a finite element model of a bridge is developed and calibrated based on the available literature. The model is then used to study the effects of a number of fastening profiles between the CWRs and steel bridge girders on track buckling in transition zone of the bridge. It is shown that girder temperature and location of lateral misalignment are the primary factors affecting the buckling temperature in the transition zone. Increasing the girder temperature by 45 °C can cause a drop of 11.5 °C in the track buckling temperature, a reduction of almost 19% compared to that of the open track. Furthermore, using zero toe load fasteners can reduce the risk of track buckling in the transition zone, yet there is little to resist the increasing gap size in case of a broken rail in winter.

The Influence of Local Tapes Misalignment in Stacked YBCO Cable on Its AC Loss

When calculating the AC loss of REBa2Cu3O7−x (REBCO, RE = rare earth) coated conductor cable with stacked geometry, it is often considered that the tapes in the cable is perfectly stacked (there is no transverse misalignment of the tapes). However, the actual stacked cable will have transverse misalignment. The influence of transverse misalignment of tapes on the AC loss of the whole cable needs to be studied in order to understand the actual situation. In this paper, the 2-D H formulation calculated the AC loss of the cable with 10 tapes stacked in three cases. In the first case, the cables are perfectly stacked without lateral misalignment between the tapes. In the second case, the tapes of the cable are oblique to one side. In the third case, the tapes are disordered with each other. The result shows that under the transport current at 50 Hz, when the transport current is less than 0.75Ic0, the transport loss of the cable with obliquely stacked cable is more than the perfectly stacked cable, and when the transport current is greater than 0.75Ic0, the transport loss of the perfectly stacked cable is slightly larger than the obliquely stacked cable. Moreover, the transport loss of disorderly stacked cable is more than perfectly stacked cable at 50 Hz. When the transport current amplitude and the misalignment distance between the tapes in the cable are constant, the transport loss of obliquely stacked cable and disorderly stacked cable relative to perfectly stacked cable both increases first and then decreases as the frequency increases. Under the 50 Hz magnetization field, the magnetization loss of the perfectly stacked cable is less than the cables with oblique misalignment and disorder misalignment. When the amplitude of the external magnetic field and the misalignment distance between the tapes in the cable are constant, the magnetization loss of obliquely stacked cable and disorderly stacked cable relative to perfectly stacked cable also increased first and then decreased as the frequency increased.

Cancellation Conditions of Magnetic Field Leakage From Inductive Power Transfer Systems

In inductive power transfer systems, a transmitter array can maintain high power transfer efficiency (PTE), despite lateral misalignment between the transmitter and receiver. However, a control method for reducing magnetic field leakage in this situation has not been found. Therefore, a novel theory of controlling the transmitter array is necessary for electromagnetic compatibility and user safety. In this study, we optimize the input currents at the transmitter array and the load impedance at the receiver to maximize PTE under the cancellation condition of the magnetic field leakage. Simulations show that the proposed method reduces magnetic field leakage by more than 10 and 38 dB, with and without ferrite plates, respectively, compared with existing PTE maximization methods, even when there is a lateral misalignment between the transmitter and receiver. Additionally, experiments using coils having ferrite plates show that the proposed method reduces magnetic field leakage by more than 6.75 dB. The decrease in PTE is within 4.17 %, which compares favorably with existing methods.

Deep Contrast and Companion Detection Using the EvWaCo Test Bed Equipped with an Achromatic Focal Plane Mask and an Adjustable Inner Working Angle

Abstract The evanescent wave coronagraph uses the principle of frustrated total internal reflection (FTIR) to suppress the light coming from the star and study its close environment. Its focal plane mask is composed of a lens and a prism placed in contact with each other to produce the coronagraphic effect. In this paper, we present the experimental results obtained using an upgraded focal plane mask of the Evanescent Wave Coronagraph (EvWaCo). These experimental results are also compared to the theoretical performance of the coronagraph obtained through simulations. Experimentally, we reach a raw contrast equal to a few 10−4 at a distance equal to 3 λ/D over the full I band (λ c = 800 nm, Δλ/λ ≈ 20%) and equal to 4 λ/D over the full R band (λ c = 650 nm, Δλ/λ ≈ 23%) in unpolarized light. However, our simulations show a raw contrast close to 10−4 over the full I band and R band at the same distance, thus confirming the theoretical achromatic advantage of the coronagraph. We also verify the stability of the mask through a series of contrast measurements over a period of 8 months. Furthermore, we measure the sensitivity of the coronagraph to the lateral and longitudinal misalignment of the focal plane mask and to the lateral misalignment of the Lyot stop.

Exciter–Quadrature–Repeater Transmitter for Wireless Electric Vehicle Charging With High Lateral Misalignment Tolerance and Low EMF Emission

In this article, an exciter–quadrature–repeater transmitter pad is proposed in order to achieve high lateral misalignment tolerance and low leakage flux emission in electric vehicle wireless charging applications. In the proposed WPT system, a single half-bridge inverter unit is needed to energize the exciter coil, which is magnetically coupled to two larger quadrature repeater coils. The currents in the two repeater coils naturally adjust based on the lateral misalignment of the receiver pad to reduce the leakage flux density around the charging zone. The system can maintain zero phase shift between excitation voltage and current and achieve constant current charging conditions with fixed compensation capacitors in the ±150-mm lateral misalignment range. In order to verify the attributes of the proposed wireless power transfer (WPT) system, a 3-kW experiment setup with a 200-mm vertical gap was built and compared to a three-coil WPT system, which consists of a small transmitter coil, a single large repeater coil, and a receiver coil. According to the experiment results, even under extreme 150-mm lateral misalignment, the proposed WPT system has 90.7% coil-to-coil transmission efficiency. Furthermore, it achieves a 30% reduction of leakage flux density compared to the three-coil system in the 150-mm lateral misalignment case.

An Analytical Framework to Design Planar Transmitting Array Antennas to Mitigate Lateral Misalignment in Wireless Power Transfer Systems

This article presents a unique mathematical analysis of the magnetic field ( H-field) forming using coil antennas to mitigate the lateral misalignment problem in the wireless power transfer (WPT) system. The state of the art emphasizes generating uniform H-field distribution as a solution to the stated problem and for that large-sized transmitters (Txs) are designed to enhance receiver (Rx) working region. In this article, by optimizing the field forming technique based on derived closed-form analytical expressions, a general nonuniform H-field distribution is proposed as an optimal solution to the misalignment problem. Through rigorous analysis, this work proposes a stepwise procedure for designing the Tx coil array antenna to generate the nonuniform H-field distribution. To validate the model, two planar antenna arrays are designed by following the proposed procedure. This results in a uniform induced voltage profile under the misaligned Rx condition and, hence, resolves the problem. The antenna designs are simulated, fabricated, and measured. The analytical results are found in agreement with the simulated results and further verified experimentally. The results indicate that the antennas designed using the proposed method are able to mitigate the lateral misalignment problem in a wider area of the Rx region with a smaller Tx size.

Compensation for Lateral Misalignment in Litz Wire Based on Multilayer Coil Technology.

This study applies a multilayer coil technology that can compensate for a decrease in transfer efficiency due to a lateral misalignment in a practical 100 kHz-band wireless power transfer system and validates its effect on the efficiency of compensation. The effectiveness is investigated using coils fabricated with Litz wires. Three-turn rectangular assistant coils 22.4 × 45.3 mm2 in size were stacked on a five-turn circular primary coil with a diameter of 45.3 mm in a 2 × 1 array. Transfer efficiency between two such coils was measured by producing lateral misalignment, while maintaining the vertical distance between the Tx and Rx coils at 7 mm. The experimental results showed that the transfer efficiency was compensated by approximately 46.1%P maximum in a misalignment state of 30 mm, which corresponded to 67% of the maximum size of the coil, compared to the transfer efficiency of the structure, in which the multilayer coil was not applied. Furthermore, transfer efficiency was compensated by 37.6%P, even in an asymmetric system in which the multilayer structure was applied only to the Tx coil, thereby confirming an excellent multilayer coil technology effect on compensation for lateral misalignment in practical cases.

Monolithic integration of microlenses on the backside of a silicon photonics chip for expanded beam coupling.

To increase the manufacturing throughput and lower the cost of silicon photonics packaging, an alignment tolerant approach is required to simplify the process of fiber-to-chip coupling. Here, we demonstrate an alignment-tolerant expanded beam backside coupling interface (in the O-band) for silicon photonics by monolithically integrating microlenses on the backside of the chip. After expanding the diffracted optical beam from a TE-mode grating through the bulk silicon substrate, the beam is collimated with the aid of microlenses resulting in an increased coupling tolerance to lateral and longitudinal misalignment. With an expanded beam diameter of 32 μm, a ±7 μm lateral and a ±0.6° angular fiber-to-microlens 1-dB alignment tolerance is demonstrated at the wavelength of 1310 nm. Also, a large 300 μm longitudinal alignment tolerance with a 0.2 dB drop in coupling efficiency is obtained when the collimated beam from the microlens is coupled into a thermally expanded core single-mode fiber.

Design of a High Power, LCC-Compensated, Dynamic, Wireless Electric Vehicle Charging System with Improved Misalignment Tolerance

Dynamic wireless power transfer (DWPT) systems are becoming increasingly important for on-the-move electric vehicle (EV) charging solutions, to overcome range anxiety and compensate for the consumed energy while the EV is in motion. In this work, a DWPT EV charging system is proposed to be implemented on a straight road stretch such that it provides the moving EV with energy at a rate of 308 Wh/km. This rate is expected to compensate for the vehicle’s average energy consumption and allow for additional energy storage in the EV battery. The proposed charging system operates at an average power transfer efficiency that is higher than 90% and provides good lateral misalignment tolerance up to ±200 mm. Details of the proposed system’s design are presented in this paper, including EV specifications, inductive link and compensation network design and power electronic circuitry.

Dynamic Wireless Power Transfer System With an Extensible Charging Area Suitable for Moving Objects

Extensible magnetic resonance coupling-based wireless power transfer (WPT) systems are presented in this article. A transmitter (Tx) containing an 8-shape loop and two resonators is proposed to construct a bipolar Tx array. A unipolar receiver (Rx) is placed above the Tx perpendicularly to overcome the power null phenomenon. The proposed structure ensures that magnetic flux lines are confined in the vicinity of the Rx, leading to a high power transfer efficiency (PTE) over a wide range of lateral misalignment distances. Experiments demonstrated that the proposed WPT system can achieve an efficiency of 87% under perfectly aligned operating conditions, and maintain over 70% efficiency from 0 to 30 mm lateral misalignment distances. Based on the proposed Tx module, a single-feed Tx array is constructed to further increase the charging area. The PTE of a $1 \times 2$ array system is between 57.5% and 71.6% without the power null phenomenon. Meanwhile, the concern of heating due to magnetic field leakage can be significantly mitigated. These designs are proved to be very good candidates for dynamic WPT (DWPT) applications.

Field orientation based three‐coil decoupled wireless transmitter for electric vehicle charging with large lateral receiver misalignment tolerance

A three-coil decoupled transmitter is developed for the inductive power transfer system of electric vehicle charging. The three-coil decoupled transmitter consists of three overlapping rectangular coils with magnetic mutual decoupling and is capable of overcoming large receiver lateral misalignment up to 20 cm. A current optimization method is advanced to derive transmitter coil currents for the multi-phase system that minimizes the coil loss through optimizing the current distribution among transmitter coils. The optimized current distribution reduces the maximum leakage flux by around 40% compared to the best alternative excitation method. The compensation strategy provides unity power factor for high-power transfer phases and allows a single set of compensation capacitors to be used regardless of receiver alignment. The three-coil decoupled transmitter is compatible with a typical three-phase inverter for industrial practical application, which halves the power electronic switches used with previous topologies. The simulation verification is performed at 3.3 kW, achieving 93.76% efficiency at perfect alignment and 92.54% efficiency at 20 cm misalignment. The experimental verification is implemented at 3.3 kW with 200 mm ground clearance, realizing a 92.97% efficiency at perfect alignment and 90.57% efficiency at 20 cm misalignment.

Influences of ballast degradation on railway track buckling

Presently, railway track buckling, caused by extreme heat, is a serious issue that causes a huge loss of assets in railway systems. The increase in rail temperature can induce a compression force in the continuous welded rail (CWR) and this may cause track buckling when the compression force reaches the buckling strength. It is important to ensure the lateral stability of railway track in order to tackle the extreme temperature. However, in fact, railway track can be progressively degraded over time resulting in poorer track stability. This includes the larger lateral track misalignment and component deteriorations. This unprecedented study highlights 3D Finite Element Modelling (FEM) of ballasted railway tracks subjected to temperature change considering different ballast fouling conditions. The buckling analysis of ballasted railway tracks considering ballast fouling conditions has been investigated previously. This paper adopts the lateral resistance obtained from the previous single sleeper (tie) push test simulations to the lateral spring model. The influences of the boundary conditions and rail misalignment on the buckling temperature are also investigated. The results clearly show that the ballast fouling may increase the likelihood of track buckling even if the fouled ballast is accumulated at the bottom of the ballast layer. More importantly, the allowable temperature can be reduced up to 50% when the ballast is completely fouled. The results can be used to predict the buckling temperature and to inspect the conditions of ballast. The new findings highlight the buckling phenomena of interspersed railway tracks and help improve the inspection regime of ballast conditions especially in summer to encounter the extreme heat.

A Novel Misalignment Tolerant Magnetic Coupler for Electric Vehicle Wireless Charging

The lateral misalignment for static electric vehicle (EV) wireless charging could be much larger than 100 mm if the parking assistance systems are unavailable. This article proposes a split flat solenoid coupler (SFSC) to significantly extend the lateral misalignment and reduce the copper and ferrite usage. To obtain a good balance among coupling, misalignment tolerance, and cost, an optimization method for SFSC is proposed where the size limitations and ferrite tile specifications are considered. The optimized SFSC is compared with two magnetic couplers recommended in SAE J2954 in terms of coupling coefficient and misalignment tolerance. To eliminate the impact of coil size and make the comparison fair, the quantified misalignment tolerance is introduced. The proposed SFSC provides much better misalignment tolerance than the recommended couplers. A 1000-W prototype is built to show the advantages of the proposed coupler. The output current keeps unchanged when the lateral misalignment is as high as 400 mm. A highest power transfer efficiency, from dc input to dc output, of 89.12% is achieved when the output power is 1000 W.

Effect of Misaligned Relay on Output Power and Efficiency in Wireless Power Transfer

In magnetic resonance-based wireless power transfer (WPT), any misalignment between resonators degrades the strength of the magnetic coupling, and the use of a relay does not always improve performance if it is misaligned with a transmitter or a receiver. It is therefore necessary to determine the proper activation of a relay depending on the degree of misalignment. In this paper, we analyze the effect of a misaligned relay on two important performance metrics in WPT, namely output power and efficiency. In particular, we derive the achievable output power and efficiency with optimal load resistance based on an equivalent circuit model, and determine whether it is beneficial to utilize the relay for a given lateral and angular misalignment. By simulation and experimental verifications under various environments, we validate the exactness of our analysis, and we also confirm two interesting observations, namely 1) with regard to performance improvement in terms of output power and efficiency, it is better to deactivate the relay if it is seriously misaligned with the other resonators and 2) output power is more vulnerable to the misalignment of a relay than efficiency.

Stacked-Coil Technology for Compensation of Lateral Misalignment in Nonradiative Wireless Power Transfer Systems

A stacked-coil technology is demonstrated that realizes size-adjustable coil systems to compensate the notorious problem of lateral misalignment in nonradiative wireless power transfer (WPT) systems. The proposed system has a simple structure that consists of multiple layers of coils with various sizes. Depending on the misalignment, the coil pair that provides the best transfer efficiency is switched on. Thus, not only the transfer null is removed, but also a very high transfer efficiency is maintained even with extreme misalignment. Experimental results at 6.78 MHz show the effectiveness of the stacked coil for both short- and mid-range wireless power transfer systems. The transfer efficiency maintains abovementioned 80% up to 87% and 65% lateral misalignment when the separation between Tx and Rx coils are 10% and 50%, respectively, relative to the largest dimension of the coil. The three-layer short-range system successfully removes the transfer null to maintain a minimum transfer efficiency of 39.7% up to 126% misalignment. The two-layer mid-range system maintains transfer efficiency abovementioned 50% up to 103% misalignment. Furthermore, the performance is virtually the same even in an asymmetric WPT system, i.e., when the technique is applied to only one of the two coils. A detailed design procedure is also provided.

Fabrication-Tolerant and Low-Loss Hybrid Plasmonic Slot Waveguide Mode Converter

Integrated plasmonic structures can concentrate light to deep-subwavelength volumes below the diffraction limit and have been explored in many applications including label-free nanophotonic sensing with single molecule sensitivity, nonlinear conversion, and lasing. However, conversion between the dielectric waveguide mode and the plasmonic mode typically suffers from large mode conversion loss and requires high nanofabrication precision because of the mode mismatch and the precise alignment requirements with the plasmonic slot structure, respectively. Here, we report low-loss conversion between a dielectric waveguide mode and a hybrid plasmonic slot waveguide mode in a structure with a large fabrication tolerance. The measured conversion loss between the dielectric waveguide mode to the hybrid plasmonic slot waveguide mode can be <; 2 dB in the wavelength range of 1.54-1.60 μm under the optimal phase match condition. The loss remains low with a lateral misalignment tolerance of >500 nm. We confirmed enhanced light-matter interaction in the plasmonic slot waveguide region by measuring the enhancement in optical absorption of graphene with and without the plasmonic slot structure. Our results demonstrate a new approach to achieve deep-subwavelength light concentration by using an easy-to-fabricate interface with dielectric waveguides.

Analysis, Design, and Implementation of a Spatially Nested Magnetic Integration Method for Inductive Power Transfer Systems

Inductive power transfer (IPT) technology uses large resonant inductors as compensation components. In this article, a spatially nested magnetic integration method is proposed to integrate discrete inductors into an IPT transformer structure. Unipolar transformer coils are employed and are decoupled orthogonally from a nested solenoidal inductance coil for various misalignment cases. The variations of the coupling coefficients and the magnetic flux density distribution are presented with the three-dimensional finite-element modeling tool. An LCC series compensation circuit is selected to implement the proposed method with an optimal efficiency design. A 4-kW prototype with a 160 mm airgap is implemented to demonstrate the validity of the proposed method. The experimental results show that the compact structure retains the outstanding performance and avoids significant cross coupling for lateral, vertical, and axial misalignment. The maximum conversion efficiency of the proposed system is 96.7% at full output power and stays above 91.6% throughout the misalignment range.