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BACKGROUND AND OBJECTIVE This study aimed to investigate if childhood primary snoring (PS) was associated with adverse cardiovascular outcomes at 5-year follow-up. METHODS This was a prospective matched cohort study. Subjects were recruited from a hospital-based cohort established from years 2006 to 2012 and they were aged 6-18 years at baseline. Each subject with PS was gender, age and BMI z-score matched with a control who had normal sleep study (obstructive apnoea-hypopnoea index [OAHI]

Background and objective We evaluated inattention and behavioural outcomes following surgery versus watchful waiting (WW) in school-aged children with mild obstructive sleep apnoea (OSA). Methods A prospective randomized controlled study was performed in pre-pubertal children aged 6-11 years with polysomnography (PSG)-confirmed mild OSA. They were assigned randomly to early surgical intervention (ES) or WW. The surgical intervention consisting of tonsillectomy with or without adenoidectomy and turbinate reduction was carried out within 4-6 weeks after randomization. Both groups underwent PSG, attention and behavioural assessment and review by an otorhinolaryngologist at baseline and 9-month follow-up. The primary outcome was omission T score from Conners' continuous performance test (CPT). Secondary outcomes were parent-reported behaviours, quality of life, symptoms and PSG parameters. Results A total of 114 participants were randomized. Data of 35 subjects from the ES and 36 from the WW group were available for final analysis. No significant treatment effect could be found in all CPT parameters and behavioural outcomes. Nevertheless, significantly greater reductions were seen in PSG parameters (obstructive apnoea-hypopnoea index [-1.4 ± 2.0 cf. +0.3 ± 4.1/h, p = 0.038] and arousal index [-1.3 ± 4.4 cf. +1.4 ± 4.5/h, p = 0.013]) and OSA-18 total symptom score (-17.3 ± 19.7 cf. -3.6 ± 14.1, p = 0.001) in the ES group. Subjects who underwent surgery also had significantly greater weight gain (+3.3 ± 2.1 cf. +2.2 ± 1.5 kg, p = 0.014) and increase in systolic blood pressure (+5.1 ± 12.4 cf. -1.2 ± 8.7 mm Hg, p = 0.016). Conclusion Despite improvements in PSG parameters and parent-reported symptoms, surgical treatment did not lead to parallel improvements in objective attention measures in school-aged children with mild OSA.

In this article, a novel method to calculate the current distribution, which enables the active sidelobe suppression of the magnetic flux density in an synthesized magnetic field focusing (SMF) system, is proposed for the first time. The proposed method calculates the current distribution, which enables further sidelobe suppression and keeping the resolution at the same time, by changing the target magnetic flux density distribution with only one varying parameter. The proposed calculation method is very intuitive and time-efficient compared with the other calculation methods, as it only changes one variable to control the sidelobe with one step of matrix multiplication. With the finite element method simulation, it is verified that the proposed method can suppress the sidelobe with any target Rx point when the SMF system has 14 coils with size of 10 cm × 10 cm, and the synthesis distance is 30 cm. When the field is synthesized at the center, over 90% of the sidelobe is suppressed for maximum case. An figure-of-merit (FoM) is constructed to optimize the system between the resolution increment and the sidelobe suppression, and 79% of the sidelobe is suppressed for the optimized case while keeping the resolution increment ratio below 30%. In addition, it is verified that the method can also be applied to the two-dimensional (2-D) SMF systems. The experimental results were in good agreement with the simulated results when the experimental prototype of the same condition with simulation was utilized, including a case in which the magnetic field is focused at the Rx point other than the center.

A new conductive-plate-integrated inductive power transfer (IPT) system for automated guided vehicles with little output power variation according to air-gap changes between the transmitter (Tx) and receiver (Rx) is proposed. The inductance change of the ferrite core due to variations in the air gap is nullified by a corresponding change in an aluminum plate. Compared to conventional ferrite IPT systems, self-inductance of the proposed Tx coil is little changed against air-gap variations, which results in robust resonant frequency and output voltage. The self-inductance was experimentally verified to remain within 0.45% even when the air gap changes by fivefold from 10 to 50 mm. The output power variation became a twelfth of that of the conventional ferrite IPT for air-gap variations of 30 ∼ 50 mm, where the efficiency was found to be 96.0% when the output power was 1 kW.

An optimal ampere-turns design for a long-distance dipole-coil-based inductive power transfer (IPT) system for maximum power efficiency is proposed in this article. Assuming that specific requirements, which are the target load power, the physical size of the transmitting (Tx) and receiving (Rx) coils, and the distance between the Tx and Rx coils, are given, quantitative analyses on the optimal ampere-turns of loosely coupled Tx and Rx coils to satisfy the constraints with maximum power efficiency have been conducted in this article. With the proposed design process, the IPT system is expected to be designed and fabricated with minimal cost and time. The maximum experimental error is only 8.8% when the delivery power ranges from 20–200 W in the experiment results, thus demonstrating that the method proposed in this article can suggest a viable design direction of the IPT system.

In this article, a novel structure of a receiving (Rx) coil with only two coils, which enables omnidirectional wireless power transfer (WPT) for any type of transmitting (Tx) system, is proposed for the first time. The coil adopts each coils into plane cross-shaped ferrite core, with each leg of the ferrite core intersecting both coils. The intersecting direction of the ferrite core for one coil is identical to that of the other one when it is rotated 90 degrees. It is verified that voltage will be induced on at least one coil with any direction of magnetic flux. With an analysis of circuit diagram, it is shown that a high quality factor of each coil can guarantee an omnidirectional power transfer even when the coupling coefficient between two coils has a nonzero value. A simulation model and an experimental prototype is built to verify the omnidirectional WPT of the proposed Rx coil structure, with loop-type Tx coil as an example among various Tx types. Omnidirectional power transfer capability of the proposed coil was verified with a light emitting diode (LED) load. The superiority of the proposed coil was verified by comparison with other Rx coil structures also.

In this article, a simple and cost-effective symmetric sensing coil set to be used for the metal object detection (MOD) in a stationary wireless electric vehicle charger is newly proposed. Compared to the conventional nonoverlapping sensing coil using the magnetic field change detection method, the proposed symmetric sensing coil set design offers the considerable advantage of eliminating all blind zones, i.e., regions where metal is undetectable in the conventional method. Moreover, by reducing the number of layers to one, the fabrication of the proposed sensing coil is easier and more cost effective. The design of the proposed sensing coil is optimized for highly sensitive MOD based on a sensitivity equation and on the finite element method simulations. An experiment conducted with a metal object 40 × 40 mm2 in size and a 20 A transmitting (Tx) coil current verifies the reliability and the blind-zone elimination feature of the proposed sensing coil.

In this paper, a novel loop coil structure for synthesized magnetic field focusing (SMF) technology and two current distribution calculating algorithms in the structure are proposed. The proposed structure enables field focusing in two-dimensional (2-D) space for the first time. The loop coil structure with a rectangular formation is adopted for a 2-D SMF system to minimize the volume and weight of the transmitting (Tx) coil array considering that conventional SMF systems inevitably have a volumetric design due to their dipole-based structure. Two algorithms to calculate the current distribution so as to focus the magnetic field at the target point are proposed. The first algorithm applies the Biot–Savart law to a loop-coil-based 2-D SMF system to calculate the distribution. The second algorithm utilizes a time-efficient synthesis method which reduces the matrix dimensions used in current distribution calculation. The second algorithm shows synthesis results with similar synthesis resolution compared with the first algorithm. Although the magnetic field distribution with the second algorithm has a little difference with that of first algorithm, its synthesis result focuses the magnetic field on the target point successfully, and it becomes more powerful as the number of coils increases. Synthesis results using two algorithms were compared with a finite-element method simulation with 100 Tx coils and 25 receiving (Rx) points. The synthesis resolution, as determined by –3 dB points, was enhanced by 4.45 times and 6.15 times for the first and the second algorithm, respectively, when compared to nonfocused case. An experimental prototype with 36 Tx coils and 9 Rx points with each coil 10 × 10 cm in size was built to demonstrate field focusing with current distributions calculated by the second algorithm at a frequency of 145 kHz. The experimental results were in good agreement with the simulated results, including a case in which the magnetic field was focused at Rx point other than center.

In this paper, an autotuning control system (ACS), which utilizes the variation of self-inductance of a transmitter (Tx) coil caused by a ferrite core of a receiver (Rx), is newly proposed for the dynamic wireless electric vehicle (EV) charging. A Tx module consists of only passive elements that include a Tx coil, a partially compensated capacitor in series with the Tx coil, and a parallel compensation capacitor. All Tx modules share an ac bus line that passes the output filter of an inverter in parallel without any active switches. The current of the coupled Tx coil increases automatically without any manipulations such as controlling the power switches, sensing, or communication when the Rx module is approaching. Not only the system efficiency is increased by the reduction of the conduction losses from the uncoupled Tx modules, but control also becomes simpler because sensors are not required for detecting EVs, and the constant output voltage characteristics can be obtained. Through experiments, it was found that the proposed ACS is suitable for applications such as a tram that runs along an orbit with a small air gap, such as a train. The results showed that the current of a coupled Tx coil increased 11.6 times larger than that of an uncoupled Tx coil, at which time the dc–dc efficiency achieved was 88.4% for an output power of 766 W (10 Ω of load resistance) at the laboratory scale.

New coreless transmitting (Tx) coils with a conductive material plate for wide-range ubiquitous inductive power transfer (IPT) zones, i.e., U-IPT zones, where electric devices can be wirelessly charged during operation, are proposed in this paper. Because commercialized IPT systems are only available for short distances of several centimeters and one-to-one charging, the demand is increasing for U-IPT zones in which long-distance wireless charging with three-dimensional (3-D) free-positioning and simultaneous charging of multiple receiving (Rx) coils can be achieved. To satisfy this demand, U-IPT zones should be constructed to have a uniform magnetic field distribution in a wide space, which also poses no risk to the human body. In addition, to generate a uniform magnetic field in a wide 3-D space, such as a single room, the system requires the installation of many Tx coils above the ceilings and behind the walls of the room, and these coils should be capable of high electrical performance to support the efficiency of the entire IPT system and should be of excellent mechanical quality. Therefore, a U-IPT zone should meet the following four criteria: human safety, free-positioning of Rx coils, magnetic field uniformity, and economization. By virtue of a conductive material plate that cancels out the undesired direction of magnetic flux generated from the return wires, the proposed coreless Tx coil does not need any heavy ferromagnetic cores, which can cause nonuniformity of the magnetic field distribution and difficult construction. A prototype coreless Tx coil with the dimensions of 1 m × 1 m × 10 cm was fabricated and experimentally verified for a 1 m × 1 m U-IPT zone. The experimental results showed that 74%, 83%, and 76% high magnetic field uniformity could be achieved for $z_{1}= {{25}}$ cm, 50 cm, and 75 cm, respectively, and a 3-D omnidirectional wireless power delivery was achieved, while the guideline of the International Commission on Non-Ionizing Radiation Protection for human safety was satisfied throughout the entire U-IPT zone. Moreover, the weight of the entire system was only 9 kg, enabling easy installation. In the multiple wireless charging experiments, 47 W of power was consumed in total by load resistors, each of them connected to nine Rx coils, respectively, with 32% power efficiency at $z_{1}= {{20}}$ cm.

In this paper, a metal object detection (MOD) system, a kind of foreign object detection (FOD), which is based on mistuned resonant circuits and utilizes the variation of self-inductance of a sensing pattern, is newly proposed for wireless electric vehicle (EV) chargers. The sensing pattern that consists of multiple loop coil sets is mounted on the transmitting (Tx) pad of an EV charger, where a loop coil set has two coils connected in series with the opposite polarity to cancel out the induced voltage generated by the Tx coil. Variation of self-inductance of the loop coil set is detected by a parallel-resonant circuit, driven by a current source and operating at near 1 MHz, in order to enhance the resolution of the proposed MOD system. To increase the detection sensitivity of the proposed MOD system, instead of an exact resonant frequency, a mistuned operating frequency near the –3 dB point is utilized for the parallel-resonant circuit. In this way, the proposed MOD system can detect very small metal objects regardless of their position and orientation on the Tx coil without any blind zone. Through simulations and experiments, it is found that the proposed MOD system detects not only horizontal but also standing upright metal objects. A prototype MOD system, operating at 85 kHz to satisfy the standard J2954, was fabricated to verify its feasibility. The results showed that output voltage change of the proposed MOD system becomes 22.7% for a piece of the aluminum foil of 3 × 3 cm2 and 40.9% for 100 Korean Won coin.

A wide-range ubiquitous wireless power environment, called a ubiquitous Wi-power zone, where any electric devices can be charged by three-dimensional (3-D)-omnidirectional wireless charging, is newly proposed in this paper. By virtue of the proposed direct-quadrature (DQ) transmitting (Tx) coils composed of multiple Tx modules with same size, a ubiquitous Wi-power zone having the transmitting (Tx) coils can be provided over wide-range 3-D space. In this area, a number of electric devices can be simultaneously charged during operation. Therefore, the proposed IPT is expected to be the next generation of wireless power transfer (WPT), as the internet of things (IoT), mobile devices, and sensor technologies evolve. For magnetic shielding behind the Tx coils and high power efficient operation of the proposed DQ Tx coils, providing an evenly distributed magnetic field, a conductive plate is adopted, and the effects of the conductive plate for the dipole coil structure were thoroughly evaluated by a 3-D FEM simulation. To create the proposed ubiquitous Wi-power zone, simulation-based optimum design procedures are established based on four design considerations and the optimized number of modularizations for the DQ Tx coils can be found by an optimum point of figure of merit (FoM). The DQ Tx module composed of the DQ Tx coils and series resonant capacitors was adopted as a standard unit of the proposed IPT so that different sizes and shapes of 3-D space can be utilized for universal use of the proposed ubiquitous IPT; hence, a general solution to create the proposed ubiquitous IPT is provided in this paper. A prototype 5 × 5 modularized IPT composed of 25 DQ Tx modules having the same size of ${\text{10 cm}} \times {\text{10 cm}}\times {\text{2 cm}}$ was fabricated and experimentally verified for a ${\text{1 m}}\times {\text{1 m}}\times {\text{0.7 m}}$ ubiquitous Wi-power zone. Experimental results showed that 95.5%, 92.1%, and 98.8% of high magnetic field uniformity for $z_{1}= {\text{25}}$ cm, 50 cm, and 75 cm, respectively, and 3-D omnidirectional wireless power delivery have been achieved; thus, meeting essential requirements for the proposed ubiquitous Wi-power zone. Nine Rx coils can be simultaneously charged with 14.2 W of total received load power and 8.2% power efficiency at $z_{1}= {\text{70}}$ cm.

For commercialization of wireless stationary electric vehicles (EV) chargers, metal object detection (MOD) on a power supply coil and detection of position (DoP) of EVs are needed. In this paper, dual-purpose nonoverlapping coil sets for both MOD and DoP, which detect a variation of magnetic flux on the power supply coil, are newly proposed, where the proposed MOD and DoP methods make no contribution to any power losses. The existence of metal objects on the power supply coil is determined by an induced voltage difference of the nonoverlapping coil sets, whereas the position of the EV is determined by an induced voltage of the nonoverlapping coil sets. A sensing circuit, which has a variable resistor that is different from the conventional overlapping coil for MOD, can make the induced voltage difference zero even when the magnetic flux distribution is distorted by moving the pick-up coil. The proposed nonoverlapping coil sets with the sensing circuit have been demonstrated by simulations and experiments. When metallic coins and aluminum sheets are located on the power supply coil, the induced voltage difference of the coil sets, which is ideally zero without metal objects, significantly increases to 62.8 and 450 mV, respectively, which is more than ten times the value without metal objects throughout experiments. In addition, when the pick-up coil approaches the power supply coil, induced voltage of each coil set increased roughly 1.6 times at 10 cm air gap.

In this paper, a sliding EE transformer (SEET) rail, which has a strong and independent magnetic coupling to the gap variation between the transmitter (Tx) line and receiver (Rx) coil for powering the sliding door, is newly proposed. In the SEET rail, the Tx line and the Rx coil share a single EE ferrite core, while the winding window of the ferrite core is considered as the gap variation. In the proposed structure, the magnetic coupling can be maintained as strong and constant even though the ferrite core moves along the door rail when the sliding door is closed or opened. Through detailed coil designs based on electric and magnetic circuit analyses, design constraints on voltage, output power, flux density, and zero voltage switching are proposed with a closed-form solution of output voltage and theoretical maximum output power. The SEET rail is successfully designed to provide a maximum load power of 200 W for the sliding door within an ambient temperature range from −40 to 125 °C by following design constraints. Moreover, optimal design parameters such as number of turns, air-gap, and ferrite thickness are provided, which maximize power transfer efficiency of the SEET rail while maintaining its performance in the temperature range. The proof-of-concept prototype shows a strong magnetic coupling, κ = 0.76 at 20 °C and the variation of the magnetizing inductance with respect to the temperature variation was measured as 13.8%. The maximum power transfer efficiency excluding the regulator at a nominal load power of 100 W was 85%, and the efficiency at the maximum load power of 200 W was measured as 82% with a 3%P variation by the temperature variation.