United States

Various industrial applications have put forward higher demands for wireless power transfer systems (WPT) [1]. Using one transmitter to simultaneously power multiple appliances with different electrical requirements is a promising system with the advantages of simplicity and good efficiency [1-2]. One of the key issues of multifrequency transmission is the power adaption and power flow control [3-5]. Most of the traditional work uses the modulation method to solve this problem. However, the signal tracking process can be difficult and complex and will inevitably cause more power losses [2], especially for high operation frequencies.&lt;br/&gt;This paper presents a new design scheme to realize the power adaption for multiple receivers. The system can realize a demand-customized output power by adjusting the current harmonics. The system uses only one simple full-bridge inverter, and the redundant modulation process can be cut away. As shown in Fig. 1, the proposed compensation circuit uses a T-type topology. Each branch of the circuit is made of a dual-band component. Based on superposition method, the output voltage of the inverter can be regarded as the combination of the first and third harmonics. Under each operation frequency, the three dual-band components can behave different equivalent impedances and the compensation circuit can thus be regarded as two individual LCC compensation for the accordant frequencies, which guarantees that the system can always operate at zero impedance angle and with adjustable output current harmonics. The simulated operating waveforms of the proposed system are shown in Fig. 2. For two identical resistive loads, the accordant receivers are designed to be resonant at 100 kHz and 300 kHz, respectively. The first and third harmonics of the input current are thus designed to be 3:1 for equivalent output. It can be observed that the compensation circuit successfully controls the output current to the desired values with the inherent harmonics of the input voltage. This work was supported by HK RGC (project no. T23-701/20-R).

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Power Adaption Design for Multifrequency Wireless Power Transfer System

2022 Joint MMM-INTERMAG

Power Adaption Design for Multifrequency Wireless Power Transfer System

The 15th Joint MMM-INTERMAG Conference (2022 Joint) is sponsored jointly by AIP Publishing and the IEEE Magnetics Society. Members of the international scientific and engineering communities interested in recent developments in fundamental and applied magnetism are invited to attend and contribute to the technical sessions. The technical program will include invited and contributed papers in oral and poster sessions, invited symposia, a plenary session, and an evening session, with about 1500 presentations overall. This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

The 2022 Joint Conference will offer both in-person and prerecorded on-demand content.

For tickets to the event, please register at the following link: https://magnetism.org/register

Please register for the Joint MMM-Intermag conference to join the event.

This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

Various industrial applications have put forward higher demands for wireless power transfer systems (WPT) [1]. Using one transmitter to simultaneously power multiple appliances with different electrical requirements is a promising system with the advantages of simplicity and good efficiency [1-2]. One of the key issues of multifrequency transmission is the power adaption and power flow control [3-5]. Most of the traditional work uses the modulation method to solve this problem. However, the signal tracking process can be difficult and complex and will inevitably cause more power losses [2], especially for high operation frequencies. This paper presents a new design scheme to realize the power adaption for multiple receivers. The system can realize a demand-customized output power by adjusting the current harmonics. The system uses only one simple full-bridge inverter, and the redundant modulation process can be cut away. As shown in Fig. 1, the proposed compensation circuit uses a T-type topology. Each branch of the circuit is made of a dual-band component. Based on superposition method, the output voltage of the inverter can be regarded as the combination of the first and third harmonics. Under each operation frequency, the three dual-band components can behave different equivalent impedances and the compensation circuit can thus be regarded as two individual LCC compensation for the accordant frequencies, which guarantees that the system can always operate at zero impedance angle and with adjustable output current harmonics. The simulated operating waveforms of the proposed system are shown in Fig. 2. For two identical resistive loads, the accordant receivers are designed to be resonant at 100 kHz and 300 kHz, respectively. The first and third harmonics of the input current are thus designed to be 3:1 for equivalent output. It can be observed that the compensation circuit successfully controls the output current to the desired values with the inherent harmonics of the input voltage. This work was supported by HK RGC (project no. T23-701/20-R).

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![](https://assets.underline.io/uploads/markdown_image/1/image/ed03e0bec700845dcc35f1a3aeb7487a.jpg)

Power Adaption Design for Multifrequency Wireless Power Transfer System

poster

Recently, it was discovered that without any external magnetic field, only by a single laser pulse, selective and reversible photo-magnetic switching in Co-doped yttrium iron garnet films (YIG:Co) can be obtained. This recording was characterized by an extremely short switching time of about 20 ps at room temperature. Moreover, because of its resonant character the write–read events are accompanied by an unprecedentedly low heat load [1]. Microscopically, in this mechanism incident linearly polarized pump pulse excites strongly anisotropic garnet ions, generating an effective field of photo-induced magnetic anisotropy [2],[3]. Here, we demonstrate the tunability of both magnetocrystalline and photo-induced anisotropies by the engineering of Co-doped thin iron garnet films and temperature variation. All experimental results were obtained using the time-resolved two-color pump and probe setup at Faraday geometry. The setup was tailored to perform the time-resolved femtosecond single-shot imaging on a CCD camera assuring obtain high temporal and spatial sensitivity. Through modifying the pump light fluence we were able to introduce a change in the light-induced anisotropy field. It allowed us to observe the change of switching times of magnetization and decrease it even more by two times but at the expense of the greater energy required to achieve the switching threshold using a single pump laser pulse. On the other hand, by steering the sample temperatures in the 100-450 K, the range we triggered a change in the magnetocrystalline anisotropy field. Increasing it allowed us to decrease the energy dissipation threshold required for switching over five times. However, decreasing the switching threshold comes at the expense of a longer switching time. Moreover, we demonstrate that the photo-magnetic recording-based garnet medium operates within an extremely large temperature range between -100°C to 100°C. This finding reveals the principles to be employed in achieving cold and ultrafast magnetic recording in dielectrics far beyond today’s state-of-the-art.

Control of switching time and energy dissipation for ultrafast photo-magnetic recording in dielectrics

A magnetic field sensor using magnetoimpedance (MI) has a higher sensitivity [1] and MI properties strongly depend on a magnetic anisotropy of a material [2]. Thus, controlling anisotropy is quite important to obtain large impedance changes. In general, an anisotropy can be controlled by a field annealing in vacuum using a furnace. The furnace is a large-scale, and consumes a lot electric power for heating and generating strong field. On the other hand, Joule-heating, a current is directly applied to an element, is a simple way and therefore achieves a compact equipment with a low power consumption. However, there are few reports that Joule-heating applies to ferromagnetic thin-film [3] and no reports that studies controlling anisotropy itself by Joule-heating. Thus, we investigated to controlling magnetoimpedance properties by Joule-heating on a thin-film element as a feasibility study. The amorphous CoNbZr thin-film element with Cu electrode was prepared. Then, a direct DC current of 80-120 mA was applied to the elements using a wafer probe with 1 minute in the atmosphere. In some cases, the element was applied to an external field parallel to the width direction of the elements by magnets during heating. Fig. 1 shows the field dependence of impedance at 100 MHz. Before heating, impedance has maximum at zero field and then decrease with increasing field intensity, which is typical profile when an element has the easy axis along with the longitudinal direction of the element. On the other hand, a double peak appears and its peak height slightly increases with increasing intensity of DC current after Joule-heating with magnets. The field intensity where the impedance has a peak, shifts to higher field with increasing intensity of DC current. Fig. 2 shows the domain structures of the element observed by a Kerr-effect microscopy before and after Joule-heating. Although the element has domains parallel to the length direction of the element before heating, 180° domains parallel to almost width direction appear after heating. This means the easy axis of the thin-film element can be controlled by Joule-heating.

![](https://assets.underline.io/uploads/markdown_image/1/image/81a717f414b1d4e3f236a72ceb55f496.jpg)

Fig. 1 Field dependence of impedance.

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Fig. 2 Changes in domain structures.

Controlling of magnetoimpedance property of thin-film element using Joule-heating

Magnetic Tunnel Junctions (MTJ) are widely used as magnetic sensors but their major disadvantage is their high noise level at low frequency. Some methods to overcome 1/f noise involve adding magnetic modulation [1] or increasing the MTJ area [2]. In order to get a linear response, in-plane MTJ are usually designed with the free layer (FL) set perpendicularly to the reference. However, for a specific application [3], a symmetric R-H characteristic is more suitable to drive a modulation and should be easily obtained by pinning the FL in the same direction as the reference. The aim of this study is to process MTJs with symmetric R-H curve and high sensitivity. The magnetic stack is composed of a pinned synthetic antiferromagnet, MgO tunnel barrier and CoFeB/NiFe free layer. After patterning micron-size junctions of different shapes, we perform a post-process annealing under magnetic field. In this work, we study different methods to achieve a coherent rotation of the FL magnetization towards the hard axis: i) applying a small external field along the easy axis; ii) using shape anisotropy; iii) using soft pinning by adding an antiferromagnetic layer on the FL separated by a thin Ta spacer [4]. Our measurements highlight the importance of FL pinning on the reversibility and smoothness of the R-H curves. Nevertheless, since pinning reduces sensitivity, an optimum trade-off must be found. We observed that shape anisotropy alone is not sufficient to pin the FL (fig.1), but a coherent rotation is achieved by applying an external field. Moreover, our results show the importance of a good alignment between the reference and the easy axis. Compensating for the process misalignement by tilting the applied field allows to reduce the pinning field to 5 Oe (fig.2) with a sensitivity of 3.5%/mT. On the other hand, soft pinning can provide internal pinning ranging from 120 to 0 Oe by increasing the Ta spacer up to 0.25 nm. Choice of the optimum spacer thickness and further process optimizations should reduce hysteresis and improve the sensitivity.

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Fig.1: R-H curves measured along easy axis Hy and hard axis Hx

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Fig. 2: R-H curves measured with respect to the reference misalignment (1.6°) and pinning fields Hpin of 5 and -5 Oe

Development of magnetic tunnel junctions with symmetric R-H curve for specific sensor application

In recent years, giant magnetoresistance (GMR) devices have been used in many applications due to their small size, high sensitivity, low power consumption, and low cost[1, 2]. For a high sensitive magnetic sensor application, the device resistance is required to be varied linearly over a wide magnetic field range. A high aspect ratio of the GMR line device is useful for the wide range high linearity of the MR curve. However, the high aspect ratio reduces MR ratio and increase signal to noise ratio (SNR) because the exchange bias for minor axis direction in the GMR line is suppressed due to the strong shape anisotropy in the pinned layer. In this study, we investigated the correlation between SNR and MR properties in GMR line devices for magnetic sensor applications. The GMR stack is composed of Si/SiO sub.//seed layer/IrMn(6)/CoFe(1.6)/ Ru(0.85)/CoFe(1.6)/Cu(2.5)/CoFe(1)/NiFe(3.5)/capping layer (all thickness in nm). The pinned layers were magnetized for minor axis direction in GMR lines. Figures 1(a)-(c) shows a schematic, cross sectional and top view of scanning electron microscope (SEM) images of the GMR device, respectively. The GMR device has ten GMR lines in the parallel configuration. The line length and space width were fixed at 100 μm and 600 nm, respectively. The line width (W) was varied from 300 nm to 2 μm. Figure 2(a)-(e) show MR curves of the GMR lines with various W with external field of ±20 Oe. The MR curves were measured 100 round trips for evaluating SNR. MR ratio increased as increasing W due to the stabilization of antiparallel configuration of free and pinned layers. On the other hand, the linearity of the MR curve decreased at W of 2 μm because of the reducton of shape anisotropy. The reduction of MR curve linearity increased device resistance variation. Figure 2(f) shows SNR values calculated from the MR ratio and coefficient of the resistance variatoin. SNR increased as increasing W. These results mean that it is important to increase W within the range that maintains the linearity of the MR curve.

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Fig. 1 (a) A schematic, (b) cross-sectional and (c) top view of SEM images of the GMR device

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Fig. 2 (a)-(e) MR curves and (f) signal to noise ratios for the various W of GMR devices.

Signal to Noise Ratio Analysis of GMR Line Devices for High Sensitive Magnetic Sensor Applications

1. Introduction Ultra-high sensitivity and micro-sized magnetic sensors are required in biomagnetic measuring devices. The GigaHertz spin rotation sensor, which is an evolution of the magneto-impedance sensor, has shown high sensitivity while transmitting GHz pulse currents [1]. Detection magnetic fields are sensed via a pickup coil wrapped around the wire when the GHz pulse currents are applied. However, the micro-mechanism in the amorphous wire, which exhibits high sensitivity, has not been characterized. Thus, we investigated the relationship between peak voltages and magnetic fields and the magnetization behavior inside the amorphous wire. 2. Calculation method and conditions The magnetization behavior was calculated using the Landau–Lifshitz–Gilbert equation, which considers eddy currents. The calculation model of the amorphous wire is shown in Fig. 1. The magnetic properties included a saturation magnetization of 1.0 T, a magnetic anisotropy constant of 250 J/m3, and exchange constants between cells in the plane and the axial direction of 1.0 × 10−11 J/m and 2.0 × 10−11 J/m, respectively. The magnetization easy axis of the amorphous wire from the outer circumference to the inside by 0.75 µm was assumed to be oriented in the circumferential direction because compressive stress is generated in the FeCoSiB amorphous wire, which is induced via rapid quenching during the fabrication processes [2]. 3. Results Fig. 2 shows the relationship between the peak voltages at the fall times of the pulse currents and magnetic fields. When the fall time was 1.0 ns, the calculated and experimental results showed the same tendency. A shorter fall time meant higher absolute values of the peak output voltages and stronger magnetic fields as shown in Fig. 2. At a fall time of 0.385 ns, only the rotations of magnetizations in the outer circumference of the amorphous wire contributed to the output voltages, whereas at a fall time of 5.0 ns, the domain wall motions inside the wire contributed to the output voltages. This was the reason why the output peak voltages increased as the fall time was shortened.

![](https://assets.underline.io/uploads/markdown_image/1/image/b0cfc2b624142dd7949f1e74c66d616b.jpg)

Fig. 1 Model of a magnetic sensor with an amorphous wire

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Fig. 2 Relationship between peak voltages and magnetic fields

Effects of fall times of pulse currents on output voltages for amorphous-wire-based magnetic sensors

Introduction It is very important to inspect the shrinkage cavity inside the cast iron, since the spheroidal graphite cast iron (FCD600) may be generated a shrinkage cavity inside it during manufacturing and the strength is extremely reduced. In this research, a new inspection method using differential vibration measurement by electromagnetic force excitation is proposed. In this method, the vibration by the electromagnetic force is generated from the static magnetic field of the permanent magnet and the eddy current inside the cast iron by the alternating excitation coil. Then, the shrinkage cavity is evaluated using the vibration strength of the cast iron surface. In this paper, 3D electromagnetic field analysis and 3D displacement analysis [1] are used to elucidate the test principle and to conduct verification experiments. Inspection Model and Conditions Fig.1 shows the proposed sensor is composed of a permanent magnet with two holes, an AC exciting coil with 500Hz and 2A, and two vibration sensors. The electromagnetic vibration is generated in the steel plate by the static flux density from the permanent magnet and the eddy current from the excitation coil. And, two vibration sensors are measured the vibration strength of the steel plate surface differentially. The shrinkage cavity inside cast iron is estimated by the differential vibration intensity. Calculated and Inspection Results Fig.2(a) shows that the calculated distribution of differential displacements by the two vibration sensors at each position on the cast iron. This figure denotes that the displacement distribution is changed near the shrinkage cavity inside the cast iron. This is because, the density in the cast iron is decreased near the shrinkage cavity in the cast iron. (3) shows the measured differential signal of two vibration sensors at each position on the actual cast iron with the shrinkage cavity. This figure denotes that the differential signal is changed near the shrinkage cavity in the cast iron. Moreover, the measured signal is a tendency similar to the calculated result as shown in Fig.2. The presence of shrinkage cavity inside the cast iron can be confirmed by this change in the differential signal.

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Proposal of Inspection Method for Shrinkage Cavity in Spheroidal Graphite Cast Iron Using Differential Vibration Measurement by Electromagnetic Force Vibration

In many applications including space missions, Anisotropic Magnetoresistors (AMR) based magnetometers raised their popularity [1,2] as they are solid-state off-the-shelf components with good radiation immunity [3]. One of the issues they suffer is low sensitivity and thus high noise induced by their bridge thermal noise as well as by preamplifier stage noise [4]. To overcome this problem, higher supply voltage of an AMR bridge can be used to raise the sensitivity. This seems to be straightforward but power dissipated on the sensor raises quadratically with bridge voltage and thus it can’t be operated in "classical" continuous mode (due to overheating and excessive power consumption). In our research we propose novel method of powering bridge by pulses allowing to obtain better sensitivity and less noise with AMR sensors. During these short pulses (100 us width and 4.5 ms period) we also perform flipping pulses (both S/R) while measuring bridge response with an analog-to-digital converter. Acquired data are then signal-processed on the fly by a microcontroller. In traditional method, 10 V in continuous mode with HMC1021 AMR sensor will dissipate 91 mW of power, while cycling power with a duty cycle of 1:45 means only 2 mW (considering zero overhead power). In mostly used triaxial version it is 273 mW vs 6 mW preserving other main parameters of the magnetometer unchanged. To verify this idea we have developed single axis magnetometer (Fig. 1) with adjustable both bridge voltage as well as flipping current, with possibility of precise timing of all events. In the first trial/test, we have tried to obtain similar noise with pulsed 10 V bridge as we were able to get in our previous research with continuous supply of 10V [4], (see Fig 2.) After achieving this milestone (solving a lot of technical troubles) we tried 20 V bridge supply to verify expected noise reduction (as sensitivity doubles), but for now without result – at this voltage, AMR's electrical offset saturates the preamplifier. In the near future we aim to tackle this issue and to test the noise drift with temperature in different flipping current configurations.

![](https://assets.underline.io/uploads/markdown_image/1/image/f21d8768f1f6f2a671e16af4a0ec4b66.jpg)

Fig.1 - Photo of the experimental prototype

![](https://assets.underline.io/uploads/markdown_image/1/image/56f845d2e47285017dd6de7e45a96175.jpg)

Fig.2 - PSD of noise with pulsed 10 V bridge voltage

Low-Power AMR Magnetometer Operated in Discontinuous Mode

1.Study Objective and Method Transformer magneto-mechanical structure deformation due to lightning impulse effect may cause damage of the transformers in terms of the noise and vibration performance. This study proposed a single-phase transformer with a voltage specification of 345 kV (high voltage)/115 kV (low voltage) and a capacity of 120 MVA [1,2]. The results of the continuous lightning impulse tests revealed that the transformer designed as parameter of K-factor, as shown in Figure 1. After testing results, there is generated significantly low noise (&lt;65 dB) and vibration (&lt;10 μm), which are remarkably lower than the IEEE standard of 85 dB. 2.Experiment Result and Discussion The pattern of the fault currents depends on the fault type and location along the winding length. Figure 2(a)-(b) shows the transformer after the lightning impulse full-wave and chopped wave for high voltage bushing level. The Figure 2(c) shows the thermal imaging results of the transformer after the lightning impulse testing, indicating that high (102 °C) and low (31.2 °C) thermal conduction were obtained at the two sides of the top collier. These thermal imaging measurement results suggest that the transformer can operate effectively because it exhibits satisfactory insulation performance after the lightning impulse and alternating current insulation tests [3,4]. The sweep frequency response analysis is a useful method to detect and diagnosis of the defects for the power transformers. The results of the frequency spectral tests are conducted using SFRA are shown in Figure 2(d). Based on the SFRA theory, the core properties affect the SFRA characteristics only at low frequencies (typically up to 1 kHz). Therefore, the noise results can be considered as correction values between the values obtained before and after the application of the SFRA. The k-factor between 0.4-0.6 for transformer insulation is maintained better performance.

![](https://assets.underline.io/uploads/markdown_image/1/image/9d741403f2a00698d2661882416560a8.jpg)


Figure 1 Lightning k-factor: (a) turn-to-turn insulation and overshoot voltage, (b) k-factor distribution.

![](https://assets.underline.io/uploads/markdown_image/1/image/232e615dfbba5ad2b0da73be6bcc9de1.jpg)


Figure 2. Lightning impulse results: (a)-(b) full wave voltage and current, (c) thermal imaging, front-back side, (d) SFRA at 10 Hz–2 MHz before and after the lightning impulse test.

Effects of the Electromagnetic Structure of the Power Transformer Core on Hysteresis Squareness Ratio, Noise and Vibration Characteristics

Studies have shown that relaxing music can lower a patient’s breathing rate, heart rate, and blood pressure by releasing stress or anxiety and promoting relaxation [1,2]. Based on the successful development of our magnetic respiratory monitoring technology for advanced healthcare [3], in this study we attempt to examine how the breathing pattern of a patient changes when the patient sleeps with and without a favorite music in the background. We observed that during sleep mode with music, the patient breathed more regularly and slowly (11 times per minute) compared to sleep without music (14 times per minute) and wake mode (17 times per minute). This indicated that the relaxing music helped the patient to relax and sleep better. Remarkably, while the abnormal breathing feature was observed at a certain time for all states (wake-up and sleep modes with and without music), the breathing pattern became more regular in the case of sleep with the relaxing music. Furthermore, we designed a musical biofeedback for breathing regulation. In this design, the respiratory motion of the patient was tracked and interpreted as a real-time variable for tempo adjustment to a stored musical file. The patient was able to adjust breathing to synchronize with a separate accompaniment line. When the breathing was regular and at the desired tempo, the resulting sound was synchronous and harmonious. These observations suggest a new possibility of integrating our magnetic respiratory monitoring technology with music to develop an innovative magnetic music therapy for Covid19 patients with breathing difficulty.

Magnetic Respiratory Monitoring Technology Based Music Therapy for Covid19 Patients: A New Perspective

Inductance and resistance of a coil are important parameters for electromagnetic sensors and actuators. If the sensors or actuators are to be operated in high temperature environments, the effect of temperature change on inductance and resistance must be evaluated [1-2]. In this paper, we propose a very simple procedure for estimating the inductance and resistance of toroidal coils operating in high temperature environment. Magnetic stainless steel (SUS430) is used as the core. The ring is wound with ceramic-coated cable. The test specimen is placed inside an oven in which the temperature is controlled up to 500°C. The winding is driven by a linear amplifier (TA330, TRUST Automation) at the command of a function generator (33120A, Agilent). The current is measured by a current probe (80i-110s, Fluke). Fig. 1 illustrates the test setup and shows a picture of the test specimen in the oven. The current through the coil is related to the applied voltage through V = L (di/dt) + Ri. Transfer function between the voltage and current can be obtained as G = 1/(Ls + R). Introducing a new operator λ=1/(1+τs), we can set up a time-domain identification scheme [3]. The inductance and resistance can be estimated through the following recursive least square estimation algorithm. Defining the parameter vector theta = [ L R ], (1) θ(k) = θ(k-1)+P(k)φ(k)e(k) (2) e(k) = y(k) - φ(k)θ(k-1) (3) P(k) = P(k-1) - P(k-1)φ(k)φ(k)P(k-1)/(1+φ(k)P(k-1)φ(k)) The parameter τ determines the convergence speed. In order to validate the method, the resistance of the coil is measured using a precision multimeter (34401A, Agilent) and the inductance is measured with an LCR meter (4263B, Agilent). Fig. 2(a) shows the estimation results compared with the measurements. Fig. 2(b) displays the comparison of resistance estimation with measurements. The estimation for inductance is better than the resistance in terms of agreement with measurements. Since the estimation model is the first order, it is not possible to obtain good estimation quality both for inductance and resistance. Since the resistance is stationary, it may be possible to have another procedure to estimate the resistance, thereby enhancing the quality. This work is supported by National Research Foundation of Korea (NRF-2020R1F1A1067740)

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Estimation of inductance and resistance of toroidal coils in high temperature environment

Power Adaption Design for Multifrequency Wireless Power Transfer System

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