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Although the classic radar equation has been widely used to analyze the link budget of an automotive radar, it is valid only when the targets are located in the far-field region of the transmitted field and the receiving antenna is located in the far-field region of the scattered field. This paper confirms this hypothesis using measured and simulated data for short-range radars. Furthermore, a novel radar equation based on the Fresnel diffraction formula is proposed for application in situations where the receiving antenna is located in the radiative near-field region (or Fresnel region) of a target, but the target is situated in the far-field region of the transmitting antenna. In addition, the proposed radar equation is assessed by comparing the measured and simulated data.

This paper proposes a novel incremental theory of diffraction (ITD) formulation to calculate the fringe field from a wedge characterized by impedance surfaces and arbitrary exterior angles. The ITD formula was originally based on the Fourier transform pair relationship between the solution for the canonical wedge problem and incremental field contribution. However, this procedure can be utilized to report the ITD formula only for planar and half-planar impedance surfaces. Therefore, this paper develops a heuristic ITD formula by conceptually deriving the incremental diffracted field contribution from the uniform theory of diffraction coefficient and inferring the physical optics edge-diffracted field contribution from the terms related to the incidence shadow and reflection shadow boundaries. The proposed formula is applied to simple triangular impedance cylinder and disk models with impedance surfaces, and the results are compared with those of the method-of-moment and VIRAF’s ITD solver to show that is performs similar to the former and better than the latter.

Obesity leads to the development of metabolic syndrome and comorbidities. Overweight and obesity continue to be a relentless global issue. Sipyimigwanjung-tang (SGT), a traditional herbal medication, was first mentioned in Dongui Sasang Shinpyun and has been used to treat edema, meteorism, and jaundice, which are common findings associated with obesity. The main physiological feature of obesity is expanded adipose tissue, which causes several impairments in liver metabolism. Therefore, this study aimed to investigate the anti-obesity effects of SGT in the epididymal white adipose tissue (eWAT) and livers of high-fat diet (HFD)-induced obese mice. SGT significantly blocked HFD-induced weight gain in C57BL/6N mice. In addition, SGT effectively reduced the increased weight and adipocyte size in eWAT of HFD-induced obese C57BL/6 N mice. Moreover, SGT significantly decreased the elevated gene expression of Peroxisome proliferator-activated receptor γ, CCAAT/enhancer-binding protein α, and Sterol regulatory element-binding protein 1 in the eWAT of HFD-induced obese mice. Furthermore, SGT significantly decreased lipid accumulation in the livers of HFD-induced obese mice and differentiated 3T3-L1 adipocytes. Hence, the present study provides substantial evidence that SGT has potential therapeutic effects on obesity.

Chaff is a radar countermeasure used to interfere with ground radar detection or missile target detection by disrupting the radar. As radar is essential in modern electronic warfare, chaff is also essentially used in many military vehicles. A large amount of chaffs in the form of a thin and long wire is contained in a cylindrical or rectangular cartridge and is launched to form a chaff cloud to disturb the radar. It is virtually impossible to examine the chaff cloud analytically because it is released at once into the air in large quantities. Therefore, for chaff cloud analysis, an approximation method or statistical characteristics are used, or real data is measured directly through experiments. The study of chaff consists of two parts: chaff cloud modeling, which determines the dynamic characteristics of chaff, and estimation of electromagnetic scattering properties, which determines the signal characteristics of the chaff. This review paper focuses on the techniques used in chaff cloud modeling and the estimation of electromagnetic scattering properties. We categorized the techniques by statistical, numerical, and empirical methods. In chaff cloud modeling, studies for the purpose of scattering analysis generally use typical distribution, whereas if chaff cloud modeling itself is the purpose, it is aimed at realizing a realistic chaff cloud by referring to experimental data. For estimation of electromagnetic scattering properties, a conventional method that simply multiplies the average radar cross-section of chaff element to obtain the total radar cross-section of the chaff cloud is used, and a method that allows rapid calculation while considering the distribution of the chaff cloud is being studied.

In this paper, a deformed radiating element is proposed to design a comb-line array antenna for low sidelobe levels in the millimeter-wave band. To design the comb-line array antenna with a low sidelobe level, the use of the wide radiating elements for a relatively large radiation conductance is required. However, the conventional rectangular radiating element has transverse current flows on it, resulting in undesirable transverse radiation conductance for cross-polarization. On the contrary, in the proposed radiating element, which is implemented by cutting obliquely the connection part to the feeding line from a rectangular element, the radiations from the transverse currents cancel each other, and low radiation conductance for cross-polarization and dominant radiation conductance for co-polarization are achieved. A 17-element linear comb-line array antenna with the sidelobe below −20 dB is designed and measured at 79 GHz. Using the proposed radiating elements, we obtained the sidelobe level of −21.9 dB in the array, but the array using the conventional radiating elements shows the sidelobe level of −16.9 dB. This letter demonstrates the availability of the proposed element for the easy and accurate design of the comb-line array antenna with the low sidelobe level.

Dynamic wireless power transfer (DWPT) has emerged as a technology for delivering sustainable energy to mobile electric vehicles without charging cables. Magnetic beamforming is a well-known DWPT strategy for increasing power transfer efficiency (PTE) by calculating an optimal weight for focusing the magnetic fields from the transmitting (TX) coils to the desired receiving (RX) coils. However, when magnetic beamforming is applied to multi-inputs and multi-outputs (MIMO) WPT, the cross-coupling at TX and RX coils inevitably emerges, resulting in deterioration of the PTE and power factor (PF). This paper presents a magnetically decoupled modular coil array for MIMO-WPT applicable to a DWPT environment. First, we present a mathematical analysis of the influences of magnetic couplings in MIMO-WPT. Then, we derive the criteria of magnetic couplings in terms of improved PTE and PF and design a modular coil array that satisfies the derived criteria. Finally, we compare the proposed modular coil array with an existing square coil array in a DWPT environment via a 3D finite element analysis simulator. The proposed modular coil array achieves PTE improvement of up to 30 %, whereas the existing square coil array ends up to 18 %, as the number of receiving coils increases from one to five. In addition, the PF of the proposed modular coil array is close to 1.0, whereas that of the existing square coil array is attenuated up to 0.5.

Wireless power transfer (WPT) technology has been widely introduced and developed over the past few years. Nevertheless, the basic WPT configuration using one transmitting (Tx) coil and one receiving (Rx) coil still achieves very limited performance in terms of power transfer distance. To overcome this limitation, various multi-coil WPT systems using three or more coils have been studied. Among them, a multiple-input single-output (MISO) structure can provide the Rx with advanced freedom in an extensive lateral area. However, few studies have investigated how far multi-Tx coils can increase the transfer distance. In this paper, we analyze the transfer distance and lateral coverage based on the generalized critical coupling condition and system energy efficiency according to the number of additional Tx coils in the MISO WPT system. The results demonstrate that the MISO WPT system using planarly arranged Tx coils improves by barely 1% in the optimal transfer distance, which achieves the maximum output power condition in a single-Tx WPT system. To validate our analysis, the MISO WPT system with seven Tx coils and seven LCC inverters was implemented and its performance was assessed. The measured results agreed well with the theoretically calculated results.

It is essential to obtain a large amount of inverse synthetic aperture radar (ISAR) image data for ISAR automatic target recognition. For a super-resolution ISAR image for a complex perfect electric conducting (PEC) computer-aided design (CAD) model, parameter estimation methods should be applied to $M \times N$ scattered far-field data over $M$ frequencies and $N$ angles, which is conventionally obtained by using the shooting and bouncing ray (SBR) technique. Therefore, $N$ -time ray tracing processes are required for $N$ angles, and $M \times N$ -time field calculations are required for $M$ frequencies. In this paper, to reduce the computation time for $M \times N$ -time field calculations, we introduce a fast scattered far-field prediction method for a super-resolution ISAR image of a complex PEC CAD model using the SBR technique. This method consists of two main ideas. First, under the small-angle approximation, we derive a DFT-based ISAR image formula in closed form, which allows the rapid acquisition of DFT-based ISAR image through just a one-time ray tracing process at the center frequency and angle. In addition, the scattered far-field data are also obtained by inverse discrete Fourier transforming the DFT-based ISAR image without $N$ ray tracing processes and $M \times N$ field calculations. Second, a field truncation method is employed to suppress errors in the scattered far-field data caused by the proposed closed-form formula. Further, by applying a parameter estimation method to the scattered far-field data, a super-resolution ISAR image is obtained quickly. Simulation results for complex PEC CAD models are in good agreement with the results for the conventional method, while the computation times are tremendously reduced.

One of the major issues in multifunction radars is time resource allocation to maximize the radar’s ability. If jet engine modulation (JEM) is more efficiently performed in an insufficient dwell-time environment, the remaining time can be allocated for other tasks. This study presents a novel automatic algorithm for estimating the jet engine blade number of insufficient JEM signals. We employed a harmonic selection rule and a modified empirical mode decomposition (EMD) with an adaptive low-pass filtering. For a refined autocorrelation waveform, the analysis focuses on a desirable combination of intrinsic mode functions derived from the modified EMD. The approach is significant because it enables reliable estimation despite the insufficient JEM signal. Also, the proposed algorithm is innovative because it uses only the time-domain method, not the frequency-domain method. The application is expected to enhance the efficiency of radar resource management.

Chaff is a passive jammer widely used to disrupt radar or radio-frequency sensors. A mass of chaff fibers dispersed in the air is commonly referred to as a chaff cloud. It is nearly impossible to numerically simulate in real-time the enormous amount of chaff fibers composing the chaff cloud. In this paper, we model the behavior of numerically estimated chaff clouds as probability density functions (PDFs) and apply approximation techniques to estimate the radar cross-section (RCS) of the chaff cloud in real time. To model the aerodynamics of the chaff cloud, we represented the combination of PDFs as functions of time and wind speed. The applied approximation techniques—vector radiative transfer and generalized equivalent conductor method—showed a computation time that cannot be achieved by low-frequency methods such as the method of moments or finite-difference time-domain. Moreover, the dynamic RCS results of the approximation techniques showed a similar trend to those of other studies simulating similar situations. The proposed scheme is effective for real-time chaff cloud simulation, and the modeled dynamics and estimated dynamic RCSs can be a standard baseline for developing new analysis methods for chaff clouds. In the future, the proposed scheme will extend to more chaff fibers and more diverse environmental parameters.

Micro-Doppler signatures from the rotating propellers of a drone can be utilized to distinguish the drone from clutter or airborne organisms with similar radar cross section (RCS) levels, such as birds and bats. To obtain the micro-Doppler signatures of a drone, calculation or measurement of the electric field scattered from the rotating propellers is essential. In this paper, using the relative angle concept and far-field approximation, we propose a way to rapidly estimate the dynamic RCS of a drone with several propellers according to its movement. In addition, based on the fact that the shape of the propeller does not change even if it rotates, we construct an impedance matrix only once and apply the matrix to the method of moments instead of the iterative process of calculating the impedance matrix and inverse matrix for each rotation angle of the propeller. Finally, by using the Fourier transform of the results from the proposed method, the rotation frequencies of the propellers according to the movement of the drone can be obtained.

It is common knowledge that wireless power transfer (WPT) systems with multiple transmitters (Txs) and a single receiver (Rx) have robust efficiency against lateral misalignment. However, the unnecessary coupling among Txs in actual multi-Tx WPT systems causes transmission efficiency degradation, and then additional tuning work is required to adjust some system parameters, such as the phase or frequency of Tx sources. Moreover, the frequency-splitting phenomenon caused by over-coupling between the Txs and Rx still occurs in multi-Tx systems. Thus, output power degradation is inevitable in the over-coupled state. In this article, we propose an optimal capacitance tuning method that is applicable to multi-Tx WPT systems. A multi-Tx WPT system tuned with the optimal capacitances, which are obtained from the critical coupling condition between Txs and Rx, not only compensates the inner coupling among Txs but also achieves the maximum output power in the over-coupled state. To verify the validity of the proposed method, we implemented two-and three-Tx and single Rx WPT systems and measured the output power of load with respect to the Rx position along the x- and y-axes. As a result, with the proposed method without any changes in the operating frequency or phase, the systems could deliver higher output power than the conventional phase-controlled system. In particular, with the proposed method, the systems maintained the constant maximum transmission efficiency of 80% in the over-coupled state.

It is obvious that the conventional two-coil wireless power transfer (WPT) system has a short power transmission distance, which is determined by system parameters such as the loaded Q of the resonators and the coupling coefficient. There have been many attempts to improve the power transfer efficiency (PTE) or transmission distance. A typical approach is to use multiple coils like a three- or four-coil WPT system. In this paper, we propose a new method to obtain the PTE of a multi-coil WPT system based on the scattering parameter and impedance parameter. Also, we compare the two- and three-coil WPT systems in terms of their transmission efficiency rather than their system energy efficiency. For high transmission efficiency, we determined that the three-coil WPT system should have a symmetric structure and the coupling coefficient between the transmitting and receiving coils has to be as zero as possible. Additionally, we found that 1/√3 of the conventional critical coupling is the boundary coupling coefficient at which the two- and three-coil WPT systems have the same transmission efficiency. We successfully verified these theoretical analyses by implementing two- and three-coil WPT systems at the operating frequency of 6.78 MHz and measuring their transmission efficiency and spectra.

The material parameters of a metamaterial (MTM) are determined by the transformation function used in the optical transformation. Some previously reported MTMs, such as the invisibility cloak, the field rotator, and the field concentrator, were designed by a linear transformation. Their impedance was matched to the background so that no reflection was found; however, the material parameters were mismatched to the background due to the linear transformation function. In the present work, the parameters were matched by using high-order polynomial functions as the transformation function. Since similar materials are filled in boundary cells of the finite-difference time-domain (FDTD) algorithm, the stair-casing error was reduced and the tolerance against boundary abrasion was increased. The frequency response of the proposed method was analyzed. The proposed method is applicable to MTM structures that have complex boundary shapes. In this work, circular and elliptic boundary shapes were considered as examples.

Classifying space targets from debris is critical for radar resource management as well as rapid response during the mid-course phase of space target flight. Due to advances in deep learning techniques, various approaches have been studied to classify space targets by using micro-Doppler signatures. Previous studies have only used micro-Doppler signatures such as spectrogram and cadence velocity diagram (CVD), but in this paper, we propose a method to generate micro-Doppler signatures taking into account the relative incident angle that a radar can obtain during the target tracking process. The AlexNet and ResNet-18 networks, which are representative convolutional neural network architectures, are transfer-learned using two types of datasets constructed using the proposed and conventional signatures to classify six classes of space targets and a debris–cone, rounded cone, cone with empennages, cylinder, curved plate, and square plate. Among the proposed signatures, the spectrogram had lower classification accuracy than the conventional spectrogram, but the classification accuracy increased from 88.97% to 92.11% for CVD. Furthermore, when recalculated not with six classes but simply with only two classes of precessing space targets and tumbling debris, the proposed spectrogram and CVD show the classification accuracy of over 99.82% for both AlexNet and ResNet-18. Specially, for two classes, CVD provided results with higher accuracy than the spectrogram.

T Crosstalk between coil array components in magnetic systems has to be minimized to achieve enhanced performance, such as high data rate, high-power transfer efficiency, and simultaneous wireless information and power transfer. This paper presents a scalable non-coupling coil array composed of perpendicularly arranged quadrupole loop coils. The proposed coil array permits the number of fully or nearly independent channel streams to be increased to meet user's requirements, unlike conventional coil arrays which have a limited number of channel streams. The proposed non-coupling coil array structure is investigated by theoretical analysis and 3-D electromagnetic simulation, and the performance of the proposed non-coupling coil array is verified with a prototype implementation. The proposed coil array shows relatively high signal-to-interference and noise power ratio of around 20 dB even at the three times further distance of a coil diameter.

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Magnetic beamforming techniques can enhance the power transfer efficiency using focused magnetic fields by the multiple transmitters to the receivers. However, the intra-couplings that cause power leakage and phase distortion among the arrayed coils inevitably occur due to the deployment of coils having strong couplings between each other. Here, we analyze the adverse influences of intra-couplings and present the advantages of magnetically independent transmitters for multiple-inputs and single-output (MISO) WPT. The independent coil array can achieve focused magnetic fields by simply adjusting the amplitude of the transmitter voltage source without phase adjustment. The system also can eliminate the reactive power with the independent coil array to efficiently use the supplying power from the source. The analytical studies are verified by numerical and circuit simulation and experiments. Our analysis can be generalized to the MISO-WPT with an arbitrary number of transmitters. It can provide insight into designing and implementing the MISO-WPT applying magnetic beamforming.

Radar target classification is an important task in the missile defense system. State-of-the-art studies using micro-doppler frequency have been conducted to classify the space object targets. However, existing studies rely highly on feature extraction methods. Therefore, the generalization performance of the classifier is limited and there is room for improvement. Recently, to improve the classification performance, the popular approaches are to build a convolutional neural network (CNN) architecture with the help of transfer learning and use the generative adversarial network (GAN) to increase the training datasets. However, these methods still have drawbacks. First, they use only one feature to train the network. Therefore, the existing methods cannot guarantee that the classifier learns more robust target characteristics. Second, it is difficult to obtain large amounts of data that accurately mimic real-world target features by performing data augmentation via GAN instead of simulation. To mitigate the above problem, we propose a transfer learning-based parallel network with the spectrogram and the cadence velocity diagram (CVD) as the inputs. In addition, we obtain an EM simulation-based dataset. The radar-received signal is simulated according to a variety of dynamics using the concept of shooting and bouncing rays with relative aspect angles rather than the scattering center reconstruction method. Our proposed model is evaluated on our generated dataset. The proposed method achieved about 0.01 to 0.39% higher accuracy than the pre-trained networks with a single input feature.

Typically, the actual volume of the residual limb changes over time. This causes the prosthesis to not fit, and then pain and skin disease. In this study, a prosthetic socket was developed to compensate for the volume change of the residual limb. Using an inflatable air bladder, the proposed socket monitors the pressure in the socket and keeps the pressure distribution uniform and constant while walking. The socket has three air bladders on anterior and posterior tibia areas, a latching type 3-way pneumatic valve and a portable control device. In the paper, the mechanical properties of the air bladder were investigated, and the electromagnetic analysis was performed to design the pneumatic valve. The controller is based on a hysteresis control algorithm with a closed loop, which keeps the pressure in the socket close to the initial set point over a long period of time. In experiments, the proposed prosthesis was tested through the gait simulator that can imitate a human’s gait cycle. The active volume compensation of the socket was successfully verified during repetitive gait cycle using the weight loads of 50, 70, and 90 kg and the residual limb model with a variety of volumes. It was confirmed that the pressure of the residual limb recovered to the initial state through the active control. The pressure inside the socket had a steady state error of less than 0.75% even if the volume of the residual limb was changed from −7% to +7%.

In our previous work, we proposed the method to maximize the output power even in the overcoupled state of the wireless power transfer (WPT) system by controlling free resonant frequencies and derived closed-form expression for optimum free resonant frequencies of the primary and secondary resonators. In this paper, we propose the mutual coupling approach to derive the optimum free resonant frequencies and show the measured power transfer efficiency (PTE) using the transmission efficiency as well as the system energy efficiency. The results of the proposed approach exactly coincide with those of the previous work, and the fabricated prototype achieves the transmission efficiency of about 80% by tuning the free resonant frequencies to the optimum values in the overcoupled state.

In this paper, we propose a measurement method with a simple procedure based on the definition of the impedance parameter using a two-port network analyzer. The main advantage of the proposed measurement method is that there is no limit on the number of measuring coils, and the method has a simple measurement procedure. To verify the proposed method, we measured the coupling coefficient among three coils with respect to the distance between the two farthest coils at 6.78 and 13.56 MHz, which are frequencies most common for a wireless power transfer (WPT) system in high-frequency band. As a result, the proposed method showed good agreement with results of the conventional S-parameter measurement methods.

We developed an implantable electrocardiogram (ECG) monitoring system and demonstrated its performance through an in vivo test. In the system, the implantable device senses not only the ECG signal of the animal but also the voltage level of the secondary cell and temperature inside the implantable device, and users can check the transmitted information through a PC program or a mobile application. The adoption of wireless charging technology eliminates the use of a lead wire and repetitive surgery to replace the implantable device. The proposed wireless charging technology demonstrated experimentally a wireless power transfer efficiency of approximately 30%. To minimize the size of the implantable device, the antenna and coil were integrated into a size of 34 mm × 14 mm. Communication between the implantable device and the basestation can reach up to 2.4 m when the implantable device is inserted into a porcine skin sample.

We propose the integration of the resonant coil for wireless power transfer (WPT) and the implantable antenna for physiological signal transfer. The integration allows for a compact biomedical implantable system such as electrocardiogram (ECG) recorder and pacemaker. While the resonant coils resonate at the frequency of 13.56 MHz for the WPT, the implantable antenna works in the medical implant communications service (MICS) band of 402–405 MHz for wireless communications. They share the narrow substrate area of a bar-type shape; the coil has the current path on the outer part of the substrate and the meandered planar inverted-F antenna (PIFA) occupies the inside of the coil. To verify the potentials of the proposed structure, a prototype is fabricated and tested in vitro. The power transfer efficiency (PTE) of about 20% is obtained at a distance of 15 mm and the antenna gain of roughly −40 dBi is achieved.