This research proposes a 1-bit programmable metasurface that is capable of focusing and steering the beam for enhancing the power transfer efficiency in wireless power transfer applications. The proposed metasurface is comprised of 16 ´ 16 unit cells which are designed with a fractal structure and the operating frequency of 5.8 GHz. One PIN diode is integrated with the unit cell which enables two states with 1800 phase difference of the reflected signal at the unit cell. The two states of the unit cell correspond to the ON and OFF states of the PIN diode or "0" and "1" coding in the metasurface. By appropriately handle the ON/OFF state of the coding metasurface, we can control the reflected electromagnetic wave impinged on the metasurface.  Hence, a control board is designed to controlling the ON/OFF state of each unit cell. The control board is consist of Shift Register, Decoder, and D Flip-flop IC and designed such that by connecting to FPGA/DAQ, we can control the state of each unicell.

In the next step, first, we will design larger metasurface board that comprised of 64 x 64 unit cell. The objective of this research is to obtain higher steering capability and increasing the efficiency. Then, we want to design a new metasurface board which can work at 28 GHz and consist of 10.000+ unicell.

In this research topic, we study the radio frequency(RF) power transfer technique that makes use of electromagnetic(EM) wave  as a medium for carrying power.

In the RF wireless power transfer system, a microwave beam formed by the multi-antenna transmitter can be focused at the receiver for high power transfer efficiency as long as the receiver is within the radiative near-field region of the transmitter.

  1) Design and fabricate a prototype consists of transmitter and receiver part with high-density phase antenna array

  2) Develope integrated algorithm which is able to  control active beam focusing from transmitter to reciever for high efficiencient wireless power transfer.

The Research proposes a system in which a wireless power camera that operates by being wirelessly powered and actively maintains energy. The power management includes not only transmission power control in the power transmission apparatus as the transmitting end but also control in the wireless power camera operating unit as the receiving end. For such control, the power transmitter and the wireless power camera operator may exchange control information through a transceiver. The wireless power camera operating unit measures the remaining energy of the energy storage connected to the wireless power camera operating unit. When the residual energy is below a certain level, power is requested to the power transmitter through the transceiver. The power transmitter determines beamforming based on the position of the wireless power camera operating unit according to the request. The wireless power camera operating unit transmits photographing and data as motion is detected, and can actively request energy from the power transmitter based on the remaining energy. An object of the present research is to implement a fully wireless camera that can maintain the camera without replacing the battery in a place difficult to access through this.

In a communication system utilizing beamforming, a beam alignment process is essential, and the overhead in this process is significant. In the case of A6G (Above 6GHz), more than 1000 beams are used. In order to satisfy various requirements of 5G, efficient beam alignment method is required in each scenario, the beam must be electrically steering In the direction of the terminal belonging to the cell, interference should be minimized through nulling. That is, a beamforming technique is needed to quickly find a terminal device where it may be located, start communication by aligning the beams, track movement well, and quickly recover when a communication link is broken due to surrounding conditions. We have optimized the algorithm using the Gradient Descent method so that it has various directivity and nulls and a radiation pattern of various beam-widths. We propose a method of adjusting only the phase of the feed signal by optimizing it with the objective function and computation process. We propose a beam synthesis method that can be effectively used in a communication system with a lot of limitations, and propose an initial access method of a millimeter wave communication system utilizing a planar array antenna using a synthesized beam. In order to effectively utilize the beam, research for forming various beams through beam synthesis is required. And initial access process is introduced by using several beam form to shoot the optimum beam.

The research proposes a beam steering algorithm to formulate the optimal phased antenna array weight that maximizes the received power on the target (IoT device) and at the same time maintains the amount of radiated microwave power toward human body below the recommended exposure limit. The research is motivated by the scientific studies about the human health risk that could be caused by microwave radiation exposure (e.g., heart disease,  burns,  skin cancer, etc).

In this research, the information of the exact location of human body is required to apply the algorithm to the system. Therefore, by incorporating a depth camera which utilizes the sensing technology based on human stereo vision  with a deep learning-based real-time object detection system, the human presence can be detected, the distance from the power beacon to human body can be measured, and the window size of detected object can be obtained.

The proposed algorithm has the main advantage to assure the use of RF radiated energy in wireless power transfer environment complies with the limit of human exposure to the microwave energy, which is regulated by communication international commission. The proposed algorithm can be easily applied and adapted to the receive power-based wireless power transfer employing a large number of antenna.

Machine Learning is essential to studies that need to analyze Big Data or to find optimal values. By using Machine Learning properly we can reduce a large amount of time. Starting from basic part like gradient descent, back propagation, we learn several kinds of machine learning (e.g. Deep Learning, convolutional neural network, reinforcement learning). The main part of our research is applying machine learning to other research in our lab. By using collected or streamed data we calculate optimal antenna setting for beam forming, detect object by RF signal, visualize RF signal using 3D tracking camera.

In this research topic, we study the radio frequency (RF) power transfer technique that makes use of an electromagnetic (EM) wave as a medium for carrying power. Differently from other wireless power transfer techniques (e.g., inductive coupling and magnetic resonant coupling), the RF energy transfer technique enjoys an advantage of longer energy transfer distance compared to other competing technologies thanks to the characteristics of the EM wave. Especially, we study a multi-antenna wireless-powered sensor network (WPSN), in which a power beacon wirelessly transfers electric energy to a sensor node via an EM wave.

In the coming era of Internet-of-Things (IoT), we are expected to be surrounded by communicating things deployed everywhere in our daily life. This explosive increase of communicating things poses a very challenging problem of high power consumption of current wireless communication technologies. In this research topic, we study a novel ultra-low power wireless communication technology for IoT devices in the cellular long-range communication networks. We adopt an RFID technique such as envelope detection in the downlink and backscattering in the uplink direction. To overcome the short range of RFID communication techniques, we consider a base station equipped with a massive number of antennas for transmit and receive beamforming, and IoT devices with the retroreflective modulation technology.

The visible light communication (VLC) is a new wireless communication paradigm that transfers digital data via visible light spectrum instead of microwave. In VLC, the light emitting diode (LED) is modulated in a very fast speed so that information is embedded in the light while no blinking is perceived by human eyes. In this research, we study a novel architecture that combines the VLC and the RF communication to benefit from the advantages of high data rate and stability at the same time. Moreover, high-speed camera-based VLC for smart car application is studied.