• Journal of the Institute of Convergence Signal Processing
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• v.19 no.3
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• pp.89-96
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• 2018

This study aims to develop a fully passive smart sensing tag utilizing RF (Radio Frequency) energy harvesting technology at UHF (Ultra High Frequency) band of 915MHz. To optimize the power collected under various radiated conditions, an efficient energy harvesting module exploiting a boost circuit with maximum power point tracking (MPPT) is employed. Specifically, the proposed tag features two orthogonal antennas to enhance its capability of both energy scavenging and data transmissions. The experimental result shows that the developed smart sensor tag can scavenge an RF input power of as low as 0.19mW at a distance of 4 meters for a 3.6Vdc output. Furthermore, the proposed smart sensor tag performs the feasibility of completely autonomous monitoring food freshness at 2 meters with a low-power sensor array.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.15 no.3
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• pp.1-6
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• 2015

The IoT(Internet of things) technology enable objects around user to be connected with each other for sharing information. To support security is the mandatory requirement in IoT because it is related to the disclosure of private information but also directly related to the human safety. However, it is difficult to apply traditional security mechanism into lightweight devices. This is owing to the fact that many IoT devices are generally resource constrained and powered by battery. PSK(Pre-Shared Key) based approach, which share secret key in advance between communication entities thereafter operate security functions, is suitable for light-weight device. That is because PSK is costly efficient than a session key establishment approach based on public key algorithm. However, how to safely set a PSK of the lightweight device in advance is a difficult issue because input/output interfaces such as keyboard or display are constrained in general lightweight devices. To solve the problem, we propose and develop a secure PSK configuration scheme for resource constrained devices in IoT.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.2
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• pp.216-219
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• 2016

In this paper, the SIW(Substrate Integrated Waveguide)-based feeding antenna for the application of SDR(Software Defined Radar) is designed and manufactured. It is usually well-known that SIWs are easily integrated on PCB and have low transmission loss toward high powered input signal. Also, it is recommended that SIWs are strongly immunized to Electromagnetic Interferences(EMI). In particular, the manufactured antennas are loaded on the USRP(Universal Software Radio Peripheral) platform and employed to detect target RCS as an experiment in this paper. The operating frequency of the proposed antenna is in ISM(Industrial, Scientific and Medical) band(2.4~2.48 GHz) and the measured gain is over 8 dBi at 2.44 GHz.

• Journal of the Ergonomics Society of Korea
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• v.29 no.6
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• pp.875-887
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• 2010

The quantitative effectiveness of powered support surfaces such as APAM in preventing and treating pressure ulcers has not been sufficiently evaluated because of uncertainty of alternating pressure load input and lack of interpretation of dynamic perfusion characteristics of soft tissue. The aim was to verify the dynamic loading effects to sacral tissue perfusion characteristics from alternating set pressure changes. We developed integrated experiment system to supply alternating load to supinely positioned sacrum and concurrently measured $TcPO_2$, $TcPCO_2$ and air cell pressure. Ten aged subjects (5 female, 5 male) were tested with alternating set pressure 20, 30, 40, 50 and 60mmHg. From the dynamic perfusion response eight characteristic parameters were proposed such as average, minimum, maximum and perfusion range regarding to $TcPO_2$ and $TcPCO_2$. A one-way ANOVA was carried out to determine whether the manipulation of alternating set pressure had any effect on $TcPO_2$ and $TcPCO_2$. From the dynamic tissue perfusion response we found mean $TcPO_2$ decreased exponentially as alternating pressure load increased and perfusion range varied mainly because of minimum level change of $TcPO_2$. And perfusion range of $TcPCO_2$ affected by increase of maximum value of $TcPCO_2$. From the results we can get more strict insights about actual physiological dynamic tissue perfusion mechanism under alternating pressure load.

• The Transactions of the Korean Institute of Power Electronics
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• v.16 no.3
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• pp.302-308
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• 2011

The HVAC(Heating Ventilation and Air Conditioning) system is only controlled by turn on/turn off operations with AC 380V input. Therefore, the efficiency of the system is reduced and accoustic noise problem occurs. Also, the blower is shut down at the AC power failure. In this paper, the inverter system with UPS function for the A/C(Air Conditioning) blower is proposed. Proposed inverter system which is powered from the AC and DC voltage can control speed, operation mode, and soft-start time using CAN communication. In case of the CAN communication failure, RS-232 communication could be used to control the hardware directly by the engineer that can solve existing problems. To verify the validity of proposed inverter system, simulations and experiments are carried out.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.30 no.4
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• pp.314-319
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• 2019

In this study, we propose a W-band frequency modulated continuous wave(FMCW) radar altimeter that can measure the altitude based on the frequency differences of transmitted and received signals. This W-band FMCW system is powered by an altitude control algorithm, which we propose to help prevent collisions of drones with obstacles in real deployment by measuring the relative altitude. It is shown that this algorithm enables the drone to be positioned within a 3 % error of altitude from the desired input height. The chip used in the W-band transmitter and receiver was fabricated using a 65-nm CMOS process, and a horn antenna was directly fed by incorporating an embedded waveguide feeder into the chip. The clutter spectra observed in terrains including soil, grass, and calm lake water were measured and compared, confirming the reflectivity characteristics of various surfaces of different water contents.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.6
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• pp.11-18
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• 2018

A pulse detonation engine (PDE) requires high operating frequency greater than 100 Hz to get meaning thrust as a propulsion devise. Thus a PDE needs an ignition circuit operating precisely at high operating frequencies. In this paper AC(alternating current) and DC(direct current) types of ignition circuits were designed and compared. Each circuit was tested at operating frequencies from 16.66 to 100.00 Hz by measuring the input signal of each circuit and the voltage change in the primary coil of the transformer. Results show that the DC power circuit can attain a maximum error rate of 5.15% at higher operating frequencies, whereas the AC power circuit displays a negligible agreement with the operating signal at frequencies greater than 33.33 Hz. Therefore it is confirmed that DC-powered ignition circuit is preferable for the PDE operating at high frequencies.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2014.10a
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• pp.267-270
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• 2014

This paper presents a CMOS interface circuit for vibration energy harvesting. The proposed circuit consists of an AC-DC converter and a DC-DC boost converter. The AC-DC converter rectifies the AC signals from vibration devices(PZT), and the DC-DC boost converter generates a boosted and regulated output at a predefined level. A full-wave rectifier using active diodes is used as the AC-DC converter for high efficiency, and a schottky diode type DC-DC boost converter is used for a simple control circuitry. A MPPT(Maximum Power Point Tracking) control is also employed to harvest the maximum power from the PZT. The proposed circuit has been designed in a 0.35um CMOS process. The chip area is $530um{\times}325um$. Simulation results shows that the maximum efficiencies of the AC-DC converter and DC-DC boost converter are 97.7% and 89.2%, respectively. The maximum efficiency of the entire system is 87.2%.

• Journal of the Korean Society of Industry Convergence
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• v.26 no.6_2
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• pp.1083-1095
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• 2023

Recently, the demand for low-voltage, high-capacity ESS is rapidly increasing due to the revitalization of the e-mobility industry, which is mainly powered by electricity. In addition, the demand for portable power banks is rapidly increasing due to the revitalization of leisure industries such as camping and fishing. The ESS with this structure consists of a small number of series cells and many parallel cells, resulting in a system with a large rated current. Therefore, the number of power devices for cell balancing configured in series is small, but a balancing device with a large current capacity is required. Construction of a constant temperature device in such a low-voltage, high-current ESS is difficult due to economic issues. The demand for an active balancing system that can solve the passive balancing heating problem is rapidly increasing. In this paper, propose a power feedback fly-back topology that can solve the balancing heating problem. The characteristic of the proposed topology is that a series-connected voltage sharing voltage is used as the input of the flyback converter, and the converter output is connected to one transformer. In this structure, the converter output for cell voltage balancing shares magnetic flux through one high-frequency transformer, so the cell voltage connected to the converter automatically converges to the same voltage.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.6
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• pp.1250-1259
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• 2012

In this paper, a time-domain comparator is proposed for a successive approximation (SA) analog-to-digital converter (ADC) with a low power and high resolution. The proposed time-domain comparator consists of a voltage-controlled delay converter with a clock feed-through compensation circuit, a time amplifier, and binary phase detector. It has a small input capacitance and compensates the clock feed-through noise. To analyze the performance of the proposed time-domain comparator, two 1V 10-bit 200-kS/s SA ADCs with a different time-domain comparator are implemented by using 0.18-${\mu}m$ 1-poly 6-metal CMOS process. The measured SNDR of the implemented SA ADC is 56.27 dB for the analog input signal of 11.1 kHz, and the clock feed-through compensation circuit and time amplifier of the proposed time-domain comparator enhance the SNDR of about 6 dB. The power consumption and area of the implemented SA ADC are 10.39 ${\mu}W$ and 0.126 mm2, respectively.