• Journal of the Korean Society of Industry Convergence
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• v.27 no.5
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• pp.1199-1207
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• 2024

Automation systems have gained great attention with the evolution of communications technology. A smart automation is an Internet of Things (IoT) application that employs the Internet to monitor and control appliances using an automation system. Lack of IoT technology adoption, unattractive user interface, restricted wireless transmission range, and expensive costs are the constraints of existing home automation systems. The idea of integrating a large number of devices has a substantial impact on the widespread advancement in the field of autonomous systems. The Internet of Things is being used more and more to create internet-connected gadgets. In addition, a wide range of data and services centered on human connection are accessible through mobile sensing devices powered by the Internet of Things, such as smartphones, tablets, digital cameras, sensors, etc. This study describes the implementation and analysis of a MQTT protocol-based IoT-based home automation system utilizing NodeMCU. This enables customers to use a mobile application over the internet to monitor and manage household appliances from a distance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.2A
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• pp.152-161
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• 2007

IEEE 802.11 Wireless Local Area Network (WLAN) became a prevailing technology for the broadband wireless Internet access, and new applications such as Voice over WLAM (VoWLAN) are fast emerging today. For the battery-powered VoWLAN devices, the standby time extension is a key concern for the market acceptance while today's 802.11 is not optimized for such an operation. In this paper, we propose a novel Idle Mode operation, which comprises paging, idle handoff, and delayed handoff. Under the idle mode operation, a Mobile Host (MH) does not need to perform a handoff within a predefined Paging Area (PA). Only when the MH enters a new PA, an idle handoff is performed with a minimum level of signaling. Due to the absence of such an idle mode operation, both IP paging and Power Saving Mode (PSM) have been considered the alternatives so far even though they are not efficient approaches. We implement our proposed scheme in order to prove the feasibility. The implemented prototype demonstrates that the proposed scheme outperforms the legacy alternatives with respect to energy consumption, thus extending the standby time.

• Journal of the Korea Society for Simulation
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• v.19 no.1
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• pp.53-61
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• 2010

In wireless sensor networks(WSNs) individual sensor nodes are subject to security compromises. An adversary can physically capture sensor nodes and obtain the security information. And the adversary injects false reports into the network using compromised nodes. If undetected, these false reports are forwarded to the base station. False reports injection attacks can not only result in false alarms but also depletion of the limited amount of energy in battery powered sensor nodes. To combat these false reports injection attacks, several filtering schemes have been proposed. The statistical en-routing filtering(SEF) scheme can detect and drop false reports during the forwarding process. In SEF, The number of the message authentication codes(threshold) is important for detecting false reports and saving energy. In this paper, we propose a dynamic threshold determination method for energy efficient SEF using fuzzy-logic in wireless sensor networks. The proposed method consider false reports rate and the number of compromised partitions. If low rate of false reports in the networks, the threshold should low. If high rate of false reports in networks, the threshold should high. We evaluated the proposed method’s performance via simulation.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.10
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• pp.45-52
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• 2008

We investigated the design of an RF-powered, wireless temperature sensor tag chip using $0.18-{\mu}m$ CMOS technology. The transponder generates its own power supply from small incident RF signal using Schottky diodes in voltage multiplier. Ambient temperature is measured using a new low-power temperature-to-voltage converter, and an 8-bit single-slope ADC converts the measured voltage to digital data. ASK demodulator and digital control are combined to identify unique transponder (ID) sent by base station for multi-transponder applications. The measurement of the temperature sensor tag chip showed a resolution of $0.64^{\circ}C/LSB$ in the range from $20^{\circ}C$ to $100^{\circ}C$, which is suitable for environmental temperature monitoring. The chip size is $1.1{\times}0.34mm^2$, and operates at clock frequency of 100 kHz while consuming $64{\mu}W$ power. The temperature sensor required a -11 dBm RF input power, supported a conversion rate of 12.5 k-samples/sec, and a maximum error of $0.5^{\circ}C$.

• Journal of Sensor Science and Technology
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• v.33 no.1
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• pp.34-39
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• 2024

Energy harvesting technology that converts the wasted energy resources into electrical energy is emerging as a semipermanent power source for self-powered electronics and wireless low-power sensor systems. Among the various energy conversion techniques, flexible piezoelectric energy harvesters (f-PEHs), using materials with piezoelectric effects, have attracted significant interest because they can harvest a small mechanical energy into electrical signals without constraints of time and space in various environments. In this study, we used a flexible piezoelectric composite film fabricated by dispersing BaHf_xTi_(1-x)O₃ (x = 0, 0.01, 0.05, 0.1) piezoelectric powders inside a polymeric matrix to facilitate f-PEHs. The fabricated f-PEH with optimal Hf contents (x = 0.05) generated a maximum output voltage of 0.95 V and current signal of 130 nA with stable electrical/mechanical disabilities under periodically bending deformations. In addition, we demonstrated a cantilever-type f-PEH and investigated its potential as a sensor by characterizing the output performance under mechanical vibrations at various frequencies. This study provides the breakthrough for realizing self-powered energy harvesting and sensing systems by adopting the lead-free piezoelectric composites under vibrational environments.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.397-397
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• 2016

Triboelectric nanogenerators (TENG) can produce power from ambient mechanical sources and have strong points of high output performance, light weight, low cost, and easy manufacturing process. It is expected that TENG can be utilized in the fields of wireless electronics and self-powered devices in the world which pays attention to healthcare and the IoT. In this work, we focus on scavenging ambient rotational energy by using a durably designed TENG. In previous studies regarding harvesting rotation mode energy, the devices were based on sliding mechanism and durability was not considered as a major issue. However friction by rotation causes reliability problems due to wear and tear. Therefore, in this study, we convert rotary motion to linear motion utilizing a cam by which we can then utilize contact-mode TENG and improve device reliability. In order to increase output performance, bumper springs were used below the TENG and the optimum value for the bumper spring constant was analyzed theoretically. Furthermore, the inserting a soft substrate was proposed and its effect on high output was determined to be due to an increase in the contact area. By increasing the number of cam noses, the output frequency was shown to increase linearly. For the purpose of maximum power transfer, the input impedance of the device was determined. Finally, to demonstrate the use of the C-TENG as a direct power source, it was installed on a commercial bicycle wheel and connected to 180 LEDs. In conclusion we present a rotational motion TENG energy scavenger system designed for enhanced durability and optimized output by appropriate choice of spring constants and substrate.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.1
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• pp.81-88
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• 2011

A real time monitoring system from a PC has been developed which can be accessed through transmitted data, which incorporates an established low powered transport system equipped with a single chip combined with wireless sensor network technology from a three-axis acceleration sensor. In order to distinguish between static posture and dynamic posture, the extracted parameter from the rapidly transmitted data needs differentiation of movement and activity structures and status for an accurate measurement. When results interpret a static formation, statistics referring to each respective formation, known as the K-mean algorithm is utilized to carry out a determination of detailed positioning, and when results alter towards dynamic activity, fuzzy algorithm (fuzzy categorizer), which is the relationship between speed and ISVM, is used to categorize activity levels into 4 stages. Also, the ISVM is calculated with the instrumented acceleration speed on the running machine according to various speeds and its relationship with kinetic energy goes through correlation analysis. With the evaluation of the proposed system, the accuracy level stands at 100% at a static formation and also a 96.79% accuracy with kinetic energy and we can easily determine the energy consumption through the relationship between ISVM and kinetic energy.

• Journal of Institute of Control, Robotics and Systems
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• v.17 no.6
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• pp.566-572
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• 2011

In recent semiconductor and FPD (Flat Panel Display) manufacturing processes, high clean-class delivery operation is required more and more for short working time and better product quality. Traditionally SLIM (Single-sided Linear Induction Motor) is widely used in the liner drive applications because of its simplicity in the rail structure. A magnetically levitated (Maglev) unmanned vehicle with SLIM traction, which is powered by a CPS (Contactless Power Supply) can be a high precision delivery solution for this industry. In this paper unmanned FPD-carrying vehicle, which can levitate without contacting the rail structure, is suggested for high clean-class FPD delivery applications. It can be more acceptable for the complex facilities composed with many processes which require longer rails, because of simple rail structure. The test setup consists of a test vehicle and a rounded rail, in which the vehicle can load and unload products at arbitrary position commanded through wireless communications of host computer. The experimental results show that the suggested vehicle and rail have reasonable traction servo and robust electromagnetic suspensions without any contact. The resolution of point servo errors in the SLIM traction system is accomplished under 1mm. The maximum gap error is ${\pm}0.25mm$ with nominal air gap length of 4.0mm in the electromagnetic suspensions. This type of automated delivery vehicle is expected to have significant role in the clean delivery like FPD glass delivery.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.489.2-489.2
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• 2014

The planar type flexible piezoelectric energy harvesters (PEH) based on PbZr0.52Ti0.48O3 (PZT) thin films on the flexible substrates are demonstrated to convert mechanical energy to electrical energy. The planar type energy harvesters have been realized, which have an electrode pair on the PZT thin films. The PZT thin films were deposited on double side polished sapphire substrates using conventional RF-magnetron sputtering. The PZT thin films on the sapphire substrates were transferred by PDMS stamp with laser lift-off (LLO) process. KrF excimer laser (wavelength: 248nm) were used for the LLO process. The PDMS stamp was attached to the top of the PZT thin films and the excimer laser induced onto back side of the sapphire substrate to detach the thin films. The detached thin films on the PDMS stamp transferred to adhesive layer coated on the flexible polyimide substrate. Structural properties of the PZT thin films were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). To measure piezoelectric power generation characteristics, Au/Cr inter digital electrode (IDE) was formed on the PZT thin films using the e-beam evaporation. The ferroelectric and piezoelectric properties were measured by a ferroelectric test system (Precision Premier-II) and piezoelectric force microscopy (PFM), respectively. The output signals of the flexible PEHs were evaluated by electrometer (6517A, Keithley). In the result, the transferred PZT thin films showed the ferroelectric and piezoelectric characteristics without electrical degradation and the fabricated flexible PEHs generated an AC-type output power electrical energy during periodically bending and releasing motion. We expect that the flexible PEHs based on laser transferred PZT thin film is able to be applied on self-powered electronic devices in wireless sensor networks technologies. Also, it has a lot of potential for high performance flexible piezoelectric energy harvester.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.3
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• pp.580-585
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• 2009

Real Time Locating Systems (RTLS) are used to track and identify the location of objects in real time using simple, inexpensive tags attached to or embedded in objects and readers that receive the wireless signals from these tags to determine their locations. A tag is powered an internal source such as a battery. The blink frequency of a tag affects the energy efficiency and the locating accuracy of RTLS. The mobility of a tag also affects the locating accuracy. In this paper, we introduce a RTLS tag design which improves the locating accuracy and the power efficiency. We propose an adaptive transmission-rate control algorithm using a motion sensor. By analyzing the signal pattern of the motion sensor, we can build a model to estimate the speed of the motion. Using this model, our algorithm can achieve better locating accuracy and lower power consumption than those of the conventional method. In our experiments, the number of transmission reduced as 40%, keeping similar locating accuracy.