• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.4A
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• pp.287-293
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• 2011

This paper investigates the applicability of a piezoelectric cantilever for energy supply of wireless sensor node used in structural health monitoring of bridges. By combining the constitutive equation of piezoelectric material and the dynamic equation of cantilever structure, the coupled governing equation for cantilever equipped piezoelectric patches has been addressed in matrix form. Forced excitation tests were carried out to validate the numerical model and to investigate the power output characteristics of the energy harvester. From the numerical simulation based on the measured bridge accelerations under KTX, Saemaul, Mugunghwa trains, the peak powers generated from the device were found to be 28.5 mW, 0.65 mW, 0.51 mW respectively. It is revealed from the results that bridge vibrations caused by moving loads is not a practical source for energy harvesting because of its low acceleration level, low frequency and short duration.

• Journal of Electrical Engineering and Technology
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• v.8 no.6
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• pp.1320-1327
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• 2013

In this paper, two different electromagnetic energy harvesters using bulk micromachined silicon spiral springs and Polydimethylsiloxane (PDMS) packaging technique have been fabricated, characterized, and compared to generate electrical energy from ultra-low ambient vibrations under 0.3g. The proposed energy harvesters were comprised of a highly miniaturized Neodymium Iron Boron (NdFeB) magnet, silicon spiral spring, multi-turned copper coil, and PDMS housing in order to improve the electrical output powers and reduce their sizes/volumes. When an external vibration moves directly the magnet mounted as a seismic mass at the center of the spiral spring, the mechanical energy of the moving mass is transformed to electrical energy through the 183 turns of solenoid copper coils. The silicon spiral springs were applied to generate high electrical output power by maximizing the deflection of the movable mass at the low level vibrations. The fabricated energy harvesters using these two different spiral springs exhibited the resonant frequencies of 36Hz and 63Hz and the optimal load resistances of $99{\Omega}$ and $55{\Omega}$, respectively. In particular, the energy harvester using the spiral spring with two links exhibited much better linearity characteristics than the one with four links. It generated $29.02{\mu}W$ of output power and 107.3mV of load voltage at the vibration acceleration of 0.3g. It also exhibited power density and normalized power density of $48.37{\mu}W{\cdot}cm-3$ and $537.41{\mu}W{\cdot}cm-3{\cdot}g-2$, respectively. The total volume of the fabricated energy harvesters was $1cm{\times}1cm{\times}0.6cm$ (height).

• Journal of Korea Multimedia Society
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• v.11 no.10
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• pp.1376-1384
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• 2008

Numerous researches on network self-configuration have been conducted on Wireless Sensor Network (WSN) and Ad Hoc network but the results have not been applied yet for factory automation. This paper presents development of intelligent process management systems conducting process monitoring and control irrelevant to physical position of a plant operator. The systems are indispensable for diagnosis of rotating machines which cannot exploit wired network. The system was implemented in a Personal Digital Assistant (PDA) using Bluetooth communication protocol. When a mobile terminal reaches to communication range of the process management server, the server detects the mobile terminal to reconfigure plant network automatically. The server authenticates a user of the terminal to download and installs monitoring and control program considering authorized level of the user. If the terminal leaves communication range of the server, it deletes the node from the network and removes the program automatically to save resources and prevent security problems such as missing terminal. Operation of developed functions was verified in a testbed emulating steel-making plant.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.1
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• pp.220-226
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• 2011

Device of the ECG and pulse signal was made to measure PTT signal using non-invasive method and possible to wearable. PTT alterations were observed according to position change using implemented system.It was needed to ECG and pulse to detect the PTT, used the photoplethymorgraphy appeared to change the blood volume. And also wireless sensor node which was able to Zigbee compatibility was used to transfer the detected ECG and pulse signal to PC. Noise was removed from transit data and algorithm was applied to calculate the PTT. After the evaluation of both the conventional measuring systems and the proposed photoplethymography measuring system, a highly effective and efficient formation and distribution sequences were found within the proposed photoplethymography measuring system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.5B
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• pp.801-808
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• 2010

LEACH, one of hierarchical based routing protocols, was proposed for energy efficiency which is the most important requirement of Wireless Sensor Network(WSN). LEACH protocol is composed of a cluster of certain large number of clusters, which have a cluster head and member nodes. Member nodes send sensing data to their cluster heads, and the cluster heads aggregate the sensing data and transmit it to BS. The challenges of LEACH protocol are that cluster heads are not evenly distributed, and energy consumption to transmit aggregated data from Cluster heads directly to BS is excessive. This study, to improve LEACH protocol, suggests LECEEP that transmit data to contiguity cluster head that is the nearest and not far away BS forming chain between cluster head, and then the nearest cluster head from BS transmit aggregated data finally to BS. According to simulation, LECEEP consumes less energy and retains more number of survival node than LEACH protocol.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.4
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• pp.2002-2019
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• 2017

RPL routing protocol for low-power and lossy networks is an Internet Engineering Task Force (IETF) recommended IPv6 based protocol for routing over Low power Lossy Networks (LLNs). RPL is proposed for networks with characteristics like small packet size, low bandwidth, low data rate, lossy wireless links and low power. RPL is a proactive routing protocol that creates a Directed Acyclic Graph (DAG) of the network topology. RPL is increasingly used for Internet of Things (IoT) which comprises of heterogeneous networks and applications. RPL proposes a single path routing strategy. The forwarding technique of RPL does not support multiple paths between source and destination. Multipath routing is an important strategy used in both sensor and ad-hoc network for performance enhancement. Multipath routing is also used to achieve multi-fold objectives including higher reliability, increase in throughput, fault tolerance, congestion mitigation and hole avoidance. In this paper, M-RPL (Multi-path extension of RPL) is proposed, which aims to provide temporary multiple paths during congestion over a single routing path. Congestion is primarily detected using buffer size and packet delivery ratio at forwarding nodes. Congestion is mitigated by creating partially disjoint multiple paths and by avoiding forwarding of packets through the congested node. Detailed simulation analysis of M-RPL against RPL in both grid and random topologies shows that M-RPL successfully mitigates congestion and it enhances overall network throughput.

• Journal of the Korea Society of Computer and Information
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• v.16 no.3
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• pp.121-129
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• 2011

One of the major challenges of minimum energy consumption for wireless sensor networks(WSN) environment. LEACH protocol is hierarchical routing protocol that obtains energy efficiency by using clustering. However, LEACH protocol in each round, because the new cluster configuration, cluster configuration, whenever the energy consumed shorten the life of the network. Therefore in this paper, the cluster is formed in WSN environment in early stage and the problems with energy waste have been solved by selecting C-node. In the initial round of proposed model uses 26 percent more than traditional LEACH energy consumption. However, as the round is ongoing, it has been proved by the network simulation tool that the waste of energy could be diminished up to 35%.

• Journal of KIISE:Computing Practices and Letters
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• v.16 no.3
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• pp.331-335
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• 2010

Previous low-energy time synchronization methods have mainly focused on reducing the number of transmission or reception packets. However, this paper proposes a method that reduces the percentage of time a node has to be awake (the duty cycle), assuming that a periodic sleep-wake cycle is used to conserve energy. Based on our experience with actual WSN devices, a system model is proposed, and the potential performance of the proposed method, with different parameter values, is analyzed. To further demonstrate the feasibility of our method, experiments were conducted using nine WSN devices in a $3{\times}3$ grid network topology. The results show the average synchronization error is 107.57 $\mu{s}$ in duty cycle 5% and synchronization period 10 sec, and 130 $\mu{s}$ in duty cycle 2.5% and synchronization period 20 sec.

• Smart Media Journal
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• v.8 no.1
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• pp.43-50
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• 2019

As numerous devices are connected through a wireless network, there exist many studies conducted to efficiently connect the devices. While earlier studies often use clustering for efficient device management, there is a load-intensive cluster node which may lead the entire network to be unstable. In order to solve this problem, we propose a scheduling model for centralized unequal chain clustering for efficient management of sensor nodes. For the cluster configuration, this study is based on the cluster head range and the distance to the base station(BS). The main vector projection technique is used to construct clustering with concentricity where the positions of the base stations are not the same. We utilize a multiple radio access interface, multiple-input multiple-output (MIMO), for data transmission. Experiments show that cluster head energy consumption is reduced and network lifetime is improved.

• Journal of the Korea Society of Computer and Information
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• v.14 no.10
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• pp.101-110
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• 2009

The 6LoWPAN(IPv6 Low-power Wireless Personal Area Network) performs IPv6 header compression, TCP/UDP/IGMP header compression, packet fragmentation and re-assemble to transmit IPv6 packet over IEEE 802,15.4 MAC/PHY. However, from the point of view of security. It has the existing security threats issued by IP packet fragmenting and reassembling, and new security threats issued by 6LoWPAN packet fragmenting and reassembling would be introduced additionally. If fragmented packets are retransmitted by replay attacks frequently, sensor nodes will be confronted with the communication disruption. This paper analysis security threats introduced by 6LoWPAN fragmenting and reassembling, and proposes a re-transmission mechanism that could minimize re-transmission to be issued by replay attacks. Re-transmission procedure and fragmented packet structure based on the 6LoWPAN standard(RFC4944) are designed. We estimate also re-transmission delay of the proposed mechanism. The mechanism utilizes timestamp, nonce, and checksum to protect replay attacks. It could minimize reassemble buffer overflow, waste of computing resource, node rebooting etc., by removing packet fragmentation and reassemble unnecessary.