This paper describes pixel-parallel image-matching circuit schemes that provide the optimal binarization, the high-speed low-power comparison, and the accurate matching of fingerprint images needed for fingerprint verification. Image binarizing is adjusted adaptively during the fingerprint sensing operation. The obtained image is compared with the template in the pixel array, and the results from all of the pixels are totaled by a variable-delay circuit at high speed and low power. For accurate matching, the image is scanned by shifting it in the pixel array while maintaining whole image. The experimental results demonstrate that the proposed schemes provide optimal binary images of most fingers under any condition and environment, 11-µs 147-µW totaling of results from 20,584 pixels, and wide-range image scanning and accurate matching for fingerprint images. These schemes are effective for fast and low-power fingerprint verification for a single-chip fingerprint sensor and identifier.

We have implemented a distributed sensor system based on an array of fiber Bragg gratings (FBGs), which can measure up to 1000 points with a single piece of fiber. The system consists of FBGs having the same resonant wavelengths and small reflectivities (0.1 dB), and a wavelength tunable optical time-domain reflectometer (OTDR). To interrogate the distributed grating sensors and to address the event locations simultaneously, we have utilized the tunable OTDR. A thermoelectric temperature controller was used to tune the emission wavelength of the OTDR. The operating temperature of the laser diode was changed. By tuning the pulse wavelength of the OTDR, we could identify the FBGs whose resonant wavelengths were under change within the operating wavelength range of the DFB LD. A novel sensor cable with dry core structure and tensile cable was fabricated to realize significant construction savings at an industrial field and in-door and out-door applications. For experiments, a sensor cable having 52 gratings with 10 m separations was fabricated. To prevent confusion with unexpected signals from the front-panel connector zone of the OTDR, a 1 km buffer cable was installed in front of the OTDR. The proposed system could distinguish and locate the gratings that were under temperature variation from 20 to 70.

Programmable Logic Controller (PLC) has been widely used in the industrial control. Inherently, the PLC-based system is a class of Hybrid Dynamical System (HDS) in which continuous state of the plant is controlled by the discrete logic-based controller. This paper firstly presents the formal algebraic model of the PLC-based control systems which enable the designer to formulate the various kinds of optimization problem. Secondly, the optimization problem of the 'sensor parameters,' such as the location of the limit switch in the material handling system, the threshold temperature of the thermostat in the temperature control system, is addressed. Finally, we formulate this problem as Mixed Logical Dynamical Systems (MLDS) form which enables us to optimize the sensor parameters by applying the Mixed Integer Programming.

A flooding algorithm is an indispensable and fundamental network control mechanism for achieving some tasks, such notifying all nodes of some information, transferring data with high reliability, getting some information from all nodes, or to reserve a route by flooding the messages in the network. In particular, the flooding algorithm is greatly effective in the heterogeneous and dynamic network environment such as so-called ubiquitous networks, whose topology is indefinite or changes dynamically and whose nodal function may be simple and less intelligent. Actually, it is applied to grasp the network topology in a sensor network or an ad-hoc network, or to retrieve content information by mobile agent systems. A flooding algorithm has the advantages of robustness and optimality by parallel processing of messages. However, the flooding mechanism has a fundamental disadvantages: it causes the message congestion in the network, and eventually increases the processing time until the flooding control is finished. In this paper, we propose and evaluate methods for producing a more efficient flooding algorithm by adopting the growth processes of primitive creatures, such as molds or microbes.

By deploying hundreds or thousands of microsensors and organizing a network of them, one can monitor and obtain information of environments or objects for use by users, applications, or systems. Since sensor nodes are usually powered by batteries, an energy-efficient data gathering scheme is needed to prolong the lifetime of the sensor network. In this paper, we propose a novel scheme for data gathering where sensor information periodically propagates from the edge of a sensor network to a base station as the propagation forms a concentric circle. Since it is unrealistic to assume any type of centralized control in a sensor network whose nodes are deployed in an uncontrolled way, a sensor node independently determines the cycle and the timing at which it emits sensor information in synchrony by observing the radio signals emitted by sensor nodes in its vicinity. For this purpose, we adopt a pulse-coupled oscillator model based on biological mutual synchronization such as that used by flashing fireflies, chirping crickets, and pacemaker cells. We conducted simulation experiments, and verified that our scheme could gather sensor information in a fully-distributed, self-organizing, robust, adaptive, scalable, and energy-efficient manner.

Energy-efficient operations are essential to prolonging the lifetime of wireless sensor networks. Clustering sensor nodes is one approach that can reduce energy consumption by aggregating data, controlling transmission power levels, and putting redundant sensor nodes to sleep. To distribute the role of a cluster head, clustering approaches should be based on efficient cluster configuration schemes. Therefore, low overhead in the cluster configuration process is one of the key constraints for energy-efficient clustering. In this paper, we present an autonomous clustering approach using a coverage estimation-based self-pruning algorithm. Our strategy for clustering is to allow the best candidate node within its own cluster range to declare itself as a cluster head and to dominate the other nodes in the range. This same self-declaration strategy is also used in the active sensor election process. As a result, the proposed scheme can minimize clustering overheads by obviating both the requirements of collecting neighbor information beforehand and the iterative negotiating steps of electing cluster heads. The proposed scheme allows any type of sensor network application, including spatial query execution or periodic environment monitoring, to operate in an energy-efficient manner.

This paper considers the problem of recursive filtering for linear discrete-time systems with uncertain observation. A new approximate adaptive filter with a parallel structure is herein proposed. It is based on the optimal mean square combination of arbitrary number of correlated estimates which is also derived. The equation for error covariance characterizing the mean-square accuracy of the new filter is derived. In consequence of parallel structure of the filtering equations the parallel computers can be used for their design. It is shown that this filter is very effective for multisensor systems containing different types of sensors. A practical implementation issue to consider this filter is also addressed. Example demonstrates the accuracy and efficiency of the proposed filter.

In this paper, we present Scalable Data Collection (SDC) protocol, a tree-based protocol for collecting data over multi-hop, wireless sensor networks. The design of the protocol aims to satisfy the requirements of sensor networks that every sensor transmits sensed data to a sink node periodically or spontaneously. The sink nodes construct the tree by broadcasting a HELLO packet to discover the child nodes. The sensor receiving this packet decides an appropriate parent to which it will attach, it then broadcasts the HELLO packet to discover its child nodes. Based on this process, the tree is quickly created without flooding of any routing packets. SDC avoids periodic updating of routing information but the tree will be reconstructed upon node failures or adding of new nodes. The states required on each sensor are constant and independent of network size, thereby SDC scales better than the existing protocols. Moreover, each sensor can make forwarding decisions regardless of the knowledge on geographical information. We evaluate the performance of SDC by using the ns-2 simulator and comparing with Directed Diffusion, DSR, AODV, and OLSR. The simulation results demonstrate that SDC achieves much higher delivery ratio and lower delay as well as scalability in various scenarios.

We investigate the effects of the performance of sensor networks on network availability and in turn evaluate the impact of protocols and network configuration on these effects. The typical wireless sensor network of the future consists of a large number of micro-sized sensors that are equipped with batteries of limited capacity. In such a network, energy consumption is one of the most important issues. Several representative protocols that are applied in ring and linear network configurations are analyzed, and explicit formulae for network availability are derived for each of them. Numerical values derived by using these formulae yielded the surprising result that backup routes do not always improve network availability. This is because the loads imposed by the backup routes on network segments that do not include dead sensor nodes reduce sensor-node lifetimes in these segments.

An event-driven sensor network composed of a large number of sensor nodes has been widely studied. A sensor node sends packets to a sink when the node detects an event. For the sink to receive packets it fails to acquire, the sink must send re-transmission requests to the sensor node. To send the requests to the sensor node using unicast, the network address of the sensor node is required to distinguish the sensor node from others. Since it is difficult to allocate the address manually to a number of nodes, a reasonable option is to use existing address autoconfiguration methods. However, the methods waste the limited energy of the sensor nodes due to using a number of control messages to allocate a permanent address to every node. In this paper, we propose an energy-efficient address autoconfiguration method for the event-driven sensor network. The proposed method allocates a temporary address only to a sensor node which detects an event, on an on-demand basis. By performing simulation studies, we evaluated the proposed method and compared it with one of the existing methods based on the number of control messages for the address allocation. The results show that the number of control messages of the proposed method is small compared to that of the existing method. We also evaluated the process time overhead of the proposed method using the implemented system. Although the proposed method has little extra overhead, the results show the processing time is short enough for practical use.

Limited energy is a big challenge for large scale wireless sensor networks (WSN). Previous research works show that modulation scaling is an efficient technique to reduce energy consumption. However, the impacts of using modulation scaling on packet delivery latency and loss are not considered, which may have adverse effects on the application qualities. In this paper, we study this problem and propose control schemes to minimize energy consumption while ensuring application qualities. We first analyze the relationships of modulation scaling and energy consumption, end-to-end delivery latency and packet loss ratio. With the analytical model, we develop a centralized control scheme to adaptively adjust the modulation levels, in order to minimize energy consumption and ensure the application qualities. To improve the scalability of the centralized control scheme, we also propose a distributed control scheme. In this scheme, the sink will send the differences between the required and measured application qualities to the sensors. The sensors will update their modulation levels with the local information and feedback from the sink. Experimental results show the effectiveness of energy saving and QoS guarantee of the control schemes. The control schemes can adapt efficiently to the time-varying requirements on application qualities.

In the microwave band, Optical Electric Field Sensors (OEFS) provide an attractive method to measure electromagnetic fields precisely. It is difficult however, to develop an OEFS that operates with both wide bandwidth and high sensitivity. In this paper, we propose a Log-Periodic Dipole antenna Array (LPDA)-type OEFS that achieves high sensitivity over a wide bandwidth. The LPDA-type OEFS has a large number of electrodes that are attached to each of the antenna elements. Not only the lengths of the antenna elements but also the lengths of electrodes vary log-periodically. The OEFS responds to microwaves by synchronizing the propagation direction of light with the propagation direction of the microwave. An OEFS constructed of y-cut z-propagation Lithium Niobate (LN) demonstrates good stability against temperature variation. Theoretical analysis with respect to the refractive index variation and optical modulator with the crystal orientation will be provided in this paper. In addition, the characteristics of the proposed LPDA-type OEFS will be shown over wide bandwidth in the microwave band.

A simple, novel and low cost optical device with the possibility of being integrated into a network of wireless sensors has been developed for the colorimetric detection of iron (II). The proposed device used is based on two light emitting diodes (LEDs) configured so that one acts as an emitter and the other as a light detector, and a simple threshold detection/timer circuit to measure the photocurrent at the detector LED. The colorimetric reaction is based on the chelating reaction of divalent iron with the ligand 1,10-phenanthroline. The calibration graph shows that the detection limit (DL) of iron (II) using this approach is 5 ppb with a RSD of 0.08%. All experiments were carried out in triplicate (N = 3). The effect of some cations on the determination of Fe (II) using the proposed method was also studied. Results found showed that the system is relatively free from interferences.

A smell reproduction technique is useful in the field of virtual reality. We have developed the system called an odor recorder for reproducing the smell recorded using the odor sensing technique. We proposed the new type of the odor recorder using the inkjet devices together with a mesh heater. Droplets with tiny volume were forcibly evaporated to generate smell rapidly and reproducibly. Moreover, the mesh heater was directly connected to the sensors without plumbing tubes and the sensors were placed away from the wall of sensor cell. The recording time of the odor with high odor intensity became much shorter than that of the previous system. Then, the recipe of jasmine scent composed of benzyl acetate and Ylang Ylang was successfully determined using the proposed system.

Chemical sensor which can be used for a multi-purpose chemical measurement to detect various chemical substances with a small number of a sensor array was investigated. It was confirmed that chemical compounds adsorbed strongly and irreversibly on a platinum surface using conventional electrochemical methods and an instrumental surface analysis. The adsorbates were also analyzed by means of an electrochemical impedance spectroscopy under dynamic potential scan; measured impedance reflects CPE (constant phase element) properties of the electrode surface. The method provides a convenient technique for the surface analysis of adsorbing chemicals. The CPE response profile was modified through chemical adsorption/desorption and the interaction between the polarized surface and chemical substances. Consequently, various profiles depending on chemical substances were obtained and it had quantitative and qualitative information about chemicals interacting with the surface. The present method which does not require a specific electrochemical reaction can be applied for multi-purpose chemical sensors and also simple chemical analyses.

In this paper, we present a pixel-level color image sensor with efficient ambient light suppression using a modulated RGB flashlight to support a recognition system. The image sensor employs bidirectional photocurrent integrators for pixel-level demodulation and ambient light suppression. It demodulates a projected flashlight with suppression of an ambient light at short intervals during an exposure period. In the imaging system using an RGB modulated flashlight, every pixel provides innate color and depth information of a target object for color-based categorization and depth-key object extraction. We have designed and fabricated a prototype chip with 6464 pixels using a 0.35 µm CMOS process. Color image reconstruction and time-of-flight range finding have been performed for the feasibility test.

Sensor networks, in which a large number of sensor nodes are connected with each other through communication networks, are potential to provide extensive new applications with various research and technical challenges and attracting much attention all over the world. In this paper we describe information and signal processing for sensor networks with emphasis on the concepts of collaboration and fusion as one of the most important issues for the sensor networks. We also review some basic aspects of sensor networks in terms of their features and the network architecture.

Sensor nodes are prone to failure and have limited power capacity, so the evaluation of fault tolerance and the creation of technology for improved tolerance are among the most important issues for wireless sensor networks. The placement of sensor nodes is also important, since this affects the availability of nodes within sensing range of a target in a given location and of routes to the base station. However, there has been little research on the placement of sensor nodes. Furthermore, all research to date has been based on deterministic node placement, which is not suitable when a great many sensor nodes are to be placed over a large area. In such a situation, we require stochastic node placement, where the sensor-positions are in accord with a probability density function. In this paper, we examine how fault tolerance can be improved by stochastic node placement that produces scale-free characteristics, that is, where the degree of the nodes follows a power law.

The Camera sensor network is a new advent of technology in which each sensor node can capture video signal, process and communicate with other nodes. We have investigated a dense node configuration. The requested processing task in this network is arbitrary view generation among nodes view. To avoid unnecessary communication between nodes in this network and to speed up the processing time, we propose a distributed processing architecture where the number of nodes sharing image data are optimized. Therefore, each sensor node processes part of the interpolation algorithm with local communication between sensor nodes. Two processing methods are used based on the image size shared. These two methods are F-DP (Fully image shared Distributed Processing) and P-DP (Partially image shared Distributed Processing). In this research, the network processing time has been theoretically analyzed for one user. The theoretical results are compatible with the experimental results. In addition, the performance of proposed DP methods were compared with Centralized Processing (CP). As a result, the best processing method for optimum number of nodes can be chosen based on (i) communication delay of the network, (ii) whether the network has one or more channels for communication among nodes and (iii) the processing ability of nodes.

A single solid-state magnetic sensor can be used to measure a current by sensing the field near the conductor in a non-contact way. In order to improve the accuracy of the measuring system, magnetic sensor arrays have been introduced in the current measurement around the conductor. An analytical algorithm based on Discrete Fourier Transform (DFT) is presented in this paper, which can separate the effects of the field generated by the current under measurement from the interference fields. A general mathematical model of the interference analysis is set up, which can be used for both DC and AC current measurement and has no restriction on the shape and number of the current conductors. Numerical simulations associated with preliminary experimental results confirm the validity of the approach.