• Journal of the Optical Society of Korea
• /
• v.10 no.1
• /
• pp.16-22
• /
• 2006

Wavefront sensing using a Shack-Hartmann sensor has been widely used for estimating wavefront errors or distortions. The sensor combines the local slopes, which are estimated from the centroids of each lenslet image, to give the overall wavefront reconstruction. It was previously shown that the pupil-plane irradiance profile effects the centroid estimation. Furthermore, a previous study reported that the reconstructed wavefront from a planar wavefront with a Gaussian pupil irradiance profile contains large focus and spherical aberration terms when there is a focus error. However, it has not been reported yet how seriously the pupil irradiance profiles, which can occur in practical applications, effect the sensing errors. This paper considered two cases when the irradiance profiles are not uniform: 1) when the light source is Gaussian and 2) when there is a partial interference due to a double reflection by a beam splitting element. The images formed by a Shack-Hartmann sensor were simulated through fast Fourier transform and were then supposed to be detected by a noiseless CCD camera. The simulations found that sensing errors, due to the Gaussian irradiance profile and the partial interference, were found to be smaller than RMS ${\lambda}/50$ when ${\lambda}$ is $0.6328\;{\mu}m$, which can be ignored in most practical cases where the reference and test beams have the same irradiance profiles.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.13 no.5
• /
• pp.2454-2468
• /
• 2019

The existing direct position determinations(DPD) for coherently distributed(CD) sources are mostly applicable for uniform linear array(ULA), which result in a low degree of freedom(DOF), and it is difficult for them to realize the effective positioning in underdetermined condition. In this paper, a novel DPD algorithm for coherently distributed sources based on compressed sensing with a moving nested array is present. In this algorithm, the nested array is introduced to DPD firstly, and a positioning model of signal moving station based on nested array is constructed. Owing to the features of coherently distributed sources, the cost function of compressed sensing is established based on vectorization. For the sake of convenience, unconstrained transformation and convex transformation of cost functions are carried out. Finally, the position coordinates of the distribution source signals are obtained according to the theory of optimization. At the same time, the complexity is analyzed, and the simulation results show that, in comparison with two-step positioning algorithms and subspace-based algorithms, the proposed algorithm effectively solves the positioning problem in underdetermined condition with the same physical element number.

• Journal of Sensor Science and Technology
• /
• v.28 no.2
• /
• pp.76-80
• /
• 2019

The characteristics of a titanium oxide layer prepared using a plasma electrolytic oxidation (PEO) process were investigated, using an extended gate ion sensitive field effect transistor (EG-ISFET) to confirm the layer's capability to react with hydrogen ions. The surface morphology and element distribution of the PEO-processed titanium oxide were observed and analyzed using field-emission scanning-electron microscopy (FE-SEM) and energy-distribution spectroscopy (EDS). The titanium oxide prepared by the PEO process was utilized as a hydrogen-ion sensing membrane and an extended gate insulator. A commercially available n-channel enhancement MOS-FET (metal-oxide-semiconductor FET) played a role as a transducer. The responses of the PEO-processed titanium oxide to different pH solutions were analyzed. The output drain current was linearly related to the pH solutions in the range of pH 4 to pH 12. It was confirmed that the titanium-oxide layer prepared by the PEO process could feasibly be used as a hydrogen-ion-sensing membrane for EGFET measurements.

• Smart Structures and Systems
• /
• v.6 no.5_6
• /
• pp.731-748
• /
• 2010

Impact detection and health monitoring are very important tasks for civil infrastructures, such as bridges. Piezoceramic based transducers are widely researched for these tasks due to the piezoceramic material's inherent advantages of dual sensing and actuation ability, which enables the active sensing method for structural health monitoring with a network of piezoceramic transducers. Wireless sensor networks, which are easy for deployment, have great potential in health monitoring systems for large civil infrastructures to identify early-age damages. However, most commercial wireless sensor networks are general purpose and may not be optimized for a network of piezoceramic based transducers. Wireless networks of piezoceramic transducers for active sensing have special requirements, such as relatively high sampling rate (at a few-thousand Hz), incorporation of an amplifier for the piezoceramic element for actuation, and low energy consumption for actuation. In this paper, a wireless network is specially designed for piezoceramic transducers to implement impact detection and active sensing for structural health monitoring. A power efficient embedded system is designed to form the wireless sensor network that is capable of high sampling rate. A 32 bit RISC wireless microcontroller is chosen as the main processor. Detailed design of the hardware system and software system of the wireless sensor network is presented in this paper. To verify the functionality of the wireless sensor network, it is deployed on a two-story concrete frame with embedded piezoceramic transducers, and the active sensing property of piezoceramic material is used to detect the damage in the structure. Experimental results show that the wireless sensor network can effectively implement active sensing and impact detection with high sampling rate while maintaining low power consumption by performing offline data processing and minimizing wireless communication.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2002.07a
• /
• pp.151-155
• /
• 2002

This paper presents a micro fluxgate magnetic sensor in printed circuit board (PCB). The fluxgate sensor consists of five PCB stack layers including one layer magnetic core and four layers of excitation and pick-up coils. The center layer as a magnetic core is made of a micro patterned amorphous magnetic ribbon with extremely high DC permeability of ∼100,000 and the core has a rectangular-ring shape. The amorphous magnetic core is easily saturated due to the low coercive field and closed magnetic path for the excitation field. Four outer layers as an excitation and pick-up coils have a planar solenoid structure. The chip size of the fabricated sensing element is 7.3${\times}$5.7m㎡. Excellent linear response over the range of -100${\mu}$T to +100${\mu}$T is obtained with 540V/T sensitivity at excitation square wave of 3V$\_$P-P/ and 360kHz. The very low power consumption of ∼8mW was measured. This magnetic sensing element which measures the lower fields than 50${\mu}$T, is very useful for various applications such as: portable navigation systems, military research, medical research, and space research.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.15 no.8
• /
• pp.702-707
• /
• 2002

This paper presents a micro fluxgate sensor in printed circuit board (PCB). The fluxgate sensor consists of five PCB stack layers including one layer magnetic core and four layers of excitation and pick-up coils. The center layer as a magnetic core is made of a micro patterned amorphous magnetic ribbon and the core has a rectangular-ring shape. The amorphous magnetic core is easily saturated due to the low coercive field and closed magnetic path for the excitation field. Four outer layers as an excitation and pick-up coils have a planar solenoid structure. The chip size of the fabricated sensing element is 7.3$\times$5.7$\textrm{mm}^2$. Excellent linear response over the range of -100$\mu$T to +100$\mu$T is obtained with 540V/T sensitivity at excitation square wave of 3 $V_{p-p}$ and 360kHz. The very low power consumption of ~8mW was measured. This magnetic sensing element, which measures the lower fields than 50$\mu$T, is very useful for various applications such as: portable navigation systems, military research, medical research, and space research.h.

• Journal of Sensor Science and Technology
• /
• v.2 no.1
• /
• pp.11-17
• /
• 1993

We have constructed an acceleration sensor which is based on the maximum magnetic induction changes of amorphous wire as a measurand. The frequency bandwith of the constructed sensor depends on the mass of a sensing element. For $Co_{72.5}Si_{12.5}B_{15}$ amorphous wire, the bandwith is DC-700 Hz for $1{\times}10^{-3}kg$ sensing element and DC-200 Hz for $5{\times}10^{-3}kg$. The linearity of the acceleration sensor was less than 1% within the acceleration of 5 g.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.22 no.2
• /
• pp.177-186
• /
• 2002

This paper describes the magnetic flux leakage(MFL) type non-destructive testing(NDT) system to detect the 3D defects in underground gas pipe. Magnetic systems with permanent magnets and yokes are analyzed by 3D non-lineal finite element method(FEM) with optimum design. In case of under-saturation of gas pipe, sensing signals are too weak to detect. In case of over-saturation, the changes of the sensing signals are too low to detect the defects sensitively. So, the operating points of the magnetic system are optimized to increase the changes of the MFL signals. The effects of the depth and size of the defects on the sensing signals are analyzed to define the range and resolution of the MFL sensors. To increase the sensor's sensitivity, the back-yoke sensors are introduced and tested.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2002.05a
• /
• pp.11-20
• /
• 2002

This paper describes the magnetic flux leakage(MFL) type non-destructive testing(NDT) system to detect the 3D defects on underground gas pipe. Magnetic systems with permanent magnets and yokes are analyzed by 3D non-lineal finite element method(FEM) with optimum design. In case of under-saturation of gas pipe, sensing signals are too weak to detect. In case of over-saturation, the changes of the sensing signals are too low to detect the defects sensitively. So, the operating points of the magnetic system are optimized to increase the changes of the MFL signals. The effects of the depth and size of the defects on the sensing signals are analyzed to define the range and resolution of the MFL sensors. To increase the sensor's sensitivity, the back-yoke sensors are introduced and tested.

• Journal of Sensor Science and Technology
• /
• v.6 no.4
• /
• pp.337-345
• /
• 1997

The micro heater with PSG/$Si_{3}N_{4}$ diaphragm and platinum heater pattern was designed for micro-gas sensor fabrication. The platinum heater and the platinum electrode for sensing layer were designed on the same plane and fabricated in the single photolithography process. The thermal analyses including temperature distribution over the diaphragm and power consumption of the heater were carried by finite element method. The thermal properties of the microsensor with both heater and sensing electrode on the same plane was compared with that of the typical microsensor which had the structure of sensing layer/insulator/heater on the diaphragm.