In the last three decades, the terahertz science has achieved great development, possibility to be utilized in a wide variety of fields such as biology, quality control, and security. Especially terahertz time-domain spectroscopy is very useful for nondestructive measurement of materials. Many excellent researchers have approached the commercialization of terahertz technology. However, in the ambient atmosphere, not in the laboratory environment, the signal is distorted due to absorption of water vapor. As a result, unintentional noise is generated in the absorption line, resulting in a great difficulty in spectroscopy. We propose an algorithm that selects a frequency band with no signal distortion and performs spectroscopy. It has an advantage that it can apply algorithms without complex calculation and additional optical components. We measure terahertz time-domain signals of several samples within nitrogen filled chamber, and then the nitrogen was removed to measure the signal in a high relativity humidity environment. We extract optical parameters from the obtained signals. The algorithm is verified by comparison of experimental results and literature value. The values of absorption peaks of samples from our algorithm show good agreement with a literature value. We compared these values and conclude that the thickness was measured and we can check the peak of the absorption line. We find that the proposed algorithm can extract optical parameters even in a high relativity humidity environment.
Fiber Bragg grating is used in a variety of applications. In this study, we suggest compact, cost-effective coherent anti- Stokes Raman spectroscopy which is based on the pulse shaping methods via commercialized fiber Bragg grating. The experiment is performed incorporating a commercialized femtosecond pulse laser system (MICRA, Coherent) with a 100 mm length of 780-HP fiber which is inscribed 50 mm of Bragg grating. The pump laser for coherent anti-Stokes Raman spectroscopy has a bandwidth of 90 nm and central wavelength of 815 nm with a notch shaped at 785 nm. The positive chirped pulse is compensated by chirped mirror set. We compensate almost 14000 fs2 of positive group delay dispersion for the transform-limited pulse at the sample position. The pulse duration was 15 fs with average power of 50 mW, and showed an adequate notch shape. Finally, coherent anti-Stokes Raman signals are observed using a spectrometer (Jobin Yvon Triax320 and TE-cooled Andor Newton EMCCD). We obtained coherent anti-Stokes Raman signal of acetone sample which have Raman peak at the spectral finger-print region. In conclusion, the proposed method is more simple and cost-effective than the methods of previous research which use grating pairs and resonant photonic crystal slab. Furthermore, the proposed method can be used as endoscope application.
We present qualitative monitoring of multilayered films by noninvasive investigation in the terahertz frequencies. Three multilayered films composed of marine paint are characterized in reflective, non-orthogonal measurements in ambient atmosphere. The spectra of the constituent marine paint layers EH2350, Interthane 989, BEA777, and ENA300 present sufficient spectral information for effective monitoring of the multilayered structures. Our experimental findings show promise in noninvasive monitoring of layered structures in realistic industrial evaluation applications.
Single-pulse coherently controlled nonlinear Raman spectroscopy is the simplest method among the coherent anti-Stokes Raman spectroscopy systems. In recent research, it has been proven that notch-shaped femtosecond pulse laser can be used to collect the coherent anti-Stokes Raman signals. In this study, we applied a fiber Bragg grating to the notch filtering component on the femtosecond pulse lasers. The experiment was performed incorporating a titanium sapphire femtosecond pulse laser source with a 100 mm length of 780-HP fiber which is inscribed 30 mm of Bragg grating. The fiber Bragg grating has 785 nm Bragg wavelength with 0.9 nm bandwidth. We proved that if the pulse lasers have above a certain level of positive group delay dispersion, it is sufficient to propagate in the fiber Bragg grating without any spectral distortion. After passing through the fiber Bragg grating, the pulse laser is reflected on the chirped mirror for 40 times to make the transform-limited pulse. Finally, the pulse time duration was 37 fs, average power was 50mW, and showed an adequate notch shape. Furthermore, the simulation of third order polarization signal is performed using MATLAB tools and the simulation result shows that spectral characteristic and time duration of the pulse is sufficient to use as an excitation source for single-pulse coherent anti-Stokes Raman spectroscopy. In conclusion, the proposed method is more simple and cost-effective than the methods of previous research which use grating pairs and resonant photonic crystal slab.
This paper presents a method to obtain spectral ring-down information simultaneously via double-looped Mach-Zehnder interferometry. The symmetric split-step Fourier method was used to simulate the pulse propagation through the fiber loop to check fiber-induced effects on the pulse. The loop was built with a segment of fiber, output coupler, and fiber Bragg grating. The fiber Bragg grating was used as an artificial sample. We found that the pulse spectrum is not distorted as the pulse propagates the fiber loop. We have also demonstrated the possibility to extract the ring-down signals from spectrum variation via simulation. This approach can be applied to sample detection which requires high sensitivity and high spectral resolution.
The concentration of trace sample can be determined by, and therefore an indicator of, the absorption property in fiber-loop ring-down spectroscopy. The aim of this study was to investigate the use of an ultrashort-pulse laser as a source of the fiber-loop ring-down spectroscopy and its applicability for loss-compensated fiber loops. A composite-type carbon-nanotube saturable absorber mode-locked fiber laser was built to be used as a source of experimental setup. The simulation has been done to check dispersion effects on ring-down signals, and it was found that the initial pulse duration affected ring-down information. To avoid this limitation, we just used the chirped pulses without any compensation process in the experiment. A loss-compensated fiber loop was constructed to measure the concentration of water in water/acetone mixture samples. The measurements were shown to lead to an accurate determination of the ring-down time. The result indicates that it is possible to measure the sample-induced absorption with the ultrashort-pulse laser source and loss-compensated fiber loop to determine the concentration of the sample.
In this research we proposed the circuit for storing electric energy by converting mechanical energy at capacitor using
EAP Pad. We used the Smartspice program which is a circuit analysis program for checking level of electric energy. We
mainly analyzed into 4 effecting factors to electric energy, and 4 factors are firstly applied voltage, secondly the capacitor
of source part and the capacitor of capacitor part, thirdly capacitor of EAP and its change of capacitor value, and for last
an applied frequency. For addition, research for EAP generators are needed electric power to circuit at all time till now.
But different from that, this research focused on not all time.
A non-invasive, phase-insensitive optical coherence angiography method has been demonstrated for in vivo human
retinal imaging based on high-speed spectral-domain optical coherence tomography with a center wavelength of 840nm.
Three-dimensional view of the choroidal vasculature was obtained by segmenting choroidal vessels using threshold
values from the intensity distribution at each depth plane relative to the retinal pigment epithelium layer. A vascular
projection image was obtained by integrating the segmented choroidal vasculature.
We measure the concentration of oxy-, deoxy- and total hemoglobin by using the frequency-domain, near-infrared spectroscopy(NIRS) scanner. It is a non-invasive instrument that can provide real-time measurements of the changes in concentration. It can provide a diagnostic tool for the study of the brain in infants and children. However, it is difficult to apply it to the baby's head because of the contact of the probe on the soft baby's head. Therefore, we suggest the NIRS scanning system that can track the baby' head movement and detect NIRS parameters on the same position of the head. This system has three key components. The vision system performs the pattern matching for tracking the head by using the normalized cross correlation method with the target as a cross-line on the head during the diagnostic experiment. We can use the change of the position of the baby's head to re-target the light by the scanning system that uses four laser sources, a wavelength selector, and an x-y scanner. The detector system analyzes the resulting signal from the head using the diffusion model. Therefore, NIRS scanning system can provide a diagnostic tool to measure the changes of the NIRS parameters for the study of the baby's brain.
Ellipsometry is known as high precision metrology for thin film thickness measurements with sub-angstrom resolution. In ellipsometric measurements it does not measure film thickness or optical constants directly. It measures ellipsometric parameters, ψ and Δ, namely, defined as the ratio of reflection coefficients for p- and s-polarized light. Generally in rotating component ellipsometry, light intensity values at more than 256 angular positions of polarizer or analyzer with discrete Fourier transform methods are used to evaluate Fourier coefficients, which can be calculated to ellipsometric parameters explicitly. Using this scheme it is well suited in single point measuring ellipsometry, but it degrades measurement speed in imaging ellipsometry. In imaging ellipsometry due to the limitation in CCD detection speed, rotating components must move stepwisely, so more discrete positions of polarizer or analyzer takes more measurement time dramatically. So we propose four frame method which can be easily substituted for conventional discrete Fourier transform methods. Four frame method can save measurement time, but natively intensity measurements at only four angular positions can cause erroneous results in Fourier coefficients compared with that of discrete Fourier transform method. In the four frame method, many repetitive measurements for light intensity at each angular position can solve these shortcomings. That is, conceptually to reduce random noise in ellipsometric measurements, conventional discrete Fourier transform method uses spatial averaging technique, but four frame method uses temporal averaging technique. In our experiments we could get more than ten times fast measurements with four frame method.
The ellipsometry is known as high precision metrology for thin film thickness measurements and its optical properties by measuring ellipsometric parameters, ψ and Δ, defined as amplitude and phase values of the ratio of Fourier reflection coefficients for p- and s-polarized light. With conventional ellipsometers, we can get average values of ellipsometric parameters in the region of interest determined by spot size of measurement beam. However, we can expand the measurement scheme to two dimensional spectral imaging with additional imaging spectrograph compatible to the structure of ellipsometer. That is, we can simultaneously get spatial and spectroscopic ellipsometric parameters using two dimensional imaging detectors. Using this type of ellipsometers, polarization state dependent response of imaging spectrograph must be considered carefully during azimuth calibration procedures as well as ellipsometric parameters measurement. In this paper, we suggest Jones calculus model for ellipsometer with considering dichroic response in spectrograph and background signal levels in detector. And we show experimental calibration results comparison with that of simulation using suggested Jones calculus model.
This paper proposes a new approach of fusing skin color and motion information to detect face areas in moving pictures. For reducing the computation time and also the effect of lighting conditions, the block based analysis technique is used in the fusion process. Motion is detected from a difference image segmented into blocks having 4x4 pixels, and a block is classified as a MB (motion block) if the sum of pixel values in the blocks is larger than a specific threshold. Similarly, each block is marked as a FB (face block) if it contains more than one skin color pixels. Then the candidates for face regions (CF) are selected by fusing MB and FB images using the logical AND operation. Among CFs, the face regions are selected by using the heuristic rules on human faces such as the ratio of width and height, the high frequency portion in a face region, etc. In the final step, the selected CFs are tested by the facial feature scoring scheme which selects the CF having a score larger than a threshold as a face. The experimental results have shown that the proposed algorithm determines face regions in 0.08 sec with the correct decision rate of 91.7% and false detection rate 4.26%.
We found the simple, effective and low-cost fabrication method of scanning probe tip with carbon nanotube. The assembling apparatus has been discussed and a plausible explanation about attachment mechanism based on dielectrophoretic force has been suggested. In order to find the proper assembling condition, electric field analysis for the round shape tip has been accomplished. Using this condition, the scanning probe tips with carbon nanotube were fabricated at 25% success rate.
As the mapping of the human genome has been completed, increasing emphasis is being placed on large-scale protein separation and identification methods to define the function of proteins and their associated genes. Within the last decade the sensing technique using the surface plasmon resonance(SPR) has received a great deal of attention and has become a leading technology for affinity-based biosensing. In this paper I report a novel design of SPR fiber optic sensing elements which allows developing highly miniaturized SPR probes. A fiber-optic chemical sensor is presented which utilizes surface plasmon resonance excitation. The sensing element of the fiber has been made by removing a section of the fiber cladding and symmetrically depositing a thin layer of highly reflecting metal onto the fiber core. A white light source is used to introduce a range of wavelengths into the fiber optic. Changes in the sensed parameters are determined by measuring the transmitted spectral intensity distribution. Therefore, when a protein layer is adsorbed on the metal surface, an increase in the refractive index occurs and can be detected. Based on theoretical analysis, the sensor structure is optimized to achieve the maximum sensitivity.
Optical triangulation displacement sensors detect linear displacements of objects without mechanical contact. They have simple structure, good resolution, and long operating range. However, there are several errors generated from speckle effects, environmental effects, and electronic noises, etc. To reduce errors from the electronic noises, the easiest way is to average the measurement outputs. Because the electronic noises are random in nature, their variance can be reduced with the averaging operation. However, this method is inherently time consuming process. To decrease the averaging time, several sensors or better signal processing hardwares are needed. So it increases the size of the measurement system and is not costeffective. In this paper, we propose a simple and cost-effective system structure for optical triangulation displacement sensors, which simplifies the averaging by inserting a transmission-type diffraction grating. When an incident ray enters to the diffraction grating, the grating separates the incident ray into several rays by the diffraction effect. The diffraction grating helps us to attain several signals simultaneously. Theoretical analysis is given and the feasibility of the proposed system is verified through experiments.
Optical triangulation displacement sensors are widely used for their non-contact measurement characteristics, sub-micron order resolution, simple structure, and long operation range. However, errors originating from surface inclination, speckle effect, light source fluctuation, and detector noise limit the wider use. In order to minimize these errors, the structure for optical triangulation displacement sensors, which is composed of an incoherent source and a linear CCD, has been proposed. But using a linear CCD causes several problems in signal processing. In this paper, we propose an adequate signal processing system for the proposed structure. With the help of the proposed algorithm, the limited resolution problem of CCD can be solved.
This paper describes a newly designed multipoint process monitoring system based on an acousto-optic tunable filter. In order to prove the feasibility of the suggested multipoint monitoring system for use in the NIR spectral region, some experiments were carried out in the visible range. The multipoint process monitoring system consists of an AOTF device for wavelength selecting, a CCD imaging sensor, and a specially designed in-line type of optical fiber probe. Unlike an FTS (Fourier Transform Spectrometry) based monitoring system, an AOTF has no moving parts, and it can be rapidly tuned to any wavelength in its operating range within microseconds. Thus, the AOTF is advantageous in terms of faster spectral imaging capability and rigidity required for industrial monitoring environment. Also, Fourier Transform Spectrometry experiments were conducted for comparison with the AOTF based monitoring system. In the current feasibility evaluation, an enhanced optical fiber probe with 3 monitoring points was used. However, the number of monitoring points can be easily expanded to dozens more points as required.
We have developed an in-situ single wavelength ellipsometer applicable to a vacuum sputter to monitor ellipsometric parameters during thin film deposition. The translation and tilting stages in the polarizer and analyzer make it easy to adjust optical axis and the angle of incidence. To calibrate inherent offset in the azimuth axis of the polarizer and analyzer, regression and residual calibration procedures are conducted. This work also includes the measurement results of the silver target deposition on the alloy, made of chrome and nickel, and silicon wafers. The manufactured ellipsometer will be used to investigate optical properties of the thin film and substrate in the vacuum state with various temperature ranges.
Ceramic is an important material for electrical engineering fields because it has high creep, chemical, and temperature resistances. MEMS technology sometimes needs transparency and chemical resistance, so glass is often used. As the system size becomes smaller and smaller, however, it is impossible to machine such materials by conventional methods because they are hard and brittle. Some unconventional methods are suitable for non-conducting ceramic materials regardless of their properties of hardness, toughness, and brittleness. Electrochemical discharge machining (ECDM) is one of the unconventional methods for ceramic materials. However, ECDM usually requires tools fabricated by other machining. As the machining size becomes smaller, the coordinate system of the tool tip can be easily changed when we fix or replace the tools. This paper proposes a new machining system; the system has two fabrication modes. It makes a tungsten tool by electrochemical process (ECP), and then, ceramic materials are machined by ECDM with this tool. These two machining systems can be easily transformed from only one system by the regulation of the concentration of the electrolyte and the electric power controller. We illustrate and analyze some experimental results of the machining of tungsten tools and ceramic holes which have various geometric shapes.
12 Current technological development toward miniaturization requires smaller components. These components usually generate complex multi-DOF motions other than simple 1-DOF mission. Therefore it is essential to develop measurement methodology for 6-DOF motions. In this paper, a new 6-DOF measurement system for milli-structure is presented. This methodology basically employs the Optical Beam Deflection Method with a diffraction grating. A laser beam is emitted toward the diffraction grating which could be attached on the surface of a milli-structure and the incident ray is diffracted in several directions. Among these diffracted beams, 0th and +/- 1th order diffracted rays are detected by 4 Quadrant Photodiodes. From coordinate values from each detector, we can get information for 6-DOF motions with linearization method. Required resolutions for milli- structure measurement are sub-micrometer in translation and arcsec in rotation. Experimental results indicate that proposed system has possibility to satisfy this requirement. This method can be applied to measurement of various applications such as arm head of HDD, micro positioning stages.
Point triangulation probes (PTBs) fall into a general category of noncontact height or displacement measurement devices. PTBs are widely used for their simple structure, high resolution, and long operating range. However, there are several factors that must be taken into account in order to obtain high accuracy and reliability; measurement errors from inclinations of an object surface, probe signal fluctuations generated by speckle effects, power variation of a light source, electronic noises, and so on. In this paper, we propose a novel signal processing algorithm, named as EASDF (expanded average square difference function), for a newly designed PTB which is composed of an incoherent source (LED), a line scan array detector, a specially selected diffuse reflecting surface, and several optical components. The EASDF, which is a modified correlation function, is able to calculate displacement between the probe and the object surface effectively even if there are inclinations, power fluctuations, and noises.
Multi-degree-of-freedom (MDOF) displacement measurement systems are needed in many application fields; precision machine control, precision assembly, vibration analysis, and so on. This paper presents a new MDOF displacement measurement system that is composed of a laser diode (LD), two position- sensitive detectors (PSDs), and a conventional diffraction grating. It utilizes typical features of a diffraction grating to obtain the information of MDOF displacement. MDOF displacement is calculated from the independent coordinate values of the diffracted ray spots on the PSDs. Forward and inverse kinematic problems were solved to compute the MDOF displacement of an object. Experimental results show maximum absolute errors of less than plus or minus 10 micrometers in translation and plus or minus 30 arcsecs in rotation.
A dynamic model for a vibrating microgyroscope with respect to angular rate is derived. Using the dynamic model, responses of the vibrating microgyroscope with respect to angular rate input is analyzed. A microgyroscope, which vibrates on the substrate plane, is designed and fabricated by simplified fabrication processes using single polysilicon on insulator structure. The validity of the derived dynamic model is tested by comparing simulation results with and experiments. The performance of the fabricated microgyroscope is investigated in a vacuum chamber of 100 mtorr. The obtained sensitivity of the microgyroscope at a typical static angular rate is 5 mV s/degree.
A new hardware compensation method reducing displacement measurement errors, caused by tilt of index scale in moire type linear encoder, has been developed. In the conventional moire type linear encoders, the detectors are aligned perpendicular to the line of moire fringes and this structure is very sensitive to an unwanted tilt of the gratings. In this paper, newly designed grating, named as phase shifted grating, is developed to compensate non-orthogonal error. By adopting the phase shifted grating instead of conventional index one, it is possible to reduce non-orthogonal error of the moire type linear encoder.
A microgyroscope, which vibrates in two orthogonal axes on the substrate plane, is designed and fabricated. The shuttle mass of the vibrating gyroscope consists of two parts. The one is outer shuttle mass which vibrates in driving mode guided by four folded sprints attached to anchors. And the other is inner shuttle mass which vibrates in driving mode as the outer frame does and also can vibrate in sensing mode guided by four folded springs attached to the outer shuttle mass. Due to the directions of vibrating modes, it is possible to fabricate the gyroscope with simplified process by using polysilicon on insulator structure. Fabrication processes of the microgyroscope are composed of anisotropic silicon etching by RIE, gas-phase etching of the buried sacrificial oxide layer, metal electrode formation. An electromechanical model of the vibrating microgyroscope was modeled and bandwidth characteristics of the gyroscope were analyzed firstly. The analyzed characteristics of the gyroscope were evaluated by experiment. The gyroscope operates at DC 4V and AC 0.1V in a vacuum chamber of 100mtorr. The detection circuit consists of a discrete sense amplifier and a noise canceling circuit. Using the evaluated electromechanical mode, an operating condition for high performance of the gyroscope is obtained.
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