Takahiro Matsuo

Measurement of low gas concentration using photonic bandgap fiber

Abstract A high-sensitivity, compact set-up, enabling the precise measurement of a very low concentration of gas was designed. The micro-capillary gas flow phenomenon and the gas absorption inside fiber were estimated. Darcy - Weisbach equation for non-compressible flow and quasi - Panhandle equation for compressible gas flow were used for the calculation of the gas flow rate and gas velocity inside the photonic bandgap fiber. It was assumed that gas flowed mostly in the core. During the experimental part of work several types of optic fiber of various parameters were used. The core diameters ranged from 10.9 to 19.9 μm. It was possible to measure the flow rate of the nitrogen gas inside the fiber with various pressure differences on the opposite ends. Average velocity (Δp = 0.9 atm) ranged 0.17 m/s and was a little bit lower than expected.

Development of Highly Integrated Quartz Micro-Electro-Mechanical System Tilt Sensor

In this paper, we report the research progress of a recently developed quartz micro-electro-mechanical system (MEMS)-based capacitive tilt sensor using bulk micromachining technology. The sensor, which is composed of a sensitive cantilever, proof mass and high-aspect-ratio vertical comb electrodes in wafer thickness, was fabricated using an anisotropic wet etching process on a 100-µm-thick z-cut quartz wafer. A ceramic package was designed for mounting the sensor and integrating the capacitance to a digital AD7746 circuit (Analog Devices). The sensor was mounted on the package using a flip chip method via a AuSn alloy solder. The dimensions of the integrated sensing system are 12 ×12 ×3.2 mm3 and the weight of the system is below 1 g. The measured typical sensor sensitivity is 632 fF/° when the applied voltage is 0.625 V. The peak-to-peak output signal drift is limited to 1 fF in 2 h. Good linearity was achieved in the range of ±1°. High-precision detection at 0.001°, which corresponds to micro-g acceleration, was also demonstrated.

A novel lift off process and its application for capacitive tilt sensor

This paper presents a novel bi-layer (top image resist Shipley S1808 and bottom liftoff resist LOL2000) lift off process for patterning 3D devices. Resists are coated and patterned with an overhang profile on substrate before it is etched and before the film deposition. The key feature of the new lift off process is to create a resist undercut profile, which should be deep enough to reduce step coverage and durable to aggressive substrate etchant. Two-step development method was demonstrated effective. The resist profile is optimized by development time in the two step development process. Proposed lift off process was successively used for fabricating quartz based capacitive tilt sensor.

Study on a Diode-bridge Type Capacitance Detection Circuit for Differential Capacitive Sensor

Diode-bridge type capacitance detection circuit was developed in order to detect very small variation of differential capacitances in higher resolution. The circuit was designed for a comb structure tilt sensor, which was made of quartz crystal and had several movable electrodes between fixed electrodes. The circuits output was almost proportional to the displacement of the movable electrode. Over 100 kHz AC voltage was supplied to obtain output signal sufficiently. In order to prevent decrease of the sensitivity, the diode-bridge part was composed of commercial PIN diodes, which had very low junction capacitance (less than 1 pF), and was mounted in small ceramic package with the tilt sensor. At present, the resolution of 0.0015 degree was obtained using the combination of the sensor and the detection circuit. It corresponded to the resolution of about less than 4.5 aF.

A study on a diode-bridge type differential capacitance detection circuit

Abstract Differential capacitance sensor with movable electrodes is usually applied for accelerometers, pressure gauges, etc. because of its high sensitivity and resolution. Two axis inclination sensor with differential capacitance structure using MEMS (Micro Electro Mechanical Systems) technology has recently been designed for industrial and environmental purposes. The initial capacitance of the sensor should be very low, as few pF, therefore, a C-V converter circuit, which is able to detect very small capacitance variations is required. In this study, the particular principle of a “diode-bridge type differential capacitance detection circuit” has been analyzed. After the mathematical simulations performed by using PSpice simulator, the detection of the capacitance variations in fF order resolution are considered.

Sensing of Carbon Dioxide and Hydrocarbons Using Photonic Bandgap Fiber

The sensing setup for detection and measurement of carbon dioxide and methane was designed. Absorption spectra of many compounds indicate several weak peaks around 1400-1600 nm wavelength. Thus, tunable lasers with 20 micron core photonic bandgap fiber matching above wavelengths were chosen for the optical measurement system. Measurements were performed at low pressure to eliminate pressure broadening effect and to sharpen the absorption peaks. The angled cut was performed to improve signal to noise ratio.

High-Precision Gas Sensor Based on Photonic Bandgap Fiber Cell

As one of applications for Microstructured Optical Fiber, a new device for measurement of low gas concentration was designed. In the developed system the Photonic Bandgap Fiber (PBGF) was used as a gas cell. Proposed technique allowed reducing gas sample volume to 0.01 cc. The gas flow inside core of fiber was simulated and result was confirmed experimentally. During the experimental work several types of fibers of various parameters were specially designed, produced and used. Core diameters ranged from 10.9 μm to 700 μm. Various cutting techniques for fibers such as using the fiber cleaver, Focused Ion Beam and Cross Section Polisher were investigated.

PBG Fiber Low Concentration Gas Sensor

The photonic bandgap fiber for a high-sensitivity, compact set-up, which enables the precise measurement of low concentration of gas was designed. Fiber was used instead the traditional glass gas cell during the spectroscopic measurements. Ar ion beam was proposed among the other methods to process the inlet and outlet surface of fiber and adjust it to the required parameters. The gas flow inside PBF fiber and its optical properties were investigated.

Measurement of NH 3 concentration using optic fiber sensor

New generation of light fibers: Photonic Bandgap fibers (PBG fiber) were applied as gas cells in the concentration measurement sensor. Several types of PBG fibers of various parameters were designed. Core diameters ranged from 10.9 to 26.25 μm. The precise cutting method for the PBG fiber was proposed. Capillary gas flow rate within the fiber was simulated and measured. Attenuation of newly produced fibers was investigated and concentration of ammonia gas was measured using the new type sensing system.

Sensing of Gas Concentration Using Photonic Bandgap Fiber

Photonic bandgap (PBG) fiber was developed for a new gas-sensing device. The micro-capillary gas flow inside fiber and light guiding parameters were estimated in order to develop a high-sensitivity gas concentration measuring system. Darcy-Weisbach equation for non-compressible flow and quasi-Panhandle equation for compressible gas flow were used for the calculation of gas velocity. Core diameters of fibers ranged from 10.9 to 700 mum. The results of numerical simulations were compared with experimental results. Attenuation was calculated and concentrations of ammonia and CO2 were measured.