Yen-Chang Chu

Preparation of bismuth oxide photocatalyst and its application in white-light LEDs

Bismuth oxide photocatalysts were synthesized and coated on the front surface of phosphor-converted white light-emitting diodes to produce a safe and environmentally benign lighting source. Bismuth oxide photocatalyst powders were synthesized with a spray pyrolysis method at 500°C, 600°C, 700°C, and 800°C. Using the absorption spectrum in the blue and UV regions of the bismuth oxide photocatalysts, the blue light and UV leakage problems of phosphor-converted white LEDs can be significantly reduced. The experimental results showed that bismuth oxide photocatalyst synthesized at 700°C exhibited the most superior spectrum inhibiting ability. The suppressed ratio reached 52.33% in the blue and UV regions from 360 to 420 nm. Related colorimetric parameters and the photocatalyst decomposition ability of fabricated white-light LEDs were tested. The CIE chromaticity coordinates (x, y) were (0.349, 0.393), and the correlated color temperature was 4991K. In addition, the coating layer of photocatalyst can act as an air purifier and diffuser to reduce glare. A value of 66.2 ± 0.60 ppmv of molecular formaldehyde gas can be decomposed in 120mins.

A novel optical method for measuring the thin film stress

This paper proposes a thin-film stress measurement system. By applying a constant velocity to the projection grating along the grating plane, a series of sampling points of the sinusoidal wave can be recorded using a CCD camera. The phase distribution of the optimized heterodyne moiré signal can be extracted by the least-squares sine fitting algorithm and then the surface profile of the tested flexible substrate can subsequently be acquired. Using polynomial fitting method to depict the cross-section curve of the substrate, estimating the resultant curvature radii of the uncoated and coated substrates, and substituting these two radii into the corrected Stoney formula, the thin-film stress of the flexible substrate can consequently be obtained. This method features high stability and high resolution due to the introduction of the projection moiré and heterodyne interferometry.

Alternative phase-shifting technique for measuring full-field refractive index

Abstract. This study proposes an alternative and simple method for measuring full-field refractive index. This method is based on the phase-shifting technique with a modulated electro-optical (EO) modulator and the phenomenon of total internal reflection. To this purpose, a linear polarized light is expanded and incident on the interface between the prism and the tested specimen, and the reflected light passes through an analyzer for interference. The phase difference between the s- and p-polarized light is sensitive to the refractive index of the tested specimen when the total internal reflection appears on this interface. Based on this effect, the resulting phase differences make it possible to analyze the refractive index of the tested specimen through a phase-shifting technique with a modulated EO modulator. The feasibility of this method was verified by experiment, and the measurement resolution can reach a value of refractive index unit of at least 3.552×10−4. This method has advantages of simple installation, ease of operation, and fast measurement.

A dipole antenna with helix structure applied to the WLAN systems

A novel printed dipole antenna with helix structure fed by a coplanar waveguide, suitable for 2.4 GHz and 5.2~5.85 GHz WLAN application is presented and investigated in this paper. The helix structure is designed so that the antenna length has a reduction then traditional printed dipole antenna. Some effects of many important parameters on the return loss and gain value of the proposed antenna have been investigated. In order to operate as WLAN device, the dipole antenna with helix structure should be cover the operation bandwidth of the 2.4 GHz and 5.2~5.85 GHz, and omni-directional radiation patterns are achieved at two operating bands.

Measurement of two-dimensional distribution of temperature with surface plasmon resonance

This study proposes a simple method for measuring two-dimensional temperature distributions. Using the significant phase difference between p- and s-polarizations of the reflected light of a surface plasmon resonance (SPR) detector, the variation in the phase difference, which is caused by a variation in the temperature, can be accurately measured by phase-shifting interferometry. Then, by substituting the phase distribution into special derived equation, the temperature distribution can be determined. In order to show the feasibility of this method, different temperature distributions were measured. The measurement resolution is about 0.186°C. Due to the introduced common-path configuration and the high-sensitivity characteristic of surface plasmon resonance, this method should have merits of easy operation, high sensitivity, high accuracy and rapidly measurement.