Chen Y.-C.,National Taiwan University |
Chen T.-H.,National Taiwan University |
Chien C.-J.,National Taiwan University |
Chang W.-C.,National Taiwan University |
And 6 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010
Electret-based electrostatic devices have been used in the electro-acoustic field for decades. Recently, the improvement of its charge retention has been of interest for application to the field of smart materials. Hence, the flexible electret-based loudspeaker has become an important research topic for futuristic applications such as 3C (computers, communications and consumer electronics) and smart curtains. The volume velocity and the on-axis sound pressure level (SPL) of an electret loudspeaker are the key parameters of interest. To study the vibration characteristics of an electret diaphragm, a finite element analysis (FEA) was introduced to facilitate the design. To validate the finite element analysis (FEA) model, an out-of plane full-field non-destructive optical detection method which incorporates electronic speckle pattern interferometry (ESPI), was applied to determine the vibration mode shape of thin film. By driving the electret loudspeaker at different frequencies, a corresponding vibration mode of interest was detected with the ESPI set-up. Both the simulations and the experimental results obtained on the measurement platform are detailed in this paper. © 2010 SPIE.
Jan C.-M.,National Taiwan University |
Lee Y.-H.,National Taiwan University |
Wu K.-C.,National Taiwan University |
Wu K.-C.,National Applied Research Laboratories NARL |
And 2 more authors.
Optics Express | Year: 2011
A circularly polarized ellipsometer was developed to enable realtime measurements of the optical properties of materials. Using a four photo-detector quadrature configuration, a phase modulated ellipsometer was substantially miniaturized which has the ability to achieve a high precision detection limit. With a proven angular resolution of 0.0001 deg achieved by controlling the relative positions of a triangular prism, a paraboloidal and a spherical mirror pair, this new ellipsometer possesses a higher resolution than traditional complex mechanically controlled configurations. Moreover, the addition of an algorithm, FTA (fault tolerance algorithm) was adopted to compensate for the imperfections of the optomechanical system which can decrease system measurement reliability. This newly developed system requires only one millisecond or less to complete the measurement task without having to adopt any other modulation approach. The resolution achieved can be as high as 4x10-7 RIU (refractive index unit) which is highly competitive when compared with other commercially available instruments. Our experimental results agreed well with the simulation data which confirms that our quadrature-based circularly polarized ellipsometer with FTA is an effective tool for precise detection of the optical properties of thin films. It also has the potential to be used to monitor the refractive index change of molecules in liquids. © 2011 Optical Society of America.
Cheng C.-C.,National Taiwan University |
Lin C.-Y.,National Taiwan University |
Ho J.-H.,National Taiwan University |
Shieh J.,National Taiwan University |
And 6 more authors.
Journal of Mechanics | Year: 2010
We investigated the design parameters of a compact pot-like ultrasonic sensor which possesses a highly anisotropic beam pattern. As the sensor size is small due to its application constraint, the parameters are thus highly coupled to one another. We analyzed the respective effects of the parameters in the case where there is a vertical beam width reduction. The parameters investigated include resonant frequency, vibrating plate width-expanded angle, and ratio of thickness discontinuity of the vibrating plate. Numerical models developed by combining finite-element analysis and spatial Fourier transforms were adopted to predict the far-field radiating beam pattern of the various design configurations. The displacement distribution of the vibrating plate was measured using a microscopic laser Doppler vibrometer and the far-field pressure beam patterns were measured using a standard microphone in a semianechoic environment. The three configurations we used to validate the simulation model resulted in an H-V ratio of 2.67, 2.68 and 3.13, respectively which all agreed well with the numerical calculations. We found that by increasing the operating resonant frequency from 40kHz to 58kHz, the vertical far-field beam width of an ultrasonic sensor can be reduced by 31.62. We found that the vertical beam width can be significantly reduced when the ratio of the thickness discontinuity of the vibrating plate decreases from 1 to 0.4 and is incorporated with its optimal width-expanded angle of the vibrating plate. It appears that an ultrasonic sensor with this type of anisotropic beam pattern can be ideally adopted for today's automotive applications.
Wang C.-H.,National Applied Research Laboratories NARL |
Huang J.-D.,National Applied Research Laboratories NARL |
Chen C.-R.,National Applied Research Laboratories NARL
Procedia Engineering | Year: 2014
The FORMOSAT-7 (FS-7) satellite constellation collect atmospheric and ionospheric data primarily for operational weather forecasting and space weather monitoring to fulfill the needs of Taiwan, the US, and the rest of the world. Because of the relative high power consumption and limited temperature requirement, TriG receiver (TriGR) becomes a critical component for thermal control. A thermal model is developed to examine the temperature feasibility of TriGR at the preliminary design phase. Parametric studies including the sizes of radiators, the thicknesses and the lateral thermal conductances of honeycomb panels. Results show that the effect of thermal conduction is more significant than thermal radiation by comparing the influences of the lateral thermal conductance of honeycomb panel and the sizes of radiators. Moreover, it is found that both the thermal conductance between middle platform and wall panels, and the lateral thermal conductance of honeycomb panel are the main factors for thermal control of TriGR. A careful consideration for the bracket used between the middle platform and wall panels is therefore needed to guarantee the performance of it. © 2014 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.
National Applied Research Laboratories Narl | Date: 2013-03-18
A glitch-free data fusion method for combining multiple attitude solutions is disclosed, wherein a star camera is set as the master star camera. After acquiring attitude solutions from the star cameras, a rotation difference is calculated between a master attitude solution acquired from the master star camera and a slave attitude solution acquired from other star cameras. Then, a steady difference is acquired from the rotation difference via a low pass filter for correcting the slave attitude solution. When combining the corrected slave attitude solutions with the master attitude solution, the attitude glitches or attitude jumps, which occur while transitioning between data fusion configurations with different number of available attitude solutions, can be eliminated.