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Title: Feasibility study of NiTi shape memory alloy thin film far infrared imaging sensor arrays
Other Titles: Nie tai ji yi he jin bo mo yong yu yuan hong wai tu xiang tan ce qi de ke xing xing yan jiu
Authors: Ng, Ki Cheong (吳奇昌)
Department: Dept. of Physics and Materials Science
Degree: Master of Philosophy
Issue Date: 2005
Publisher: City University of Hong Kong
Subjects: Infrared imaging
Nickel-titanium alloys
Shape memory alloys
Thin films
Notes: CityU Call Number: TA1570.N45 2005
Includes bibliographical references (leaves 69-69)
Thesis (M.Phil.)--City University of Hong Kong, 2005
x, 69 leaves : ill. ; 30 cm.
Type: Thesis
Abstract: Infrared Imaging (IR) devices without expensive cooling system are needed to lower the manufacturing cost of the IR imaging system. Without the cooling system, or with a smaller cooling system, the size and weight of the imaging device will also be reduced. In this investigation, the operation concept of an uncooled imaging sensor design that utilize the thermo-mechanical properties of nickel-titanium (NiTi) shape memory alloys (SMAs) for detecting far infrared radiation (FIR) is demonstrated. Based on the curving of the microcantilever, which is made of thin film NiTi SMA, as a function of the IR radiation intensity incident on the cantilever surface, it was found that it is possible to reconstruct an infrared image of a heat source by an array of thin film cantilever pixels. When a NiTi cantilever is heated up due to the absorption of IR radiation, the tilting angle associated with these pixels will change because of the reverse martensitic transformation of the NiTi SMAs. This change in tilt angle will in turn be detected by illuminating the pixel element with a laser beam. In the initial stage of this project, the bending property of a single NiTi strip was determined for providing the idea, and the result was also compared with the bending property of the bimatellic, or bimaterials cantilevers. A Michelson interferometer was used to detect the displacement of the NiTi cantilever. The input frequencies of 4 Hz and 18 Hz were used. It showed that the output intensity frequencies match with the input chopper frequencies: this infers that the IR impacting radiations can be converted to the readable signal through the curving of the NiTi cantilever. Meanwhile, the temperature to angular deformation curve of the sample was determined. The slopes of these transformations are very important parameters for determining the sensitivity of the IR detector. The positive result had proved the concept that the proposed use of NiTi SMA cantilever for indirect IR visualization is possible. In the second stage, the fabrication and the result of the far infrared imaging sensor by SMA were described. TiNi was used in thin film form as the basis of the infrared sensor. The thin film with composition of approximately 50:50 TiNi was sputterdeposited in high vacuum system. X-ray fluorescence (XRF) was used to determine the composition of the film, while the transformation temperatures were determined from the differential scanning calorimetry (DSC). Arrays of NiTi cantilevers were fabricated though the optical lithography and the wet etching process with the mixture of hydrofluoric acid (HF), nitric acid (HNO3) and deionized water. Array was fabricated, at which the pixel size was 50μm × 100μm. The success of this focal plane imaging approach, which should operate under room temperature conditions, will greatly simplify the complexity of infrared imaging devices.
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