In optical measurement techniques, such as holographic and shearographic interferometry, digital speckle pattern interferometry, and 3-D computer vision, phase is used as a carrier for different physical quantities. For example, phase could stand for information concerning shape and deformation. The useful information is coded and wrapped into the range of − to + rad in a phase map. Phase unwrapping is the basic technique to resolve 2 ambiguities and recover expected physical quantities. We describe a novel method for unwrapping phase in a noise-disturbed phase map, which is characterized by broken fringes induced by different sources, such as a poor coherence length, high light or weak reflection on the sample surface, too dense fringes due to stress concentration, etc. In our method, broken fringes are detected and estimated. The phase map is segmented into different regions based on the quality of phase. Regions are ranked and arranged to construct a systematic unwrapping sequence. Unwrapping errors brought by broken fringes are minimized by the proposed unwrapping scheme. Several applications are presented to validate the new method.
In optical measurement techniques, such as holographic interferometry, shearographic interferometry, and 3D-computer vision, phase is used as a carrier for different physical properties. For example, phase could stand for the information of shape, deformation, or strain. The useful information is coded and wrapped into -π to +π range in phase map. Phase unwrapping is the basic technique to resolve 2π ambiguities and recover physical properties. In this paper, we describe a novel method for unwrapping phase in a noise-disturbed phase map, which is characterized with broken fringes. In this method, phase map is well analyzed before phase unwrapping. Broken fringes are detected and fixed. Phase map is segmented into different regions based on phase quality. Those regions with good phase quality will be unwrapped first and errors introduced by noise will be minimized. Several applications will be presented to testify our new method.
A digital laser microinterferometer with a capability to measure both static and dynamic properties of MEMS (Micro-Electro-Mechanical Systems) and microstructures has been developed. This system is designed to exploit a static and a dynamic measurements of microstructure such as MEMS with either a smooth or a rough surface. The method is based on digital laser Michelson interferometry and digital speckle pattern speckle interferometry (TV - holography) incorporated with optoelectronic devices including a special illumination system, a long distance microscope (LDM), a CCD camera, a high precise phase shifting unit and a signal generator for vibration measurement. The special illumination system can perform both a continuous (for static measurements) and a stroboscopic (for dynamic measurements) illumination by utilizing a Acoustic-Optic-Modulator (AOM). In this paper, the theory and methodology of the digital laser micro-interferometer with the stroboscopic illumination method are described. The usefulness of the micro-interferometer is demonstrated by examples of static and dynamic measurements for different MEMS.
Resistance spot welding is now widely used in the fabrication of sheet metals, mainly due to the cost and time considerations. Friction stir spot welding is getting more and more acceptance in the automotive industries. Such spot welds are found in nearly all products where sheet metal is joined. Obviously the quality of the spot weld has a direct impact on the quality of the product. The most important quality target of spot welds is the size of the weld nuggets. If the weld nuggets are improperly or incompletely formed, or the area surrounding the nugget is smaller than required, the structural integrity of the entire part may be uncertain. Furthermore these inconsistencies are usually internal and are seldom visible to optical inspection. This study is focused on the quality analysis of the spot welds by using "Digital Shearography". The paper mainly focuses on developing a novel, whole field technique for non-destructive inspecting the size of spot-welds, both for the resistance spot weld and the friction stir spot weld.
Bone is a mechanosensitive tissue that adapts its mass, architecture and mechanical properties to mechanical loading. Appropriate mechanical loads provide an effective means to stimulate bone remodeling and prevent from bone loss. It is controversial whether in situ strain in bone is a critical determinant in enhancement of bone formation, and it is therefore important to evaluate load-driven strain in bone. Using electronic speckle pattern interferometry, we determined high-resolution three-dimensional strains on the mouse femur in response to two loading modalities: an axial loading modality (ALM) and a knee loading modality (KLM). We demonstrated that these two loading modalities induced a different pattern of strain distributions. ALM generated strain in the midshaft of cortical bone, while strains with KLM were concentrated on the distal epiphysis of the mouse femur. Since KLM is capable of enhancing bone formation in cortical bone distant from the knee, the current results indicate that in situ strain is not always necessary for load-driven bone formation.