Key Engineering Materials Vols. 295-296

Abstract: Porous silicon with pore size in the range of a few nanometers can be used as multifunctional material in different MEMS applications. Via an electrochemical etching method, porous silicon is fabricated on the silicon substrate and removed as a sacrificial layer by using KOH solution to form a micro structure. This technique is typical in micro fabrication. Three-dimensional size is the basic geometric feature to describe microstructure surface characteristics. It is important to investigate measurement methods for it. UBM Microfocus Measurement System based on defocusing error detection is adopted to measure eroded depth of silicon cup. The measured data in the experiments are analyzed. The influence of etching time, current density and silicon type on etching depth can be acquired. Effective reference data can be provided for studying micro fabrication methods.

Abstract: For effective medical treatment, sensors that can find foreign bodies such as tumors in early stage are required. This paper describes a new sensor for foreign body detection utilizing the fact that the property hardness of foreign bodies differs from that of normal tissues. It consists of a balloon probe, which is constructed with a thin rubber membrane inflated with compressed air, and an optical deformation analyzing system. Experiments are carried out using samples in which single hard balls are embedded to model single tumor in soft tissue. It was confirmed that this sensor can detect the existence of the hard ball and can also distinguish the inequality of size and hardness of the ball. Furthermore, experimental results detecting multi-objects showed that this sensor has the ability to detect the existence of multi objects and their relative positions simultaneously. By measuring the consistence of the arm and the abdomen of human body, it is proved that the sensor is also suitable for consistence measurement of human anatomy.

Abstract: The osseointegration trans-femoral implant is a new orthopedic anchoring method to attach prosthetic limb. The success of this technique depends on how healthy the osseointegration between implant and bone can be achieved and how the post-surgical rehabilitation is progressed. The current clinical practice is based on patient fitness feeling. To achieve a high success rate of osseointegration and an optimal rehabilitation process, a quantitative measurement of the degree of osseointegration is required. In this paper, the authors present a non-invasive method to determine the stability of an osseointegration trans-femoral implant system. It uses resonant frequency of implant system to observe the integration between the implant and bone. The vibration signals of a trans-femoral implant system were collected using an accelerometer attached to the implant abutment and analyzed using Fast Fourier Transform (FFT). The results of in vitro tests are presented to demonstrate that the developed instrument system can be used in future in vivo clinical research.

Abstract: This research develops an innovative free-form surface scanning system using laser triangulation for 3D dental data required for crown reconstruction. This novel design employs double laser diodes to produce two 45° structured-light lines projecting onto the plaster tooth models and three CCD cameras to capture deformed fringes to achieve fast and accurate 3D surface measurement of plaster tooth models. Effective strategies were implemented to overcome problems such as potential measurement occlusion and data registration inaccuracy, commonly encountered by other data scanning methods. The developed system has distinctive features such as laser projecting angles for complete surface measurement coverage, digitizing accuracy, and compact scanner volume for potential applications on 3D surface digitization of tiny industrial components. Experimental results verified that the proposed system achieves a 20µm digitizing accuracy and possesses fast scanning capability. Maximum one minute is used for a single-tooth model and 30 minutes are used for scanning the whole jaw.

Abstract: A hybrid correlation system incorporates an optical correlator, spatial light modulators(SLM), digital cameras and a computer. Spatial light modulators and cameras are used to dynamically update the input and the spatial filter. The hybrid correlation system integrates the parallel processing capability of the optical correlator and the flexibility of the digital system. It can be used as a high-speed multi-function information processor. This paper focuses on the design and fabrication of a hybrid optical correlator and how it is used as an intelligent instrument. We address the issues of rigorous requirements for filter registration and matched filtering by proposing practical approaches. We include the analysis and use of intensity filters based on commercial SLMs for real-time pattern recognition. We present the engineering details of a specific hybrid optical correlator for applications to the real-time identification of an aircraft.

Abstract: By reason of their sensitivity, accuracy and non-contact as well as non-destructive characteristics, modern optical methods such as digital speckle shearography have found an increasing interest for NDT applications on factory floors. With new carbon fiber technologies and other lightweight constructions in aircraft and automotive manufacturing, adapted examination designs and especially developed testing methods are necessary. Shearography as a coherent optical method has been widely accepted as a useful NDT tool. It is a robust interferometric method to determine locations with maximum stress on various material structures. However, limitations of this technique can be found in the bulky equipment components, the interpretation of complex shearographic result images and at the work with non-cooperative surfaces such as dark absorber and bright shining reflectors. We report a mobile shearography system that was especially designed for investigations at aircraft and automotive construction sites. It is also useful to find out the current conditions of artworks.

Abstract: Automatic measurement of an object shape is very important in solid modeling, machine vision, industrial inspection, and medical diagnostics, etc. We propose an optical sensor, which comprises a telecentric projector with a sinusoidal grating and a linear CCD camera. We use the FTP (Fourier transform profilometry) method to make a measurement on three-dimensional object. In the FTP method, a grating pattern projected onto the object surface is modulated by the height distribution of the object. The deformed fringe pattern is Fourier transformed and processed in the spatial frequency domain as well as in the space signal domain to demodulate the object shape from the main frequency component in the Fourier spectra. This optical sensor provides a rapid and non-invasive three-dimensional image acquisition. The repeatability is better than 5 µm within the 3σ limits.

Abstract: This paper describes the development of a confocal Fabry-Perot interferometer (CFPI) for non-contact and non-destructive detection of broadband ultrasound generated by a pulsed laser. The operation theory of CFPI is introduced. The transmission and reflection modes of operation were investigated theoretically and verified experimentally. For the present study, a CFPI cavity of 50cm with 95.4% reflectivity spherical mirrors was constructed with associated resonant cavity control and signal detection electronics. The design is capable of providing detection frequency bandwidth from 140kHz to 50MHz. For the first step of verification, the input signal simulated by an electro-optical modulator (EOM) was used for verifying the feasibility of surface wave measurement. Signals obtained from an avalanche detector were compared with the results through theoretical analysis of the CFPI transfer function in a transmission mode. The results show a favorable agreement between the two. Furthermore, transmitted ultrasound signals from a 5MHz contact ultrasound transducer were detected and compared between the CFPI system and a Michaelson interferometer. Patterns of ultrasound arrival and reflection were clearly detected by both. Because an intrinsic transfer function is embedded in the operation of CFPI, the output signal will be distorted when measuring surface displacement. A digital filtering process was considered for compensation for the surface displacement signal. From the comparative results, it was further concluded that the present CFPI design has a displacement resolution of 0.05nm. Future studies will be focused on the reflection mode operation for fully utilization of non-contact laser ultrasound generation and detection.

Abstract: A novel unattached laser feedback interferometer by combining the laser feedback effect with the frequency splitting technology is presented and demonstrated. Light source is the birefringence dual frequency He Ne laser which generates o-light and e-light with orthogonally polarized states. When the feedback mirror is moved along the laser axis, the intensity of both o-light and e-light is changed periodically. If a threshold intensity for the output light is appropriately given by the signal processing circuits, the remaining intensity curves in each period shows four different polarization states: e-light, e-light and o-light, o-light, and no-light. Each change of polarization state corresponds to λ/8 displacement of the feedback mirror. We determine the movement direction by the difference of the order of the polarization state appearance. The resolution of the system is 0.079µm. In the experiment, the reflectivity of feedback has no influence on waveform. The laser feedback interferometer is likely to become an instrument which has no real contact with a measured object.