Non-destructive testing of composite materials is a key technology issue in equipment testing. Among the emerging new
testing methods, Lamb-wave technology is getting more and more attention. This paper proposed a sensing method to
acquire the Lamb-wave signal in thin plate based on optical low-coherence principles. Methods to acquire Lamb-wave in
thin plate using optical low-coherence technology were analyzed, and the technical path of non-contact, high-precision
method was chosen. Complete in-line experimental system and methods were designed and built up for testing. A sensor
system based on Michelson low-coherence interferometer was set up. The distributed optical fiber sensors were arranged
on the top of sample materials for signal detection. Mirrors to enhance reflection intensity were attached on the sample.
The phase of sensing arm was modulated by PZT vibration. Then signals were detected and processed by Daubechies10
wavelet and Gabor wavelet. In-line testing of thin plate with features of high-precision and high signal-noise-ratio was
realized, which is meaningful to dynamic testing of large-scale structure.
It briefly introduces the international development status of the high resolution for air-to-ground remote sensing satellite.
High resolution for the air-to-ground observation is also the civil and martial pursuing target. Because of the rising cost
along with the large-diameter telescope, the weight, cubage will also become large. Nowadays, how to get high
resolution with light weight, small cubage launch and large diameter is one of the important research directions in many
countries. We raise a method of large field-of-view and high resolution optical synthesis telescope which can solve this
problem. It is a co-phased segment mirrors which synthetic aperture diameter is about 1 m. Four 50cm diameter segment
mirrors can fulfill the requirement. It is folded during its launch and is spread after it reaches to its working spot. In this
way, it can reach the requirement of low launch weight, small launch cubage and can get high resolution observation.
This method contains the key technologies of real-time UV coverage, optics design optimization, co-phase measurement
and adjustment, micro-displacement sensor technology, the optics design and structure design. We explore the
technology which can fulfill field-of-view of 1.86° and the resolution of 0.4m. We will discuss the UV-coverage method
which includes the aperture arrangement, the relationship between the aperture number and the synthetic aperture
diameter. There are much more detail calculation and analysis to it. Something is discussed about its structure design and
optics design in the paper.
In order to determine the properties of thin films with the required performance and reliability, a sensing system for
dynamic monitoring is proposed to measure the thickness of thin films. The system is based on the principle of
white-light interference, and is combination of spectrum analysis and optical fiber techniques. When two reflected lights
interfere within white-light coherent length range, relationship of between interference intensity and the wavelength of
incident light is achieved according to the equation of interference light's intensity. According to different thickness of
film, the relevant method is selected to calculate the thickness of thin film. So the interference can be analyzed in
spectral domain. The scheme of the system is set up including white-light source, multi-mode optical fiber, beam splitter,
spectrometer. With the help of optical fiber, the interference pattern is captured by spectrometer. When thickness of thin
film is varying, spectra curve will shift. The original spectra curve is processed in the computer. In order to determine
accurate extreme points, many methods of curve processing are used to decrease the noise. The spectra curve is
smoothed by signal processing method called empirical mode decomposition (EMD). This method is suitable for
non-linear and non-stationary data processing. The experimental data is contrast to the calibrated value. The results
show that the relative error of this method is lower 1%. This method has advantages over other measuring methods, such
as higher accuracy, low-cost instrument, extensive measurement range, simple structure and non-destructive.