Development of nondestructive non-contact acousto-thermal evaluation technique for damage detection in materials.
This paper presents the development of a new non-contact acousto-thermal signature (NCATS) nondestructive evaluation technique. The physical basis of the method is the measurement of the efficiency of the material to convert acoustic energy into heat, and a theoretical model has been used to evaluate this. The increase in temperature due to conversion of acoustic energy injected into the material without direct contact was found to depend on the thermal and elastic properties of the material. In addition, it depends on the experimental parameters of the acoustic source power, the distance between sample and acoustic source, and the period of acoustic excitation. Systematic experimental approaches to optimize each of the experimental variables to maximize the observed temperature changes are described. The potential of the NCATS technique to detect microstructural-level changes in materials is demonstrated by evaluating accumulated damage due to plasticity in Ti-6Al-4V and low level thermal damage in polymer matrix composites. The ability of the technique for macroscopic applications in nondestructive evaluation is demonstrated by imaging a crack in an aluminum test sample.
NETD test of high-sensitivity infrared camera
Infrared camera has more and more application in military, judicature, rescue, industry, hospital and science. Nowadays the NETD (Noise Equivalent Temperature Difference) of high-sensitivity cooled infrared camera is less than 10 mK. If we test the NETD from the analog video output port of infrared camera using 8-bit and 10-bit ADC frame grabber, the NETD accuracy is 7.81 mK and 2.76 mK which correspond to relative error 78.7% and 27.6% for a 10 mK NETD infrared camera. Such kind of accuracy is obviously not proper for the performance evaluation of high-sensitivity infrared camera with NETD less than 10 mK. The NETD test accuracy can be improved by increasing the effective bit number of the ADC of frame grabber. The quantization error of ADC of frame grabber has become the main factor which contributes most to the NETD error of the high-sensitivity infrared camera. It is difficult to evaluate the electrooptical performance of the high-sensitivity infrared camera through its analog video. Although the NETD test accuracy can be improved by reducing the linear temperature range or increasing the effective bits of the ADC of frame grabber under analog video interface test condition, it is difficult to meet the test needs. But under the 14 bits digital video interface test condition and 1 K linear range, the NETD test accuracy of 0.24 mK can be achieved. The NETD accuracy can be also improved by reducing the linear temperature range. The NETD test accuracy can be 0.488 mK through 14-bit digital video under 2 K linear temperature range and its relative error equals 4.9% for a 10 mK NETD high-sensitivity infrared camera which meets the requirement. The test result through the digital video port of an infrared camera shows that the test result through digital video port matches with its nominal value. This necessitates the need of digital video interface of high-sensitivity infrared camera in NETD test in order to evaluate its performance accuracy.
An analysis of patients discharged from a hospital‐based glaucoma case‐finding clinic over a 3‐year period
Purpose:  To analyse the false positive referrals by community optometrists to a glaucoma case‐finding clinic over a 3‐year period.