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Flexible eddy current array sensor has the characteristics of flexibility, light weight and convenient installation, and has great application prospects in metal structure crack monitoring. In allusion to the low sensitivity of traditional rosette flexible eddy current array sensor to crack identification, a co-directional excitation coil layout method is proposed, which significantly improves the sensitivity of sensor to crack identification . Firstly, by establishing the finite element model, the sensitivity of three sensing coils of the traditional sensor to crack identification is calculated to be 4.1%, 1.7% and 3.5%, respectively. The conclusion that the disturbed backflow between the excitation coils affects the sensitivity of each sensing coil to crack identification is obtained. In order to improve the sensitivity of the sensor, a new type of sensor using the co-directional excitation layout is proposed by changing the layout of the excitation coil. The simulation results show that the sensitivity of three sensing coils to crack identification is increased by 11.2, 43.1 and 36.0 times, respectively. Then, the sensitivity tests of the two sensors are carried out. The experimental results show that the sensitivity of three sensing coils of the sensor adopted co-directional excitation layout increases sequentially, which is 8.9, 23.7 and 13.3 times higher than the traditional sensor, indicating that the sensor adopted co-directional excitation layout is more sensitive to crack identification. Finally, the error analysis shows that the difference between the sensitivity of experimental results and simulation results is caused by the difference of lift-off. The research results privide an important way to improve the sensitivity of crack identification.

Abstract. Fast, simple and effective registration methods are needed in a wide variety of computer-assisted surgical procedures in which readily locatable anatomical landmarks are not available. Surface-based leastsquares registration methods can be used, but are susceptible to poor initial pose estimates and to error contamination during intraoperative data collection. We have developed a fast, statistically robust method for surface-based registration during orthopedic surgery. The method, based on the iterative closest point (ICP) algorithm, fits a set of sparsely measured data points to a planar facet model. A first registration estimate is obtained by having the user contact the anatomy in a set of general anatomical regions (rather than contacting distinctive features). A small number of additional data points are acquired to refine the registration. Starting from the refined estimate, a robust scored perturbation method is used to find a better registration. This is followed by an M-estimate registration that is taken as the final registration. Simulation results show that this method is robust for data sets containing up to 25% gross outliers. The method has been tested in vitro on plastic bone models, where it outperformed the least-squares estimate and maintained the required 1mm/2• accuracy. The in vivo use of spotlights in computer-enhanced osteotomies of the knee have confirmed the usefulness of the method.

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Flexible eddy current array sensor has the characteristics of flexibility and light weight. It has a wide application prospect for surface crack monitoring of metal structures. In order to solve the problem of low sensitivity of crack identification of traditional flexible eddy current array sensor, the methods of changing the spacing between the excitation coil and the sensing coil (SES) of the sensor and pasting the permalloy film on one side of the sensor are adopted to improve the sensitivity of crack identification. Firstly, a finite element model is established to analyze the influence of the permalloy film on the eddy current density on the surface of the specimen and the influence of the SES on the sensitivity of crack identification of the sensor. The simulation results show that when the SES increases from 0.1 mm to 0.4 mm, the sensitivity of the three sensing coils of the sensor to crack identification increases by 144.96%, 181.63% and 136.36%, respectively. And the sensitivity of the sensor to crack identification is improved when the permalloy film is stuck on the upper surface of the sensor, which is up to 81.88%. Then, the experimental results show that when the SES increases from 0.1 mm to 0.4 mm, the sensitivity of the three sensing coils to crack identification increases by 114.68%, 161.66% and 131.24%, respectively. The sensitivity of the sensor to crack identification is increased by 68.21% when the permalloy film is pasted on the surface of the sensor. The error between simulation results and experimental results is introduced by lift-off. The research results can be used to improve the sensitivity of crack identification.