Industrialization of a Large Advanced Ultrasonic Flexible Probe for Non-destructive Testing of Austenitic Steel Pieces with Irregular Surface

Because the UT （ultrasonic testing） flexible probe technology may be an appropriate answer to examine components with uneven surface, AREVA has developed an industrial application of the CEA＇s （French Atomic Energy and Alternative Energies） flexible phased arrays sensors. As a ＂first of a kind＂ project, the challenges faced were significant, including developing a phased array smart probe suitable for industrial use on rather simple but large scale geometries, permitting UT propagation within a constraining media structure and then targeting a qualification according to ENIQ （European Network for Inspection Qualification） methodology. A prototype flexible probe, designed for UT validation, and final flexible linear array probes permitting the UT behavior （as, e.g., detection and sizing from diffraction type echoes） to be maintained on wavy coupling surfaces, have been manufactured. These probes include a profilemeter with optical sensors control and a specifically designed coupling circuit （avoiding probe housing tightness issues）. Qualification has been performed using open test blocks, （where known ＂defects＂ exist, for procedure qualification）, and blind test blocks, （where ＂defects＂ are unknown, for qualification of testing personnel）. One open test bloc was customized to represent a ＂real＂ surface condition, with gaps up to 2.5 mm under the regular rigid probes. AREVAI/BGSI in Germany was selected to lead the project, with assistance in development and manufacturing sub-contracted to ＂CEA/LIST＂ laboratory, and the companies ＂IMASONIC＂ and ＂M2M＂. This paper describes the development of these probes and explains a few features （ENIQ qualification objectives fulfilled, UT data acquired on actual perturbed surface） that made their industrial implementation successful.

Progress in Mechanical Modeling of Implantable Flexible Neural Probes

Implanted neural probes can detect weak discharges of neurons in the brain by piercing soft brain tissue,thus as important tools for brain science research,as well as diagnosis and treatment of brain diseases.However,the rigid neural probes,such as Utah arrays,Michigan probes,and metal microfilament electrodes,are mechanically unmatched with brain tissue and are prone to rejection and glial scarring after implantation,which leads to a significant degradation in the signal quality with the implantation time.In recent years,flexible neural electrodes are rapidly developed with less damage to biological tissues,excellent biocompatibility,and mechanical compliance to alleviate scarring.Among them,the mechanical modeling is important for the optimization of the structure and the implantation process.In this review,the theoretical calculation of the flexible neural probes is firstly summarized with the processes of buckling,insertion,and relative interaction with soft brain tissue for flexible probes from outside to inside.Then,the corresponding mechanical simulation methods are organized considering multiple impact factors to realize minimally invasive implantation.Finally,the technical difficulties and future trends of mechanical modeling are discussed for the next-generation flexible neural probes,which is critical to realize low-invasiveness and long-term coexistence in vivo.

Lift-Off Effect of Koch and Circular Differential Pickup Eddy Current Probes

A flexible or planar eddy current probe with a differential structure can suppress the lift-off noise during the inspection of defects.However,the extent of the lift-off effect on differential probes,including different coil structures,varies.In this study,two planar eddy current probes with differential pickup structures and the same size,Koch and circular probes,were used to compare lift-off effects.The eddy current distributions of the probes perturbed by 0°and 90°cracks were obtained by finite element analysis.The analysis results show that the 90°crack can impede the eddy current induced by the Koch probe even further at relatively low lift-off distance.The peak-to-peak values of the signal output from the two probes were compared at different lift-off distances using finite element analysis and experimental methods.In addition,the effects of different frequencies on the lift-off were studied experimentally.The results show that the signal peak-to-peak value of the Koch probe for the inspection of cracks in 90°orientation is larger than that of the circular probe when the lift-off distance is smaller than 1.2 mm.In addition,the influence of the lift-off distance on the peak-to-peak signal value of the two probes was studied via normalization.This indicates that the influence becomes more evident with an increase in excitation frequency.This research discloses the lift-off effect of differential planar eddy current probes with different coil shapes and proves the detection merit of the Koch probe for 90°cracks at low lift-off distances.

Effects of Micro-Milling and Laser Engraving on Processing Quality and Implantation Mechanics of PEG-Dexamethasone Coated Neural Probe

Compared with stiff silicon-based probes,flexible neural probes can alleviate biological inflammation and tissue rejection.A polyethylene glycol(PEG)coating can facilitate the insertion of flexible probes,and the fabrication methods have a significant impact on the dimensional accuracy and structural strength of the coating.In this study,a novel melting injection moulding method is used to process a PEG-dexamethasone(PEG-DEX)coating with high structural strength for a type of mesh-shaped photosensitive polyimide(PSPI)based neural probe.Combined with the digital image correlation(DIC)method,an in vitro test system with high accuracy is developed to evaluate the effects of the elastic modulus of the PEG component and two fabrication methods,i.e.,computer-numerical-control(CNC)micro-milling and laser engraving,on the processing quality and implantation mechanics of a PEG-DEX coated probe.The results show that compared with laser engraving,CNC micro-milling can ensure high dimensional accuracy and sharpness for the composite coating,thus leading to small damage from implantation,whereas the elastic modulus of the composite coating has a limited effect on the implantation mechanics of the PEG-DEX coated probe.