SiGnal Processing Techniques For Nondestructive Evaluation Using Laser Ultrasonics
Laser ultrasonics is a form of ultrasonic evaluation in which a pulsed laser generates an ultrasonic wave in a sample which interrogates a specific feature. When this wave returns to the surface a separate laser interferometer detects the small resulting displacement. This technique is strictly noncontact and is thus suitable for in-process inspection of parts at high temperature or moving at high speed. In many applications the acquired temporal signals have features which differ from those acquired using conventional transducers. In this paper we will describe these features and discuss techniques which have been used to process these signals.
Laser Ultrasonic Inspection of Adhesives Used in Auto Body Manufacture
Adhesive bonding is widely used in automotive production, especially for body assembly. It is critical to be able to measure the strength of adhesive bonds during manufacture in a nondestructive, effective and rapid manner. There is no current means for inspecting these bonds in real time. The specific inspection requirement is to (1) map the adhesive spread, (2) measure the thickness over the full area, and (3) measure the bond strength. All inspections must be performed from one side and must be able to function on contoured surfaces with ~1 mm spatial resolution. The ideal tool must be able to perform the above measurements simultaneously (i.e., in one pass across the bond). We have applied the technique of laser ultrasonics to the adhesive inspection requirements described above. In this paper, we describe the preliminary results of our study.
Studies on root enamel (2). Enamel pearls. A review of their morphology, localization, nomenclature, occurrence, classification, histogenesis and incidence.
Enamel pearls are one of a number of different enamel structures that can be found on the roots of deciduous and permanent teeth. They have a distinct predilection for the furcation areas of molar teeth, particularly the maxillary third and second molars. They can consist primarily of enamel, but in most instances, a core of dentin is contained within them. On rare occasions, even pulpal tissues can be found. Enamel pearls usually occur singularly, but up to 4 enamel pearls have been observed on the same tooth. Depending on the study, enamel pearls on permanent molar teeth have an incidence rate of between 1.1%-9.7% with distinct differences among racial and national groups. The incidence of enamel pearls increases greatly in histological studies, suggesting that they are often obscured by a covering of cementum.