A method to detect production faults in plastic packages using terahertz (THz) radiation is presented. Relying on the large difference between the absorption coefficients of plastic and water (for water-filled defects), and on the refraction index difference between plastic and air (for air-filled defects), our technique consists of focusing and scanning a terahertz beam on the sealed area of the package, followed by the detection of the transmitted signal. Compared to previous methods such as visual and ultrasound inspection, our technique can be applied for optically opaque packages and does not require immersion in a matching liquid. We tested our terahertz system on defects simulated by water-filled and air-filled round channels imbedded in polyethylene films, with diameters ranging from 10 to 100 µm. The results show that detection is possible down to 30 µm for water-filled and 40 µm for air-filled channels. The results are the same for both transparent and opaque packages.
High-speed holographic microscopy is applied to take three successive photographs of rapidly bifurcating cracks. A crack propagates in a PMMA specimen at a speed more than 600 m/s, and bifurcates into two cracks in the observation area at the center of the specimen. The position at which the crack bifurcates is controlled by varying the tensile stress applied to the specimen. When it bifurcates, the fast propagating crack is recorded as three holograms. The holograms reconstruct the real images of the crack, which are photographed through a conventional microscope. From the photographs, crack speed before and after bifurcation is obtained. Crack speed after bifurcation is slightly lower than that before bifurcation. Crack opening displacement (COD) is also measured along a crack both before and after bifurcation. The COD before bifurcation is proportional to square root of the distance from the crack tip. After bifurcation, the COD of a mother crack is proportional to square root of the distance from the nominal tip of the mother crack. However, the CODs of two branch cracks are not always proportional to square root of the distance from each of the crack tips.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.