Browsing by Subject "Nondestructive examination"
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Item Open Access A new detection method for capacitive micromachined ultrasonic transducers(IEEE, 1998) Ergun, A. S.; Temelkuran, B.; Özbay, Ekmel; Atalar, AbdullahCapacitive micromachined ultrasonic transducers (cMUT) have become an alternative to piezoelectric transducers in the past few years. They usually consist of many small membranes all in parallel. In this work we report a new detection method for cMUT's. We arrange the membranes in the form of an artificial transmission line by inserting small inductances between the membranes. The vibrations of the membranes modulate the electrical length of the transmission line, which is proportional to the total capacitance and the frequency of the signal through it. By measuring the electrical length of the artificial line at a RF frequency in the GHz range, the vibrations of the membranes can be detected in a very sensitive manner. For the detector structure we considered a minimum detectable displacement in the order of 10-7 angstroms/√Hz is expected.Item Open Access On-chip characterization of THz Schottky diodes using non-contact probes(IEEE Computer Society, 2016) Khan, T. M.; Ghobadi, A.; Celik, O.; Caglayan, C.; Bıyıklı, Necmi; Okyay, Ali Kemal; Topalli, K.; Sertel, K.We present non-contact characterization of GaAs Schottky contacts in the 140-220 GHz band. The non-contact probing technique utilizes planar on-chip antennas that are monolithically integrated with the coplanar waveguide environment housing the Schottky diode under test. The diode contact is fabricated through a 6 mask lithographic process with a 5 μm deep-trench under the contact to minimize parasitics and extend operation into the THz band. A quasi-optical link between the VNA ports and on-chip probe antennas enables efficient signal coupling into the test device. The non-contact probe station is calibrated using on-chip quick-offset-short method and the effectiveness of this approach is demonstrated for integrated diodes for under various bias conditions.Item Open Access Response of acoustic imaging systems using convergent leaky waves to cylindrical flaws(IEEE, 1989) Gonalp, N.; Atalar, AbdullahCharacterization of near-surface properties of materials by acoustic means is most convenienth done by surface-acoustic-waves (SAW) that are spatially confined to the surface. There are several techniques available to excite focused SAW's on the surfaces of non-piezoelectric materials for imaging purposes. A conventional acoustic microscope lens excites focused SANI's on the object surface, but with a low efficiency. SAW can be excited with a high efficiency using conical wavefronts as obtained from a conical axicon. Such methods can be used in a scanning arrangement to generate images of surface inho-mogeneities. In this paper, an analysis of imaging systems making use of convergent SAW's is given using angular spectrum approach and T-matrix formulation. Inhomogeneities on the object surface are assumed to be circular cylinders whose axes are perpendicular to the surface. The response of imaging systems to such defects is found as a function of defect position with respect to the focus point. Theoretical and experimental results are compared and are found to be in good agreement. © 1989 IEEE