Nonlinear Response of HTSC Thin Film Microwave Resonators in an Applied DC Magnetic Field

The non-linear microwave surface impedance of patterned YBCO thin films, was measured using a suspended line resonator in the presence of a perpendicular DC magnetic field of magnitude comparable to that of the microwave field. Signature of the virgin state was found to be absent even for relatively low microwave power levels. The microwave loss was initially found to decrease for small applied DC field before increasing again. Also, non-linearities inherent in the sample were found to be substantially suppressed at low powers at these applied fields. These two features together can lead to significant improvement in device performance.Comment: 4 pages, LaTeX type, Uses IEEE style files, 600 dpi PostScript file with color figures available at http://sagar.physics.neu.edu/preprints.html Submitted to IEEE Transactions on Applied Superconductivit

Large Pyroelectric Response from Reactively Sputtered Aluminum Nitride Thin Films

We report the pyroelectric response of c-axis oriented, undoped, wurtzite, aluminum nitride reactively sputtered onto polished silicon wafers. The voltage between a metallic contact on the AlN surface and the n+ -doped silicon substrate was monitored during pulsed infrared, radiant heating. From analysis of the data, a pyroelectric voltage coefficient, PV, in excess of 0.5 x 106 V/m/K was extracted for films in the 600 to 2500 Å thickness range

Two-Element Dielectric Antenna Serially Excited by Optical Wavelength Multiplexing

A single pulsed laser beam containing multiple wavelengths (wavelength multiplexing) is employed to activate two semiconductor antennas in series. The dielectric nature of the semiconductors permits serial cascading of the antenna elements. Recently observed nonlinear characteristics of the radiated field as a function of the free carrier accelerating (bias) voltage are used to minimize the small interactions between elements. We demonstrate that the temporal electromagnetic radiation distribution of two serial antennas is sensitive to the three-dimensional pattern of the optical excitation source. One can, in turn, vary this distribution continuously by optical means to reconfigure the array

Nonlinear Response of HTSC Thin Film Microwave Resonators in an Applied DC Magnetic Field

The non-linear microwave surface impedance, Zs = Rs + iXs , of patterned YBCO thin films, was measured using a suspended line resonator in the presence of a perpendicular DC magnetic field, HDC , of magnitude comparable to that of the microwave field, Hrf . Signature of the virgin state was found to be absent even for relatively low microwave power levels. The microwave loss was initially found to decrease for small applied HDC before increasing again. Also, non-linearities inherent in the sample were found to be substantially suppressed at low powers at these applied fields. These two features together can lead to significant improvement in device performance. I. Introduction The microwave response of high-T c superconductors (HTSC) is important both from the point of view of microwave applications of HTSC[1] and fundamental physics[2]. An understanding of the loss mechanisms, field and current profiles and nature of non-linearities can lead to improvement in fabricated devices tha..

An optical device for measuring bending strain to 5000 microstrain and compatible with optical fiber installations

An optical sensor is described which can be attached to a structure and used as a gage for measuring bending strain. This device can be adjusted to maximize the gage factor for predetermined strain ranges. The sensor consists of glass capillaries coated on the outer surfaces with an optical absorbing layer followed by a reflecting layer. A mechanical strengthening layer can be included to extend the range of strain response. A source laser beam from an optical fiber is injected into one end of the gage. The light remaining in the beam after traveling through the gage is collected via another optical fiber. The optically active layer is adjusted during manufacture to provide a predetermined gage factor. For a given thickness of the absorber layer, the detected light is proportional to the amount of bending. Thus, by rigidly affixing the sensor to a structural member, the strain experienced by the member can be monitored. © 2005 IEEE

Surface etching of YBCO films by xenon difluoride

We have demonstrated that xenon difluoride (Xe F2) etches thin films of Y Ba2 Cu3 O7-x, the superconducting form of yttrium-barium-copper-oxide (YBCO), during dry etch processing. Both c -axis and mixed ac -axis YBCO films show evidence of such etching with a axis being more reactive. Profiles of YBCO films examined by ESCA show that the surfaces of both etched and unetched films are barium rich at the expense of yttrium. After Xe F2 etching, fluorine was found to be present to a depth of at least 40 nm. Despite the etching and the presence of fluorine in the YBCO films, the superconducting transition temperature, Tc, was unaffected by the Xe F2 treatment. © 2005 American Vacuum Society