 |
 |
 |
 |
 |
 |
 |
 |
Electromagnetic Field Imaging Mode
One can instead apply energy to a microwave circuit to be imaged, and scan the circuit beneath an open-ended probe which is connected to a resonant section of transmission line. By monitoring the microwave power present in the resonator, one can image the electric fields above the microwave circuit sample. One can also measure nonlinear effects, such as intermodulation in superconductors.
Figure (a) shows an image of the absolute magnitude of Ez above the Cu microstrip resonator at 77 K. During the scan, the frequency of the source was fixed at the resonant frequency (9.95 GHz) and the probe was held about 1 mm above the microstrip. The image shows a maximum signal at the two open ends of the microstrip conductor (corresponding to the voltage antinodes), and a minimum in the middle (corresponding to the voltage node), as expected. The absolute magnitude of Ez is obtained by relating the net induced charge on the center conductor of the probe to the power P detected at the diode. Neglecting loss, using standard transmission line theory, one finds Ez2 = P / (A2w2eo2Zo). Here, A >>0.03 mm2 is the area of the center conductor and Z0 = 50 Ωis the impedance of the transmission line.
Figure (b) shows an image of |Ez| above the Tl2Ba2CaCu2O8 microstrip resonator, measured at 77 K. The frequency of the source is fixed at the resonant frequency (8.21 GHz) and the probe is 180 μm above the microstrip. As with the Cu resonator, we observe a maximum electric field at the two open ends, as expected for the fundamental mode. For comparison, Fig. (c) shows an electric field image obtained at f = 16.2 GHz, i.e, the second-harmonic frequency. For this image the probe was held 250 μm above the microstrip. We see a complete standing wave pattern with antinodes at the two open ends and the middle of the microstrip, as expected for the second-harmonic resonance.
 |
 |
 |
For more details please refer to: "Microwave Near-Field Imaging of Electric Field in a Superconducting Microstrip Resonator." Ashfaq S. Thanawalla, S. K. Dutta, C. P. Vlahacos, D. E. Steinhauer, B. J. Feenstra, Steven M. Anlage and F. C. Wellstood.
Center for Superconducity Research, University of Maryland, College Park, MD 20742-4111
Phone: 301.405.6129 Fax: 301.405.3779
Copyright © 2001 University of Maryland
Contact us with comments, questions and feedback