Prof. Zbigniew Celinski
Center for Magnetism and Magnetic Nanostructures
University of Colorado - Colorado Springs
We will present results for tunable microwave devices based on a microstrip and co-planar waveguide geometries. These structures, prepared by sputtering on GaAs, Si or SiO2 substrates, are compatible in size and growth process with on-chip high-frequency electronics. We will discuss on-wafer notch filters, band pass filters, nonreciprocal devices such as isolators, and true delay lines.
For the notch filters, we observed power attenuation up to 100 dB/cm and an insertion loss on the order of 2–3 dB for both Permalloy- and Fe-based structures. The operational frequency ranges from 5 to 35 GHz for external fields below 5 kOe. The operational frequency, which can be obtained from the ferromagnetic resonance condition, is set by material properties such as saturation magnetization, anisotropy fields, the gyromagnetic ratio, and the magnitude of an applied field. Thus, by using different materials and external fields we can create devices which function over a wide range of frequencies.
We fabricated a novel band-pass filter using ferrite nanoparticles as the active element in microstrip geometry. It is very compact and has very wide frequency tunability. Linear dependence is obtained between the resonance frequency and the applied dc magnetic field. The bandwidth and Q-factor of the filter are observed to be almost constant over the field range studied.
We use Ni nanowires to build microwave isolators (non-reciprocal devices). The attenuation of the wave in forward and reverse direction shows a difference in transmission coefficients. The isolation is ~ 6 dB/cm at 23 GHz. The bandwidth of the device is relatively large (5-7 GHz) in comparison to ferrite-based devices.
We demonstrate an on-wafer liquid crystal phase shifter which has a tunable 0 - 300o/cm phase shift at 110 GHz. The results show no dispersion over the entire frequency range indicating a tunable "true time delay" of up to 2.5 ps/cm at all frequencies. The inherent losses in the liquid crystal are small, less than 1 dB/cm over the range of 1 – 110 GHz. The full tunability is achieved using small voltages, close to 10 V.
Zbigniew Celinski is Professor of Physics at the University of Colorado - Colorado Springs. He received PhD degree in 1992 from Simon Fraser University, Burnaby Canada. His work concentrates in the area magnetism, magnetic materials, their high frequency characterizations, and on-wafer microwave devices. He published over 140 papers and holds a few patents. Zbigniew Celinski currently also serves as the Director of Center Magnetism and Magnetic Nanostructures.