Block diagram of regenerative feedback resonant circuit used to monitor transient changes in material properties. Amplifiers have their usual symbol, and BPF denotes “band pass filter.” Upper amplifier is a low noise (LNA) amplifier, while the lower feedback amplifier is a cascade power amplifier stage with excellent isolation.
(Left) Layout of regenerative feedback resonant circuit with 8.2 GHz split-post dielectric resonator mounted on a thermo-electric cooling system. (Right) Commercial resonant cavities (QWED) used in the circuit: (top) 7.85 GHz dielectric ring resonator and (bottom) 8.2 GHz split-post dielectric resonator.
Illustrations of the sharpening of the resonance that happens as a result of introducing feedback and frequency shift due to material introduction. (a) Comparison of static (VNA) and dynamic (RTSA) resonances for empty and Si-loaded SPDR; (b) VNA signal for unloaded SPDR; (c) VNA signal for Si-loaded SPDR; (d) RTSA average of 10 sweeps for unloaded SPDR; (e) RTSA average of 10 sweeps for Si-loaded SPDR. Insets in (b) through (e) show the full signal (same axes designations as the main figure) while the main portion of each shows a closeup used in determining the Q-factor.
Digital phosphor spectrum display of regenerative feedback circuit response with silicon wafer inserted into SPDR. (a) Before perturbation; (b) illuminated with red laser pointer; (c) illuminated with Xe camera flashbulb. Note that the frequency content of the flashbulb response continues out to higher frequencies than is shown in this figure.
Resonator experiments with the DRR. (a) Static VNA measurements of empty, YIG-loaded (demagnetized), and YIG-loaded (magnetized); note that a demagnetized YIG-loaded DRR resonates at higher frequency than the empty cavity, but a magnetized YIG-loaded DRR resonates at slightly lower frequency than the empty cavity; (b) static versus dynamic (feedback) measurements for empty (main figure) and demagnetized YIG-loaded (inset) DRR; note the dramatic sharpening of the resonance and slight shift to higher frequency for the empty DRR but large positive frequency shift, resulting in a resonance >8.5 GHz, for the YIG-loaded DRR; (c) RTSA digital phosphor display of a permanent magnet perturbing a YIG-loaded DRR. The center frequency (center of figure) is 8.52146 GHz. It can be seen that interaction with the external magnetic field shifts the feedback resonance to higher frequencies and dampens it.
Measured frequency and Q-factor values for static and dynamic resonator/material configurations.
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