Mechanically-Tunable Composite Filter at Low Frequencies

Previous studies into the possibility of a plasmonic medium of a coiled conductor array in air have shown promise. This work serves to evaluate the possibility of creating a mechanically-tunable composite filter at low frequencies. Copper springs were created with varying starting pitches using a coil winder. These springs were then embedded into a flexible host polymer. The mechanical and electromagnetic properties of each spring design were predicted and tested. Two horn antennas were used to characterize the overall electromagnetic (EM) properties of the composite. The pitch of each spring was increased mechanically through application of force to the entire polymermetal composite at equal intervals, with an EM test completed at each step. Using an Agilent 8510C Vector Network Analyzer (VNA), the frequency spectrum within the microwave range was scanned. Relative amplitude and phase measurements were taken at equal frequency and pitch steps. With no polymer surrounding the springs, plasmon turn-on frequencies were observed to span the microwave bands as the pitch of the springs were increased. Similar results are expected with the springs embedded in a polymeric matrix. These results suggest a method of creating a mechanically-tunable composite filter for use at low frequencies.