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Summary
Nowadays, negative parameters have been originally brought up and investigated in the electromagnetic met-amaterial, where the epsilon-near-zero (ENZ) response was dominated by collective plasma frequencies and carrier concentration. However, the ENZ response is missing at the radio frequency, leading to limitations on novel antennas and printed circuit board. Therefore, ternary copper/silica coated copper/polyvinylidene fluoride (Cu/Cu@SiO2/PVDF) composites were prepared to investigate the ENZ response at the radio frequency. With increasing the content of Cu granules, a transition from positive to negative permittivity was observed in the binary Cu/PVDF composites, in which negative permittivity was related to an inductive character. On the contrary, the binary Cu@SiO2/PVDF composites without any uncoated Cu granules exhibit positive permittivity, showing a capacitive character. In fact, negative permittivity was derived from the collective plasma oscillation of percolative Cu networks, and Cu@SiO2 granules were responsible for diluting effective electron concentration of Cu. For the ternary Cu/Cu@SiO2/PVDF composites, values of negative permittivity were suppressed to several orders of magnitude to-178 (measured at 1 MHz) and plasma frequency decreased to radio frequency about 106 rad/s. Besides, with the construction of percolative Cu networks, the Ac conduction mechanism was transformed from hopping conduction to metal-like conduction. Based on the equivalent circuit analysis, it showed that a permittivity transition was responsible for the capacitive to inductive character.
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Institution复旦大学; 浙江大学
