Paper-based plasma sanitizers

This work describes disposable plasma generators made from metallized paper. The fabricated plasma generators with layered and patterned sheets of paper provide a simple and flexible format for dielectric barrier discharge to create atmospheric plasma without an applied vacuum. The porosity of paper allows gas to permeate its bulk volume and fuel plasma, while plasma-induced forced convection cools the substrate. When electrically driven with oscillating peak-to-peak potentials of ±1 to ±10 kV, the paper-based devices produced both volume and surface plasmas capable of killing microbes. The plasma sanitizers deactivated greater than 99% of Saccharomyces cerevisiae and greater than 99.9% of Escherichia coli cells with 30 s of noncontact treatment. Characterization of plasma generated from the sanitizers revealed a detectable level of UV-C (1.9 nW⋅cm−2⋅nm−1), modest surface temperature (60 °C with 60 s of activation), and a high level of ozone (13 ppm with 60 s of activation). These results deliver insights into the mechanisms and suitability of paper-based substrates for active antimicrobial sanitization with scalable, flexible sheets. In addition, this work shows how paper-based generators are conformable to curved surfaces, appropriate for kirigami-like “stretchy” structures, compatible with user interfaces, and suitable for sanitization of microbes aerosolized onto a surface. In general, these disposable plasma generators represent progress toward biodegradable devices based on flexible renewable materials, which may impact the future design of protective garments, skin-like sensors for robots or prosthetics, and user interfaces in contaminated environments.

Second-Order Nonlinearity in Triangular Lattice Perforated Gold Film due to Surface Plasmas Resonance

We have studied the excitation second-order nonlinearity through a triangular lattice perforated gold film instead of square lattice in many papers. Under the excitation of surface plasmas resonance effect, the second order nonlinearity exists in the noncentrosymmetric split-ring resonators arrays. Reflection of fundamental frequency wave through a triangular lattice perforated gold film is obtained. We also described the second harmonic conversion efficiencies in the second order nonlinear optical process with the spectra. Moreover, the electric field distributions of fundamental frequency above the gold film region are calculated. The light propagation through the holes results in the enhancement of the second order nonlinearity including second harmonic generation as well as the sum (difference) frequency generation.

Expanded Thermochromic Color Changes in VO2 Thin Film Devices Using Structured Plasmonic Metal Layers

ABSTRACTWe investigate metallic thin films on VO2 and show that the magnitude of the reflected color change in that visible portion of the spectrum as VO2 undergoes the insulating to metallic phase transition can be controlled by changing the type of metal, the thickness of the metal and by patterning the metal at the nano scale. We consider the role of surface plasmas in the metal film and show that in the near infrared, the magnitude of the reflectivity increase for metal coated VO2 films, but decrease for uncoated VO2 thin films. This is explained in the context of Fresnel equations and considering the large change in the imaginary part of the dielectric constant as the VO2 changes state from the insulating to metallic phase.

Development mechanism of cathode surface plasmas of high current pulsed electron beam sources for microwave irradiation generation

This paper presents the development mechanism of surface plasmas of carbon-fiber-cathode electron beam source and its effects on the operation of a high-power microwave source, reflex triode vircator powered by about 400 kV, 9 kA, about 350 ns pulsed power accelerator. Based on the current and voltage characteristics of diodes using carbon fiber cathode, the axial expansion velocity is 1.2 cm/μs and the delay time of explosive emission is 2 ns. Further, the comparison of carbon fiber and stainless steel cathodes is made. It was found that the threshold electric field for carbon fiber cathode is about 25 kV/cm, and the delay time of explosive emission and threshold electric field for stainless steel cathode is, respectively, 4.5 ns and 40 kV/cm. The radial expansion velocity of individual emitting centers is estimated to be 1.2 cm/μs, equal to the axial expansion velocity, and this shows the cathode plasma spots spherically expand. In the optimal diode gap for microwave irradiation or at the average current density of 230 A/cm2using carbon fiber cathode, the screening radius was 0.67 cm, the lifetime of cathode emitting centers was about 60 ns, the cathode plasma density was 5 × 1015 cm−3, and the Debye radius of cathode plasma was <3 × 10−5 cm−3. The self-quenching behavior of explosive emission centers occurs, due to the process of cathode surface material release and cooling. The generation and self-quenching of emitting centers, and screening effect of cathode plasmas determine the increase and decrease of cathode emitting area, which is independent of the current density and background pressure. The relation between the lifetime of virtual cathode and background pressure was discussed. It was found, both theoretically and experimentally, that a lower background pressure indicates a longer microwave pulse or a better microwave waveform. It was observed by comparison that the temporary behavior of cathode emitting area is similar to the development process of microwave pulse. The changes of emitting area affects the stability of beam current injected into the virtual cathode region, further leading to the fluctuation of microwave pulse of vircator.