We report the experimental demonstration of plasma generation by time-reversal focusing. After a learning phase, the amplified time reversed signal built at a central frequency of 2.45 GHz injected in a low loss metallic cavity allows us to ignite and maintain a localized centimeter-sized plasma in argon at 133 Pa. The plasma spatial position is totally controlled by the signal waveform.
International audienceUne nouvelle approche multirésolution en FDTD est présentée. La FDTD à grilles duales (DG-FDTD) s'avère être précise, rapide, et facile à mettre en oeuvre
In the present paper, a detailed investigation of the spatio-temporal dynamics of the recently developed time reversal microwave plasma source is presented. This novel source allows to ignite a plasma at a desired location in a reverberant cavity by focusing the electromagnetic energy in time and space. An important feature is the possibility to control the plasma position only by changing the input microwave waveform. The source is operated in a repetitive pulsed mode with very low duty cycle (typically 5 × 10−2%). Nanosecond pulses have rise time lower than 1 ns. The generated plasmas have typical sizes in the millimeter range and are observed using imaging for dozens of nanoseconds. The plasma behavior is investigated for different pressures and repetition frequencies. A strong dependence is observed between each discharge pulse suggesting the existence of an important memory effect. The latter is probably due to argon metastable atoms and/or residual charges remaining in the post-discharge and allowing the next breakdown to occur at a moderate electric field.
The demonstration of enhanced spatial control of nanosecond microwave plasmas generated by the time reversal plasma source is presented in this paper. This new microwave plasma source relies on the spatio-temporal control of the electric field inside an all-metal plasma reactor by modifying the waveform of a high power microwave signal. More specifically, it originally used the spatio-temporal focusing capabilities of the time reversal method to focus a high electric field in a small location. However, a parasitic microwave breakdown can still occur at sharp corners or wedges inside the cavity due to the local enhancement of the residual electric field during time reversal focusing. Thus, it is proposed to use the linear combination of configuration field method to improve field control inside the reactor. Its transient electric field shaping capabilities turn out to be a good candidate for the development of a low pressure microwave "plasma brush".
In this letter, we study the design of three-dimensional (3D)-printed ceramics exhibiting anisotropic dielectric permittivities at microwave frequencies for dielectric resonator antenna (DRA) applications. The anisotropy is engineered by using periodic structures made up of subwavelength asymmetric unit cells filled with zirconia and air. Ceramic samples with uniaxial anisotropy are designed, 3D-printed, and measured. Birefringence up to 8 is achieved by controlling the volume fill rate of the unit cell. Besides, a single-fed circularly polarised (CP) DRA that relies on a 3-D-printed uniaxial anisotropic ceramic is proposed in the 2.45 GHz ISM band. Its simulated and measured reflection coefficient, axial ratio, and realised gain patterns are in good agreement, thus demonstrating the possibility of exploiting 3-D-printed anisotropic ceramics for DRA applications.
An original electrically small antenna concept relying on plasma discharges is presented in this paper. It consists of a small coaxial probe placed above a ground plane and surrounded by a hemispherical inductively coupled plasma discharge. This plasma discharge behaves as a subwavelength epsilon-negative resonator exhibiting a localized surface plasmon resonance at microwave frequencies with significant radiation efficiency. Measurements show that the plasma allows impedance matching of the radiating element and frequency agility from 310 to 390 MHz by controlling the power delivered to the discharge. Meanwhile, significant radiation enhancement up to 20 dB at 300 MHz is measured. The existence of the localized surface plasmon resonance is finally confirmed by a Mie analysis considering the measured plasma characteristics.
The use of microplasma discharges as power‐induced limiter elements in microstrip devices is proposed to protect receivers against high‐power microwave threats. A microstrip bandpass filter integrating such a microplasma‐based active microwave power limiter has been designed and measured. Power limitation is observed when the input power exceeds 19 dBm with a leakage power of 14 dBm. Due to the gaseous properties of the active medium, the proposed structure exhibits a very low additional insertion loss of 0.06 dB.
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