Variable Power, Short Microwave Pulses Generation using a CW Magnetron

Fine control of microwave power radiation in medical and scientific applications is a challenging task. Since a commercial Continuous Wave (CW) magnetron is the most inexpensive microwave device available today on the market, it becomes the best candidate for a microwave power generator used in medical diathermy and hyperthermia treatments or high efficiency chemical reactions using microwave reactors as well. This article presents a new method for driving a CW magnetron with short pulses, using a modified commercial Zero Voltage Switching (ZVS) inverter, software driven by a custom embedded system. The microwave power generator designed with this method can be programmed for output microwave pulses down to 1% of the magnetron's power and allows microwave low frequency pulse modulation in the range of human brain electrical activity, intended for medical applications. Microwave output power continuous control is also possible with the magnetron running in the oscillating area, using a dual frequency Pulse Width Modulation (PWM), where the low frequency PWM pulse is modulating a higher resonant frequency required by the ZVS inverter's transformer. The method presented allows a continuous control of both power and energy (duty-cycle) at the inverter's output

Dielectric properties measurement method in the microwave frequencies range for non-polar/polar liquid mixtures characterization

International audienceWe present a method based on dielectric properties measurements over a large spectrum of frequencies, in themicrowave (MW) domain, in order to characterize a liquid mixture. The liquid mixtures consist of non-polar fluids(silicone oil, diesel fuel) and polar additives, in order to increase the specific MW absorption of the mixture for furtherMW power processing. We have measured the MW specific absorptions for mixtures of silicone oil with 20% and 30%(w/w) isopropanol. In both cases, the mixtures are sufficiently stable over time to allow further studies of thermalconvection dynamics initiated by MW heating. For a mixture of diesel fuel with 10% (w/w) alkyl polyglycoside, the mainobservation was that its MW specific absorption varies over time after the mechanical mixing process

Microwave heating device for internal heating convection experiments, applied to Earth's mantle dynamics

International audienceWe report the design, construction, and performances of a microwave (MW) heating device for laboratory experiments with non-contact, homogeneous internal heating. The device generates MW radiation at 2.47 GHz from a commercial magnetron supplied by a pulsed current inverter using proprietary, feedback based command and control hardware and software. Specially designed MW launchers direct the MW radiation into the sample through a MW homogenizer, devised to even the MW power distribution into the sample's volume. An adjustable MW circuit adapts the MW generator to the load (i.e., the sample) placed in the experiment chamber. Dedicated heatsinks maintain the MW circuits at constant temperature throughout the experiment. Openings for laser scanning for image acquisition with a CCD camera and for the cooling circuits are protected by special MW filters. The performances of the device are analyzed in terms of heating uniformity, long term output power stability, and load matching. The device is used for small scale experiments simulating Earth's mantle convection. The 30 × 30 × 5 cm3 convection tank is filled with a water-based viscous fluid. A uniform and constant temperature is maintained at the upper boundary by an aluminum heat exchanger and adiabatic conditions apply at the tank base. We characterize the geometry of the convective regime as well as its bulk thermal evolution by measuring the velocity field by Particle Image Velocimetry and the temperature field by using Thermochromic Liquid Crystals

The Sandblaster Software-Defined Radio Platform for Mobile 4G Wireless Communications

We present a tier 2 Software Defined-Radio platform (SDR), built around the latest Sandbridge Technologies' multithreaded Digital Signal Processor (DSP) SB3500, along with the description of major design steps taken to ensure the best radio link and computational performance. This SDR platform is capable of executing 4G wireless communication standards such as WiMAX Wave 2, WLAN 802.11 g, and LTE. Performance results for WiMAX are presented in the conclusion section

Microwave-based, internally-heated convection: New perspectives for the heterogeneous case

International audienceThe thermal evolution of telluric planets is primarily controlled by the balance between internal heating - due to radioactivedecay - and efficiency of convective heat transfer in their mantle. In the Earth, the problem is particularly complex due tothe heterogeneous distribution of heat sources in the mantle and the non-linear coupling between this distribution and convectivemixing. To tackle this issue, we have developed a new technology to produce internally-heated convection based on microwavesabsorption. This technology has the unique capability to selectively heat different zones of a convective fluid (heterogeneous convection)through the careful control of the absorption properties of the different fluids. Here we illustrate with two examples thenew geophysical perspectives offered by microwave-based internally-heated convection: the problem of lithosphere stability andthe evolution of a hidden enriched reservoir in the lowermost mantle

Microwave-based laboratory experiments for internally-heated mantle convection

International audienceThe thermal evolution of terrestrial planets is mainly controlled by the amount of radioactive heat sources in their mantle, and by the geometry and efficiency of solid state thermo-chemical convection within. So far, these systems have been studied using numerical methods only and cross validation by laboratory analogous experiments has not been conducted yet. To fill this gap we perform the first laboratory experiments of mantle convection driven by microwave-generated internal heating. We use a 30×30×5 cm3 experimental tank filled with 0.5 % Natrosol in water mixture (viscosity 0.6 Pa.s at 20°C). The fluid is heated from within by a microwave device that delivers a uniform volumetric heating from 10 to 70 kW/m3; the upper boundary of the fluid is kept at constant temperature, whereas the lower boundary is adiabatic. The velocity field is determined with particle image velocimetry and the temperature field is measured using thermochromic liquid crystals which enable us to charaterize the geometry of the convective regime as well as its bulk thermal evolution. Numerical simulations, conducted using Stag-3D in 3D cartesian geometry, reproduce the experimental setup (i.e., boundary conditions, box aspect ratio, temperature dependence of physical parameters, internal heating rate). The successful comparison between the experimental and numerical results validates our approach of modelling internal heating using microwaves