Four à micro-ondes | EPFL Graph Search

Un four à micro-ondes, ou plus simplement un micro-ondes ou même un microonde, est un appareil électroménager utilisé principalement pour le chauffage et la cuisson rapide d'aliments, par l'agitation des molécules d'eau qu'ils contiennent, sous l'effet d'un rayonnement micro-onde. Contrairement à ce qu'affirment certaines croyances populaires, cuire ou chauffer sa nourriture au micro-ondes n'est pas nocif pour la santé et ne retire pas de nutriments aux aliments. vignette|Intérieur d’un four à micro-ondes. Histoire L'invention du four à micro-ondes est un exemple classique de sérendipité, c'est-à-dire une découverte accidentelle d'un effet physique suivi d'une exploitation commerciale. Découverte vignette|Raytheon RadaRange à bord du NS Savannah, 1961. Selon la légende, en 1946, l'ingénieur américain Percy Spencer, alors qu'il dirigeait chez Raytheon une usine de magnétrons pour radars, avait ressenti de la chaleur dans la poche de sa blouse alors qu'il passa

Inflight Microwave Drying Process of Micro-droplets for High Resolution 3D printing

Kwanghoon Choi

A new Additive-Manufacturing (AM) or 3D printing concept is proposed to improve the printing resolution for metal additive manufacturing in the frame of the SFA-AM project, Powder Focusing for Beam-Induced Laser 3D Printing. The project aims to transport small powder particles (largest diameter < 10 um) at a high throughput to a spot smaller than 20 µm. To realize the objective, a metal ion included liquid is suggested as a source medium similar to the inkjet process, and the droplet is employed as a container for the metal ion transport. The key challenges of achieving this goal are 1) droplet size control and 2) efficient microwave heating that can dry the liquid portion of the dynamic droplet at a high-speed (3 m/s). The most demanding part is the development of a miniaturized, very concentrated field density microwave resonator where the droplet is passing through. This follows from the extremely short interaction time between the microwave and the ejected droplets (research: 0.5 ms) which results from the requirement for a small system size for its integration. The primary medium examined for the experiment is water due to 1) a high dielectric loss proportional to the drying efficiency and 2) avoiding explosion risks at the laser sintering stage compared to organic solutions. Various droplet generation conditions were investigated to determine the optimum conditions for the custom droplet generator, in particular, two key parameters were focused on: frequency and flow rate. The droplets obtained were analyzed with respect to size, gap distance, and linearity affecting the uniformity of the AM process. Moreover, Navier-Stokes-based fluid dynamics simulations enabled understanding of droplets behaviors, especially break-up formation. Eventually, the optimal condition for producing the smallest droplets with a diameter of 100 µm is determined to be 15 kHz and 0.5 ml/min. Such droplets loaded with metallic particles could result in smaller than 20 um of remaining metal powders aggregate after the drying process.A new TEM (Transverse ElectroMagnetic) resonator has been developed for drying and sensing applications. A full-wave electromagnetic simulation software, CST Microwave Studio, supported the working mode of the device. Firstly, it is used for the dielectric characterizations of different water-ethanol mixtures contained in a micro capillary. The sensing relies on electric field perturbation due to the inserted sample, and is measured based on the change of both resonance frequency and Q-factor. These sample-dependent variations were analyzed to estimate the complex permittivity using different methods such as the Perturbation Method (PM), Least-Square Model (LSM), and Log-Linear Model (LLM). This work demonstrates that the proposed microwave module is capable of sensing nano-liter volume ranges even though the samples only partially influence the sensing area (error < 13 % in permittivity). In microwave heating, the developed resonator achieved a temperature increase of 28 K in the microwave exposal time of 0.5 ms when the microwave power of 45 W was applied. Finally, numerical models have been proposed to estimate the maximum temperature of the initial droplet before cooling starts attributable to heat and mass transfer. This model well corresponds to the microwave electromagnetic simulation resulting in similar temperature deviations. It helps to determine the net heating efficiency of the microwave device.

EPFL2022

Demonstration of microwave generation by a ferroelectric-cathode tube

Catherine Pralong

A ferroelectric cathode is employed in a cyclotron-resonance maser (CRM). The CRM oscillator device operates at similar to 7 GHz, near the cutoff frequency of a hollow cylindrical cavity. The cathode is made of a PLZT 12/65/35 ceramic with high-dielectric constant (epsilon(r)similar to 4000). Electrons are extracted from the plasma excited on the cathode surface by similar to 1 kV short rise-time pulses. The use of ferroelectric cathodes may advance the microwave tube technology for various applications. (C) 1999 American Institute of Physics. [S0003-6951(99)03403-8].

1999

Optical-Microwave Pump-Probe Studies of Electronic Properties in Novel Materials

András Bojtor, Karoly Holczer, Sándor Kollarics, Bence Gábor Márkus, Ferenc Simon

Combined microwave-optical pump-probe methods are emerging to study the quantum state of spin qubit centers and the charge dynamics in semiconductors. A major hindrance is the limited bandwidth of microwave irradiation/detection circuitry which can be overcome with the use of broadband coplanar waveguides (CPWs). The development and performance characterization of two spectrometers is presented as follows: an optically detected magnetic resonance spectrometer (ODMR) and a microwave-detected photoconductivity measurement. In the first method, light serves as detection and microwaves excite the investigated medium, whereas in the second, the roles are interchanged. The performance is demonstrated by measuring ODMR maps on the nitrogen-vacancy (NV) center in diamond and time-resolved photoconductivity in p-doped silicon. The results demonstrate both an efficient coupling of the microwave irradiation to the samples as well as an excellent sensitivity for minute changes in sample conductivity.

WILEY-V C H VERLAG GMBH2020

Inflight Microwave Drying Process of Micro-droplets for High Resolution 3D printing

Kwanghoon Choi

EPFL2022