V. Dikhtyar

Theoretical analysis of the microwave-drill near-field localized heating effect

The microwave-drill principle [Jerby et al., Science 298, 587 (2002)] is based on a localized hot-spot effect induced by a near-field coaxial applicator. The microwave drill melts the nonmetallic material locally and penetrates mechanically into it to shape the hole. This paper presents a theoretical analysis of the thermal-runaway effect induced in front of the microwave drill. The model couples the Maxwell’s and heat equations including the material’s temperature-dependent properties. A finite-difference time-domain algorithm is applied in a two-time-scale numerical model. The simulation is demonstrated for mullite, and benchmarked in simplified cases. The results show a temperature rise of ∼103K∕s up to 1300K within a hot spot confined to a ∼4-mm width (∼0.1 wavelength). The input-port response to this near-field effect is modeled by equivalent time-varying lumped-circuit elements. Besides the physical insight, this theoretical study provides computational tools for design and analysis of microwave dri...

Drilling Into Hard Non-Conductive Materials by Localized Microwave Radiation

The paper describes a novel method of drilling into hard non-conductive materials by localized microwave energy (US patent 6,114,676). The Microwave Drill implementation may utilize a conventional 2.45GHz magnetron, to form a portable and relatively simple drilling tool. The drilling head consists of a coaxial guide and a near-field concentrator. The latter focuses the microwave radiation into a small volume under the drilled material surface. The concentrator itself penetrates into the hot spot created in a fast thermal runaway process. The microwave drill has been tested on concrete, silicon, ceramics (in both slab and coating forms), rocks, glass, plastic, and wood. The paper describes the method and its experimental implementations, and presents a theoretical model for the microwave drill operation. The applicability of the method for industrial processes is discussed.

Cyclotron-resonance-maser arrays

The cyclotron-resonance-maser (CRM) array is a radiation source which consists of CRM elements coupled together under a common magnetic field. Each CRM-element employs a low-energy electron-beam which performs a cyclotron interaction with the local electromagnetic wave. These waves can be coupled together among the CRM elements, hence the interaction is coherently synchronized in the entire array. The implementation of the CRM-array approach may alleviate several technological difficulties which impede the development of single-beam gyro-devices. Furthermore, it proposes new features, such as the phased-array antenna incorporated in the CRM-array itself. The CRM-array studies may lead to the development of compact, high-power radiation sources operating at low voltages. This paper introduces new conceptual schemes of CRM-arrays, and presents the progress in related theoretical and experimental studies in our laboratory. These include a multimode analysis of a CRM-array, and a first operation of this device with five carbon-fiber cathodes.

The Microwave-Drill

Summary form only given, as follows. The microwave drill is a novel method to cut and drill into hard non-conductive materials by localized microwave energy. The method has been tested on various materials, including concrete, glass, silicon, ceramics, and ceramic coatings. It yields holes in diameters from 0.3 mm to > 10 mm (in concrete). A theoretical model simulates the electromagnetic (EM) wave dissipation coupled to thermal effects in lossy dielectric media in which the dielectric properties depend on temperature. The simulation describes the rapid thermal runaway above a critical temperature, and the creation of the hot spot enabling the microwave-drill operation. However, our experiments attain the hot-spot melting stage faster than predicted by the EM model. We attribute the boosting effect to the plasma created at the early stage of the microwave-drill ignition. This plasma may increase the local temperature toward the critical point, thus accelerating the microwave-drill operation.

The microwave-drill technology

The microwave-drill technology employs concentrated microwave energy in order to drill thermally in hard nonmetallic materials such as silicon, ceramics, glasses, concrete, and rocks. Besides drilling, this technology enables insertion of pins and nails, melting, cutting, and jointing operations. The paper describes the microwave-drill principles and its experimental implementations, and presents some of its possible applications.

Flying plasma disks in basalt microwave furnace

Summary form only given, as follows. Our experiments study microwave heating phenomena of small basalt stones (/spl sim/10 cm/sup 3/) in a rectangular cavity (WR340) powered by a 650 W, 2.45 GHz magnetron. Occasionally, we observe the creation of a silvery cloud of plasma, in a disk shape. This occurs first on the top of the basalt stone. Then, the plasma ring (of 2-3 cm diameter) is flying about 20 cm from the stone along the cavity to the magnetron antenna, where it disappears. Soon after, another plasma ring is generated near the stone, flies to the magnetron, and repeatedly. The repetition period and the flying disk life cycle are approximately I sec. The effect is accompanied by a unique sound, and it ceases after 15-20 sec of heating when ordinary heating effects occur. We interpret the flying disks as plasmoids produced by a nonlinear interaction of non-stationary standing microwaves with the stones surface. The paper discusses this effect in view of Kapitzas idea on spherical plasmoids (lighting fireballs) generated by intensive standing radio-waves, in atmosphere and in laboratory experiments. Astrophysics and geophysics effects related to our observation are discussed as well.