E. Jerby

Investigation of the gain regimes and gain parameters of the free electron laser dispersion equation

We compute the small signal gain curve and various gain parameters by solving numerically the generalized gain-dispersion equation of free electron lasers (FEL), which characterizes the conventional magnetic bremsstrahlung FEL, as well as a large number of other FEL devices. The model includes high gain, collective, and axial velocity spread effects, and some waveguide effects. The FEL gain regimes are investigated and presented in terms of only three universal FEL characteristic parameters. The approximative analytic gain expressions are compared to the numerical computation results, and the approximation error is computed and displayed. In the intermediate regimes (high-low gain, tenuous-collective beam, cold-warm beam), the gain parameters are given in terms of useful curves, and a heuristic approximative formula is suggested for estimating the axial velocity spread gain reduction factor in all gain regimes. We also define and compute gain bandwidth and beam quality acceptance parameters in all gain regimes.

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...

Coupled thermal-electromagnetic model for microwave heating of temperature-dependent dielectric media

Microwave heating processes involve electromagnetic and thermal effects coupled together through the local temperature dependence of the material dielectric properties. This paper presents a one dimensional model for the coupled electromagnetic-thermal process and demonstrates its solutions for typical problems. The local temperature dependence of the lossy dielectric medium is taken into account in two different time scales. One is the heat-generation time scale due the microwave radiation, and the other is the temperature diffusion time scale. The two time-scale approach minimizes the computation time and provides an efficient simulation tool for the analysis of various phenomena. The two-scale model presented in this paper is benchmarked by a comparison of its numerical results with other models published in the literature. Several examples of microwave heating processes in various materials are simulated. Effects of heat-wave propagation in matter are predicted by the model. The results show the temporal and spatial evolution of the temperature and power-dissipation profiles. Variations in the (microwave) impedance profile in the medium due to the heating are computed. A further development of this model, including more complicated geometries and various loss mechanisms, may yield useful numerical tools for the synthesis and design of microwave heaters in which the heated material acts as a nonlinear load in the microwave circuit.

Increased Levels of Numerical Chromosome Aberrations after In Vitro Exposure of Human Peripheral Blood Lymphocytes to Radiofrequency Electromagnetic Fields for 72 Hours

Abstract Mazor, R., Korenstein-Ilan, A., Barbul, A., Eshet, Y., Shahadi, A., Jerby, E. and Korenstein, R. Increased Levels of Numerical Chromosome Aberrations after In Vitro Exposure of Human Peripheral Blood Lymphocytes to Radiofrequency Electromagnetic Fields for 72 Hours. Radiat. Res. 169, 28–37 (2008). We investigated the effects of 72 h in vitro exposure of 10 human lymphocyte samples to radiofrequency electromagnetic fields (800 MHz, continuous wave) on genomic instability. The lymphyocytes were exposed in a specially designed waveguide resonator at specific absorption rates (SARs) of 2.9 and 4.1 W/kg in a temperature range of 36–37°C. The induced aneuploidy of chromosomes 1, 10, 11 and 17 was determined by interphase FISH using semi-automated image analysis. We observed increased levels of aneuploidy depending on the chromosome studied as well as on the level of exposure. In chromosomes 1 and 10, there was increased aneuploidy at the higher SAR, while for chromosomes 11 and 17, the increases were observed only for the lower SAR. Multisomy (chromosomal gains) appeared to be the primary contributor to the increased aneuploidy. The effect of temperature on the level of aneuploidy was examined over the range of 33.5–40°C for 72 h with no statistically significant difference in the level of aneuploidy compared to 37°C. These findings suggest the possible existence of an athermal effect of RF radiation that causes increased levels of aneuploidy. These results contribute to the assessment of potential health risks after continuous chronic exposure to RF radiation at SARs close to the current levels set by ICNIRP guidelines.

Nanoparticle plasma ejected directly from solid copper by localized microwaves

A plasma column ejected directly from solid copper by localized microwaves is studied. The effect stems from an induced hotspot that melts and emits ionized copper vapors as a confined fire column. Nanoparticles of ∼20–120 nm size were revealed in the ejected column by in situ small-angle x-ray scattering. Optical spectroscopy confirmed the dominance of copper particles in the plasma column originating directly from the copper substrate. Nano- and macroparticles of copper were verified also by ex situ scanning electron microscopy. The direct conversion of solid metals to nanoparticles is demonstrated and various applications are proposed.

Localized Rapid Heating by Low-Power Solid-State Microwave Drill

This paper presents a theoretical and experimental study of a locally induced microwave-heating effect implemented by a low-power transistor-based microwave drill. A coupled thermal-electromagnetic model shows that the thermal-runaway instability can be excited also by relatively low microwave power, in the range ~ 10-100 W, hence by solid-state sources rather than magnetrons. Local melting then occurs in a millimeter scale within seconds in various materials, such as glass, ceramics, basalts, and plastics. The experimental device employs an LDMOS transistor in an oscillator scheme, feeding a miniature microwave-drill applicator. The experimental results verify the rapid heating effect, similarly to the theoretical model. These findings may lead to various material-processing applications of local microwave heating implemented by solid-state devices, including local melting (for surface treatments, chemical reactions, joining, etc.), delicate drilling (e.g., of bones in orthopedic operations), local evaporation, ignition, and plasma ejection (e.g., in microwave-induced breakdown spectroscopy (MIBS) for material identification).

Microwave drilling of bones

This paper presents a feasibility study of drilling in fresh wet bone tissue in vitro using the microwave drill method [Derby et ab, 2002], toward testing its applicability in orthopaedic surgery. The microwave drill uses a near-field focused energy (typically, power under /spl sim/200 W at 2.45-GHz frequency) in order to penetrate bone in a drilling speed of /spl sim/1 mm/s. The effect of microwave drilling on mechanical properties of whole ovine tibial and chicken femoral bones drilled in vitro was studied using three-point-bending strength and fatigue tests. Properties were compared to those of geometrically similar bones that were equivalently drilled using the currently accepted mechanical rotary drilling method. Strength of mid-shaft, elastic moduli, and cycles to failure in fatigue were statistically indistinguishable between specimen groups assigned for microwave and mechanical drilling. Carbonized margins around the microwave-drilled hole were /spl sim/15% the hole diameter. Optical and scanning electron microscopy studies showed that the microwave drill produces substantially smoother holes in cortical bone than those produced by a mechanical drill. The hot spot produced by the microwave drill has the potential for overcoming two major problems presently associated with mechanical drilling in cortical and trabecular bone during orthopaedic surgeries: formation of debris and rupture of bone vasculature during drilling.

Lifetime of ferroelectric Pb(Zr, Ti)O3 ceramic cathodes with high current density

Electron emission from ferroelectric cathodes is investigated, it is commonly suggested as an electron source for different applications due to its special characteristics such as high current density, easy treatment, and operation. In this experimental research, a lifetime of lead zirconate-titanate ceramic cathode with composition related to a ferroelectric phase was studied. The strong plasma emission from the cathode was excited in a nonreversal (nonswitching) mode by application of unipolar high stress. Severe damage to the cathodes was observed, especially in a high repetition rate. An upper limit of the lifetime of the ferroelectric cathode with plasma-induced emission was estimated at about ∼106 pulses of ∼200 ns each at ∼100 Hz repetition rate. Possible applications of the limited lifetime ferroelectric cathode are discussed.

Demonstration of microwave generation by a ferroelectric-cathode tube

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

High-repetition-rate ferroelectric-cathode gyrotron

The intensive research on ferroelectric electron-emission mechanisms in the last decade has resulted in a wide understanding of the physics and characteristics of this plasma-assisted electron source. Nevertheless, practical devices employing this cathode were hardly introduced. In this experimental study, a high-repetition-rate microwave oscillator based on a ferroelectric electron gun has been developed. The device operates as a cyclotron-resonance maser in the gyrotron mode. Microwave pulses exceeding 1.5 kW at ∼7 GHz are measured in repetition rates above 3 MHz and duty cycles of ∼50%. These experimental results encourage the implementation of ferroelectric cathodes in practical high-power microwave tubes.