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We present the results of an experimental and computational pilot study of cranberry crop yield prediction using low-power microwave sensing and machine learning. We simulated backscattered radiation from cranberry canopies using plane-wave illumination with frequency content from 300 to 2400 MHz. The computational canopy domains allowed for variable soil moisture and cranberry yield in terms of cranberry mass per 1 ft² of canopy surface area. We collected experimental field data with a prototype open-ended waveguide sensor operating between 600 and 1300 MHz. We measured experimental microwave signals by placing our sensor directly on top of cranberry-crop bed canopies in central Wisconsin and recording reflection coefficients across the operating band. We implemented a machine learning approach to map the microwave reflection coefficients to yield. The mapping procedure involves dimensionality reduction with principal component analysis, supervised learning with linear discriminant analysis, and error-correcting output codes. The idealized computational results demonstrate the feasibility of discriminating three cranberry volume fractions that are representative of central Wisconsin field conditions, at frequencies below 2 GHz. Performance evaluations of the machine learning algorithm applied to the measured field data indicated that, in 81% of test cases, the predicted crop yield had less than 8% error. Most importantly, the average yield prediction error was less than 1.3%. These pilot study results provide strong evidence that machine learning enables accurate cranberry yield estimation when trained with in situ (field) microwave backscattered signals.

Theory and simulations predict the metamaterial-enhanced resistive wall amplifier (MERWA) may offer improvements to megawatt-level high-power microwave (HPM) amplifiers in terms of combined bandwidth and gain rates. A low-power proof-of-concept test prototype has been designed using a metamaterial (MTM) consisting of a linear array of periodically spaced thin lossy meandered wires. Direct simulations of these arrays of thin meandering wires using typical 3-D particle-in-cell (PIC) solvers are inaccurate, creating significant challenges for obtaining trustworthy hot test simulations of the prototype device. This work enables predictive PIC simulations of the experimental MERWA prototype by replacing the thin lossy wire structure with an equivalent effective-medium model. We find that a finite-width rod having an anisotropic Drude–Lorentz permittivity is a suitable model to replace the lossy wire MTM structure. We detail our modeling process and assumptions, fitting procedures, and model fitting results. The model is validated by comparing PIC simulations to experimental results.

We present a pilot investigation of near-field microwave sensing for cranberry crop yield estimation using an open-ended rectangular waveguide suspended above the cranberry canopy surface. We compare the performance of two estimation techniques applied to 1.0-1.3 GHz reflection coefficient data measured at 20 unique test sites in a bed in central Wisconsin. The maximum cranberry yield at these test sites was 900 cubic centimeters (cc) per square-foot surface area. A linear discriminant analysis (LDA) with principal component analysis (PCA) and error-correcting-output codes applied to the measured microwave data was able to correctly estimate the volume within 125 cc (roughly 50–60 berries) of the true canopy berry volumes in 71% of the test cases.

Conventional resistive wall amplifiers using naturally occurring dielectric materials provide wide bandwidth but weak gain 1. We have shown that theory and simulations predict that metamaterial-enhanced resistive wall amplifiers (MERWAs) are candidates for wideband, high gain, and high power microwave amplification2, Implementation of a MERWA requires the use of an epsilon-negative (ENG) liner in a waveguide structure. We have designed proof-of-concept experiments to test the theoretical predictions. This talk will describe recent results of experimental measurements and data analysis to extract and characterize the effective complex permittivity parameters of a metamaterial liner in a rectangular waveguide. The results include examination of the effects of the liner's material composition, its lossiness and its unit cell structural features.

Recent improvements in high-power micro-wave (HPM) source power and portability make protecting sensitive electronics from electronic attack critically important. The research reported in this paper examined basic phenomena associated with a distributed area, highly attenuating gas discharge for HPM attack protection. In particular, the research examined gas breakdown delay since effective protection against HPM attack requires rapid activation, significantly faster than the hundreds of nanoseconds typical of HPM pulses. These studies, conducted in mixtures of neon, argon, helium, and xenon gases from 50 to 150 torr, demonstrate how polycarbonate window precharging metastable-excited atoms and appropriate gas composition enable Penning effects to significantly reduce breakdown delay.

We present an experimental and computational study to investigate the feasibility of microwave radar for non-invasively and accurately estimating fruit yields in cranberry beds prior to harvesting and within agricultural research plots. Dielectric measurements of the fruit and leaves show a significant contrast in the 0.5–7.5 GHz range. Full-wave computational electromagnetics simulations of microwave scattering from random distributions of cranberries show a monotonic increase in cross-polarized backscatter signal strength as a function of fractional cranberry volume. The results provide evidence of the potential of microwave reflectometry for accurate and rapid estimation and spatial mapping of cranberry crop yields.

Resistive wall amplifiers are wideband vacuum electron devices that suffer from low gain due to available resistive materials 1. Metamaterial-enhanced resistive wall amplifiers (MERWAs) have been demonstrated, theoretically, to be a candidate for wideband, high gain, and high power microwave amplification 2. Implementation of a MERWA requires the use of an epsilon-negative (ENG) liner in a waveguide structure. A periodic array of inductively meandered wires have been demonstrated as one possible implementation of the ENG liner 3. In this work, we investigated how the choice of material for the periodic elements affects the device's performance. In particular, we have constructed metamaterial (MTM) structures using meander elements constructed from metals with very different conductivity values, copper and stainless steel. Modification of the element's conductivity drastically changes the performance of both the electromagnetic waves that propagate in the structure as well as the resistive wall mechanism.

Electromagnetic metamaterials offer a significant potential to enable new capabilities in many applications. Under high-power illumination, metamaterials and periodic structures experience internal breakdown, altering frequency response, and/or yielding thermal damage. Our prior research observed simultaneous breakdown discharges at two separate sites within a multiresonator metamaterial unit cell, even though the electric field intensities at one of the resonator sites should have been well below the threshold intensity required for breakdown. Here, we investigate three candidate mechanisms for the simultaneous breakdown discharges: energetic electrons, ultraviolet (UV) radiation, and vacuum UV (VUV) radiation. Experiments inserting different dielectric barriers between the two resonators of a multiresonator unit cell were able to selectively isolate the coupling influence of the candidate mechanisms. It was established that, VUV radiation from the discharge at the resonator with a lower electric field breakdown threshold causes simultaneous breakdown at the other resonator where the field intensities are otherwise too low to induce breakdown.

Many applications demand high-brightness, low-emittance electron beams, including vacuum electronic devices and high-power microwave sources [1]. For this reason, we have constructed an experimental system around a field emission microscope and pepper-pot anode to study the field emission characteristics and emittance of novel cathodes and geometries.

The metamaterial-enhanced resistive wall amplifier (ME-RWA) is a wideband, high power, vacuum electron device1. In the ME-RWA, the resistive liner of the traditional resistive wall amplifier has been replaced with a lossy epsilon negative (ENG) metamaterial. This work investigated a relativistic, high power microwave (HPM) ME-RWA. Specifically, we examined the feasibility of a 50 MW, L-Band ME-RWA. The investigation of the relativistic HPM ME-RWA includes a theoretical investigation and particle-in-cell (PIC) simulations. In our theoretical analysis, we have modified the traditional resistive wall theory, presented by Birdsall and Whinnery2, to include relativistic effects. To simulate the ME-RWA's performance, we have used the CST Particle Studio software and used homogenous dielectrics with a Drude dispersion response, with the plasma frequency higher than the operating frequency, to emulate materials with negative permittivity. The results of our relativistic ME-RWA theory as well as the results of our PIC simulation will be presented to demonstrate the superior performance of the ME-RWA.

A method has been developed to fabricate waveguide-to-waveguide couplers and tapered dielectric rod antennas for the millimeter-wave regime from microetched silicon. A proof-of-concept study shows that the structures can be realized using relatively simple wet etching and robotic process control. Experimental measurements of the waveguide-waveguide couplers agree in key features with simulations. The results indicate that two-stepped tapers perform nearly as well as smooth linear tapers, but are much easier to fabricate. Coupling transmissivity of better than -1 dB, and peak antenna gain of 8-10 dB are indicated at W-band frequencies. Lateral dimension etch control of 5-mum precision was realized. To solve a challenge of controlling the length of the first step, either an improved masking method or a switch to dry etching processes is required.

In recent years, there has been an exponential growth of the use of millimeter-wave (MMW) frequencies for various communications, sensing, and imaging applications. One contributing factor to this growth is the exhaustion of the available radio-wave spectrum that can be used for high-speed wireless communications at lower microwave frequencies. Consequently, the 5th generation cell phones are planned to operate at MMW frequencies to provide the high-speed data rates required for streaming video and voice applications. The efficient utilization of MMW frequency bands for the new emerging applications, however, requires the development of affordable phased-array antennas that can provide video-frame rates of scanning. A phased-array antenna is a high-gain antenna that can rapidly and dynamically change the direction of its radiated beam (e.g., to track a moving receiver). While various phased-array antennas operating at microwave frequencies have been developed, their extreme cost and complexity has limited their application only to the most expensive pieces of military hardware. Indeed, the development of affordable phased-array antenna technology remains an unaddressed challenge in the applied electromagnetic area.

The development of ultrawideband (UWB) microwave diagnostic and therapeutic technologies, such as UWB microwave breast cancer detection and hyperthermia treatment, is facilitated by accurate knowledge of the temperature- and frequency-dependent dielectric properties of biological tissues. To this end, we characterize the temperature-dependent dielectric properties of a representative tissue type-animal liver-from 0.5 to 20 GHz. Since discrete-frequency linear temperature coefficients are impractical and inappropriate for applications spanning wide frequency and temperature ranges, we propose a novel and compact data representation technique. A single-pole Cole-Cole model is used to fit the dielectric properties data as a function of frequency, and a second-order polynomial is used to fit the Cole-Cole parameters as a function of temperature. This approach permits rapid estimation of tissue dielectric properties at any temperature and frequency.

Hermetic stainless-steel open-ended coaxial probes have been designed for precision dielectric spectroscopy of biological tissue, such as breast tissue, over the 0.5-20-GHz frequency range. Robust data-processing techniques have also been developed for extracting the unknown permittivity of the tissue under test from the reflection coefficient measured with the precision probe and a vector network analyzer. The first technique, referred to as a reflection-coefficient deembedding method, converts the reflection coefficient measured at the probe's calibration plane to the desired aperture-plane reflection coefficient. The second technique uses a rational function model to solve the inverse problem, i.e., to convert the aperture-plane reflection coefficient to the tissue permittivity. The results of the characterization and validation studies demonstrate that these precision probes, used with the prescribed measurement protocols and data-processing techniques, provide highly accurate and reliable in vivo and ex vivo biological tissue measurements, including breast tissue spectroscopy.

Microfabricated folded waveguide traveling-wave tubes (TWTs) are potential compact sources of wide-band, high-power terahertz radiation. We present feasibility studies of an oscillator concept using an amplifier with delayed feedback. Simulations of a 560-GHz oscillator and experimental evaluation of the concept at 50 GHz are presented. Additionally, results from various fabrication methods that are under investigation, such as X-ray lithography, electroforming, and molding (LIGA), UV LIGA, and deep reactive ion etching are presented. Observations and measurements are reported on the generation of stable single-frequency oscillation states. On varying the feedback level, the oscillation changes from a stable single-frequency state at the threshold to multifrequency spectra in the overdriven state. Simulation and experimental results on amplifier characterization and dynamics of the regenerative TWT oscillator include spectral evolution and phase stability of the generated frequencies. The results of the experiment are in good agreement with the simulations.

The creation of low resistivity, ultrashallow source/drain regions in MOS device structures requires rapid thermal processing (RTP) techniques that restrict diffusion and activate a significant percentage of the implanted dopant species. While current heating techniques depend upon illumination based heating, a new technology, electromagnetic induction heating (EMIH), achieves a rapid heating of the silicon by coupling electromagnetic radiation directly into the silicon wafer. Heating rates of 125/spl deg/C/s to temperatures in excess of 1050/spl deg/C have been achieved for 75- and 100-mm-diameter wafers at input powers of 1000 and 1300 W, respectively. These ramp rates are suitable for ultrashallow junction formation, and junctions shallower than 30 nm with sheet resistances lower than 600 /spl Omega//square have been achieved. This paper details the application of electromagnetic heating using radiation in the microwave, 2450 MHz, frequency regime. Experimental results, comparing microwave annealed implants to the well documented SEMATECH requirements, and simulations, utilizing a coupled electromagnetic-thermal computer model, of the heating process are discussed.

We have used open-ended coaxial probes to determine the dielectric properties of freshly excised normal and diseased breast tissue specimens. The considerable variability in size and composition of these specimens predicates the need for determining the minimum surgical specimen size that yields accurate measurements for a given probe diameter. We investigate the sensing volume of 2.2- and 3.58-mm-diameter flange-free coaxial probes for both lowand high-water-content tissue using standard liquids that exhibit dielectric properties similar to breast tissue over the microwave frequency range from 1 to 20 GHz. We also present an innovative graphical technique based on the use of Cole-Cole diagrams to determine the error thresholds in the magnitude and phase of the reflection coefficient, which bound the errors in the measured complex permittivity to an acceptable level. Results from self-consistent experiments and finite-difference time-domain simulations indicate that a tissue specimen with a thickness of 3.0 mm and a transverse dimension of 1.1 cm is the minimum size that yields accurate measurements with the 3.58-mm-diameter probe. For the 2.2-mm-diameter probe, the specimen's thickness and width should be at least 1.5 and 5 mm, respectively. These conclusions are relevant not only to breast tissue characterization, but also more generally to the dielectric characterization of a variety of low- and high-water-content biological tissues.

We present a formulation for achieving stable high-concentration (up to 20 mg/ml) aqueous dispersions of carbon nanotubes (CNTs) with exceptionally high microwave-frequency (0.5-6 GHz) dielectric properties. The formulation involves functionalizing CVD-synthesized CNTs via sonication in nitric and sulfuric acid. The overall chemical integrity of the CNTs is largely preserved, as demonstrated via physical and chemical characterizations, despite significant shortening and functionalization with oxygen-containing groups. This is attributed to the protected inner walls of double-walled CNTs in the samples. The resulting CNT dispersions show greatly enhanced dielectric properties compared to a CNT-free control. For example, at 3 GHz, the average relative permittivity and effective conductivity across several 20 mg/ml CNT samples were increased by ∼ 70% and ∼ 400%, respectively, compared to the control. These CNT dispersions exhibit the stability and extraordinary microwave properties desired in systemically administered theranostic agents for microwave diagnostic imaging and/or thermal therapy.

The efficacy of protecting electronics from high power microwaves (HPM) through plasma creation depends on how quickly the plasma forms in the protective gas chamber when illuminated with microwave radiation. A cylindrical chamber with polycarbonate windows was filled with a neon, krypton gas mixture and illuminated with a train of ∼25kW, 800ns long pulses at 43Hz repetition rate as a simulation of the HPM attack scenario. In order to facilitate the formation of a plasma, a set of metamaterial, stainless steel masks for the incident polycarbonate window were created to increase the effective electric field. In addition to the masks, we investigated the effect chamber pressure had on the breakdown delay.

In this paper, we present an experimental study of the microwave-frequency dielectric properties and heating response of aqueous dispersions of single- and double-walled carbon nanotubes (CNTs). The CNTs were chemically treated using a method that enables the creation of stable dispersions of isolated tubes at very high concentrations. The CNT dispersions show significantly enhanced dielectric properties and heating response compared to the control (an aqueous sample without CNTs). The observed enhancement with this specific CNT dispersion formulation is far greater than any previously reported. The results suggest that these modified CNTs are promising candidates as contrast agents for microwave diagnostic imaging and heating agents for nanoparticle-mediated microwave thermal therapy for cancer.

The finite difference time domain (FDTD) method is widely used as a computational tool for development, validation, and optimization of emerging microwave breast cancer detection and treatment techniques. When expressed in terms of Debye parameters, dispersive breast tissue dielectric properties can be efficiently incorporated into FDTD codes. Previously, we experimentally characterized the dielectric properties of a large number of excised normal and malignant breast tissue samples from 0.5 to 20 GHz. We subdivided the large database of normal tissue data into three groups based on the percent adipose tissue present in a particular sample. In addition, we formed a group of all cancer samples that contained at least 30% malignant tissue. We summarized the data using one-pole Cole-Cole models that were rigorously fit to the median dielectric properties of the three normal tissue groups and one malignant tissue group. In this letter, we present computationally simpler one- and two-pole Debye models that retain the high accuracy of the Cole-Cole models. Model parameters are derived for two sets of frequency ranges: the entire measurement frequency range from 0.5 to 20 GHz, and the 3.1-10.6 GHz FCC band allocated for ultrawideband medical applications. The proposed Debye models provide a means for creating computationally efficient FDTD breast models with realistic wideband dielectric properties derived from the largest and most comprehensive experimental study conducted to date on human breast tissue.

The shape of the gain curve and physics of interaction between microwave fields and the electron beam for a periodic rectangular grating slow-wave Traveling Wave Tube (TWT) amplifier are investigated. This research focuses on the collective (ωpτ≫1) low-voltage (⩽10 kV) interaction in the backward wave regime for the Ku-band (12.5–17.5 GHz) range of frequencies. For amplifier experiments, a round “probe” beam (10 kV, 0.25 A, 1 mm diameter) confined by a 1 kG solenoidal focusing magnetic field was utilized. Simultaneous single-pass collective gain and electron-beam velocity spread measurements are performed by means of a Faraday cup repeller energy analyzer configured as the beam collector. Experiments near 13.0 GHz show the maximum normalized single-pass gain to be in agreement with the theoretical prediction for several axial velocity spreads (δv‖/v‖). Collective single-pass experimental results are presented and compared with theory. The effect of an increased interaction length which is accomplished by ...

A numerical model was developed to simulate and study microwave-induced transport in ionic solids. The model is based on continuum equations, is very general, and could be applied to many materials. The assumptions, boundary conditions, initial conditions, and numerical techniques used in the model are described. Results are presented from a study of microwave driven defect transport in sodium chloride. Static, high-frequency, and quasistatic results show that ponderomotive rectification of vacancy fluxes will act to deplete the vacancies in a near-surface region and will continue to pull vacancies to the surface through diffusion kinetics. The ponderomotive driving force for this transport is characterized over a wide range of variable space. The magnitude of the driving force falls right in the range such that it can explain why microwave-enhanced mass transport is observed in some experimental cases but not in others.

Numerous observations have been reported in the literature of enhanced mass transport and solid-state reaction rates during microwave heating of a variety of ceramic, glass, and polymer materials. An explanation for these controversial observations has eluded researchers for over a decade. This paper describes a series of recent experimental and theoretical investigations that provide an explanation for these intriguing observations in terms of ponderomotive forces acting on mobile ionic species. The ponderomotive phenomenon, like its conventional-plasma analog, can be described in the continuum model limit by combining the continuity, Poisson’s, and transport equations. However, the solid-state plasma version typically manifests as a result of gradients in mobile charge mobility (e.g., near physical surfaces or interfaces), whereas the conventional plasma ponderomotive transport is typically a consequence of gradients in the radiation field intensity. Both cases can be captured in a single, general, mathematical articulation developed in terms of the mobile particle fluxes.

&p.1: Numerous observations have been reported in the literature of enhanced mass transport and solid-state reaction rates during microwave heating or processing of a variety of ceramic, glass, and polymer materials. These empirical observations of microwave enhancements have been broadly called the “microwave effect”. In the past, these claims have been the source of significant controversy, due in part to the lack of a credible and verifiable theoretical explanation. Moreover, certain notable microwave heating experiments have failed to observe any resolvable reaction or transport rate enhancements. This paper describes a series of recent experimental and numerical investigations that have established the fact that strong microwave electric fields induce a (previously unknown) nonlinear driving force for (ionic) mass transport near surfaces and structural interfaces (e.g., grain boundaries) in ceramic materials. This driving force can influence reaction kinetics by enhancing mass transport rates in heterogeneous solid-state reactions. Most of the previously reported observations regarding “microwave effects” (both for and against) are consistent with the characteristics of this newly identified microwave-induced driving force. &kwd: Microwave processing · Microwave effect · Ponderomotive force · Ionic transport · Nonthermal · Sintering&bdy

The recent theory of averaged ponderomotive action of microwave fields in solids is expanded to describe quasistationary ionic currents driven by that action. Several limiting cases are explored in detail, and in all cases the effect is shown to depend upon the interfacial properties of the ionic crystal. Experimental results on the dynamics of the microwave-induced currents in AgCl and NaCl are presented. Agreement between experiment and theory provides further and stronger evidence for the general validity of the theoretical model.

Summary form only given. Development of high power microwave (HPM) distributed discharge limiters relies critically on minimizing the delay time between HPM incidence and diffuse plasma creation. We present a range of pulsed plasma experiments conducted in neon, argon, helium, and mixtures of these gases, from 50-760 torr. Breakdown is achieved by illuminating a gas cell with a ~25kW, ~2 kV/cm, 800ns-long pulse as well as 41Hz pulse trains. Current results focus on preliminary experiments with metamaterial window coatings that indicate significant improvement opportunities for controlling breakdown thresholds and reducing breakdown delay. New results with gas mixtures in which observed breakdown occurs in

Observations of rapidly formed (

A theoretical model of microwave absorption in linear dielectric ~nonferroelectric! ionic crystals that takes into account the presence of point defects has been synthesized and specifically applied to NaCl single crystals by considering all relevant interaction mechanisms between a harmonic electric field and single-crystal ionic crystalline solids, including ionic conduction, dielectric relaxation, and multiphonon processes. The loss factor e9 has been measured by a cavity resonator insertion technique for nearly pure and Ca 21 doped NaCl single crystals at frequencies from 2 to 16 GHz and at the temperatures from 300 to 700 K. The experimental results are in good agreement with the theoretical model. The theoretical model predicts a transition between low- and high-temperature absorption processes that may partly account for the phenomenon of thermal runaway observed during microwave processing of ceramics.

Many experimenters over the past few years have observed rate enhancements when using microwave processing compared to conventional processing. The results have remained somewhat controversial because the driving forces are not constant throughout the experiments and because of the possibility of inaccurate temperature measurement. This paper describes a different experimental approach that avoids the pitfalls of the previous experiments. Specifically, the alternative approach involves fixed driving forces and short duration experiments. Reliable and accurate knowledge of the sample temperature is ensured by restricting the amount of microwave heating to negligible levels and using conventional ohmic heating to control temperature. This approach has allowed us to confirm the presence of a ‘‘microwave effect’’ on kinetic processes in ionic ceramic materials. With this configuration, many further experiments are possible with different materials and conditions.

A system has been developed for measuring the complex permittivities of low loss ceramic materials at frequencies from 2 to 20 GHz and over a temperature range 20–1000 °C. The measurement technique involves a modified version of the conventional cavity perturbation method. Details of the design and fabrication of the circular cylindrical cavity and the input and output coupling transmission lines are discussed. Particular features related to high‐temperature operation and temperature cycling are described. Data are presented for an illustrative measurement of the complex microwave dielectric properties of NaCl single crystals between 20 and 400 °C. The experimental results are in excellent agreement with theoretical models.

An improved measurement technique to determine the complex dielectric properties of materials has been developed that extends the validity of the conventional cavity perturbation technique for circular cylindrical rod-shaped samples in circular cylindrical cavities resonating in TM/sub 0n0/ modes. The method is particularly useful for the dielectric characterization of fragile, low-loss materials that are difficult to machine to typically required thin dimensions. The method further allows for multi-frequency measurements using higher-order radial modes and somewhat alleviates the very small cavity dimensions typically required by the conventional perturbation technique at higher microwave frequencies. A validity criterion for the extended method is given. Measurements of the complex permittivity of NaCl single crystals are presented, showing excellent agreement with theory. >

Summary form only given. Development of high power microwave (HPM) distributed discharge limiters relies critically on minimizing the delay time between HPM incidence and diffuse plasma creation. We present a series of pulsed plasma experiments conducted in neon, argon, and a 9∶1 mixture of the two gases from 50–760 torr. Breakdown is achieved by illuminating a gas cell with a train of ∼25kW, ∼2 kV/cm, 800ns-long pulses at 41Hz repetition rate. The results suggest that surface charge accumulation on the gas cell's polycarbonate window from many low density precursor discharges eventually results in rapid (

Sheet electron beams are attractive for high-power microwave sources due to their ability to transport high current, at reduced current density, through thin clearance apertures and in close proximity to walls or RF structures. This paper reports on the theoretical investigation of magnetic quadrupole formation of elliptical sheet electron beams for use in high-power microwave devices. The beam envelope equations for an initially round beam passing through a physical non-symmetric quadrupole pair in the presence of space-charge, finite beam emittance, and under the effects of third-order field components and longitudinal velocity variations are presented. The presence of space-charge compensates for over-focusing in the thin beam-dimension and allows for the formation of highly elliptic sheet electron beams. As an example, the results of our study were applied to an existing Pierce gun source with a beam radius of 0.6 cm, beam energy of 10 keV and current density of 2.0 A/cm/sup 2/. We find that an elliptical beam with major radius r/sub a/=3.61 cm, minor radius r/sub b/=0.16 cm and ellipticity (r/sub a//r/sub b/) of 22.5 can be produced with only modest quadrupole gradients of 64 G/cm and 18 G/cm. Quadrupole formation of elliptical sheet-beams may be particularly suited for experimental research applications since existing round-beam electron guns may be used and changes in beam ellipticity may be made without breaking the vacuum system. >

Electromagnetic induction heating (EMIH) is a novel rapid thermal processing technique that uses microwave and radio frequency (RF) radiation to directly heat silicon wafers. Heating rates of 125/spl deg/C/s have been achieved and 75 mm diameter wafers have been heated above 1000/spl deg/C using only 950 W of power. EMIH has been used to activate shallow implanted dopants with minimal diffusion of the junction depth. It is speculated that the exposure of the wafer to intense electric fields during the anneal may provide an additional driving force for dopant activation, allowing for higher activation at lower temperatures. Post-anneal junction depths less than 25 nm with sheet resistances between 700 and 1000 ohms/square have been achieved without the use of a controlled low oxygen ambient. The EMIH Rs-Xj curve penetrates the SEMATECH 100 nm technology box and with further optimizations may satisfy the 70 nm technology node.

Preliminary observations of rapidly formed (

This chapter contains sections titled: Introduction Photonic Bandgap (PBG) Structures Quasi-Optical Open Structures Multimode Structures for Harmonic and Frequency-Multiplying Gyrotrons Multiple-Beam Configurations Smart, Adaptive MVEDs Conclusions This chapter contains sections titled: References

The design, fabrication and initial measurements and analysis of an X-band high power microwave (HPM) limiter are presented. The microwave discharge test chamber is an L-band rectangular waveguide with Lexan or Rexolite microwave windows. The chamber is illuminated by the output of an X-band waveguide pressed against the chamber window. The objective is to study conditions and configurations that enable rapid (< 50 ns) discharge formation above a pre-set power density threshold. A 25 kW X-band magnetron (9.38 GHz) with a 0. 8 |is pulse width is used to produce the breakdown. Incident, reflected and transmitted microwave powers and optical emission intensities are measured to observe the discharge breakdown and extinction rates near Paschen minimum pressures for Ar and Ar/Ne mixtures in the 10s of Torr range. Design modeling, preliminary experimental data and data analyses are presented.

The design, fabrication, initial measurements and analysis of an X-band high power microwave (HPM) limiter are presented. The microwave discharge test chamber is an L-band rectangular waveguide with Lexan or Rexolite microwave windows. The chamber is illuminated by the output of an X-band waveguide pressed against the chamber window. The objective is to study conditions and configurations that enable rapid (< 50 ns) discharge formation above a pre-set power density threshold. A 25 kW X-band magnetron (9.38 GHz) with a 0.8 µs pulse width is used to produce the breakdown. Incident, reflected and transmitted microwave powers and optical emission intensity are measured to observe the discharge breakdown and extinction rates. Pressures used are in the 10s of Torr range, near Paschen minimum pressures for Ar and Ne/Ar mixtures‥ Design modeling, preliminary experimental data and data analyses are presented.

The experimental results reported in this letter suggest that single-walled carbon nanotubes (SWCNTs) have the potential to enhance dielectric contrast between malignant and normal tissue for microwave detection of breast cancer and facilitate selective heating of malignant tissue for microwave hyperthermia treatment of breast cancer. In this study, we constructed tissue-mimicking materials with varying concentrations of SWCNTs and characterized their dielectric properties and heating response. At SWCNT concentrations of less than 0.5% by weight, we observed significant increases in the relative permittivity and effective conductivity. In microwave heating experiments, we observed significantly greater temperature increases in mixtures containing SWCNTs. These temperature increases scaled linearly with the effective conductivity of the mixtures. This work is a first step towards the development of functionalized, tumor-targeting SWCNTs as theranostic (integrated therapeutic and diagnostic) agents for microwave breast cancer detection and treatment.

Models for nonthermal effects on ionic motion during microwave heating of crystalline solids are considered to explain the anomolous reductions of activation energy for diffusion and the overall faster kinetics noted in microwave sintering experiments and other microwave processing studies. We propose that radiation energy couples into low (microwave) frequency elastic lattice oscillations, generating a nonthermal phonon distribution that enhances ion mobility and thus diffusion rates. Viewed in this manner, it is argued that the effect of the microwaves would not be to reduce the activation energy, but rather to make the use of a Boltzmann thermal model inappropriate for the inference of activation energy from sintering-rate or tracer-diffusion data. A highly simplified linear oscillator lattice model is used to qualitatively explore coupling from microwave photons to lattice oscillations. The linear mechanism possibilities include resonant coupling to weak-bond surface and point defect modes, and nonresonant coupling to zero-frequency displacement modes. Nonlinear mechanisms such as inverse Brillouin scattering are suggested for resonant coupling of electromagnetic and elastic traveling waves in crystalline solids. The models suggest that nonthermal effects should be more pronounced in polycrystalline (rather than single crystal) forms, and at elevated bulk temperatures.

We are investigating the feasibility of single-walled carbon nanotubes (SWCNTs) as contrast agents for microwave breast cancer detection. We hypothesize that the accumulation of SWCNTs in a tumor will enhance the dielectric contrast between normal and malignant tissue and potentially improve the efficacy of microwave imaging techniques. As an initial step, we constructed tissue-mimicking phantom materials with varying concentrations of SWCNTs. We characterized their dielectric properties and estimated the pressure wave induced in the phantom materials under microwave illumination. At SWCNT concentrations of less than 0.5% by weight, we observed significant changes in both the relative permittivity and effective conductivity of these SWCNT/tissue-mimicking material mixtures. Our estimates suggest a similarly significant change in the thermoacoustic response relative to the phantom material mixtures without carbon nanotubes.

Carbon (C) fibers with electron emission enhancing cesium iodide (CsI) surface coatings are utilized as field emission cathodes and have been investigated as promising electron sources. Possible applications include not only High Power Microwave (HPM) devices, but also conventional microwave devices, x-ray tubes, and field emission displays [1]. Upon appropriate conditioning of the cathode to remove adsorbed water vapor, stable operation for more than one million pulses, little or no plasma formation, and low turn on E-fields, compared to un-coated C fibers, have been observed.

This work examines the role of 672 nm optical illumination on the diffusion and activation of B in Si as a function of various factors. The factors studied include length of anneal, maximum temperature of anneal, type of co-implanted and pre-amorphizing species and ambient oxygen concentration. The anneal conditions fell into one of three categories: (1) high-temperature (900 degrees C) spike and 10-second anneals; (2) low temperature (550 degrees C) 30-minute anneals; and (3) room-temperature long-term "anneals". Implanted species included BF2 implants, pre-amorphized B-only implants, and pre-amorphized BF2 implants. Finally, the ambient oxygen concentration was varied from atmospheric pressure to 100 ppm. The results show that illumination: (1) affects the diffusion of B on spike anneal time frames; (2) has limited effect on diffusion over 10-second time frames; and (3) fails to enhance the activation of B during low-temperature solid phase epitaxy and at room temperature. Additionally, illumination has no effect on B-diffusion when oxygen is present in ambient concentrations but does show an effect when the presence of oxygen is restricted. Finally, the presence of F affects both the net diffusion of B in Si and the relative effect of illumination on the diffusion of B.

Experiments were conducted to compare the annealing of nano-porous aluminum oxide membranes by 2.45 GHz microwave radiation and by conventional (resistive element) furnace heating. The starting material was Al2O3 membranes that were 60 microm thick, 13 mm in diameter, and containing pores of approximately 200 nm diameter. Changes in the porosity and morphology were recorded from digital processing of scanning electron microscope (SEM) images. The data indicates that both microwave and conventionally-heated annealing resulted in a decrease of surface porosity and an apparent increase in the number of pores. However, microwave annealing consistently resulted in a 4-5% greater reduction in porosity and a greater increase in the number of (small) pores than conventionally-heated annealing. These results are consistent with a non-thermal mechanism for microwave-enhanced surface diffusion, although the complex morphology of the pores precluded a quantitative theoretical analysis.

Microwave-induced thermoacoustic tomography (MI-TAT) is an imaging technique that exploits dielectric contrast at microwave frequencies while creating images with ultrasound resolution. We propose the use of microbubbles as a dielectric contrast agent for enhancing the sensitivity of MI-TAT for breast cancer detection. As an initial investigation of this concept, we experimentally studied the extent to which the microwave-induced thermoacoustic response of a dielectric target is modified by the presence of air-filled glass microbubbles. We created mixtures of ethylene glycol with varying weight percentages of microbubbles and characterized both their microwave properties (0.5-6 GHz) and thermoacoustic response when irradiated with microwave energy at 3 GHz. Our data shows that the microbubbles considerably lowered the relative permittivity, electrical conductivity, and thermoacoustic response of the ethylene glycol mixtures. We hypothesize that the interstitial infusion of microbubbles to a tumor site will similarly create a smaller thermoacoustic response compared to the pre-contrast-agent response, thereby enhancing sensitivity through the use of differential imaging techniques.

Cavity Q's and reflection coefficients for cavities excited by single “ergodic” eigenmodes are quantitatively calculated based on the available expressions derived from the Hamiltonian formulation. The results are compared with those obtained for multimode excitation in large, “untuned” resonant cavities. Applications relevant to the microwave and millimeter-wave regime are discussed. In addition to absorption spectroscopy and materials processing, ergodic cavities may used as radiation-beam dumps for high-power testing of millimeter-wave sources.

The clinical efficacy of emerging microwave breast cancer detection and hyperthermia treatment techniques (see [X. Li et al., 2005], [M. Converse et al., 2004] and references therein) depend on the microwave dielectric properties of normal, malignant, and benign breast tissues. Knowledge of these properties has been limited by gaps and discrepancies in previously published small-scale studies reporting the dielectric properties of normal and malignant breast tissues obtained from cancer surgeries [L. Sha et al., 2002]. To address these limitations, we have conducted a large-scale joint study at the Universities of Wisconsin and Calgary to experimentally characterize the wideband dielectric properties at microwave frequencies (from 0.5 to 20 GHz) of freshly excised normal, benign, and malignant breast tissues obtained from breast reduction as well as cancer surgeries. In our presentation, we will highlight the conclusions from all aspects of our completed study. Due to space limitations in this conference paper summary, here we focus on the results of a comparison of the dielectric properties of normal breast tissues obtained from both reduction and cancer surgeries.

The efficacy of emerging microwave breast cancer detection and treatment techniques will depend, in part, on the dielectric properties of normal breast tissue. However, knowledge of these properties at microwave frequencies has been limited due to gaps and discrepancies in previously reported small-scale studies. To address these issues, we experimentally characterized the wideband microwave-frequency dielectric properties of a large number of normal breast tissue samples obtained from breast reduction surgeries at the University of Wisconsin and University of Calgary hospitals. The dielectric spectroscopy measurements were conducted from 0.5 to 20 GHz using a precision openended coaxial probe. The tissue composition within the probe’s sensing region was quantified in terms of percentages of adipose, fibroconnective and glandular tissues. We fit a one-pole Cole–Cole model to the complex permittivity data set obtained for each sample and determined median Cole–Cole parameters for three groups of normal breast tissues, categorized by adipose tissue content (0–30%, 31–84% and 85–100%). Our analysis of the dielectric properties data for 354 tissue samples reveals that there is a large variation in the dielectric properties of normal breast tissue due to substantial tissue heterogeneity. We observed no statistically significant difference between the within-patient and between-patient variability in the dielectric properties. (Some figures in this article are in colour only in the electronic version)