Coupling medium for microwave medical imaging applications

Sodium meta silicate gel is proposed as a novel coupling medium with a better coupling and a lesser dielectric loss than the conventionally used media. Dielectric constants between 8 and 20 exhibited for various relative density and pH, makes the material in perfect match with that of the various tissues. It is also useful as a phantom model material in microwave medical imaging.     

A MULTIRATE PROCESSING APPROACH FOR MICROWAVE IMAGING

In this paper,a multirate processing approach for microwave imaging is presented.This approach has the advantages of largely compressing the raw spectral data for imaging,greatly reducing the storage requirement and enhancing the processing efficiency.To demonstrateits applicability,the proposed approach is tested on both simulated and experimental data.     

New approach to Doppler tomography for microwave imaging

A new approach to microwave imaging is presented. The requirements for large bandwidth and the computational burden in conventional range-Doppler imaging are reduced. In conventional microwave imaging, one of the steps in reconstructing a Doppler tomogram is to perform a two-dimensional Fourier transform which utilizes and produces data points in a Cartesian raster. The computational burden associated with this reconstruction is high. In contrast, the approach proposed in this paper is, in essence, a phase-based process rather than an amplitude-based process. Backscattered signals from the illuminated target are received and analysed using the wavelet transform to extract the Doppler variation information which contains the spatial distribution information of the scattering centres. Diagrams which are very similar to the 'sinogram’ used in X-ray tomography are obtained and are used to reconstruct the two-dimensional images. Simulated and experimental results are shown to confirm the practicality of the proposed approach. The quality of the images shown in this paper is satisfactory and the computational burden is greatly reduced.     

Complex resonant frequencies of biological targets for microwave imaging applications

The authors report on the complex resonant frequencies of a lossy dielectric sphere immersed in a lossy dielectric medium and their potential application to the classification of suspicious growths in breast cancer diagnosis using microwave imaging.     

Active microwave imaging: a model-based approach

A model-based approach that improves the spatial resolution of a buried inhomogeneous object using an active microwave imaging system is discussed. Algorithms are developed for quasi-real-time processing using a microwave camera specifically constructed for civil engineering applications using reflection mode imaging. The model is generated by numerically solving an integral equation representing the ideal scattered field of the object. The model is used to develop an optimal spatial filter to process the measured field. Finally, the inverse problem is solved using an imaging algorithm based on diffraction tomography and Fourier transforms. Experimental results indicate a reasonable performance of the approach     

Two-dimensional microwave imaging approach based on a geneticalgorithm

A multi-illumination multiview approach to microwave imaging is proposed, which is based on a genetic algorithm (GA). The inverse problem is recast in an optimization problem, solved in the framework of the Born approximation. The formulation of the approach is described and images of reconstructed circular (multilayer) cylinders are reported     

On the use of regularization techniques in numericalinverse-scattering solutions for microwave imaging applications

This paper deals with integral-equation-based numerical methods for microwave imaging using regularization procedures to overcome ill-conditioning problems. The strong dependence of reconstruction quality on “a priori” information is discussed. Such information is required to select a suitable number of independent columns when using truncated pseudoinversions (or other regularization parameters, in different cases) for accurate dielectric reconstructions. Moreover, a criterion for the choice of the optimal number of independent columns is proposed, and the possibility of making this choice less critical by using a multiview version of the method is explored. Finally, a modified procedure is presented that further increases the range from which to choose the number of independent columns that allows one to achieve acceptable reconstructions     

Optoelectronic isolator for microwave applications

The analysis, design, and implementation of a hybrid optoelectronic isolator for microwave applications is described. The device is designed to operate over a 300-MHz bandwidth centered at 3 GHz. The prototype achieves isolation greater than 80 dB and a forward power gain of 0.13 dB at its center frequency. Prototype results indicate that use of this device in an operating system can control self-oscillation in high-gain receivers and/or provide useful isolation of sensitive radars. Furthermore, the required size is smaller, especially with monolithic implementation, while providing isolation far in excess of competing technologies. For comparison, a packaged ferrite isolator would be about twice the size of the prototype while providing only 30 dB of isolation     

D-MOS transistor for microwave applications

A new n-channel silicon MOS transistor is described that can be fabricated with channel lengths of less than 1 µ by using a double-diffusion process similar to that used in bipolar transistor fabrication. The dimensional tolerances are not tighter than those used in the processing of conventional MOS transistors. This device (called D-MOST) shows gain in the GHz range and a noise figure comparable to that of microwave transistors. The fmaxis 10 GHz and the noise figure is 4.0 dB at 1 GHz. A brief theory of the D-MOST is followed by the design considerations for a discrete microwave device. Results from s-parameter measurements in the range of 0.1-2.5 GHz are presented along with graphs showing the gains and the stability factor. A simple equivalent circuit is derived from the measurements. Applications of the D-MOST are described.     

Parallel scrambler for high-speed applications

In order to improve the speed limitation of serial scrambler, we propose a new parallel scrambler architecture and circuit to overcome the limitation of serial scrambler. A very systematic parallel scrambler design methodology is first proposed. The critical path delay is only one D-register and one xor gate of two inputs. Thus, it is superior to other proposed circuits in high-speed applications. A new DET D-register with embedded xor operation is used as a basic circuit block of the parallel scrambler. Measurement results show the proposed parallel scrambler can operate in 40 Gbps with 16 outputs in TSMC 0.18-/spl mu/m CMOS process.     

Integrated optic devices for microwave applications

Integrated optic devices designed for use in microwave applications are reviewed, and the prospects for these technologies are discussed. The interaction of lightwave and microwave signals, especially the modulation of light at microwave frequencies, is briefly summarized, and features of integrated optic devices are pointed out     

Multifrequency microwave thermograph for biomedical applications

This paper presents problems related to thermal radiation of human bodies in microwave range with respect to diagnosis of breast carcinoma. A mathematical model of thermal radiation transfer through tissues is introduced and methods of measurement of temperature, depth and size of a heat source, by means of multifrequency microwave thermograph are described. Theoretical considerations are supplemented by presentation of experimental results.     

Coherent Doppler tomography for microwave imaging

A tomographic extension of the type of microwave Doppler imaging typified by synthetic aperture radar has recently been developed and shown experimentally to exhibit a high degree of spatial resolution. When CW irradiation is used, the sidelobes in the pointspread function are inherently high and tend to limit the dynamic range of the reconstructed images. The point-spread function of a system using CW irradiation and an aperture that completely surrounds the object has a central lobe of width of λ/5, but the first sidelobe is only 8 dB below the central peak. The limitation due to the high sidelobes can be partially overcome by using wide-band signals or bistatic diversity. One of the steps in reconstructing a coherent Doppler tomogram is to perform a two-dimensional Fourier transform. The ordinary two-dimensional discrete Fourier transform (DFT) produces points in the transform space on a Cartesian raster. In coherent Doppler tomography (CDT), however, the data are sampled on a polar raster. To diminish the computational burden associated with converting to the Cartesian raster and interpolating, we have developed an alternative algorithm which requires no interpolation and is based on interpreting the two-dimensional Fourier transform as a one-dimensional circular convolution integral. The quality of the images computed in this fashion compares favorably with that for the old method and the computational burden is greatly reduced.     

90-nm CMOS for microwave power applications

We report, for the first time, the experimental evaluation of a very short channel 90-nm CMOS transistor under RF over-voltage conditions. At 9 GHz and 1.5 V supply a 40 /spl mu/m gate width device is able to deliver 370 mW/mm output power with a PAE of 42% and a transducer power gain of 15 dB. Measurement results at 3 and 6 GHz is also presented. The transistor does not show any degradation in either dc or RF performance after prolonged operation at 1 and 6 dB compression. Simulation show, that the peak voltage, V/sub ds/ at this condition is 3.0 V, while the maximum allowed dc supply voltage is limited by the design rules to 1.2 V. We show for the first time that nanometer-scale CMOS can be used for microwave power applications with severe RF over-voltage conditions without any observable degradation.     

Design rule development for microwave flip-chip applications

This paper presents a novel experimental approach for the analysis of factors to be considered when designing a flip-chip package. It includes the design of an experiment and statistical analysis of the outputs and uses both test-structure measurements and full-wave simulation techniques in the 1-35-GHz frequency range. The most significant factors are found to be, from the most to least important, the length of the area where the device and substrate overlap (referred to as conductor overlap), the bump diameter, and the width of the coplanar-waveguide transmission-line launch. These results are valid for conductor overlaps between 300-500 μm. For a lower value (120 μm), the significance level of the overlap decreases and the bump height also becomes significant. Test-structure measurements in the 120-200-μm overlap range validate this result and demonstrate the decrease in the significance level. The substrate thickness in the 10-25-mil interval is found to be statistically insignificant, therefore, it can be eliminated from further analysis. This approach provides a foundation for development of a set of design rules for RF and microwave flip-chip similar to RF integrated-circuit design rules     

Compound semiconductors for low-noise microwave MESFET applications

In order to determine the low-noise potential of microwave MESFET's fabricated from materials other than GaAs, a one-dimensional FET model is employed. From material parameters and device geometry the model enables the calculation of a small-signal equivalent circuit from which performance information is acquired. Material parameters, as predicted from Monte Carlo calculations, are used to simulate 1-µm devices fabricated from GaAs as well as InP, Ga0.47In0.53As, InP0.8As0.2, Ga0.27In0.73P0.4As0.6, and Ga0.5In0.5As0.96Sb0.04. Results obtained from simulations comparing a Ga0.5In0.5As0.96- Sb0.04device to an equivalent GaAs device indicate that a decrease in minimum noise figure of almost a factor of two is possible. Considerable improvement in noise performance over a GaAs device is also predicted for devices fabricated from Ga0.47In0.53As and Ga0.27In0.73P0.4As0.6. In addition, the quaternary and ternary devices as well as the InP device should exhibit superior gain and high-frequency performance compared to GaAs devices.     

Wide-angle microwave lens for line source applications

A new "time-delay" scanner consists of a constrained wide-angle two-dimensional microwave lens with a straight front face in which lens elements connect arbitrary points on the inner and outer contours. The lens can operate at very short pulse lengths and can scan more beamwidths than any previously known device of its type. A phase analysis shows that this design has very small coma aberrations and that the lens can generate fractional degree beams. Criteria developed for selecting optimum lens parameters are given. The radiation patterns of an experimental model in which the lens elements consist of coaxial cables show the expected wide-angle characteristics. In further tests incremental scanning was obtained through the use of phase shifters in the coaxial lens elements. The design of symmetrical three-dimensional lenses is briefly discussed. A table of lens contour parameters is given for an optimum lens design with scan anglealphaof30deg.     

A coaxially packaged MADT for microwave applications

A coaxially packaged transistor capable of delivering greater than 11 db of power gain at 1000 Mc, with a resultant maximum frequency of oscillation of 3500 Mc, has been developed. This device is a p-n-p micro-alloy diffused-base transistor (MADT). The principal difference between this device and a standard high-frequency MADT amplifier is the reduction of electrode size and use of a coaxial construction. The parasitic elements, rb', and emitter and collector transition capacities, have very striking effects. Also, the excess phase of alpha at alpha cutoff, as described by Thomas and Moll, can be very large (150° on this device); for this reason, fTrather than fcαshould be used as the figure of merit for graded-base transistors. Because of this excess phase, the value of K(0.85 for homogeneous-base transistors), which is used to relate fTto fcα, can be as low as 0.43 in graded-base transistors of this type.