Microwave Diagnostic System Research Articles

Ground experimental study of the electron density of plasma sheath reduced by pulsed discharge

Abstract A plasma sheath will be generated around the hypersonic vehicle during reentry, where a large number of electrons will significantly affect the propagation of EM waves, resulting in the phenomenon of communication blackout. This paper proposes a method of reducing the electron density of reentry vehicle plasma sheath by pulsed discharge. Experiments were conducted in a high-speed plasma wind tunnel to study the effects and scope of pulsed discharge on the plasma sheath electron density using an ultrahigh-speed camera and microwave diagnostic system. The experimental results show that the application of pulsed discharge resulted in the formation of a light intensity attenuation region measuring 14 × 19 × 4 cm around the discharge area, with an attenuation degree ranging from 30% to 58%. The microwave diagnostic results indicate that after the actuator discharge, the electron density of the plasma sheath within a 4 cm height above the vehicle wall is significantly reduced compared to before the actuator discharge, with a maximum reduction of approximately 86%. These results demonstrate that this method has significant effects on reducing plasma sheath electron density. Furthermore, the low power consumption, load, and space requirements suggest that it has potential for practical applications.

Investigation of near cut‐off properties of electromagnetic wave propagation in homogeneous, collisional plasma slab

AbstractFluctuations in the signal of optical coefficients of propagative electromagnetic (EM) waves in plasma, can cause problems in phase analysis, especially in microwave diagnostic systems which are based on the reflection, and transmission of EM waves in the vicinity of cut‐off layer of the plasma. In this study, optical properties of EM wave propagation in a single layer, homogeneous, and partially ionized plasma slab are investigated. For realistic analysis of propagation characteristics of the EM wave in the plasma slab, multiple reflections of the EM wave from plasma‐vacuum boundaries, known as incoherent internal reflections (IIR) are considered. Optical coefficients of the EM wave are numerically simulated in terms of the plasma parameters and wave frequency, with and without consideration of the incoherent internal reflections effect. It was found that in the low‐loss collision regime, the cut‐off fluctuations of the optical coefficients can be filtered considering the incoherent internal reflections of the EM wave. Such analysis of the EM wave propagation in plasma slab can be considered the primary physical design of diagnostic facilities and EM wave absorbing structures operating in the cut‐off frequency ranges.

Classification of rat mammary carcinoma with large scale in vivo microwave measurements

Mammary carcinoma, breast cancer, is the most commonly diagnosed cancer type among women. Therefore, potential new technologies for the diagnosis and treatment of the disease are being investigated. One promising technique is microwave applications designed to exploit the inherent dielectric property discrepancy between the malignant and normal tissues. In theory, the anomalies can be characterized by simply measuring the dielectric properties. However, the current measurement technique is error-prone and a single measurement is not accurate enough to detect anomalies with high confidence. This work proposes to classify the rat mammary carcinoma, based on collected large-scale in vivo S_{11} measurements and corresponding tissue dielectric properties with a circular diffraction antenna. The tissues were classified with high accuracy in a reproducible way by leveraging a learning-based linear classifier. Moreover, the most discriminative S_{11} measurement was identified, and to our surprise, using the discriminative measurement along with a linear classifier an 86.92% accuracy was achieved. These findings suggest that a narrow band microwave circuitry can support the antenna enabling a low-cost automated microwave diagnostic system.

Development of a Solid and Flexible Matching Medium for Microwave Medical Diagnostic Systems.

This paper reports the development of a new composite material as a matching medium for medical microwave diagnostic systems, where maximizing the microwave energy that penetrates the interrogated tissue is critical for improving the quality of the diagnostic images. The proposed material has several advantages over what is commonly used in microwave diagnostic systems: it is semi-flexible and rigid, and it can maximize microwave energy coupling by matching the tissue’s dielectric constant without introducing high loss. The developed matching medium is a mirocomposite of barium titanate filler in polydimethylsiloxane (PDMS) in different weight-based mixing ratios. Dielectric properties of the material are measured using a Keysight open-ended coaxial slim probe from 0.5 to 10 GHz. To avoid systematic errors, a full dielectric properties calibration is performed before measurements of sample materials. Furthermore, the repeatability of the measurements and the homogeneity of the sample of interest are considered. Finally, to evaluate the proposed matching medium, its impact on a printed monopole antenna is studied. We demonstrate that the permittivity of the investigated mixtures can be increased in a controlled manner to reach values that have been previously shown to be optimal for medical microwave imaging (MWI) such as stroke and breast cancer diagnostic applications. As a result, the material is a good candidate for supporting antenna arrays designed for portable MWI scanners in applications such as stroke detection.

An Ultra-Wideband Microwave Diagnostic Method for Detecting Cracks in Polymeric Insulators

To realize an embedded online diagnosis system for accurate detection of internal defects in high voltage polymeric insulators, a novel ultra-wideband (UWB) microwave diagnostic system for fault detection is proposed in this article. The UWB system is based on the multimode transferring theory on dielectric waveguides, where the level difference of transmission signals of mode transferring has been employed to detect internal defects, such as cracks. First, an investigation by simulations is performed regarding the interfacial millimeter-order cracks in both transverse and longitudinal orientations. Differences of 30-50 and 20-40 dB in receiving signals of mode-transferring between non-crack and crack cases have been observed over 3-10 GHz to transverse and longitudinal oriented cracks, respectively. Then, a test prototype is designed and manufactured for experimental verification. The measurement results have a significant 40-60 dB receiving signal level difference between the non-crack reference case and the crack case. The proposed method is promising for further development of online systems to detect millimeter-order cracks in energized polymeric insulators.

Bayesian inference using JET’s microwave diagnostic system

At the JET tokamak, three electron cyclotron emission (ECE) diagnostics (two Martin-Puplett interferometers and a heterodyne radiometer) and a reflectometer form the basic microwave diagnostic system. The standard analysis approaches deduce electron density and temperature profiles independently of each diagnostic measurement. Via the Bayesian framework Minerva, the microwave diagnostic system is modelled, and electron temperature and density profiles are inferred jointly for an Ohmic JET plasma. Furthermore, profile length-scales for different plasma domains, a magnetic field correction, distinct reflection properties of the high-field side and low-field side walls, and radiometer sensitivities are estimated together. This inference scheme can use one of two models to predict broadband ECE spectra; one is less accurate but fast for a single prediction, and a more accurate model, relying on the ray-tracer SPECE parallelised via web services. The faster model allows the investigation of correlations between parameters and the execution of a numerical marginalisation, i.e. an uncertainty propagation.

Using Dielectric Properties of Solid Fraction and Water Content to Characterize Tissues at Different Health and Age Conditions

Precise dielectric properties (DPs) of biological tissues play an essential role in the development of non-invasive microwave diagnostic and therapeutic systems. There is much information in the literature about DPs of healthy tissues; however, there is a gap in DPs of unhealthy tissues and DPs of tissues at different ages. Each tissue can be described by DPs of its solid fraction and water content values. The observed DPs of tissue changes with the level of tissue’ s water content (increase or decrease) according to the condition of the tissue (i.e., pathology and age). For the current study, DPs of solid fraction and water content of 19 different tissues from 61 pigs of different ages were measured and used to generate DPs of those tissues under different conditions using a simple mathematical model. The dry-weighing method was used to determine the water content of tissues, and DPs of their solid fractions were measured. Then, the DPs of those tissues were generated using the proposed method and found to be in a good agreement with previously published data, as well as with the measured data in this article. This article confirms the potential of using DPs of the solid fraction and water content to calculate DPs of tissues at any age or pathology.

Progress of microwave diagnostics development on the HL-2A tokamak

Sets of powerful microwave diagnostic systems have been developed on the HL-2A tokamak, including 18 subsystems with high spatial and temporal resolutions. These systems have been applied in the HL-2A tokamak experiments to investigate the core plasma transport, turbulence, MHD, energetic particle physics and so on. In this paper, the microwave diagnostics and their applications are reviewed. Some new technologies, including GHz sampling digital correlation electron cyclotron emission (DCECE), multi-channel correlation reflectometers, and solid state terahertz interferometers, are also presented in the paper.

An accurate automated technique for quasi-optics measurement of the microwave diagnostics for fusion plasma

A new integrated technique for fast and accurate measurement of the quasi-optics, especially for the microwave/millimeter wave diagnostic systems of fusion plasma, has been developed. Using the LabVIEW-based comprehensive scanning system, we can realize not only automatic but also fast and accurate measurement, which will help to eliminate the effects of temperature drift and standing wave/multi-reflection. With the Matlab-based asymmetric two-dimensional Gaussian fitting method, all the desired parameters of the microwave beam can be obtained. This technique can be used in the design and testing of microwave diagnostic systems such as reflectometers and the electron cyclotron emission imaging diagnostic systems of the Experimental Advanced Superconducting Tokamak.

Microwave medicals

Researchers at the University of Queensland, Australia, have published results suggesting microwave imaging could be used to detect even early-stage lung tumours. This imaging would also be suitable for frequent monitoring as it doesn't involve ionising radiation and can be made portable for small clinic and even home use for a range of diseases. The authors working with the test setup for the microwave imaging system in the lab at the University of Queensland There is currently great interest in building portable microwave imaging systems as safe, low-cost and reliable diagnostic tools for medical applications. This is because microwave-based diagnostic systems use non-ionising radiation and are non-invasive so they can be used frequently as a monitoring tool. “By virtue of being low-cost and portable, microwave diagnostic systems will provide a technology platform that is easy to use and offers a significant complement to the existing diagnostic technologies, such as MRI and X-rays. In contrast to the current tools that are only available in major medical centres, microwave-based systems can be deployed in ambulances, rural clinics, and doctors’ offices. They could also be used as a self-monitoring tool for healthcare at home leading to a huge reduction in healthcare costs,” explained Queensland team member Ali Zamani. “Lung cancer is the number one cancer killer in the world. Unfortunately, there is no fully reliable and accepted screening tool for the early detection of lung cancer. The significant difference in the dielectric properties between cancerous and healthy lung tissues at microwave frequencies motivated us to investigate the feasibility of building a microwave imaging tool for early-stage lung cancer detection.” The difficulty with using a microwave approach for lung cancer detection is that the human torso also contains different healthy tissues with a wide range of dielectric properties, making microwave signal propagation and penetration complex, and introducing signal clutter. The resulting signals need to be processed to remove this clutter. The complexity and the sheer size of the torso mean that the results of traditional microwave imaging algorithms are very slow to process, and inaccurate. In addition, strong reflections, especially from the outer layers of the torso tissues, mask cancerous tissue signals. To address these problems, the Queensland team's algorithms process the signals in the frequency domain to remove the effect of the clutter, while at the same time a field intensity enhancement factor is used to enhance the signals from abnormal tissues for more accurate tumour detection. As well as developing new algorithms for this system the team have created a compact, unidirectional wideband three-dimensional slot-rotated antenna, working at the 1.5-3 GHz frequency band and integrated it into the imaging platform. In this issue of Electronics Letters the team report results from using their system to image an artificial torso phantom with an emulated lung cancer. Running off a laptop, the results show that their system can detect smaller abnormalities than previous approaches; detecting an emulated cancer only two cubic centimetres in size. The microwave group at the University of Queensland is now looking to gain the proper ethical clearances to proceed with human trials of this approach. They expect human trials to introduce several new challenges, including the effect of normal body movements like heartbeat and breathing, and for this reason they plan to use a three-dimensional multi-static scanning system so that the whole torso can be scanned and imaged in a fraction of a second. The imaging results for the torso phantom containing an emulated lung tumour In addition to this work, the group has been active in building portable microwave imaging systems for medical applications including detection of strokes, brain tumours, heart failure and pulmonary oedema. They currently have ethical approval for human trials on the early detection of strokes, and congestive heart failure. Looking ahead the authors see this imaging technology becoming commonplace and freeing medical imaging from being confined to major medical establishments. “In the next decade, microwave imaging systems are likely to become a reliable diagnostic tool for many medical applications. Those tools will also be available as a monitoring tool, not only in major clinical centres but also at home for self-monitoring.”

Microwave Reflectometric Tool for Non-Destructive Assessment of Decay on Timber Structures

Timber structures can be degraded during their life both by structural problems and, mainly, by biological degradation factors like fungi, and insects (Coleoptera and termites). The occurrence of these biodegradation agents leads, in the absence of appropriate maintenance interventions, to the loss of their structural integrity. Furthermore, if these biological agents decay old buildings, the loss of mechanical resistance of timber structures can be added to loss of cultural heritages. Just in these contexts an early evaluation of decay is crucial to design remedial treatments and a less invasive restoration intervention. This work presents a new microwave diagnostic system for the in situ evaluation of timber structures based on microwave reflectometry, i.e on the measurement of the microwave reflection coefficient as a function of frequency. The continuous-wave (CW) microwave signal is launched by a double-ridged antenna, which also measures the wave reflected by the material under investigation. The measurement system allows diagnosing the effects of biodegradation during a first quick survey in a non-destructive and non-invasive manner. Measurements on laboratory models demonstrated the feasibility of the method. Results obtained on timber beam sections, compared with the findings of traditional investigation methodologies, demonstrate the potentiality of microwave reflectometry, suggesting its usefulness for decay detection and as a support to invasive diagnostic tools.

Hanbit microwave plasma diagnostic system

Abstract As a part of the plasma diagnostic system for the Hanbit device, various microwave plasma diagnostic systems have been designed and developed from the initial stage of the Hanbit project. These include the interferometer, reflectometer, and electron cyclotron emission radiometer. In this work, we present the current activities related to the development of the microwave diagnostic systems. The brief descriptions of each system are as follows. The probing wave frequency of the interferometer is 94 GHz. Two types of interferometer have been developed. One is a conventional heterodyne-type interferometer with two microwave sources (94 GHz, 94.2 GHz Gunn oscillators). The other system uses a heterodyne-type phase detection method with one microwave source (94 GHz, Gunn oscillator) and a single sideband upconverter. For the plasma density profile measurements, an FM-CW reflectometer with a 7–18 GHz YIG source will be installed at the Hanbit central cell. If the O-mode propagation is adopted, it can cover one half portion of the central cell plasma density profile under the density 5×1012 cm−3. A heterodyne phase detection method is also used for this reflectometer with a single sideband upconverter.

Microwave Plume Measurements of a Closed Drift Hall Thruster

The plasma plume from a closed drift hall thruster has been characterized using a 17-GHz microwave diagnostic system. Electron number density profiles are obtained throughout the thruster plume via differential phase measurements. A functional model of plasma density has been developed combining a near-field Gaussian beam term and a far-field point source expansion term. An outcome of this work is a mapping of the transition region between the nearand far-field plume. An indication of slight plume asymmetry is obtained by evaluating total integrated density measurements along rays emanating from the thruster. Additional evaluations have determined the plasma plume effect on attenuation and spectral characteristics of a wave transmitted through the plume. The attenuation was small, with slightly over 2 dB loss at 0.09 m along the thruster axis. However, ray-tracing attenuation modeling based on plasma density profiles indicates a greater effect for lower-frequency operation. The spectral data of the signal transmitted through the plume exhibited clear 26-kHz harmonic sidebands and added broadband noise. Estimates of potential impact to communication and other electromagnetic satellite systems can be obtained directly from the measurements and from the electron number density distribution models derived from the measurements.

A Lecher Wire Microwave Interferometer for Measurements of Electron Density and Electron Temperature in a Flowing Transient Plasma

A microwave diagnostic system for measurement of electron density and temperature in a transient plasma flow, generated by a laser pulse focused on a solid target, has been constructed using a twin conductor (Lecher wire) probing element coupled to X-band waveguide components by tapered parallel planes. The analysis of the operation of the probing section has required the solution of a symmetric seven layer dielectric problem, which models the transmission, reflection, and attenuation of the microwave signal by plasma located around Lecher wires. Simultaneous measurements of the phase and amplitude of the transmitted signal, together with an experimental configuration which accurately defines the interaction of the plasma with the Lecher wire section, have made possible the reliable determination of plasma properties with a spatial resolution of ∼0.5 cm and a temporal resolution of ∼5×10−8 sec.

Microwave Diagnostic Studies in Electrodeless Discharge Plasmas

This paper reports an experimental study of microwave diagostic techniques as applied to electrodeless discharge plasmas. Here relatively dense plasmas (~1012. electrons/cm3) are created by inductive coupling from a radio frequency (40 mc) coil using only a one kilowatt generator. A microwave diagnostic system has been developed which permits X-band (8840 mc) waveguide transmission in the TM01 mode through this plasma without appreciably loading the RF excitation coil. Simple slotted line probing techniques have been developed which are capable of measuring the point by point plasma densities with a high degree of accuracy in relatively dense plasmas using only a single microwave frequency. The techniques described here are to be applied to a large 100 kilowatt plama generator now nearing completion.

A MULTIPLE-PROBE MICROWAVE SYSTEM FOR PLASMA STUDIES

This paper describes a fast-acting microwave diagnostic system which was developed for use with non-repetitive plasmas, such as those in shock tubes and pulsed discharges, and which has proved useful in a wide variety of experimental configurations. The system may be used for either reflection or transmission measurements and gives a polar display of phase and amplitude in conjunction with timing marks. Some of the principal features are wide dynamic range, expansion of high attenuation regions of the display, and a presentation of data which is readily assessed visually. The system has been used at microwave frequencies of 9.2 kMc, 9.7 kMc, 23.5 kMc, and 34.5 kMc, with sampling periods from 0.1 msec to 0.1 μsec at 50% duty cycles.

Microwave Diagnostic Systems and Techniques for Use in Controlled Fusion Research

Microwave Diagnostic Systems and Techniques for Use in Controlled Fusion Research