This study describes the techniques and signal properties of a large, powerful, and linear-scanning 1.5 MHz induction field scanner. The mechanical system is capable of quickly reading the volume of relative large objects, e.g., a test person. The general approach mirrors Magnetic Induction Tomography (MIT), but the details differ considerably from currently-described MIT systems: the setup is asymmetrical, and it operates in gradiometric modalities, either with coaxial excitation with destructive interference or with a single excitation loop and tilted receivers. Following this approach, the primary signals were almost completely nulled, and test objects' real or imaginary imprint was obtained directly. The coaxial gradiometer appeared advantageous: exposure to strong fields was reduced due to destructive interference. Meanwhile, the signals included enhanced components at higher spatial frequencies, thereby obtaining a gradually improved capability for localization. For robust signals, the excitation field can be powered towards the rated limits of human exposure to time-varying magnetic fields. Repeated measurements assessed the important signal integrity, which is affected by the scanner´s imperfections, particularly any motions or respiratory changes in living beings during or between repeated scans. The currently achieved and overall figure of merit for artifacts was 58 dB for inanimate test objects and 44 dB for a test person. Both numbers should be understood as worst case levels: a repeated scan with intermediate breathing and drift/dislocations requires 50 seconds, whereas a single measurement (with respiratory arrest) takes only about 5 seconds.
Optoacoustic imaging (OAI) is an emerging biomedical technique that allows visualization of in-depth tissues by using ultrasonic signals generated by short laser pulses. In this work, the authors combine the optical power of several pulsed high-power diode lasers (HPDLs) at 870 nm and 905 nm to a 7-to-1 675-μm fiber bundle to generate optoacoustic (OA) signals from different mixtures of two gold nanorods solutions with absorbance peak at ~860 nm and ~900 nm, respectively. The pulses produced to generate OA signals are alternated between the two wavelengths by a microcontroller circuit with fast switching (0.5 ms). From the amplitude of the OA signals, the concentrations of the nanoparticles solutions are easily estimated with high accuracy using a fluence model. The results achieved with the proposed system show very good agreement between the concentrations of gold nanorods estimated from measurements and the expected values.
This study proposes a real-time method to solve the electromagnetic inverse scattering problem. This technique converts this problem into a regression problem using a support vector machine (SVM). The SVM-based solution successfully deals with the nonlinearity and ill-posedness inherent in thisproblem. Simulation results show the feasibility and effectiveness of the proposed method. The method can effectively locate the tumor target of the stomach regardless of the presence of noise. The positioning effect of the method improves as SNR increases. When the SNR is higher than 50 dB, noise minimally affects the results. Finally, the SVM prediction model is utilized to study the effect of the number of sampling locations on the prediction results. The results show that the more sampling locations, the better the prediction results.
The distorted Born approximation (DBA) of volume scattering was previously combined with the numerical solution of Maxwell equations (NMM3D) for rough surfaces to calculate radar backscattering coefficients for the Soil Moisture Active Passive (SMAP) mission. The model results were validated with the Soil Moisture Active Passive Validation Experiment 2012 (SMAPVEX12) data. In this paper, we extend the existing model to calculate the bistatic scattering coefficients for each of the three scattering mechanisms: volume, double bounce and surface scattering. Emissivities are calculated by integrating the bistatic scattering coefficients over the hemispherical solid angle. The backscattering coefficients and emissivities calculated using this approach form a consistent model for combined active and passive microwave remote sensing. This has the advantage that the active and passive microwave remote sensing models are founded on the same theoretical basis and hence allow the use of the same physical parameters such as crop density, plant height, stalk orientation, leaf radius, and surface roughness, amongst others. In this paper, this combined active and passive model is applied to four vegetation types to calculate both backscattering coefficients and brightness temperature: wheat, winter wheat, pasture and canola. This model uses a single-scattering and incoherent vegetation model, which is applicable for the vegetation fields studied in this paper but not suitable for vegetation types where collective scattering or multiple scattering effects are important. We demonstrate the use of the DBA/NMM3D for both active and passive using the same input parameters for matching active and passive coincident data. The model results are validated using coincident airborne Passive Active L-band System (PALS) low-altitude radiometer data and Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) data taken during the SMAPVEX12 field campaign. Results show an average root mean squared error (RMSE) of 1.04 dB and 1.21 dB for backscatter at VV and HH, respectively, and 4.65 K and 6.44 K for brightness temperature at V-pol and H-pol, respectively. The results are comparable to those from the tau-omega model which is commonly used to compute the brightness temperature, though the physical parameters used in this model are different from the empirically adjusted parameters used in the tau-omega model.
In this paper, a hybrid algorithm of binary lightning search algorithm and simulated annealing (BLSA-SA) is proposed to optimize the design of multilayer microwave absorbers for normal incidence. The multilayer absorber is designed to find a set of coatings that minimize the reflection coefficient over the desired frequency. The design problem is translated into solving the binary problem. Three different design examples are presented to verify the performance of the BLSA-SA. The results show that the reflection coefficient and thickness of BLSA-SA are better than those of other heuristic algorithms for multilayer absorber design. In the five-layer design, the standard deviation of BLSA-SA is the smallest among the 20 independent test results of the algorithms, which indicates that the BLSA-SA algorithm, has a strong stability.
The power flow for electromagnetic wave absorbers consisting of pattern conductor layers acting as frequency selective surfaces, absorption layers, and short circuit layers was investigated by Poynting vectors. A method was developed to evaluate the flow of electromagnetic wave power by an electromagnetic wave absorber upon irradiation with electromagnetic waves. The results indicate that the electromagnetic wave absorption phenomenon involves generation of true power, a real part of the time averaged Poynting vector, which moves horizontally along the pattern surface after the incident wave has irradiated the pattern conductor from the vertical direction, and the direction of power flow changes to enter the polymer layer from the pattern interval, causing an accumulation of power inside the polymer layer, followed by absorption, which is converted into heat due to the loss factor.
Phantoms provide valuable test platforms for developing medical devices. Solid materials in particular allow fabrication of stable and robust models. This paper presents a novel, anatomically realistic, multi-layered head phantom made from dielectrically accurate, stable, easily mouldable, low-cost tissue-mimicking materials for testing of microwave diagnostic systems. Also incorporated is a mechanism for inserting reconfigurable lesions and a novel circulatory system modelling physiology. Tissue-mimicking materials composed of graphite, carbon black, and polyurethane with small volumes of acetone or isopropanol were fabricated and dielectric properties were measured across the 1 - 8.5 GHz band. The tissuemimicking material properties were adjusted until their dielectric properties matched those of reference values for target tissues of interest, thereby emulating: weighted aggregates of head tissues external to the brain, tissues comprising the brain, and blood. 3D printed anatomically realistic head and brain moulds cast the phantom mixtures for each layer. Cylindrical holes in the brain layer allow insertion of pathological lesion phantoms, such as haemorrhages. Tubing embedded in the brain layer forms a symmetrical loop providing a novel simplistic model of circulation. The resulting head phantom is anatomically realistic, dielectrically stable, enables pathology modelling, and has, uniquely, a circulatory loop. This novel head phantom provides a valuable test platform for microwave diagnostic studies.
Objective: As well known, using a single body worn sensor exposimeter introduces systematic errors on the measurement of the incident free space electric field strength. This is because the body creates around it high, intermediate and low level field zones, which depend on the direction of arrival of the incident field. The goal of this work is to propose an efficient method for the reduction of these errors. Methods: After classifying the perturbations induced by the body on the measured electric and magnetic fields thanks to realistic numerical simulations, we then propose a two-sensor setup in conjunction with simple semi-empirical correction formulas, in order to compensate these perturbations. Results: At 942 MHz, when the two sensors are placed in any opposite sides of the body at chest height, the worst case, maximum and average errors respectively decrease to 12% and 3% compared to 83% and 22% for measurement techniques using a single sensor, or 32% and 11% when using the average value of the measurements. Conclusion: The error related to the measurement in the presence of the body was significantly reduced by the proposed method making use of two opposite sensors, E-field and H-field at the chest. Significance: The conformity of exposure to EMF in terms of reference values according to the ICNIRP is given in the abscence of the human body. The interest of this work lies in the reduction of the errors made when measuring the field in the presence of the body.
In stomach tumor imaging, traditional time domain algorithm, i.e., back projection (BP) algorithm, and traditional frequency domain algorithm, i.e., frequency wave number migration (F-K) algorithm, can locate tumor target accurately. However, BP and F-K algorithms perform poorly in identifying tumor sizes and shapes. The algorithms must consider the influence of various tissues in the human body: the attenuation of the signal strength of electromagnetic waves, the decrease in speed and the refraction due to the different permittivities between different organs of the body. These factors will eventually lead to image offset and even generate a virtual image. It is effective to refrain the displacement of image with modifying the time element of the imaging algorithm by iteration. This paper proposes a method based on combination of support vector machine (SVM) with BP and F-K algorithms to solve problems in recognizing tumor shape. The method uses field strength obtained by BP and F-K algorithms as input in SVM to establish the SVM model. Based on BP algorithm, recognition method for SVM includes the following characteristics: short prediction time of SVM and good virtual elimination effect. However, the algorithm requires long periods and possibly misses tumor targets. Except the same characteristics as BP algorithm: short prediction time of SVM and good virtual elimination effect, F-K algorithm also works more efficiently, does not miss any tumor targets, and conforms more with requirements of real-time imaging. When the data are contaminated by noises, the tumor shape in the stomach can still be suitably predicted, which demonstrates the robustness of the method.
This paper presents a new hybrid switching technique for enhanced pulse mode solid-state power amplifiers (SSPAs). In the proposed technique, pulse timing for bias stabilization is effectively decoupled from pulse amplification. The decoupling allows fast pulse switching by reducing the pulse width and increasing the pulse repetition frequency (PRF). The new switching method is applied to an X-band SSPA using GaN HEMT. The advantage of the proposed method is demonstrated by its excellent pulse characteristic. The proposed technique achieves a fast PRF of 100 kHz and a narrow pulse width of 1 μsec. The measured rise/fall time (RFT) is 12.5/11.1 nsec, which is more than four times less than that of previous works. In addition, an excellent pulse droop of 0.43 dB is achieved with an output power of 51.3 dBm at 9.9 GHz. The fabricated SSPA shows a maximum output power of 135 W, a small-signal gain of 47 dB, and power added efficiency (PAE) of 28.2% at 9.9 GHz. These results show that the proposed pulse switching technique provides a promising solution for SSPAs using a high-power GaN HEMT.