Dipole Probe Research Articles

Electric Field Characteristics of Rotating Permanent Magnet Stimulation.

Neurostimulation devices that use rotating permanent magnets are being explored for their potential therapeutic benefits in patients with psychiatric and neurological disorders. This study aims to characterize the electric field (E-field) for ten configurations of rotating magnets using finite element analysis and phantom measurements. Various configurations were modeled, including single or multiple magnets, and bipolar or multipolar magnets, rotated at 10, 13.3, and 350 revolutions per second (rps). E-field strengths were also measured using a hollow sphere (r=9.2 cm) filled with a 0.9% sodium chloride solution and with a dipole probe. The E-field spatial distribution is determined by the magnets' dimensions, number of poles, direction of the magnetization, and axis of rotation, while the E-field strength is determined by the magnets' rotational frequency and magnetic field strength. The induced E-field strength on the surface of the head ranged between 0.0092 and 0.52 V/m. In the range of rotational frequencies applied, the induced E-field strengths were approximately an order or two of magnitude lower than those delivered by conventional transcranial magnetic stimulation. The impact of rotational frequency on E-field strength represents a confound in clinical trials that seek to tailor rotational frequency to individual neural oscillations. This factor could explain some of the variability observed in clinical trial outcomes.

Компенсация влияния зонда при измерениях ближнего поля антенны на плоскости

In the article, to compensate for the probe effect o during near-field measurements on the plane, the theory of plane waves is considered, thanks to which it is established that the correction can be achieved by dividing the spectra of the measured plane waves by the function of the spectral response of the probe when it operates in transmission mode. To determine the spectral characteristics of the probe, it is proposed to use an electrodynamic calibration structure consisting of a three-dimensional model of a reference antenna supplemented by a model of a measuring probe. The ability of the proposed approach to correct measurements made using a dipole probe and the open end of the waveguide is demonstrated.

Electric Field Sensor Approach to Determine Fidelity and Overmoding Region of GTEM Cell

Characterizing new electric field (E-field) sensors requires knowing the frequency limits of one’s radio-frequency (RF) chamber. A commonly used RF chamber is called a gigahertz transverse-electromagnetic (GTEM) cell that supports transverse-electromagnetic (TEM) fields through the gigahertz spectra. This manuscript proposes a new methodology for determining the range of usable frequencies within a GTEM cell having unknown characteristics (e.g., after moving a GTEM cell from one laboratory to another). Above a certain frequency, all frequencies become overmoded and yield unreliable measurements. We found that comparing international standards to measured data can provide insights into where overmoding occurs. The comparison to international standards was assisted by a derived free-space wave impedance formula in the frequency domain using both flush-plate dipole (D-dot) and magnetic field (B-dot) probes. Overall, this article proposes a new tool for determining the operating frequencies at which GTEM cells can reliably function in accordance with international standards before overmoding occurs.

A Broadband Radial Power Combiner Using a Dipole Antenna-Based TM Mode Transducer

A TM01 mode transducer based on dipole antenna is proposed to design a broadband and low-loss radial power combiner at Ka-band (26.5–40 GHz). It is an essential component in the radial power combiners to convert the electromagnetic modes between rectangular and circular waveguides. The latter feeds the cylindrical cavity in TM01 mode of which the fields exhibit a circular symmetry. The proposed TM01 mode transducer consists of the dipole antenna, microstrip, and probe on a dielectric substrate. It is an in-line mode transducer. In other words, the rectangular and circular waveguides are aligned along the same axis of wave propagation. Therefore, it does not require the waveguide components such as tee junctions, steps, and bends which are normally used in the traditional mode transducers and increase the complexity, size, and loss of entire power combiner. The eight-way radial junction is also designed using a cylindrical cavity, where the rectangular waveguides are placed along the circumference of the cylindrical cavity. The dimensions of each component are determined based on the full-wave electromagnetic simulations. The designed eight-way radial power combiner consisting of the TM01 mode transducer and radial junction is fabricated in four-split blocks by mechanical machining. In the measurements, the proposed power combiner exhibits a broadband and low-loss performance under a compact size while maintaining the magnitude and phase balances between the eight ports.

Time Domain Expressions for the Current of a Dipole Probe in a Magnetized Plasma

We derive some approximate expressions for the current through an electrically short dipole probe immersed in a cold magnetized plasma. The time-varying current signal due to an applied voltage input to the probe is proportional to plasma parameters such as electron density and electron neutral collision frequency in the ionosphere. By taking Laplace transformations and examining the parallel and perpendicular current contributions, we obtain an approximate theoretical expression for the impedance of the probe. We then infer an even simpler empirical expression based on the approximate theory and frequency domain data obtained from sweeping impedance probes (SIPs) flown on previous sounding rocket missions. The inverse Laplace transform of the expressions will be used to perform direct least mean squares curve fitting against measurements made by a time domain impedance probe (TDIP) flown on a CubeSat. We compare our results with previous analytical results of the impedance of an electrically short dipole in a plasma, and typical sounding rocket impedance data in the ionosphere E-layer. An expression taking into account the appearance of a sheath is also presented. In the frequency domain, our expressions are found to capture the significant features of data from sounding rocket experiments.

A Time-Domain Impedance Probe for Fast Measurements of Electron Plasma Parameters in the Ionosphere

A new time-domain impedance probe is presented in this paper. The new instrument is able to make measurements of absolute electron density and electron-neutral collision frequency in the ionosphere at temporal and spatial resolutions not previously attained. A single measurement is made in $100~\mu \text{s}$ , which yields an instantaneous spatial resolution of 0.1 m for sounding rocket experiments. A prototype of this instrument was integrated into the payload of a NASA Undergraduate Student Instrument Program sounding rocket launched out of Wallops Island on March 1, 2016. Here, we describe the instrument, and present the data obtained from the sounding rocket experiment. A 6-V amplitude Gaussian derivative excitation was applied to a dipole probe structure, and the current through the probe terminals measured with a balanced active bridge circuit. The time-domain current response was sampled at 5 MS/s, at 12-bit resolution. In the course of the flight, the instrument measured a highly nonlinear response of the plasma because of the large input voltage signal applied. The linear theory cannot explain this response, which obscured interpretation of the data. As a result, we used time- and frequency-domain trend analysis to obtain the variation of electron density over the upleg and downleg of the rocket trajectory. The obtained time and fast Fourier transform trends showed enhanced electron densities in the F layer, which confirmed that the instrument was able to measure the density variations during a significant portion of the flight.

Sciatic nerve injury alters the spatial arrangement of neurons and glial cells in the anterior horn of the spinal cord.

The spatial arrangement of the cell is important and considered as underlying mechanism for mathematical modeling of cell to cell interaction. The ability of cells to take on the characteristics of other cells in an organism, it is important to understand the dynamical behavior of the cells. This method implements experimental parameters of the cell-cell interaction into the mathematical simulation of cell arrangement. The purpose of this research was to explore the three-dimensional spatial distribution of anterior horn cells in the rat spinal cord to examine differences after sciatic nerve injury. Sixteen Sprague-Dawley male rats were assigned to control and axotomy groups. Twelve weeks after surgery, the anterior horn was removed for first- and second-order stereological studies. Second-order stereological techniques were applied to estimate the pair correlation and cross-correlation functions using a dipole probe superimposed onto the spinal cord sections. The findings revealed 7% and 36% reductions in the mean volume and total number of motoneurons, respectively, and a 25% increase in the neuroglial cell number in the axotomized rats compared to the control rats. In contrast, the anterior horn volume remained unchanged. The results also indicated a broader gap in the pair correlation curve for the motoneurons and neuroglial cells in the axotomized rats compared to the control rats. This finding shows a negative correlation for the distribution of motoneurons and neuroglial cells in the axotomized rats. The cross-correlation curve shows a negative correlation between the motoneurons and neuroglial cells in the axotomized rats. These findings suggest that cellular structural and functional changes after sciatic nerve injury lead to the alterations in the spatial arrangement of motoneurons and neuroglial cells, finally affecting the normal function of the central nervous system. The experimental protocol was reviewed and approved by the Animal Ethics Committee of Shahid Beheshti University of Medical Sciences (approval No. IR.SBMU.MSP.REC1395.375) on October 17, 2016.

High-sensitivity and spatial resolution transient magnetic and electric field probes for transcranial magnetic stimulator characterizations

ABSTRACTTranscranial magnetic stimulation (TMS) is widely used for noninvasive brain stimulation. However, existing TMS tools cannot deliver targeted neural stimulation to deep brain regions, even though many important neurological disorders originate from there. To design TMS tools capable of delivering deep and focused stimulation, we have developed both electric and magnetic field probes to evaluate and improve new designs and calibrate products. Previous works related to magnetic field measurement had no detailed description of probe design or optimization. In this work, we demonstrated a magnetic field probe made of a cylindrical inductor and an electrical field probe modified from Rogowski coil structure. Both have much smaller size and higher directivity than commercial dipole probes. Using probe, we can calibrate and monitor any new types of TMS coil or array design and verify measured results with the other probe. We mathematically analyze their characteristics and performance and obtained a two-dimensional vector plot of the induced electric field, which matched the measured results from the second type of probe. A commercial circular coil and a figure-8 coil, with relatively complex vector field distribution, were used as examples to demonstrate the high-resolution and accurate measurement capability of our probes.

Microscopic evaluation of the ventricular tissue using stereological and Voronoi tessellation methods: Application on doxorubicin-induced cardiotoxicity in rats

There is limited quantitative microscopic information concerning the three-dimensional arrangement of cardiomyocytes and microvessels in cardiotoxic condition. The aim of this study was to evaluate the cardiac tissue of rats under different experimental conditions using modern second-order stereology and Voronoi tessellation techniques to show the spatial arrangement of the cardiomyocytes and microvessels.Sprague-Dawley rats were randomly divided into two groups (n=6). The control group received PBS and the doxorubicin (DOX) group received 4mg/kg DOX on days 1, 8, 15, and 22. On the 24th day, the left ventricle was sectioned and prepared according to the “orientator” method for microscopically evaluations. The “covariance functions” were plotted using “linear dipole probes”. Polygonal tessellation of the ventricles was also diagrammed using ImageJ software.The plotting the covariance curves of the cardiomyocytes and microvessels forming the “gaps” by slopped down, crossing the reference line and rose again. In the control group, the gaps were placed at 35–40μm and 14–16μm for the cardiomyocytes and microvessels, respectively. In the cardiotoxic group, the curves demonstrated larger gaps in comparison with the normal hearts, indicating repulsion of these structures. The curves of the cross-correlation function of the cardiomyocytes-microvessels also demonstrated the cardiomyocytes and microvessels were not normally correlated after the toxicity. Evaluation of Voronoi tessellations for the cardiomyocytes nuclei and microvessels in the normal and cardiotoxic groups showed that the areas of polygons in the normal heart were placed in the smaller range, while the areas fell in a larger range in the cases of cardiotoxicity.Stereological and Voronoi Tessellation methods showed that ventricular tissue lost its normal spatial arrangement in doxorubicin-induced cardiotoxicity in rats.

Electron density measurements in highly electronegative plasmas

In this paper we present experimental measurements of the electron density in very electronegative ‘ion–ion’ Ar–SF6 plasmas where previous investigations using Langmuir probes have observed electronegativities of up to 5000. The electron density is measured using a short matched dipole probe technique that provides a tolerance better than ±2 · 1013 m−3. The results demonstrate that the electron density in the low pressure plasma source (which contains a magnetic filter) can be reduced to around 2.7 · 1013 m−3 with a corresponding plasma electronegativity of about 4000; close to that from fluid simulation predictions. The highest electronegativity, and lowest electron density, is achieved with a pure SF6 plasma, while adding only 6% SF6 to Ar allows the electronegativity to be increased from 0 to a few hundred with a corresponding decrease in the electron density by more than a thousand. The impedance probe based on a short matched dipole appears to be a practical diagnostic that can be used for independent measurements of the electron density in very electronegative plasmas, and opens up the possibility to further investigate and optimize electronegative plasma sources.

Measurement of spatial and temporal evolution of electromagnetic fields in a 100 MHz plasma source using B dot and double dipole probes

Very high frequency plasma sources are often accompanied by plasma density nonuniformities associated with a standing-wave effect. Electron density measurements using a plasma absorption probe show density nonuniformities that can be larger than predicted by a standing wave model. These structures have been associated with harmonics of the electric fields in the plasma. The authors present the first time and phase-resolved measurements of the spatial structure of the electromagnetic waves in a 100 MHz plasma source using argon at 40 mTorr employing a B dot probe. The authors show that the harmonic structure is related to a current reversal and subsequent circulation that appears when the sheath collapses during the radio frequency cycle. The circulation is driven by inward traveling waves that are electromagnetic in nature, not plasma waves traveling at the electron thermal velocity. Double dipole probe measurements were used to validate the B dot probe electric field measurements derived from the time derivative of Βθ which is derived from the B dot probe signal.

A dipole probe for electric field measurements in the LVPD

This paper describes the design, construction, and calibration of an electric dipole probe and demonstrates its capability by presenting results on the measurement of electric field excited by a ring electrode in the Large Volume Plasma Device (LVPD). It measures the electric field in vacuum and plasma conditions in a frequency range lying between . The results show that it measures electric field 2 mV cm−1 for frequency . The developed dipole probe works on the principle of amplitude modulation. The probe signal is transmitted through a carrier of 418 MHz, a much higher frequency than the available sources of noise present in the surrounding environment. The amplitude modulation concept of signal transmission is used to make the measurement; it is qualitatively better and less corrupted as it is not affected by the errors introduced by ac pickups. The probe is capable of measuring a variety of electric fields, namely (1) space charge field, (2) time varying field, (3) inductive field and (4) a mixed field containing both space charge and inductive fields. This makes it a useful tool for measuring electric fields in laboratory plasma devices.

Matched dipole probe for magnetized low electron density laboratory plasma diagnostics

In this paper, a diagnostic method for magnetized and unmagnetized laboratory plasma is proposed, based on impedance measurements of a short matched dipole. The range of the measured electron densities is limited to low density plasmas (1012–1015 m−3), where other diagnostic methods have strong limitations on the magnetic field strength and topology, plasma dimensions, and boundary conditions. The method is designed for use in both large- and small-dimension plasma (<10 cm) without or with strong non-homogeneous magnetic field, which can be undefined within the probe size. The design of a matched dipole probe allows to suppress the sheath resonance effects and to reach high sensitivity at relatively small probe dimensions. Validation experiments are conducted in both magnetized (B ∼ 170 G) and unmagnetized (B = 0) low density (7 × 1012 m−3–7 × 1013 m−3) low pressure (1 mTorr) 10 cm scale plasmas. The experimentally measured data show very good agreement with an analytical theory both for a non-magnetized and a magnetized case. The electron density measured by the matched dipole and Langmuir probes in the range of 7 × 1012 m−3–7 × 1013 m−3 show less than 30% difference. An experimentally measured tolerance/uncertainty of the dipole probe method is estimated to ±1% for plasma densities above 2 × 1013 m−3. A spatial resolution is estimated from the experiments to be about 3d, where d is the dipole diameter. The diagnostic method is also validated by comparing the measured plasma impedance curves with results of analytical modelling.

Neutron electric dipole moment and probe of PeV scale physics

The experimental limit on the neutron electric dipole moment is used as a possible probe of new physics beyond the standard model. Within MSSM we use the current experimental limit on the neutron EDM and possible future improvement as a probe of high scale SUSY. Quantitative analyses show that scalar masses as large as a PeV and larger could be probed in improved experiment far above the scales accessible at future colliders. We also discuss the neutron EDM as a probe of new physics models beyond MSSM. Specifically we consider an MSSM extension with a particle content including a vectorlike multiplet. Such an extension brings in new sources of CP violation beyond those in MSSM. These CP phases contribute to the EDM of the quarks and to the neutron EDM. These contributions are analyzed in this work where we include the supersymmetric loop diagrams involving the neutralinos, charginos, the gluino, squark and mirror squark exchange diagrams at the one loop level. We also take into account the contributions from the $W$, $Z$, quark and mirror quark exchanges arising from the mixings of the vectorlike generation with the three generations. It is shown that the experimental limit on the neutron EDM can be used to probe such new physics models. In the future one expects the neutron EDM to improve an order of magnitude or more allowing one to extend the probe of high scale SUSY and of new physics models. For the MSSM the probe of high scales could go up to and beyond PeV scale masses.

Near-field measurement of stochastic electromagnetic fields

Stochastic electromagnetic fields with Gaussian amplitude probability distribution can be fully described by auto- and cross correlation spectra of the field components. The cross correlation spectra have to be known for the pairs of field components taken at different spatial points. Integrated electric dipole and magnetic loop probes together with active electronics in AlGaAs/GaAs-HEMT and SiGe:C-HBT technologies are presented. While the probes allow for a spatial resolution in the 100 μm range, integrated amplifiers provide about 30 dB gain over a bandwidth of about 10 GHz.

Stress changes the spatial arrangement of neurons and glial cells of medial prefrontal cortex and sertraline and curcumin prevent it.

ObjectiveThe present study explored the three-dimensional spatial arrangements of the neurons and glial cells within the medial prefrontal cortex (mPFC) of rats.MethodsIt evaluated the arrangement for differences after stress with or without treatment with curcumin and sertraline using second-order stereology. Orientator method was applied to obtain isotropic uniform random sections of mPFC. The pair correlation g(r) and cross-correlation functions were estimated by counting dipole probes superimposed on histological sections of mPFC.ResultsThe mean total volume of neurons and glial cells was 0.80 (0.05) and 0.40 (0.07), respectively in the control group. The corresponding values decreased by 50% in the stressed group. The curve of g(r) for the neurons and glial cells showed a wider gap between the stressed rats' mPFC. Theses indicate a negative correlation (repulsion) between the neurons and glial cells in the stressed rats. Evaluation of the cross-correlation function of the neurons and glial cells also showed a negative correlation in the stressed group. The estimated values of the global degree of order in the spatial point pattern for neurons and glial cells were 0.62 and 0.20 in control and stressed animals, respectively. Curcumin and sertraline protected the spatial arrangements of the cells after stress induction in rats. In addition, the volume of the neurons and glial cells remained unchanged after stress.ConclusionDissociation of the neurons and glial cells can is seen at some places in the stressed rats' cortex. However, the spatial arrangement of the cells was remained unchanged in curcumin+stress and sertraline+stress rats.

Constructing a layered electrical conductivity model using k nearest‐neighbour predictions and a combination of two proximal sensors

SummaryA strategy to produce layered high‐resolution apparent electrical conductivity (ECa) models of agricultural fields by distance‐weighted k nearest‐neighbour prediction (kNN) was tested at three farms. Electromagnetic induction (EMI) measurements were combined with measurements made with a dipole probe. Depth‐layer‐specific ECa values from the probe measurements were interpolated in the attribute space of the EMI measurements with the distance‐weighted kNN method. This analysis resulted in high‐resolution ECa maps for depth intervals of 0–0.2 and 0.4–0.6 or 0.4–0.8 m. The ECa values measured with the dipole probe ranged between 6.1 and 40.2 mS m−1, and at two of the three farms investigated it was possible to create ECa maps at two depths with mean absolute errors of 1.1–3.8 mS m−1. At the third farm the predictions were less accurate. Combining data from two fundamentally different sensors of ECa for kNN predictions was deemed to be an efficient way to produce 3‐D information on arable soil. However, it seems to be essential that the dipole probe and the EMI measurements are made under similar conditions.

Sensing Depth of Microwave Radiation for Internal Body Temperature Measurement

This paper investigates modeling of the interaction of human tissues with a probe antenna situated on the surface of the skin. The goal is to differentiate temperature changes at different depths under the skin for passive radiometric measurements of internal body temperature. An improved metric is defined in order to differentiate thermal power radiated from a specific part of the tissue relative to the total thermal power received by the probe antenna. The frequency range between 0.5 and 3 GHz is investigated due to the sensing depth that can be achieved for a given receiver sensitivity. The general approach is to validate full-wave finite element method (FEM) EM simulations with a spectral-domain analysis for layered lossy dielectrics with a dipole at the interface between two of the layers. This was successfully done for a dipole on a water half-space and a stack of three tissues (skin, fat, and muscle). A new type of multifrequency probe was designed for 1.4, 2.7, and 4.9 GHz operation, and the predicted impedance validated experimentally. To the authors' knowledge, this is the first time that the near-field received power of a dipole probe placed in contact with lossy layered media is examined as a function of frequency. This is shown to be significantly different than the plane wave case, and is necessary knowledge for the design of a portable radiometer for microwave internal body thermometry.

Spatial arrangement of the heart structure: Application of second-order stereology in diabetic rats

The present study explored three-dimensional spatial arrangements of the cardiomyocytes and microvessels within the heart of rats and evaluated the arrangement for differences after diabetes using second-order stereology. Isector method was applied to obtain isotropic uniform random sections of the heart. The pair correlation g(r) and cross-correlation functions were estimated by counting dipole probes (with length of 3.57 μm) superimposed on histological sections of the heart. The co-variograms indicated that the curve of g(r) for the cardiomyocyte showed a gap between cardiomyocytes at r=21-25 μm in the control rats and a wider gap at r=18-50 μm in diabetic hearts. Estimates of g(r) for the vessels also showed a wider gap (at r=25-39 μm) in diabetic hearts compared to the control rats (r=25-32 μm). These indicate a negative correlation (repulsion) between the cardiomyocytes and microvessels in the diabetic hearts. Evaluation of the cross-correlation function of the cardiomyocytes and microvessels showed that at 32-36 μm, both structures had a negative correlation in the control group, but not in the diabetic rats. Dissociation of the cardiomyocytes at some places can be seen in diabetic heart. This can be seen also in microvessels. Neither cardiomyocytes nor microvessels are arranged normally after diabetes.

Application of Embedded Dual-Loaded Modulated Scatterer Technique (MST) to Multilayer Structures

Health monitoring of infrastructure and other critical components composed of complex composite materials is an important ongoing concern. The embedded modulated scatterer technique (MST) has shown potential for evaluating electrical (i.e., complex dielectric) properties of bulk materials. This paper investigates its potential utility for evaluating properties of layered composite structures. The approach is based on irradiating an MST probe with an electromagnetic wave. This incident wave induces a current along the length of the thin dipole probe as a function of its load impedance and the material surrounding it, including boundaries within a layered structure. Consequently, the MST sensor may be placed at a specific location or boundary such that the probe response can be monitored over time for critical changes in the geometrical or the material property of the structure. In order to use MST for evaluating important characteristics of layered structures, this application must be fully investigated, and its limitations established. This paper presents an inclusive study of the application of MST for the evaluation of layered materials through pertinent electromagnetic simulations as well as experimental corroboration of the simulation results. The experimental results show that embedded MST is capable of detecting boundaries between layers within a layered structure and is also sensitive to the distance to the boundary.