Electro-optic Probe Research Articles

Experimental Investigation of Parameters Influencing the Formation of Dry Bands and Related Electric Field

This paper presents an experimental investigation conducted to determine the influence of parameters such as the ambient temperature, pollution level, and substrate material on the formation of dry bands on polluted layers. To investigate these parameters, we applied a simplified insulator geometry, developed in our previous work, to experimentally control the complex process of dry band formation on a polluted surface. The simple geometry of the experimental model enabled the use of Plexiglas, RTV, and glass as construction substrate materials. RTV and glass were used to simulate a composite and ceramic insulator surface, respectively. Moreover, an electrooptic (EO) probe enabled the measurement of the axial E-field evolution at the surface of the dry band during dry band formation. The results indicated that the substrate material, ambient temperature, and pollution level substantially influence dry band formation. The effects of the first two parameters are directly associated with heat transfer phenomena in the substrate material and at the ambient air/substrate interface. The effect of the third parameter is associated with absorption and evaporation of the pollution layer. In addition, the appearance of the dry band can be clearly identified by a rapid increase in both the pollution layer resistance and the axial E-field in the dry band area. The value of the axial E-field is influenced primarily by the width of the dry band and by the pollution layer resistance, which is directly dependent on the humidification duration. Finally, because most of the results obtained herein were in accordance with those in the literature, we conclude that the proposed experimental model may provide an effective and inexpensive testing method for developing new materials and solutions for improving the dielectric performance of insulators used in polluted environments. Similarly, the simple geometry of the experimental model and the ability to easily control the experimental parameters may enable this tool to validate the results of various numerical models in studies of the thermoelectrical behavior of polluted insulators.

Potentialities and limitations of an electro-optic probe for electric field diagnostics of cold atmospheric pressure plasma jets

Potentialities and limitations of an electro-optic probe for electric field diagnostics of cold atmospheric pressure plasma jets

Antireflection Coatings Based on PEDOT:PSS Conductive Polymer Using d-Sorbitol Additives for Terahertz Spectroscopy and Imaging.

Optical antireflection has been employed for a variety of applications in terahertz spectroscopy and detectors. However, current methods encounter challenges in terms of cost, bandwidth, structural complexity, and performance. In this study, a low-cost, broadband, and easily processed THz antireflection coating scheme based on the model of impedance-matching effect is proposed, using a 6 wt % d-sorbitol-doped poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (s-PEDOT:PSS) film. By adjusting the thickness of the s-PEDOT:PSS film, these biocompatible conductive polymers enable a significant reduction of Fresnel reflection and operate over a broad bandwidth between 0.2 and 2.2 THz. Applying the antireflective coating to the surface of the sample substrate and electro-optic probe crystal in THz spectroscopy and near-field imaging shows that the spectral resolution is significantly improved, and the devices exhibit more excellent intended performance. The findings of this study could aid in improving the measurement capability of various THz time-domain spectroscopy and imaging system.

Analysis of Intentional Electromagnetic Interference on GENEC Model Using Cylindrical Mode Matching

In recent times, due to the high operating frequency and low operating voltage of modern electronic devices, intended electromagnetic interference (IEMI) has been the cause of increasing damage. In particular, targets with precision electronics such as aircrafts or missiles have shown that a high-power microwave (HPM) may cause malfunction or partial destruction of the GPS or the avionic control system. Analysis of the effects of IEMI requires electromagnetic numerical analyses. However, there are limitations to conventional numerical techniques, such as the finite element method, method of moment, or finite difference time domain method, due to the complexity and large electrical length of a real target system. In this paper, we proposed a new cylindrical mode matching (CMM) technique to analyze IEMI of the generic missile (GENEC) model, which is a hollow metal cylinder with multiple apertures. Using the CMM, we can quickly analyze the effect of the IEMI inside the GENEC model from 1.7 to 2.5 GHz. The results were compared with those of the measurements and, for verification, with the FEKO, a commercial software program developed by Altair Engineering, and showed good agreement. In this paper, the electro-optic (EO) probe was used to measure the electric field inside the GENEC model.

Calibrating a Radio Frequency Electrooptic Sensor for Field-Relevant Temperature Conditions in a Laboratory Setting

Legacy high-powered electric field measurement devices, such as flush plate dipoles (D-dots) and waveguides, are the primary diagnostic tools used for free-field experimentation. Unfortunately, these metallic devices perturb the electric field of interest via scattering and require the use of coaxial cables (fluctuate with temperature). Electrooptic (EO) probes offer a potential solution as they minimally perturb the electric field, and fiber-optic cables can be designed to correct or prevent temperature fluctuations. However, to replace the legacy diagnostics, it is critical that the EO probes are calibrated in field-relevant conditions (outdoor temperatures between <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.4~^{\circ} \text{C}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$49~^{\circ} \text{C}$ </tex-math></inline-formula> ). Characterization of a modern EO sensor is done by using an environmental chamber and a gigahertz transverse electromagnetic (GTEM) cell. The collected data in this article indicates that modern <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {LiNbO}_{{3}}$ </tex-math></inline-formula> EO sensors have linear changes across both various temperatures and electric fields. This article outlines the process of creating field-relevant conditions in laboratory settings. Because temperature effects are ubiquitous with most devices, the temperature response of the EO probe needed to be isolated from all other temperature effects. Using a novel way of applying the design of experiments (DoE) method, the temperature response of the EO probe can be isolated and a linear trend can be resolved. The data suggest that the EO probe under test can be used to measure RF fields as long as a small correction factor is applied to 0.52% per °C for every °C away from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$22.0~^{\circ} \text{C}$ </tex-math></inline-formula> in either direction.

Field-Calibrated Electrooptic Probing System for Millimeter-Wave 5G Applications

We propose field-calibrated electrooptic probes that are designed for millimeter-wave (mm-wave) 5G phased array antenna and Ka-band rectangular waveguide. A method to enhance the probes’ sensitivity and the practical limit for realization are presented. The fabricated probes are specifically minute enough to fit inside a standard mm-wave waveguide section for calibration in a minimally invasive way. The proposed calibration method is validated by analyzing the field invasiveness and through a simulation. Using a calibrated probe associated with a heterodyning probe control system, electric field distributions with absolute V/m scale from an mm-wave antenna are presented.

Electro-optic Bdot probe measurement of magnetic fluctuations in plasma.

We propose a combined use of a Pockels electro-optic sensor with a pickup loop coil (Bdot probe) for the measurement of magnetic fluctuations in plasmas. In this method, induced fluctuating voltage on the coil loop is converted into an optical signal by a compact electro-optic sensor in the vicinity of the measurement point and is transferred across optical fiber that is unaffected by electric noise or capacitive load issues. Compared with conventional Bdot probes, the electro-optic Bdot probe (1) is electrically isolated and free from noise pickup caused by the metallic transmission line and (2) can be operated at a higher-frequency range because of the smaller capacitance of the operation circuit, both of which are suitable for many plasma experiments. Conversely, the sensitivity of the current electro-optic Bdot probe arrangement is still significantly lower than that of conventional Bdot probes. A preliminary measurement result with the electro-optic Bdot probe showed the detection of a magnetic fluctuation signal around the cyclotron frequency range in the RT-1 magnetospheric plasma experiment.

Limitations of using electro-optical probes for the measurement of the electromagnetic field emitted by the new generations of wireless communication devices

The rapid evolution of communication standards caused a paradigm shift in electromagnetic field (EMF) measurement campaigns, as exposure is more likely to take place in the proximity of the device. With the increased spatial variability of EMF exposure, electro-optical (EO) technology stands out as a promising alternative to conventional near field measurement instrumentation due to their miniature sizes and dielectric structure that does not interfere with the measured field. Motivated by the recent progress in the EO sensing technology, it is this article purpose to quantify the limitations of using a set of commercially available EO probes for measurement of EMF emitted by an IEEE 802.11ax router and a VoLTE mobile phone. To our knowledge, this is the first attempt to characterize the capabilities of this emerging sensing technology for EMF exposure assessment in real world communication situations. Present findings suggest that the sensitivity of the investigated EO probes is insufficient for measuring broadband signals at field levels that characterize state-of-the-art communication devices used by the public in common usage scenarios. This work also documents the EO probes suitability and response with respect to frequency, electric field strength and signal bandwidth.

Effects of amplitude modulated discharge on growth of nanoparticles in TEOS/O2/Ar capacitively coupled plasma

We investigate the effects of the amplitude modulation (AM) discharge method on the growth of nanoparticles and the relation between growth of nanoparticles and plasma generation in tetraethylorthosilicate (TEOS)/O2/Ar plasma. The laser-light scattering (LLS) intensity, which is proportional to the density and the sixth power of the size of nanoparticles in the Rayleigh scattering regime, decreases by 18% at an AM level of 10% and by 60% at an AM level of 50%. On the other hand, the ArI emission intensity, which is roughly proportional to plasma density, is higher than that for the continuous wave discharge. Thus, AM discharges suppress growth of nanoparticles in TEOS plasma. We have shown oscillations of the axial electric field Ez with the AM frequency for AM discharge by electric field measurement using an electro-optic probe. We have discussed that these fluctuations of Ez mainly lead to the vertical oscillation of the levitation position of nanoparticles trapped in the plasma sheath boundary region by taking into account the force balance equation in the axial direction on these negatively charged nanoparticles.

Photonics-Based Near-Field Measurement and Far-Field Characterization for 300-GHz Band Antenna Testing

In this study, photonics-based near-field measurement and far-field characterization in a 300-GHz band are demonstrated using an electrooptic (EO) sensor with planar scanning. The field to be measured is up-converted to the optical domain (1550 nm) at the EO sensor and delivered to the measurement system with optical fiber. The typical phase drift of the system is 0.46° for the one-dimensional measurement time of 13 s, which is smaller than the standard deviation of the phase measurement of 1.2° for this time scale. The far-field patterns of a horn antenna calculated from the measured near-field distribution are compared with that measured with the direct far-field measurement system using a vector network analyzer. For the angular related parameters, the accuracy of the results obtained by our near-field measurement are comparable to that of those obtained by direct far-field measurements. The sidelobe level discrepancy (approximately 1 dB) between the results obtained based on our near-field measurement and those from the direct far-field measurements are attributed to the excess noise of the probe correction data. We believe that photonics-based near-field measurements with spherical EO probe scanning will pave the way for the characterization of high-gain antennas at the 300-GHz band.

Fructose recognition using novel solid-state electro-optical nanosensor based on boronate-tagged fluorophore modified graphene oxide

The level of fructose is an important indicator alongside the blood glucose level in detecting diabetes mellitus. The development of boronic acid (BA)-modified electrodes are still of interest to researchers in the sensor-based detection systems for fructose. Hence, a novel electro-optical solid-state probe based on fluorogenic dye for saccharide detection was established for the first time. A flexible ITO/PET with nano-metric electrodeposited layers of graphene oxide (GO) was used as a primary electrode. A new selectophore based on boronate-tagged 1,8-naphthalimide (NB) with a planar structure was used to form a composite film with Mg–Al layered double hydroxide (LDH) nanoplatelets. The minimum sheet resistance, uniform morphology, and high electrocatalytic activity of the modified matrix film were obtained in the fifth cycle of the LBL assembled modified electrode ((NB/LD)5/GO/ITO/PET). This solid-state electrode led to electrochemical changes due to the BA and sugar transduction at 0.59 V vs Ag/AgCl in a cyclic voltammetry technique and increased the fluorescence emission. The designed probe indicated good selectivity toward fructose within the range of 10–225 nM at the physiological pH 7.4. • A flexible GO/ITO/PET with nanometric electrodeposited layers of GO was developed. • Fluorescence conductive electrode was constructed based on a new selectophore NB with Mg–Al LDH by LbL technique. • NB shows 3.51 times emission amplytude at solid-state network against free NB. • The (NB/LDH) 5 /GO/ITO/PET platform was used to electrochemical and optical detection of fructose at nM range.

Minimally invasive optical sensors for microwave-electric-field exposure measurements

The measurement of microwave electric-field (E-field) exposure is an ever-evolving subject that has recently led the International Commission on Non-Ionizing Radiation Protection to change its recommendations. With frequencies increasing toward terahertz (THz), stimulated by 5G deployment, the measurement specifications reveal ever more demanding challenges in terms of bandwidth (BW) and miniaturization. We propose a focus on minimally invasive E-field sensors, which are crucial for the in situ and near-field characterization of E-fields both in harsh environments such as plasmas and in the vicinity of emitters. We browse the large varieties of measurement devices, among which the electro-optic (EO) probes stand out for their potential of high BW up to THz, minimal invasiveness, and ability of vector measurements. We describe and compare the three main categories of EO sensors, from bulk systems to nanoprobes. First, we show how bulk-sensors have evolved toward attractive fibered systems that are advantageously employed in plasmas, resonance magnetic imagings chambers or for radiation-pattern imaging up to THz frequencies. Then we describe how the integration of waveguides helps to gain robustness, lateral resolution, and sensitivity. The third part is dedicated to the ultra-miniaturization of components allowing ultimate steps toward electromagnetic invisibility. This review aims at pointing out the recent evolutions over the past 10 years, with a highlight on the specificities of each photonic architecture. It also shows the way to future multi-physics and multi-arrays smart sensing platforms.

Pigtailed Electrooptic Sensor for Time- and Space-Resolved Dielectric Barrier Discharges Analysis

We here demonstrate the potentialities of pigtailed electrooptic probes to perform vectorial electric field characterizations of dielectric barrier discharges (DBDs). The analysis leads to the accurate determination of the breakdown voltage and the associated electric field in the vicinity of the discharge. A polarimetric analysis of the DBDs is proposed due to real-time measurement of longitudinal and radial components of the electric field vector. Moreover, the transition from capacitive to resistive behavior is characterized at the breakdown field.

Electrooptic Measurements to Assess the Quality of Calibration Kit Design

Electromagnetic coupling between planar devices can degrade microwave calibrations and, consequently, the accuracy of a measurement. This letter describes measurement-based methods that can identify, assess, and visualize the electric field coupled between the adjacent planar calibration structures. The coupling within a printed circuit board (PCB)-based and an on-wafer impedance standard substrate is successfully demonstrated and analyzed up to 4 and 20 GHz, respectively, through S-parameter and electric-field measurements obtained using an electrooptic probing system.

Stretched grid finite difference method for computation of electric field in composite insulators with defects

A 2-dimensional stretched grid finite difference method for the calculation of electric field in composite insulators for up to 1000 kV is presented in this paper. This method is shown to be applicable for composite insulators with and without defects where the inherent axial symmetry cannot be used to simplify the modeling process. This method was initially used to evaluate healthy composite insulators of single and double strings with and without corona and grading rings. Further, a conducting defect was simulated at the high voltage electrode to evaluate 69 and 138 kV insulators. The electric field was also computed using a package based on boundary element method. The accuracy and computational time for all the cases were compared. It has been shown that the proposed method can yield fairly accurate results when compared to other methods, but in a significantly reduced time taken by the latter. The electric field computed for 69 kV composite insulator with defect was compared with the actual measurements using an electro-optic probe. The results show a good agreement. Stretched grid method promises to be an efficient way of quickly computing electric field and this paper quantifies the information obtained for insulators with wide range of system voltages.

Analysis of the RF Excitation of Endovascular Stents in Small Gap and Overlap Scenarios Using an Electro-Optical E-field Sensor

To assess the effect of the electro-magnetic coupling of endovascular stents on their RF heating potential in MRI. A custom-built electro-optic E-field probe is used to perform measurements of the scattered E-field at a distance of 2 mm to stent samples with submillimeter resolution. Various combinations of stent lengths are measured at 124 MHz (3T MRI Larmor frequency) with varying gap and overlap between the stents, with and without stent coating, and with distilled water and saline solution as surrounding media. The results are compared to theoretically derived E-field distributions. At an overlap of 10 mm the E-field pattern of two stents collapses to a single dipole indicating excellent coupling between the stents. E-field intensities substantially increase/decrease up to 5-fold/2.5-fold if the total length of the two combined stents is closer/further away from the resonance length of the single stents. Stent coating and conductivity of the surrounding medium strongly influence the E-field patterns of overlapping stents. Measured and calculated E-field patterns are in good agreement. Electro-optic E-field measurements are a valuable tool for RF safety assessments in both single as well as coupled stents. RF induced heating of single stents during MRI has been extensively studied. However, in clinical practice often two or more stents are implanted in close proximity which can substantially change the pattern of the scattered electric fields and the localization and intensity of hot spots. In this study a detailed assessment of the coupling of stents during RF excitation is given.

20 GHz Antenna Radiation Pattern Obtained From Near-Field Mapping With Electrooptic Probe on a Single Plane

The ability of an electrooptic (EO) sensor to perform near-field mapping of a 20 GHz pyramidal horn antenna without disturbance on the radiation behavior is demonstrated. The electric field is scanned on a plane close to the horn aperture with spatial resolution less than 0.1λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . The dynamic range reaches more than 40 dB. The measured magnitudes and phases of near-field pixels enable the computation of the far-field radiation pattern. The results are in excellent agreement with theory, numerical simulations and actual far-field measurement. The different approaches lead to the same antenna gain with a confidence interval lower than 1 dB. Furthermore, the behavior of the electromagnetic wave from reactive to radiative region is investigated. The weak invasiveness of the probe is also analyzed.

Development of a Multifunctional Electrochemical Probe for Detection of Anticoagulants in Whole Blood

The ability to rapidly and accurately monitor anticoagulant drugs such as heparin is critical for cardiac surgical patients. Unfortunately, this is quite challenging due to the narrow therapeutic window and heterogenous molecular weight of heparin; which has led to heparin being the second most common ICU medication error. Currently the most widely used method to monitor heparin is the activated partial thromboplastin time (aPTT), however, this is an indirect measurement of heparin dose and requires blood sampling with long turnaround times. Here we develop a minimally invasive, multifunctional electro-optical fiber optic for the detection of heparin. These probes have a local optical channel for in situ optical spectroscopy and electrical channel for quantitative electrochemical sensing. To enhance the electrochemical surface area of the fiber optic, and provide a porous medium for ion transport and support matrix for the immobilization of heparin-complexing dyes, highly conductive polymer layers were developed that can be electrochemically deposited on the probes. Strong cathodic current changes, and attenuation of light through the medium are observed in heparin-spiked buffer solutions when heparin complexes with the dye molecules, and the degree of change can be correlated to heparin concentration. Electrical sensing were also carried out in human whole blood and used to extract heparin concentrations in real time. Given the small footprint of the electro-optic fiber optic probes, they can be inserted through an intravenous catheter to provide a novel in situ solution to rapid, quantitative monitoring of heparin dose in the bloodstream.

Near-field THz micropolarimetry.

We introduce a method for rapid determination of anisotropic terahertz absorption with sub micron resolution and high spectral integrity in the terahertz range. The method is ideal for microscopic and environmentally sensitive materials such as 2-D materials and protein crystals where the anisotropic absorption is critical to understanding underlying physics. We introduce the idea of using an iso-response relationship between the THz polarization and electro optic probe polarization to enable stationary sample polarization measurements covering a full 2π polarization dependence measurement.

Micrometer Scale Resolution Limit of a Fiber-Coupled Electro-Optic Probe.

We present the practical resolution limit of a fine electrical structure based on a fiber-coupled electro-optic probing system. The spatial resolution limit was experimentally evaluated on the sub-millimeter to micrometer scale of planar electrical transmission lines. The electrical lines were fabricated to have various potential differences depending on the dimensions and geometry. The electric field between the lines was measured through an electro-optic probe, which was miniaturized up to the optical bare fiber scale so as to investigate the spatial limit of electrical signals with minimal invasiveness. The experimental results show that the technical resolution limitation of a fiber-coupled probe can reasonably approach a fraction of the mode field diameter (~10 μm) of the fiber in use.