Planar Excitation Research Articles

Planar coil-based differential electromagnetic sensor with null-offset

This paper focuses on the design and experimental test of a null-offset differential electromagnetic sensor characterized by simplicity, flexibility and low cost. This sensor consists of two planar excitation coils, which generate magnetic field and a planar acquisition coil, which senses the sample material. The differential configuration of the sensor improves signal conditioning and reduces the common-mode noise. We present analytical and numerical (simulation) studies of the working principle. Experiments were performed to test the ability of the sensor to detect non-invasively: (i) the presence of metallic samples and (ii) the variations of glucose in human blood.

An Efficient Finite-Element Approach for the Modeling of Planar Double-D Excitation Coils and Flaws in SQUID NDE Systems

Incorporating an efficient approach for the finite-element simulation of eddy current superconductive quantum interface device (SQUID) nondestructive evaluation (NDE) systems, an appropriate finite-element method (FEM) has been presented for simulating and analyzing such systems. We have introduced a new model for the planar double-D coils, which are used as the excitation source in eddy current SQUID NDE systems, and also another model for the description of the flaw effect on the induced current. We have also examined our simulation results with their associated measurements. Our system is based on a high-TC YBCO gradiometer RF-SQUID sensor with a flux noise level below 100 ??0/ ?Hz at 100 Hz in an unshielded environment while being shielded against external RF electromagnetic interference. The very good agreement between experimental and numerical approaches confirmed our model for the 3-D FEM simulation of the system, which is being done in reasonable time and using reasonable computer resources.

Study of gold nanoparticles and live cells interactions by using planar evanescent wave excitation

We present a planar evanescent wave (PEW) technique combined with phase contrast optical microscopy to study the interactions between cells and gold nanoparticles (AuNPs). The PEW method employs a dual-fiber-line guide to couple light into a thin glass slide. It produces a uniform and long evanescent wave near the glass surface, as verified by the optical near-field measurement. High-contrast AuNP images are obtained by the PEW illumination. At the same time, cells are observed only by using the phase contrast microscopy. The nanoparticles and cell images indicated that unmodified AuNPs had no interactions with cells, possibly due to the negative surface charges on both cells and nanoparticles. The electrostatic concept was further verified by coating AuNPs with positively charged poly (L-lysine). DNA aptamers for surface mucin glycoprotein were coated on AuNPs to demonstrate the application for single nanoparticle tracking.

MORE EFFICIENCY OF TRANSVERSE WAVE APPROACH (TWA) BY APPLYING ANISOTROPIC MESH TECHNIQUE (AMT) FOR FULL-WAVE ANALYSIS OF MICROWAVE PLANAR STRUCTURES

MORE EFFICIENCY OF TRANSVERSE WAVE AP-PROACH (TWA) BY APPLYING ANISOTROPIC MESHTECHNIQUE (AMT) FOR FULL-WAVE ANALYSIS OFMICROWAVE PLANAR STRUCTURESM. AyariDepartment of mathematicsVirginia Polytechnic Institute and state university-BlacksburgVA, USAT. AguiliSyscom LaboratoryNational Engineering SchoolB.P 37 Le belvedere 1002 Tunis, TunisiaH. BaudrandEM Research & Design, RCEM17 Rue Denis Papin, 31500 Toulouse, FranceAbstract—The present paper sets out to present a numericalelectromagnetic (EM) method TWA for EM field modeling of planarstructures. Combining both the benefits of TWA process and themodeling of planar excitation source, an optimization techniqueAMT is applied and evaluated in context of RF integrated-circuitapplications. The computational complexity of TWA process isexamined and the obtained simulation results are found to be ingood agreement with literature. Index Terms- Transverse waveapproach (TWA), anisotropic mesh technique (AMT), computationalcomplexity, planar structures

Compensation of curvature effects by illumination

Front deformation of initially planar excitation waves can be observed in nonplanar media or in spatially heterogeneously illuminated systems. The deformation of propagating reaction–diffusion waves in either of these systems has been investigated earlier separately. Here we present a combination of both heterogeneous systems, which can lead to a compensation of wave deformations. Our theoretical analysis of the evolution of propagating excitation waves, based on the framework of a kinematical theory, shows that the curvature effect can be compensated by illumination. Supporting experiments were performed with the light-sensitive Belousov–Zhabotinsky system.

Fully adaptive FEM based fluorescence optical tomography from time-dependent measurements with area illumination and detection

Using an area-illumination and area-detection scheme, we acquire fluorescence frequency domain measurements from a tissue phantom with an embedded fluorescent target and obtain tomographic reconstructions of the interior fluorescence absorption map with an adaptive finite element based scheme. The tissue phantom consisted of a clear acrylic cubic box (512 ml) filled with 1% Liposyn solution, while the fluorescent targets were 5 mm diameter glass bulbs filled with 1 microM Indocyanine Green dye solution in 1% Liposyn. Frequency domain area illumination and detection employed a planar excitation source using an expanded intensity modulated (100 MHz) 785 nm diode laser light and a gain modulated image intensified charge coupled device camera, respectively. The excitation pattern was characterized by isolating the singly scattered component with cross polarizers and was input into a dual adaptive finite element-based scheme for three dimensional reconstructions of fluorescent targets embedded beneath the phantom surface. Adaptive mesh refinement techniques allowed efficient simulation of the incident excitation light and the reconstruction of fluorescent targets buried at the depths of 1 and 2 cm. The results demonstrate the first clinically relevant noncontact fluorescence tomography with adaptive finite element methods.

Planar excitation of Goubau Transmission Lines for THz BioMEMS

We propose and demonstrate an original planar excitation of a single wire transmission line also known as Goubau-Line (G-Line). The excitation is based on an electromagnetic transition between a coplanar waveguide and the desired G-line in a planar configuration. We present some characteristics for this line such as its electromagnetic spatial distribution, its velocity, and results in the frequency domain analysis for the transitions. We will also show some results concerning the shape of the G-line and its influence on the transmission level. From these results, we show that there is a great interest for these structures in the field of biological characterization.

Improving the sensitivity of protein microarray by evanescent-field-induced fluorescence

To improve the sensitivity of protein microarray, a prism surface replaces the surface of the common microscope slide. The protein targets arrayed on the surface are hybridized and labelled by fluorescent probes. Evanescent excitation occurs when the convergent laser reaches the surface, and a photomultiplier tube detects the emitted fluorescent signal. A two-dimensional actuator scans the whole surface to achieve planar laser excitation and fluorescence collection. The penetration depth of the evanescent field into the protein targets is only some hundred nanometers and can be controlled by different incident angle of the laser beam, so the undesired background signals are reduced dramatically and the detection sensitivity is improved by a factor of 50 to 100 comparing to confocal excitation. This approach can detect low abundance analytes without signal amplification.

Planar coil excitation of multifrequency shear wave transducers

A transducer format that replaces the electrode of an acoustic resonator with a planar spiral coil is used to extract multifrequency spectral information from adsorbed protein films. Both amorphous silica and crystalline piezoelectric resonators are driven to resonance by forces induced across an air gap by magnetic direct generation and piezoelectric excitation induced by the electromagnetic field of the coil. Inspection of the harmonic frequencies between 6 MHz and 0.6 GHz indicates that the response of these two resonator types is described by different families of shear acoustic standing waves, with similar acoustic features to the quartz crystal microbalance. Exposure of the devices to protein solutions results in reproducible shifts of their harmonic frequencies, up to a maximum of 15 kHz and increasing linearly with frequency and operating mode. The gradient, determined from the ratio of the frequency change to the operating frequency was determined as 21.5 × 10 −6 for the quartz device and 60.9 × 10 −6 for the silica device. Consistency with the Sauerbrey equation for the piezoelectric linear shear mode was comparable at a predicted value of 22.5 × 10 −6, but not for the radial shear mode of the silica device at 12.7 × 10 −6. Opportunities resulting from the wide bandwidth of the planar coil excitation and choice of acoustic mode are discussed with respect to acoustic fingerprinting of adsorbed proteins.

High-resolution imaging of cardiac biomagnetic fields using a low-transition-temperature superconducting quantum interference device microscope

We have developed a multiloop low-temperature superconducting quantum interference device sensor with a field sensitivity of 450 fT/Hz−1/2 for imaging biomagnetic fields generated by action currents in cardiac tissue. The sensor has a diameter of 250 μm and can be brought to within 100 μm of a room-temperature sample. Magnetic fields generated by planar excitation waves are associated with a current component parallel to the wave front, in agreement with predictions of the bidomain model. Our findings provide a new basis for interpreting the magnetocardiogram.

Nonlinear dynamics of temporally excited falling liquid films

The two-dimensional spatiotemporal dynamics of falling thin liquid films on a solid vertical wall periodically oscillating in its own plane is studied within the framework of long-wave theory. A pertinent nonlinear evolution equation referred to as the temporally modulated Benney equation (TMBE) is derived and its solutions are investigated numerically. The bifurcation diagram of the Benney equation (BE) describing the film dynamics in the unforced regime is computed depicting the domains of linearly stable, linearly unstable bounded, and unbounded behaviors. The solutions obtained for film dynamics via the BE are compared to those documented for direct numerical simulations of the Navier–Stokes equations (NSE). The comparison demonstrates that the BE constitutes an accurate asymptotic reduction of the NSE in the domain preceding the transition to the regime of its unbounded solutions. It is found that periodic planar boundary excitation does not alter the fundamental unforced bifurcation structure and the spatial topological structure of the interfacial waves. The film evolution as described by TMBE is found to be primarily of quasiperiodic tori complemented by several types of strange attractors. In the case of relatively thick films increase of either the amplitude or the frequency of wall oscillation results in significant decrease of the peak-to-peak size of interfacial waves.

Micro-fluxgate sensor with closed core

Micro-fluxgate sensor with symmetrical core on both sides of the planar rectangular excitation and pick-up coils has substantially improved parameters compared to its single-core predecessor. Almost closed magnetic path for the excitation field allows much deeper saturation of the sensor core, which reduces the perming effect, hysteresis and noise. Perming of maximum 5 μT for 6 mT field shock, 28 V/T sensitivity and 24 nT rms noise were achieved for 2 mm long sensor excited by 1 MHz, 180 mA rms sinewave current, without magnetic feedback.

Uranium and plutonium solution assays by transmission-corrected x-ray fluorescence spectrometry

An x-ray fluorescence analysis technique was developed for uranium and plutonium solutions, which compensates for variations in the absorption of the exciting gamma rays and fluorescent x-rays. 57Co is used to excite efficiently the K lines of the elements, and a mixed 57Co plus 153Gd transmission source is used to correct for variations in absorption. The absorption correction is a unique feature of the technique which permits accurate calibration with a single solution standard and the measurement of a wide range of concentrations (up to 300 g l−1). Without this correction procedure, up to six solution standards are required to correct for non-linearity over this concentration range. In addition, other elements present in the specimens and not present in the standards would otherwise reduce the accuracy or even invalidate the analyses. Specially designed equipment incorporates a planar intrinsic germanium detector, excitation and transmission radioisotopes and specimen holder. The apparatus can be inserted into a rubber glove of a glove-box, keeping the apparatus outside and the solutions inside the glove-box, thereby protecting the user and the equipment from possible contamination. This technique will be tested at the Bochvar Institute of Inorganic Materials in Moscow for possible use in the Russian complex of nuclear facilities. This is part of a cooperative program between laboratories in the USA and Russia to strengthen systems of nuclear materials protection, control and accountability (MPC&A) in both countries. A part of this program is to measure accurately and track inventories of materials, hence the need for good non-destructive analytical techniques. Copyright © 1999 John Wiley & Sons, Ltd.

Uranium and plutonium solution assays by transmission‐corrected x‐ray fluorescence spectrometry

An x-ray fluorescence analysis technique was developed for uranium and plutonium solutions, which compensates for variations in the absorption of the exciting gamma rays and fluorescent x-rays. 57Co is used to excite efficiently the K lines of the elements, and a mixed 57Co plus 153Gd transmission source is used to correct for variations in absorption. The absorption correction is a unique feature of the technique which permits accurate calibration with a single solution standard and the measurement of a wide range of concentrations (up to 300 g l−1). Without this correction procedure, up to six solution standards are required to correct for non-linearity over this concentration range. In addition, other elements present in the specimens and not present in the standards would otherwise reduce the accuracy or even invalidate the analyses. Specially designed equipment incorporates a planar intrinsic germanium detector, excitation and transmission radioisotopes and specimen holder. The apparatus can be inserted into a rubber glove of a glove-box, keeping the apparatus outside and the solutions inside the glove-box, thereby protecting the user and the equipment from possible contamination. This technique will be tested at the Bochvar Institute of Inorganic Materials in Moscow for possible use in the Russian complex of nuclear facilities. This is part of a cooperative program between laboratories in the USA and Russia to strengthen systems of nuclear materials protection, control and accountability (MPC&A) in both countries. A part of this program is to measure accurately and track inventories of materials, hence the need for good non-destructive analytical techniques. Copyright © 1999 John Wiley & Sons, Ltd.

Spiral Waves in Two-Dimensional Models of Ventricular Muscle: Formation of a Stationary Core

Previous experimental studies have clearly demonstrated the existence of drifting and stationary electrical spiral waves in cardiac muscle and their involvement in cardiac arrhythmias. Here we present results of a study of reentrant excitation in computer simulations based on a membrane model of the ventricular cell. We have explored in detail the parameter space of the model, using tools derived from previous numerical studies in excitation-dynamics models. We have found appropriate parametric conditions for sustained stable spiral wave dynamics (1 s of activity or ∼10 rotations) in simulations of an anisotropic (ratio in velocity 4:1) cardiac sheet of 2 cm × 2 cm. Initially, we used a model that reproduced well the characteristics of planar electrical waves exhibited by thin sheets of sheep ventricular epicardial muscle during rapid pacing at a cycle length of 300 ms. Under these conditions, the refractory period was 147 ms; the action potential duration (APD) was 120 ms; the propagation velocity along fibers was 33 cm/s; and the wavelength along fibers was 4.85 cm. Using cross-field stimulation in this model, we obtained a stable self-sustaining spiral wave rotating around an unexcited core of 1.75 mm × 7 mm at a period of 115 ms, which reproduced well the experimental results. Thus the data demonstrate that stable spiral wave activity can occur in small cardiac sheets whose wavelength during planar wave excitation in the longitudinal direction is larger than the size of the sheet. Analysis of the mechanism of this observation demonstrates that, during rotating activity, the core exerts a strong electrotonic influence that effectively abbreviates APD (and thus wavelength) in its immediate surroundings and is responsible for the stabilization and perpetuation of the activity. We conclude that appropriate adjustments in the kinetics of the activation front (i.e., threshold for activation and upstroke velocity of the initiating beat) of currently available models of the cardiac cell allow accurate reproduction of experimentally observed self-sustaining spiral wave activity. As such, the results set the stage for an understanding of functional reentry in terms of ionic mechanisms.

On sampling continuous aperture distributions for discrete planar arrays

The theory of sampling continuous distributions for the purpose of determining planar array excitation coefficients is examined. The cause of pattern degradation associated with conventional sampling is identified, and a new method called integrated sampling is introduced which provides superior results. Implementation details are given for the specific case of a rectangular grid planar array with a roughly circular boundary. Numerical examples are provided for both uniform and Taylor distributions in order to perform comparative studies and to demonstrate the advantages of the new technique.

Experimental Investigation of Isolated and Simultaneous Internal Resonances in Suspended Cables

The near resonant response of suspended elastic cables driven by harmonic, planar excitation is investigated experimentally. Measurements of large amplitude cable motions confirm previous theoretical predictions of fundamental classes of internally-resonant responses. For particular magnitudes of equilibrium curvature, strong modal interactions arise through isolated (two-mode) or simultaneous (three-mode) internal resonances. Four qualitatively different periodic responses are observed: (1) pure planar response, (2) 2:1 internally resonant nonplanar response, (3) 1:1 internally resonant nonplanar response, and (4) simultaneous, 2:2:1 internally resonant nonplanar response. Quasiperiodic responses are also observed.

Three-dimensional oscillations of suspended cables involving simultaneous internal resonances

The near resonant response of suspended, elastic cables driven by planar excitation is investigated using a three degree-of-freedom model. The model captures the interaction of a symmetric in-plane mode with two out-of-plane modes. The modes are coupled through quadratic and cubic nonlinearities arising from nonlinear cable stretching. For particular magnitudes of equilibrium curvature, the natural frequency of the in-plane mode is simultaneously commensurable with the natural frequencies of the two out-of-plane modes in 1:1 and 2:1 ratios. A second nonlinear order perturbation analysis is used to determine the existence and stability of four classes of periodic solutions. The perturbation solutions are compared with results obtained by numerically integrating the equations of motion. Furthermore, numerical simulations demonstrate the existence of quasiperiodic responses.

Fuel Equivalence Ratio Imaging for Methane Jets

A 2-D fuel/oxygen equivalence ratio imaging system has been developed. The technique exploits the efficient quenching of the fluorescence of organic molecules by molecular oxygen in order to determine the fuel and oxygen partial pressures simultaneously. Following pulsed planar laser excitation of fluoranthene—a specially selected fluorescent dopant—two images of the fluorescence were recorded, with the second image being delayed by several nanoseconds. Use of a rapid lifetime determination algorithm yielded first a fluorescence lifetime image, and subsequently, with the assumption of Stern-Volmer quenching, an intensity image corrected for quenching. Images of the air pressure, fuel pressure, and the equivalence ratio were obtained. The technique, which uses dual gated intensifiers coupled to a sensitive CCD camera, requires only two integrated fluorescence intensities to calculate the fluorescence lifetime accurately. In the current work, images of the turbulence-induced mixing of a methane jet into quiescent air are displayed. Images can also be obtained in flames, but the analysis of the data is uncertain because the fluorescence lifetime of fluoranthene is temperature dependent.

Spectral electromagnetic modeling of a planar integrated structure with a general grounded anisotropic slab

A formulation for the solution of the electromagnetic field in vertically stratified structures with a general anisotropic grounded slab under planar electric excitation conditions is presented. The development of the solution is obtained by using the two-dimensional Fourier transform applied to the partial differential equations describing the electromagnetic field, which can be expressed in terms of dyadic electric Green's functions. Moreover, a spectral equivalent circuit representation of the solution, separated into its spectral transverse electric (TE) and transverse magnetic (TM) components (with respect to the vertical direction), is given. It is demonstrated that such a spectral circuit representation is always possible when the constitutive epsilon and mu tensors are reduced to their diagonal form. The transmission-line representation for an unbounded gyrotropic medium with vertical preferred axis is presented. This theory is applied to a planar structure with an anisotropic biaxial grounded slab and an electric horizontal point source embedded in it. Numerical examples of evaluation of the radiated pattern and noteworthy information about the radiation on the horizon plane are given. >