A Single-shot Field Measurement Procedure for Radiated Emissions using Equivalent Surface Dipoles

The new generation of communication devices operating in higher frequency bands is constantly pushing the complexity of field measurements for electromagnetic compliance and the design of field probes. These compliance are to be met for both electric and magnetic fields which demands repeating the same measurement procedure using different probes. The main objective of this paper is to provide a procedure which provides both fields in a single shot measurement using a single probe based on source reconstruction algorithm. The algorithm is based on a novel way of placing single dipole per point tangentially to a fictitious surface based on surface equivalence theorem instead of three orthogonal dipoles per point in earlier works. The control of overall accuracy by varying dipole and measurement point density is also demonstrated. We also prove the existence, uniqueness and the error bounds involved in the inverse problem rigorously. The numerical results corroborates the effectiveness of the proposed procedure in obtaining accurate fields and also locating the regions of the Device Under Test responsible for overshooting the interference limits.

A Single-shot Field Measurement Procedure for Radiated Emissions using Equivalent Surface Dipoles

The new generation of communication devices operating in higher frequency bands is constantly pushing the complexity of field measurements for electromagnetic compliance and the design of field probes. These compliance are to be met for both electric and magnetic fields which demands repeating the same measurement procedure using different probes. The main objective of this paper is to provide a procedure which provides both fields in a single shot measurement using a single probe based on source reconstruction algorithm. The algorithm is based on a novel way of placing single dipole per point tangentially to a fictitious surface based on surface equivalence theorem instead of three orthogonal dipoles per point in earlier works. The control of overall accuracy by varying dipole and measurement point density is also demonstrated. We also prove the existence, uniqueness and the error bounds involved in the inverse problem rigorously. The numerical results corroborates the effectiveness of the proposed procedure in obtaining accurate fields and also locating the regions of the Device Under Test responsible for overshooting the interference limits.

Computational and Phantom-Based Feasibility Study of 3D dcNCI With Ultra-Low-Field MRI

The possibility to directly and non-invasively localize neuronal activities in the human brain, as for instance by performing neuronal current imaging (NCI) via magnetic resonance imaging (MRI), would be a breakthrough in neuroscience. In order to assess the feasibility of 3-dimensional (3D) NCI, comprehensive computational and physical phantom experiments using low-noise ultra-low-field (ULF) MRI technology were performed using two different source models within spherical phantoms. The source models, consisting of a single dipole and an extended dipole grid, were calibrated enabling the quantitative emulation of a long-lasting neuronal activity by the application of known current waveforms. The dcNCI experiments were also simulated by solving the Bloch equations using the calculated internal magnetic field distributions of the phantoms and idealized MRI fields. The simulations were then validated by physical phantom experiments using a moderate polarization field of 17 mT. A focal activity with an equivalent current dipole of about 150 nAm and a physiologically relevant depth of 35 mm could be resolved with an isotropic voxel size of 25 mm. The simulation tool enabled the optimization of the imaging parameters for sustained neuronal activities in order to predict maximum sensitivity.

Depolarizing Chipless Tags with Polarization Insensitive Capabilities

A novel depolarizing chipless tag configuration with high angular insensitivity is presented. The basic tag comprises two dipole resonators arranged with a relative rotation of 45°. The proposed configuration improves the depolarization properties performance of a single dipole over the ground plane which provides a peak with perfect polarization conversion only if the electric field impinges at 45° with respect to the dipole resonator. The second dipole arranged at 45° compensates the cross-polar reduction which is observed when the electric field is not correctly polarized. Indeed, when the field is tilted by 90° with respect to the first dipole, it forms an angle of 45° with the second one. The proposed configuration is also analyzed for providing multiple frequency peaks. A tag with 4 angular independent frequency peaks laying between 2 GHz and 5.5 GHz is designed. Angular frequency maps are used to illustrate the peculiar frequency shifts achieved when the electric fields rotate in the plane of the dipole. Finally, a prototype of the polarization insensitive tags is fabricated and measured to confirm the simulated results.

A Comparative Study on the Difference between the Multi-dipole Sources and Vector Synthesis Source

CSAMT exploration generally adopts a single dipole as the transmitter. The single dipole source has the apparent disadvantages–there are weak areas for all components, Ey and Hx are weak in the area where Ex and Hy are reliable. Moreover, it is hard to deploy the source with a specific direction in a rugged mountainous area. Given the shortcomings of the single dipole source, multi-dipole sources are introduced into CSAMT exploration. Although the dipole sources follow the principle of vector synthesis, the length of the source in actual exploration can last for several kilometers and the offset is generally a few kilometers. In this case, the source can no longer be regarded as a single dipole in the near-field zone. The electromagnetic field in this region becomes relatively complicated. We first compare the similarities and differences of electromagnetic field generated by vector synthesis source and multi-dipole source through the Ex radiation patterns. Then, we study the factors that affect electromagnetic response due to the substitution of the double-dipole source with the vector synthesis source. The measured EM fields is affected by the source length, frequency, the source angle, the offset, and the resistivity.Finally, we apply the double-dipole source to the 1D and 3D geological model and compare the difference between the electromagnetic field generated by the double-dipole source and that generated by the vector synthesis source. Usually, the difference is very obvious in the near-field zone, and is almost negligible in the far-field zone.