Vicinity Of Transmitter Research Articles

Three-dimensional inversion of semi-airborne electromagnetic data with a second-order finite-element forward solver

SUMMARYThe analysis of controlled-source electromagnetic (EM) data recorded with semi-airborne exploration systems requires advanced simulation and inversion tools that are capable of handling realistic survey geometries. Semi-airborne EM setups with elongated transmitters deployed in mountainous terrain prohibit the exploitation of secondary-field formulations in numerical approximations without producing hardly quantifiable errors. Building upon the open-source software custEM for forward modeling and pyGIMLi for geophysical inversion, we present an inverse modeling procedure based on highly accurate second-order finite-element forward solutions on irregular grids and fast-converging Gauss–Newton minimization. Using the total-field formulation of the electric field approach in combination with a direct solver enables calculating explicit sensitivities with comparatively cheap back-substitutions for thousands of ground and airborne receiver stations in multiple flight areas. Second-order basis functions show general superiority over first-order basis-functions regarding the accuracy and performance of the forward problem. Beyond that, synthetic and real data inversion studies related to semi-airborne geometries indicate that second-order basis functions help particularly to avoid high modeling errors for the weakest field components and artifacts in the vicinity of transmitters or at the surface. This leads generally to a better convergence and final inversion results of higher robustness and quality. The presented tools are freely available such as the underlying software.

A Study on Magnetic Field Repeater in Wireless Power Transfer

It is shown that the distance of wireless power transfer is significantly increased by placing intermediate resonators (repeaters) between transmitter and receiver. The guidelines are provided to use the repeaters effectively. We first briefly review how the repeaters enhance the transfer distance. Next, the aspect of resonant frequency splitting is studied separately both for even and odd numbers of repeaters. The transferred power, efficiency, and output impedance phase are evaluated for each repeater configuration. These provide the guidelines to select the optimum repeater positions and numbers. We also propose and study a new kind of repeater which can be placed (biased) even in the vicinity of transmitter or receiver. This increases the flexibility in choosing the repeater position. The net effect of such biased repeater is approximately doubling the effective coupling coefficient between transmitter and receiver. Experimental results are provided to prove the concepts.

A High-Dynamic-Range Front End for an Upconversion Car-Radio Receiver

A monolithically integrated high-performance front end for an AM radio receiver is presented. Medium- and long-wave reception without any tuned-circuit alignments or band switches is made possible by using an intermediate frequency of 10.7 MHz, well above the maximum frequency to be received. Image- and oscillator-harmonics-related spurious responses are rejected by a simple low-pass filter. The upconversion concept puts high demands on the front-end circuits. A high intermodulation free dynamic range is realized by applying several unconventional and new circuit techniques. A low-noise low-distortion wide-band input amplifier with capacitive negative feedback realizes the required antenna match. The gain of this amplifier is automatically switched to a lower value in the vicinity of transmitters with high field strengths. A double-balanced mixer, driven by an oscillator employing a novel amplitude stabilization technique, provides the frequency conversion up to 10.7 MHz. Digital toning can be achieved very simply because only the local-oscillator frequency has to be varied. The dynamic range of this front end amounts to 130 dB. Field strengths up to about 20 and 200 mV/m can be handled without noticeable second- and third-order intermodulation, respectively.