Novel Near-Field Probes

The phenomenal development rate of wireless technologies has also brought new requirements for the radiofrequency design of transmitters. The design challenge is to optimize multiband devices with minimal dimensions and weight as well as appealing appearance which, nevertheless, operate well within varyingly complex environments, such as frequently changing device positions with respect to the human body. The optimization of such transceivers requires new analysis tools providing precise measurement of electric and magnetic field strength distributions, even in the closest proximity of RF transmitters.

During the past five years, various novel near-field probes have been developed in joint projects between IIS/IT'IS and Schmid & Partner Engineering AG (SPEAG) which were supported by KTI. Most of them have been rapidly and successfully turned into commercial products. Their applications in research is one of the fundamentals of the success of the Bio-Electromagnetics and EMC group and its partner IT'IS.

DASY3 systems are the latest generation of near-field scanners enabling various applications such as compliance testing, device evaluations, general E- and H-field measurements and more. DASY1 was the result of a former research project. DASY3p will be the platform for evaluating and testing the new probes.

In the latest project novel E- and H-field probes providing pseudo-vector information have been developed, analyzed, optimized and constructed. In combination with the developed and implemented robust and fast numerical algorithm (combination of linear matrix solver and non-linear search algorithm), the ellipse parameters of the field at any measurement point can be reconstructed based on 6 or more amplitude measurements at different spatial orientations. This enables evaluation and visualization not only of the field amplitude at any spatial location but also of the information on field polarization. A further unique characteristic of these probes is that without any loss of performance they can be used for evaluations in basically any homogeneous dielectric material (e.g., human tissue, water, etc.), as long as the calibration parameters for that particular media have been previously determined. This project was funded by KTI (Commission for Technology and Innovation).

H-field vector distribution over a microstrip hybrid 6dB coupler at 630 MHz (left) and the measurement setup (right). The vector representation provides enhanced information on field behaviour and coupling mechanisms compared to common amplitude information.

A new project will focus on the development of full time domain sensors based on optical remote sensing enabling measurements of incident electric and magnetic fields from DC to larger than 10 GHz and having a spatial resolution of down to 0.5 mm. The field of applications shall be micro-dosimetry, exposure assessment in live/work environments (near base stations, power lines, switching stations, etc.), experimental tools for analyzing EMI/EMC problems on PC boards and on MCMs, etc., as well as sensors enabling accurate instrument tracking in an MRI system.

Tips of the EV2D (electric field, left) and HV2D (magnetic field, right) probes providing pseudo vector information. EV2D: frequency range: 100 MHz to> 3 GHz; linearity: ± 0.2 dB; spherical directivity: ± 0.2 dB; dymanic range: 2 V/m - 1000 V/m. HV2D: frequency range: 200 MHz to 3 GHz; linearity: ± 0.2 dB; spherical directivity: ± 0.25 dB; dymanic range: 10 mA/m to 2 A/m at 1 GHz.