A disturber for optimising electromagnetic fields around phone antennas

As part of a smart phone relay antenna project, Sirris has been entrusted with the design and dimensioning of the support of the radiators, choice of materials, study of the connection problems and production of the demonstrators.

Sirris contributed to a project that consists in developing passive components (called auxiliary radiators) that can be programmed to be placed in front of existing telephone relay antennas to optimise the electromagnetic field. This means being able to dynamically reduce the field in certain 'sensitive' directions (schools, populated streets, etc.) and/or to strengthen it in directions where it is too weak.

This project is now completed. This is the moment to review what Sirris can provide in such a context, in principle out of its skill areas.

Sirris was entrusted with the design and dimensioning of the support of the radiators, choice of materials, study of the connection problems and production of the demonstrators. What has it contributed?

Micromachining and printed electronics technologies - Material ageing

The project required periodically positioning passive conductor elements (copper dipoles) on a structurally dimensioned support.
The concept of passive yet adjustable dipoles is based on the controlled management of length by using electronic switches placed in the middle of the component. This assumes the presence of continuous auxiliary conductor connections that potentially interfere with the correction effect required for the radiator. Adequate connections have to be developed to enable control of the switches, but whose presence does not disturb the effect of the main dipoles.

Sirris then examined several possible options, some based on the techniques of printing conductor inks onto flexible substrates using equipment such as AJP (Aerosol Jet Printing).

Many printing inks were examined. Sirris studied their ageing under the effect of temperature-humidity cycles and it turned out that their resistance over time was unsatisfactory. Only one gold ink was able to meet the requirement of the application, but the solution was too expensive.

Another option was examined, which consisted in applying carbon fibres, but their multiple strand character involved too high a risk of short-circuits.

Finally, Sirris opted for very small diameter copper wires (150 µm), sufficiently small in any case in relation to the dimensions of the dipoles.

Simulation and dimensioning

Using CFD software (Computational Fluid Dynamics), Sirris optimised the support of the disturber device in relation to its aeraulic effect. The specifications forecast a max. wind effect 10% higher than what the antenna itself generates in order to come within the safety margin planned for the mast.   

Not only does the designed device meet these requirements, but in certain configurations, it even improves the assembly's wind performance.

Prototype production

Sirris decided on the choice of raw materials required to produce the support, taking into account specific properties like dielectric losses.

The support plates of the disturber device were cut and machined in this material, the copper dipoles were mounted with all their connections and various elements 3D printed in polyamide were added to make the assembly fully functional.

NB: The yellow line added to the image represents to scale the dimension of one dipole

Today, the electromagnetism specialists at the base of the concept now have an operational demonstrator to validate their assumptions and the software developments predicting the corrected field. The figure below further illustrates an experimental result obtained in anechoic chamber which clearly shows (from all points of view) the success of the research.



See also