Development of an innovative radar absorbing composite structure for wind turbine blades
The BWEA states that more than 25% of proposed wind farms raise concerns over radar navigation for ships and aircraft and also on air defence systems. BladeRunner addresses the need to develop solutions that will enable safety of navigation whilst not detrimentally affecting the expansion of the wind energy sector.
Wind turbines reflect radar signals both from their towers and from their blades which can cause significant interference with electromagnetic (EM) waves such as radar. The turbine blades cause particular problems due to the Doppler Effect that their motion has on the reflected radar signal – it can be interpreted as being caused by a moving object.
Blade Runner’s solution is to mask the lightning conductor with low-cost, radar absorbing, impedance matched, composite structures that significantly reduces reflections. The innovative approach utilises yarns of differing electrical conductivity to produce a pre-form structure with continuously graded impedance which are incorporated internally into the wind turbine blade during manufacture, replacing part of the existing structure.
The conductive material was impregnated with resin to form a composite structure which would be compatible with the standard materials used in wind turbine manufacture. This composite material was then integrated into a section of wind turbine blade. The developed structure was subjected to electromagnetic radiation and the absorption performance monitored. The structure showed a reduction of up to 17dB in the S-band and X-band, matching the original target specification for Civil Aviation Authority approval.