Multipath Suppression with an Absorber for UWB Wind Turbine Blade Deflection Sensing Systems

The deflection of a wind turbine blade can be monitored with an ultra-wideband (UWB) deflection sensing system which consists of one transmitting antenna at the blade tip and two receiving antennas at the blade root. The blade deflection is calculated by two estimated tip-root antenna distances. Applying the tip antenna inside a blade is highly preferred in practice, but it leads to strong multipath. The multipath may cause interference and cancellation to the direct pulse, and affect the accuracy of tip-root distance estimations. In this paper, a method of utilizing an absorber inside the blade to suppress the multipath is proposed for the in-blade tip antenna. The physical mechanism of the proposed idea is described with a simplified multipath model. Simulations are performed with a 2.5 m long blade tip section to investigate the tendencies of how the absorber affects pulse waveforms. More accurate verifications of the proposed method are carried out with different full-blade measurements. From all the results, it is found that the proposed technique can efficiently suppress multipath for the in-blade tip antenna, and improve the pulse wave front fidelity, so that the UWB sensing system can also be utilized in a much longer blade. Some other conclusions are also addressed finally.