Previous studies have shown that adaptive beam-formers provide a significant increase of resolution and contrast, when the propagation speed is known precisely. This paper demonstrates the influence of sound speed errors on two adaptive beamformers; the minimum variance (MV) beamformer and the amplitude and phase (APES) beamformer. Simulations of a single point target are carried out in Field II, and a percentage error is applied on the speed of sound. As the error increases, MV and APES provide amplitude drops of 17 dB and 3 dB on the signal strength. Two approaches to overcome this amplitude drop is proposed; diagonal loading (DL) and forward-backward (FB) averaging of the covariance matrix. The investigations show that DL provides a slightly decreased resolution and amplitude compared to FB. It is noted that APES provides more robust estimates than MV at the mere expense of a slight decrease of resolution. From the investigations, it is concluded the performance of the adaptive beamformers are not outperformed by the conventional delay-and-sum beamformer.
|Title of host publication||Proceedings of the IEEE International Ultrasonics Symposium|
|Publication status||Published - 2008|
|Event||2008 IEEE International Ultrasonics Symposium - Beijing, China|
Duration: 2 Nov 2008 → 5 Nov 2008
|Conference||2008 IEEE International Ultrasonics Symposium|
|Period||02/11/2008 → 05/11/2008|