Presentation that I will give at the 2011 IEEE Ultrasonics Symposium, Orlando, Florida. In this presentation I describe 2 ideas of how to decrease grating lobes in the beam patterns, by building array transducers with non-rectangular elements.

1. Transducers with non-rectangular elements S.I. Nikolov, H. Jensen, T. Kling

2. How to reduce the number of elements and keep the transducer size without compromizing image quality?

3. 𝐴𝜃=𝐴𝛿𝜃×𝐴𝑒𝑙𝑒𝜃 Beam pattern 𝑎(𝑥) -1 0 1 sin𝜃

4. 𝐴𝜃=𝐴𝛿𝜃×𝐴𝑒𝑙𝑒𝜃 Most projects try to optimize 𝐴𝛿𝜃. We try to manipulate 𝐴𝑒𝑙𝑒𝜃.

5. <1> Rotate Transducer Elements

6. Thickness of scan planedefined by lens Grating lobe Main lobe

7. Field II 𝜆 pitch - rotated 𝜆 pitch 0 20 20 -10 -10 30 30 -20 -20 40 40 -30 -30 50 50 -40 60 -40 60 70 -50 70 -50 80 80 -60 -60 -10 0 10 20 30 -10 0 10 20 30

8. ceramic posts electrodes kerf material azimuth elevation

9. std diag 8 MHz 300 𝜇m pitch 4 mm height 100 𝜇m dicing

10. PSF 4 cm std diag 2 2 1 1 0 Elevation [cm] 0 -1 -1 -2 -2 -2 0 2 -2 0 2 Azimuth [cm] Azimuth [cm]

11. standard PSF 4 cm diag steered forward looking 0 -20 Level [dB] -40 -60 -80 -2 -1 0 1 2 -2 -1 0 1 2 Azimuth [cm] Azimuth [cm]

12. <2> Elements with width larger than the pitch

13. 𝛼=0∘ pitch – 300 𝜇m 38 dB width – 315 𝜇m width – 275 𝜇m

14. 𝛼=10∘ pitch – 300 𝜇m 25.2 dB 17.3 dB width – 315 𝜇m width – 275 𝜇m

16. 8 MHz 300 𝜇m pitch 4 mm height 100 𝜇m dicing

17. PSF 4 cm standard diag interwoven 0 -20 Level [dB] -40 -60 -80 -2 -1 0 1 2 -2 -1 0 1 2 Azimuth [cm] Azimuth [cm]

18. <3> Prototype

19. Aztec Soldering pads Element width > 100 𝜇m Symmetric response

20. 8670 Aztec 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

21. 9 MHz 6 MHz 12 MHz 0 0 0 1 1 1 2 2 2 3 3 3 4 4 4 5 5 5 6 6 6 7 7 7 -1 0 1 -1 0 1 -1 0 1

22. In –vivo trials CFM was better. “Less ghost” estmites B-mode was judged better for muscoskeletal applications Improvement insufficient to justify new transducer 8670 Aztec

23. Interwoven elements – best performance Hopes for implementation with CMUT