Towards Additive Manufacturing of Broadband Metamaterial Matching Layers using Two-Photon Polymerization Lithography

Enhancing the bandwidth (BW) of ultrasonic transducers is essential for improving medical imaging and sensing. Gradient metamaterial matching layers (MMLs) offer superior performance compared to conventional quarter-wavelength matching layers (CMLs) but are difficult to fabricate. This work demonstrates the use of Two-Photon Polymerization Lithography (TPP), an additive manufacturing technique with micron-scale resolution, to produce cone-shaped microstructures from acoustic hard (IP-Q/IP-S) materials that are filled with soft (PDMS) materials. These structures create a gradient in acoustic impedance. Fabrication was performed on glass substrates and piezocomposites, and acoustic performance was evaluated in water. Results show the TPP-fabricated MML on a glass substrate achieves a 67 % higher BW than with no ML and comparable to a CML, while also transmitting higher sound pressure. A MML transducer was fabricated with a 136 % relative BW. This proves the feasibility of TPP-fabricated MMLs and their potential for advancing ultrasonic transducer technology.