Design and 3D printing of waveguide-based ultrasonic longitudinal-torsional transducers for medical needle insertion

This paper presents a new waveguide-based longitudinal-torsional (L&T) ultrasonic transducer. For synchronization of both the longitudinal and the torsional vibrations, a new circular array of helical structures was designed and developed. The array of helical structures is used as an effective waveguide to constrain the wave propagations to achieve harmonic longitudinal-torsional vibration. Analytical modeling of the new design is presented for synchronous L&T vibration conversion. A finite element (FE) analysis was used to optimize the geometric design of the new L&T transducer. The new design was fabricated using a selective laser melting (SLM) additive manufacturing (AM) process. Lab experiments were conducted to measure the impedance and vibration performance of the novel fabricated transducers and validate the L&T transducer design. The results show that the new waveguide-based transducer is promising to deliver synchronized L&T vibration with high vibrational power efficiency. The new L&T ultrasonic transducer can be developed for a vibratory needle insertion device, effectively reducing insertion force and bending.