The dynamics of nitinol Langevin ultrasonic transducers

Liu, Yuchen (2025) The dynamics of nitinol Langevin ultrasonic transducers. PhD thesis, University of Glasgow.

Abstract

Langevin ultrasonic transducers, especially sandwiched-type piezoelectric devices, are essential in industry and medicine for applications like ultrasonic welding and surgery due to their high power capability and design flexibility. This research focuses on adaptive Langevin transducers that enable multiple operating frequencies and tuneable resonances, responding to various operational environments. By integrating shape memory alloys, particularly nickel-titanium, Nitinol, these transducers can achieve continuous resonance tuning with temperature changes, distinguishing them from traditional multi-frequency designs.

The first section details the design, manufacturing, and characterisation of conventional Langevin transducers, introducing the incorporation of Nitinol into their structure. Mathematical models were built using one-dimensional (1D) and three-dimensional (3D) constitutive equations in piezoelectricity to simulate Nitinol transducer behaviours. While the 1D model offers advantages in computational efficiency and does not require complete material properties in 3D space, transducer dimensions and modes limit its accuracy. Following the simulations, this chapter outlines the considerations for integrating Nitinol into Langevin configurations while building on established methodologies for conventional transducers.

A core focus of this thesis is the practical fabrication of Nitinol Langevin transducers and their tuneable dynamics. Prototypes were developed incorporating various transducer configurations. Characterisations validated the tuneable resonances derived from Nitinol’s phase transformation, revealing two dynamics: active modal coupling and stable resonance. Notably, resonance stability under self-heating conditions was linked to the temperature-dependent properties of Nitinol’s austenitic phase. These dynamics are influenced by the device geometry, martensitic transformation of Nitinol, self-heating within the piezoelectric elements and their temperature dependent material properties.

In the final section, a case study on acoustic levitation using the Nitinol Langevin transducer is presented, aligned with the cascaded Nitinol configuration detailed in earlier in the thesis. The hypothesis is that by implementing a stable resonance condition under self-heating, a stable acoustic field can be generated. The results demonstrated that the stability in resonant frequency influences position, evaporation rate, and levitation time for water, acetone and isopropyl alcohol droplets, compared to a Langevin transducer in similar dimensions and made from conventional metals.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: T Technology > T Technology (General)
• Colleges/Schools: College of Science and Engineering > School of Engineering
• Funder's Name: Engineering and Physical Sciences Research Council (EPSRC)
• Supervisor's Name: Feeney, Dr. Andrew and Lucas, Professor Margaret
• Date of Award: 2025
• Depositing User: Theses Team
• Unique ID: glathesis:2025-85531
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 22 Oct 2025 15:30
• Last Modified: 22 Oct 2025 15:34
• URI: https://theses.gla.ac.uk/id/eprint/85531

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