PhD Oral Exam - Shervin Foroughi, Mechanical Engineering

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

This doctoral research introduces two novel 3D printing technologies, Direct Sound Printing (DSP) and Proximal Sound Printing (PSP), which use focused ultrasound to cure heat-setting thermoset polymers without light, heat, or chemical modification. These sound-based methods form a new class of additive manufacturing (AM) techniques, addressing a major limitation in conventional 3D printing: the inability to process unmodified thermosets, despite their excellent mechanical and thermal properties. Unlike traditional AM processes that rely on photopolymerization or heat, this research uses ultrasound as an alternative energy source. Through acoustic cavitation, ultrasound produces microscopic bubbles that rapidly collapse, generating intense, localized heat and pressure. These conditions trigger fast chemical reactions, known as sonochemistry, allowing precise, spatially controlled polymerization while preserving the surrounding material. This approach unlocks previously inaccessible reaction conditions and expands the capabilities of AM.

The first technique, DSP, uses focused ultrasound to initiate polymerization deep within resin volumes, enabling the fabrication of complex structures with fine features (down to 280 μm) in materials like polydimethylsiloxane (PDMS) that cannot be printed by conventional methods. DSP was characterized using high-speed imaging, sonochemiluminescence, and process analysis. Building on this, PSP improves resolution and reliability by triggering polymerization near the acoustic aperture. It reduces power consumption fourfold and minimizes acoustic streaming by 1600 times, enabling multi-material printing and precise control over feature size, ideal for microsystems and microfluidic applications. A major outcome of this research is the concept of Remote Distance Printing (RDP), which extends DSP to print through barriers like soft tissue, opening new possibilities for noninvasive, in-body fabrication of medical structures.

Two custom systems were developed: a modular DSP platform and a compact PSP setup. By tuning parameters like power, frequency, and resin formulation, stable and high-resolution printing was achieved across a broad size range (∼200 μm to 50 mm). The printed parts demonstrated strong mechanical properties and biocompatibility.

In summary, this thesis establishes ultrasound as a novel energy source for 3D printing methods of DSP and PSP, and also introduces the concept of RDP that can significantly expand the range of printable materials and applications, particularly in advanced manufacturing and biomedical fields.