Disputas: Duyen Nu Bich Do

Duyen Nu Bich Do skal forsvare avhandlingen sin for graden philosophiae doctor (ph.d.) ved Universitetet i Sørøst-Norge.

Hun har fulgt doktorgradsprogrammet anvendte mikro- og nanosystemer ved Fakultet for teknologi, naturvitenskap og maritime fag.

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Sammendrag

The PhD project of Duyen Do was an integrated part of a collaborative research between USN and GE Vingmed Ultrasound, a manufacturer of real-time 3D trans-esophageal echocardiography (TEE) ultrasound probes. A TEE probe uses ultrasound waves to image the heart in real time in three dimensions from inside the patient’s esophagus. A starting point for the thesis was the current TEE probe’s scan head which requires manual assembly of several prefabricated parts to satisfy requirements regarding heat spreading, electromagnetic interference shielding, electrical insulation, and biocompatibility.

This project aimed at developing packaging concepts (based on materials, design, and processing methods) for a more efficient assembly of the TEE scan head, while satisfying the multi-functional demands for safe use inside the patient’s body. Packaging designs with an encapsulation consisting of two layers (e.g. a metallized polymer material or an encapsulation comprised of two different polymer composites) have been proposed and demonstrated to be alternatives for reducing the assembly complexity of the TEE scan head.

Thermal management is vital for the TEE scan head’s performance (lifetime and reliability) and for the patient’s safety (the surface temperature should not exceed 43°C to avoid damage to surrounding tissues). Therefore, new encapsulation concepts and materials for the thermal management of the TEE scan head were investigated. The thesis focused on two topics: (1) thermal management of the TEE scan head with metallized polymer encapsulation, and (2) thermally conductive polymer composites.

Experiments and simulations showed that a metallized polymer encapsulation can provide adequate thermal dissipation for the scan head, while accommodating other key requirements. Heat transfer simulations were in good agreement with experiments. To improve the thermal performance of the scan head, the outer layer of the metallized encapsulation could be an electrically insulating material with high thermal conductivity.

Polymer composites containing thermally conductive and electrically insulating boron nitride (BN) particles were therefore produced and characterized. The thermal conductivity of BN/polymer composites, processed by three methods (injection moulding, casting, and powder bed fusion 3D printing), were compared with theoretical models to understand how the conductivity was affected by particle loading, particle orientation and processing. Selecting the particle loading in the composite should be a compromise between the required properties and the processability. The heat transfer simulations have also demonstrated the applicability of BN/polymer composites in a two-layer encapsulation of a TEE scan head. A BN/polymer composite could be used as the outer layer in a metallized encapsulation, or in an encapsulation consisting of two polymer composites (with the inner layer made of a thermally and electrically conductive polymer composite).