Development of a Dry Coupling Material for Ultrasonic Transcutaneous Energy Transfer
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Ultrasonic transcutaneous energy transmission (UTET) is a novel technology with great potential for electrically powering active biomedical implants. To make UTET devices viable, a key piece of technology is required. A “dry” acoustic coupling bridges the ultrasound transducer and the patient’s skin without the need for coupling gels. This dry coupling material allows a patient to wear a device daily and for long periods of time. The dry coupling consists of a solid medium through which an external transducer delivers ultrasound to an implanted device. This thesis investigates the use of silicone as a dry coupling medium. This thesis contains two main chapters. A manufacturing chapter in which the process for producing a dry coupling material has been developed. The chapter explores the many problems and solutions encountered in creating dry coupling samples. This included acoustic impedance matching the dry coupling to skin by doping the silicone with ZnO powder, creating a bubble free silicone, development of the sample moulds, adding adhesive properties to the dry coupling, and finally, the procedures for curing thick samples, thin samples and the adhesive layer. An experiments chapter in which the validity and effectiveness of different manufacturing techniques for dry coupling is proven by experimentation and theoretical analysis. These experiments characterized the acoustic properties of the dry coupling material and porcine skin, tested the effectiveness of the adhesive layer as a means of anchoring the device to the patients skin, investigated potential avenues into increasing the dry coupling’s acoustic impedance, mapped and modeled the relationship between the ZnO loading fraction and the dry coupling’s acoustic reflectance, and finally, a power transfer efficiency (PTE) test showed that the final dry coupling design improved the PTE from 64.6%max, for untreated silicone, to 88.1%max.