A Novel Low Temperature Transcutaneous Energy Transfer System Suitable for High Power Implantable Medical Devices: Performance and Validation in Sheep

Abstract

Transcutaneous energy transfer (TET) systems use magnetic fields to transfer power across the skin without direct electrical connectivity. This offers the prospect of lifetime operation and overcomes risk of infection associated with wires passing through the skin. Previous attempts at this technology have not proved suitable due to poor efficiency, large size, or tissue damage. We have developed a novel approach utilizing frequency control that allows for wide tolerance in the alignment between internal and external coils for coupling variations of 10 to 20 mm, and relatively small size (50 mm diameter, 5 mm thickness). Using a sheep experimental model, the secondary coil was implanted under the skin in six sheep, and the system was operated to deliver a stable power output to a 15 W load continuously over 4 weeks. The maximum surface temperature of the secondary coil increased by a mean value of 3.4 +/- 0.4 degrees C (+/-SEM). The highest absolute mean temperature was 38.3 degrees C. The mean temperature rise 20 mm from the secondary coil was 0.8 +/- 0.1 degrees C. The efficiency of the system exceeded 80% across a wide range of coil orientations. Histological analysis revealed no evidence of tissue necrosis or damage after four weeks of operation. We conclude that this technology is able to offer robust transfer of power to implantable devices without excess heating causing tissue damage.

Towards Low Energy Atrial Defibrillation

“…However, a commercially viable high power TET or IPT system remains a challenging goal; predominately due to the localized heating of tissue that inevitably results from power losses in the receiver coil [ 29 , 30 , 31 , 32 ]. Recent publications have reported high power TET or IPT transcutaneous energy transfer efficiencies of up to 93% [ 29 , 30 , 31 , 32 , 33 , 34 , 35 ] while the transfer efficiency of our current implementation is closer to an average of 50% across all modes of operation. Significant additional work is therefore now required to model and optimise the coil winding configurations, misalignment tolerance, microelectronic control circuitry and rectifilter associated losses; to achieve improved energy transfer efficiency characteristics.…”

“…Significant additional work is therefore now required to model and optimise the coil winding configurations, misalignment tolerance, microelectronic control circuitry and rectifilter associated losses; to achieve improved energy transfer efficiency characteristics. Furthermore, although the power transfer requirements for successful cardioversion appear quite large (several hundred watts), the inherent pulsatile nature of the cardioversion shock waveform used (maximum 12 ms duration) effectively means that maintenance of local temperature rise (over baseline temperature) to <1° (in proximity to the receiver implant and surrounding tissue) is less problematic than in applications necessitating continuous mode operation [ 33 , 34 , 35 ]. Specifically, in the present design, continuous power is only applied for a very limited time during sense mode operation (typically only a few seconds is required to complete the ‘sense’ cycle) and hence the possibility of raising the skin temperature above 42 ° (thereby resulting in discomfort or skin damage) has been effectively mitigated.…”

“…Specifically, in the present design, continuous power is only applied for a very limited time during sense mode operation (typically only a few seconds is required to complete the ‘sense’ cycle) and hence the possibility of raising the skin temperature above 42 ° (thereby resulting in discomfort or skin damage) has been effectively mitigated. However, significant work remains on-going to develop a feedback control loop to automate this aspect of the design and to ensure that losses within the local tissue are within acceptable limits [ 29 , 30 , 31 , 32 , 33 , 34 , 35 ].…”

Artificial Organs 2010: A Year in Review

“…Thushari D. Dissanayake et al. (106) of the University of Auckland, Auckland, New Zealand reported on a low temperature transcutaneous energy transfer (TET) system for high power implantable medical devices. Using a sheep model, the secondary coil was implanted under the skin in six sheep, and the system was operated to deliver a stable power output to a 15 W load continuously over 4 weeks.…”

A Primary Side Control Method for Wireless Energy Transmission System

“…A frequency controlled power supply was used for the primary resonant converter to ensure power transfer over the complete operating range of the system and enhance charging efficiency. An experiment to monitor long-term variations in temperature was presented in [18]. According to the results of the experiment, tissue temperature was approximately 38.5 C and no apparent damage was caused to the surrounding tissue during 15-W transmission conditions while providing 80% efficiency.…”