Abstract
In this paper, an alternative strategy for the design of a bidirectional inductive power transfer (IPT) module, intended for the continuous monitoring of cardiac pressure, is presented. This new integrated implantable medical device (IMD) was designed including a precise ventricular pressure sensor, where the available implanting room is restricted to a 1.8 × 1.8 cm2 area. This work considers a robust magnetic coupling between an external reading coil and the implantable module: a three-dimensional inductor and a touch mode capacitive pressure sensor (TMCPS) set. In this approach, the coupling modules were modelled as RCL circuits tuned at a 13.56 MHz frequency. The analytical design was validated by means of Comsol Multiphysics, CoventorWare, and ANSYS HFSS software tools. A power transmission efficiency (PTE) of 94% was achieved through a 3.5 cm-thick biological tissue, based on high magnitudes for the inductance (L) and quality factor (Q) components. A specific absorption rate (SAR) of less than 1.6 W/Kg was attained, which suggests that this IPT system can be implemented in a safe way, according to IEEE C95.1 safety guidelines. The set of inductor and capacitor integrated arrays were designed over a very thin polyimide film, where the 3D coil was 18 mm in diameter and approximately 50% reduced in size, considering any conventional counterpart. Finally, this new approach for the IMD was under development using low-cost thin film manufacturing technologies for flexible electronics. Meanwhile, as an alternative test, this novel system was fabricated using a discrete printed circuit board (PCB) approach, where preliminary electromagnetic characterization demonstrates the viability of this bidirectional IPT design.
Highlights
In recent years, implantable medical devices (IMDs) have undergone rapid progress towards new analysis schemes in modern medical equipment, in which the ability to monitor vital signs and Sensors 2020, 20, 1525; doi:10.3390/s20051525 www.mdpi.com/journal/sensorsSensors 2020, 20, 1525 stimulation techniques is improving [1]
This paper presents a novel approach for the design of an optimized and integrated IMD, combining a low-cost thin-film surface micromachining technique and the use of polymers for flexible electronics
Where Lr and Ls are the self-inductance magnitudes for the external and internal coils, respectively, and k is the coupling factor calculated as a function of the geometrical dimensions of the coils (see Equation (7))
Summary
Implantable medical devices (IMDs) have undergone rapid progress towards new analysis schemes in modern medical equipment, in which the ability to monitor vital signs and Sensors 2020, 20, 1525; doi:10.3390/s20051525 www.mdpi.com/journal/sensorsSensors 2020, 20, 1525 stimulation techniques is improving [1]. IMDs is supplied by wiring lines running through the patient’s body or by utilizing integrated batteries. These methods show poor performance, since the use of batteries generates bulky modules and cables increase the possibilities of infection. A promising alternative to contactless energy supplying for long-term implantable devices is wireless power transfer (WPT) [1,6,7] systems. Inductive power transfer (IPT) is one of the techniques used to deliver power to IMDs wirelessly. In this approach, two mutual inductive coupling devices were linked, following a transformer-type approach, where bidirectional power transmission can be carried out [8]
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