The availability of ultra-low power (μW) and extremely complex integrated circuit functional blocks has been paving some recent research in human health monitoring. Wearable and implanted biomedical “smart” sensors (ECG, EEG, glucose, pH, temperature, etc.) are becoming available, in a single or network arrangement, including sensing, data processing and communication, for continuous check-up of health parameters. The power requirement of these portable health-monitoring systems depends on the application. In general, sensor nodes can consume less than 100 μW in normal operation mode.
Although these “smart” sensors are typically battery powered, it is well known that energy autonomy and battery lifetime can be improved by harvesting energy from several physical phenomena, like ambient light, vibration/motion of human body parts, temperature differences and RF electromagnetic radiation. Harvesting from the sun or ambient light is the most effective way to power a sensor node.
Funded and developed in IT, the ultimate objective of this project was to develop a batteryless energy supply system aimed at ultralow-power health-monitoring or IoT sensor nodes, composed of an organic photovoltaic cell as the energy harvesting device and a Power Management Unit (PMU) for voltage regulation, coupled as an ultra-compact (<1-2cm2) and flexible electrical energy supply system – the μFlexBatt.
Coordinated by Pedro Santos from the Wireless Circuits group of IT in Lisbon, this project comprised three main challenges: a) The development of organic photovoltaic (OPV) cells, with optimized power density of ca. 100 µW/cm2; b) The project of an ultra-compact (<5-10mm2) Power Management Unit (PMU), to convert the range of hundreds of mV delivered from the OPV to a regulated standard value (1.2V or 2.4V), either based on very-high switching frequency (<500MHz) fully CMOS (Complementary Metal Oxyde Semiconductor) or hybrid (with SMD) solution, or on very low form factor COTS (commercial off-the-shelf) SMD, in order to accomplish a low cost efficient circuit, with a footprint to fit the free area available outside the OPV active region; and Finally c) the assembly of the dedicated PMU on the OPV cell in an ultra-compact and flexible two-terminal battery like prototype – the μFlexBatt. The PMU footprint is to be placed over the OPV support area, outside the active area, in order to achieve maximum light conversion with optimized power density (work in progress). Seven PMU prototypes were studied, developed and successfully tested according to the project objectives
Photo: Printed circuit board of the commercial off-the-shelf Multilevel converter