Scientists at the Riken, a major Japanese research institute, and University of Tokyo have developed a remarkable ambient light-powered cardiac monitor that looks like a transparent bandage. The underlying technology makes possible other flexible body-worn sensors that don’t need to have an external electric source powering them, including temperature and sweat sensors. Because power is supplied directly from a built-in photovoltaic cell, the noise in the electronics is kept to a minimum, allowing for high-precision measurements.
Because electronics in devices that can measure heartbeats and other things need quite a bit of power compared to what tiny solar panels can produce, the Riken researchers developed a way of making solar panels be more efficient. The engineers used a so-called nano-grating surface to make their solar panel more efficient and able to effectively absorb light coming in from different angles. The photo-conversion efficiency (PCE) of the new device is 10.5% and a high power-per-weight ratio of 11.46 watts per gram, which is getting closer and closer to 15%, what the researchers believe is the “magic number” that will allow organic photovoltaics to compete with silicon-based panels in the larger market.
But, for now the technology is already sufficient to drive a tiny heart monitor, which has already been demonstrated in initial tests on both rats and humans. According to Kenjiro Fukuda of the RIKEN Center for Emergent Matter Science, “This is a nice step forward in the quest to make self-powered medical monitoring devices that can be placed on human tissue. There are some important remaining tasks, such as the development of flexible power storage devices, and we will continue to collaborate with other groups to produce practical devices. Importantly, for the current experiments we worked on the analog part of our device, which powers the device and conducts the measurement. There is also a digital silicon-based portion, for the transmission of data, and further work in that area will also help to make such devices practical.”