Outdoor-Useable, Wireless/Battery-Free Patch-Type Tissue Oximeter with Radiative Cooling

Abstract

For wearable electronics/optoelectronics, thermal management should be provided for accurate signal acquisition as well as thermal comfort. However, outdoor solar energy gain has restricted the efficiency of some wearable devices like oximeters. Herein, wireless/battery-free and thermally regulated patch-type tissue oximeter (PTO) with radiative cooling structures are presented, which can measure tissue oxygenation under sunlight in reliable manner and will benefit athlete training. To maximize the radiative cooling performance, a nano/microvoids polymer (NMVP) is introduced by combining two perforated polymers to both reduce sunlight absorption and maximize thermal radiation. The optimized NMVP exhibits sub-ambient cooling of 6 degrees C in daytime under various conditions such as scattered/overcast clouds, high humidity, and clear weather. The NMVP-integrated PTO enables maintaining temperature within approximate to 1 degrees C on the skin under sunlight relative to indoor measurement, whereas the normally used, black encapsulated PTO shows over 40 degrees C owing to solar absorption. The heated PTO exhibits an inaccurate tissue oxygen saturation (StO(2)) value of approximate to 67% compared with StO(2) in a normal state (i.e., approximate to 80%). However, the thermally protected PTO presents reliable StO(2) of approximate to 80%. This successful demonstration provides a feasible strategy of thermal management in wearable devices for outdoor applications.