Kai Geissdoerfer Mikolaj Chwalisz Marco Zimmerling Shepherd: a portable testbed for the batteryless IoT. 83-95 2019 SenSys https://doi.org/10.1145/3356250.3360042 conf/sensys/2019 db/conf/sensys/sensys2019.html#GeissdoerferCZ19