Runtime Extension of Autonomous Sensors Using Battery-Capacitor Storage

Batteries are an important part in autonomous sensors power supply chain, so extracting all available energy is a determinant runtime affair. Autonomous sensors have a pulsed power consumption profile that causes high voltage drops in high impedance batteries. These voltage drops can make battery voltage go under the specified autonomous sensors' voltage supply range leading to a runtime reduction from the ideal case. In this paper battery-capacitor hybrids are proposed to reduce voltage drops in autonomous sensors. Analytical expressions for the voltage transient behavior and runtime extension under pulsed loads have been presented. Minimal capacitor's value for a determined voltage drop has been also obtained. Experimental results were carried out using two types of loads, a pulsed resistor and a real autonomous sensor. The runtime extensions achieved were 185 % and 169 % respectively. The ideal runtime (assuming no voltage drop) is nearly achieved in both cases, so almost all energy can be extracted.