Overview of Batteryless Devices

Electronic devices are being deployed in an ever-increasing array of roles: monitoring, wearables, and IoT devices are just a small sampling of the varying ways that these devices are becoming part of every day life. However, with more devices comes a greater demand to power them all, which is becoming an increasingly critical issue.

For small or mobile devices, the primary energy source has usually involved batteries in some fashion, but these are also the components with the shortest lifespan and most frequent need for replacement. The need to replace (much less dispose of) batteries for an ever-growing array of devices is quickly becoming a concern, particularly in applications where accessing the devices themselves is expensive or impractical (such as a nanosatellite deployed into orbit).

At the simplest level, batteryless devices replace a battery (or other power source) with an energy collector (solar, thermal, etc.) and at least one capacitor to both store power and drive the load. Depending on design needs and the task to be performed, two primary methods of energy management may be used:

1. Intermittent operation: the device activates once a certain amount of power is accumulated, and performs task(s) until that energy is expended. Once expended, the device turns off until sufficient power is accumulated, and repeats.
2. Matched operation: the device scales its energy usage based on the current energy received from the source/capacitor.

It should be noted that the circuit designed above is the simplest implementation: more complicated configurations (such as Federated Energy Storage) are discussed in their own article.

• Power restrictions: Total power is considerably more constrained compared to a traditional device: for example, a traditional device may use its MCU to calculate whether a minimum voltage threshold has been reached, but in an intermittent circuit using the MCU in this fashion will often consume too much of the available power to be viable. Intermittent circuits must be designed not only around intermittent power supplies, but lower ones as well.
• Efficiency: Compared to a more traditional power or battery-fed circuit, an intermittent device must expend energy and processing time to record state in a non-violatile memory store in order to recover from outages. This required overhead limits the total amount of work an intermittent device can perform for a given amount of power, relative to a powered device performing a similar function.