Is there a sweet spot for energy harvesting?

The low power consumption of silicon-based electronics combined with the significant power densities of modern primary or rechargeable batteries has enabled a broad variety of battery-powered handheld, wearable and even implantable devices. All these devices need a compact, low-cost and lightweight energy source, which enables the desired portability and achieves a certain level of energy autonomy. In the 100¿W range power consumption, wearable wireless sensor nodes are situated. This paper focuses on emerging methods for power generation and power management of these wireless autonomous transducers systems that can enable energy autonomy over the entire lifetime of the device. Particularly for wireless applications, this is essential as battery replacement or remote charging is unpractical or simply not feasible. Simply increasing the size of the battery to ensure energy autonomy during the lifetime of the system would increase system size and cost beyond what is tolerable.