  Triboelectric Nanogenerator (TENG) is a class of ambient mechanical energy
harvesters used to augment the battery life of electronic devices such as
sensors in implantables, wearables, and Internet of Things (IoT) applications.
In this work, the fundamentals of pre-biasing (pre-charging) the TENG at the
start of the operation cycle to enhance the per-cycle extracted energy is
presented. The energy gain is mathematically formulated, and the optimum
pre-biasing voltage (equivalently charge) is derived by analyzing the energy
exchange between the mechanical and the electrical domain over a periodic
cycle. Further, a novel Energy Extraction Circuit (EEC) termed as "Pre-biased
Synchronous Charge Extraction (pSCE)" is introduced to 1) Realize synchronous
pre-biasing of TENG using the load battery itself and 2) Achieve enhanced
energy extraction from TENG. Energy output per-cycle is derived analytically
for the pSCE circuit and compared to the state of the art Synchronous Charge
Extraction (SCE) circuit. The experimental implementation is performed for the
proposed pSCE circuit that shows a 6.65 fold gain over the Full Wave Rectifier
(standard EEC) and 1.45 over the SCE circuit for a 5V battery load.
