A method to design contact-separation triboelectric nanogenerators (CS-TENG) for efficient vibration energy harvesting

The necessity of self-powered electronic devices for sensing and communication (IoT) has led to the development of methods for energy harvesting. Triboelectric Nanogenerators (TENG) are promising for harvesting mechanical energy from the environment, in particular energy from vibrations. The optimization of the efficiency of energy transfer from vibration energy into electrical energy is a crucial problem. This paper deals with a contact-separation TENG (CS-TENG) devoted to vibration harvesting. Optimization was carried out taking into account all the parameters of the TENG connected to a load resistance. The moving electrode of the CS-TENG was supposed to be sinusoidal. After transformation into dimensionless parameters and variables intervening in the problem, it appeared that the electrical dynamics of the TENG are intrinsically determined by only two dimensionless parameters. Consequently, the optimization of efficiency can be conducted in a two-dimensional space. It is shown that the maximum efficiency of a TENG permanently connected to the load resistance cannot be greater than 25%. However, the efficiency can be increased to nearly 100%, provided that a switch is used in series with the load resistance which opens and closes in synchronization with the electrode motion. The optimization method presented could be extended to design TENG energy harvesters operating in other modes and for arbitrary vibrations.