Electric power transmission in triboelectric generators activated through dipolar depolarization

Abstract

The entropy change causing dipolar depolarization is proposed as an origin of electrical power generation in triboelectric generators using polar materials. Rubbing mechanically forces permanent dipoles in materials to become orientationally ordered, establishing a low entropy state with an initial dipolar polarization P0. In this state, the electric field within the materials is zero, but a nonzero Helmholtz free energy F=F0=P022(Cs−C∞) arises from the entropy contribution (Cs, static capacitance; C∞, capacitance at high frequency). Consequently, this state is energetically unstable and undergoes a spontaneous transition into a disordered high entropy state with F<F0, resulting in the establishment of a non-zero electric field. Through this process, the energy bounded in materials as the entropy component of free energy is converted, and the electrical energy becomes F0η with η=1−C∞Cs(0<η<1). Electrical circuit analysis shows that this energy conversion process can be well represented by introducing a virtual resistance Rp=τCs−C∞ (τ, dipolar relaxation time). This suggests that the entropy change in finite time τ serves as the origin of electrical power generators. Under the matching condition τ=CsR, the power spectrum at the load is best aligned with that at the generator, maximizing the power transmission. The results presented here serve as a basis for understanding the principle of electric power transmission in triboelectric generators through dipolar depolarization.