Abstract
Traditional wireless sensors still face challenges such as high power consumption and bulky signal transmission modules. In this work, we report a battery-free sensor via Maxwell's displacement current for encrypted signal transmission. The sensor employs an instantaneous discharge triboelectric nanogenerator (ID-TENG) featuring a dual-contact electrode structure. It enables rapid charge transfer and instantaneous current generation (~6 ms per cycle) and then high-frequency electromagnetic wave generation. The instantaneous discharge mechanism reduces the generated voltage to 100 V while maintaining μA-level current output, addressing critical safety concerns. By integrating a resistor‒inductor‒capacitor (RLC) equivalent circuit, the sensor achieves precise amplitude and frequency modulation of wireless signals. A series of inductors (0-50 μH) is used to achieve wide frequency-domain regulation (3.91-16.97 MHz), and capacitor parallel regulation (0-50 pF) to achieve accurate regulation in the narrow frequency domain (1.95-2.63 MHz). The sensor illustrates 22 m of wireless transmission distance and sustained stability over 16,000 cycles. By pre-setting the frequency sequence of the signal as a password, the specific password transmits the specific information to realize the encryption of the wireless signal transmission. Finally, it is demonstrated to be used as a smart wireless keyboard, an interactive dance carpet and an encrypted vehicle control system with passivity, adaptability, scalability, and resistance to signal interference.