A battery-free wireless sensor for encrypted signal transmission via Maxwell's displacement current.

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.