Universal Energy Solution for Triboelectric Sensors Toward the 5G Era and Internet of Things

Abstract The launching of 5G technology provides excellent opportunity for the prosperous development of Internet of Things (IoT) devices and intelligent wireless sensor nodes. However, deploying of tremendous wireless sensor nodes network presents a great challenge to sustainable power supply and self‐powered active sensing. Triboelectric nanogenerator (TENG) has shown great capability for powering wireless sensors and work as self‐powered sensors since its discovery in 2012. Nevertheless, its inherent property of large internal impedance and pulsed “high‐voltage and low‐current” output characteristic seriously limit its direct application as stable power supply. Herein, a generic triboelectric sensor module (TSM) is developed toward managing the high output of TENG into signals that can be directly utilized by commercial electronics. Finally, an IoT‐based smart switching system is realized by integrating the TSM with a typical vertical contact–separation mode TENG and microcontroller, which is able to monitor the real‐time appliance status and location information. Such design of a universal energy solution for triboelectric sensors is applicable for managing and normalizing the wide output range generated from various working modes of TENGs and suitable for facile integration with IoT platform, representing a significant step toward scaling up TENG applications in future smart sensing.

The Hong Kong University of Science and Technology (Guangzhou) Nansha, Guangzhou, Guangdong 511400, China;

Part 1. Circuit composition and functional circuit module
The voltage follower module is composed of an integrated operational amplifier to obtain sufficient voltage through a large input impedance and output through a low output impedance to realize the impedance conversion. In the voltage follower module, the DC bias circuit is composed of two large resistors and a variable resistor potentiometer to increase the static voltage from 0 to ~2.5 to avoid distortion of the AC signal generated by the device before entering the circuit. Meanwhile, a 2MΩ variable resistor potentiometer is connected in parallel with the voltage follower module to adjust the input impedance of the entire circuit towards impedance matching, so that the voltage generated from the device can be adjusted when the original is in a wide range.
The first-order active filter module in the original TSM is a first-order active filter circuit, which consists of a resistor, a capacitor, and an integrated operational amplifier. The main function is to filter out high-frequency clutter to obtain low-frequency signals. The passband cutoff frequency can be calculated by: where is the upper limit cutoff frequency, is the resistance of R 4 and is the capacitance of C 3 .
The voltage magnification of the circuit can be given as: where is the upper limit cutoff frequency and is the current signal frequency.
In the optimized TSM, the filter module is a second-order active filter circuit consisting of three resistors, two capacitors and an integrated operational amplifier, which behaves better highfrequency filtering capability. The passband cutoff frequency for the optimized TSM can be calculated by: where is the resistance value of 4 = 5 , and is the capacitance value of 3 = 4 .
The voltage comparator module consists of two single-limit comparator circuits for each composing of a voltage comparator and two voltage divider resistors. The circuit function can be obtained by adjusting the resistance to change the threshold value of the comparison voltage. The threshold value can be calculated as: where 1 is the resistance value of the voltage divider resistor 7, 2 , 3 , 4 are 8, 9 and 10, respectively. The comparator circuit outputs a stable high and low level after comparing the amplitude of the signal, and outputs a high level after the voltage rises and falls to a certain threshold. The signal indicator circuit will drive the LED to light up when the comparator circuit has a signal output.
In the third part of the original TSM, the voltage comparator module consists of two in-phase hysteresis comparator circuits (the transmission characteristics of the single-limit comparator and the hysteresis comparator are demonstrated in Supplementary Figure S1 a- where 1 is the voltage dividing resistor 10/ 12, 2 is the voltage dividing resistor 11/ 13, is the reference voltage value, is the feedback resistor 14/ 15, is the input resistor 8, and are the high and low output voltage of the voltage comparator, respectively.
Theory S1. Impedance Theory Analysis TENG's electrical output simulation model can be equivalent to a model composed of a voltage source connected in series with a small-capacity capacitor [1] . It is precisely because of the high output impedance brought by the capacitance effect that impedance matching as an important link most important part of TENG's signal management circuit, which should be considered and resolved at first. The impedance of the capacitor in the TENG electrical output equivalent model can be calculated by the following formula: Among them, is the equivalent impedance of the equivalent capacitance of TENG, in ; is the frequency of the signal generated by TENG, in ; is the size of the equivalent capacitance of TENG, in .
According to Ohm's law, the voltage divided by the load after the internal resistance and the load is shown in the following formula: Among them, is the external load voltage of the TENG equivalent circuit in V; is the internal impedance of the TENG equivalent circuit, in ; is the load resistance of the TENG equivalent circuit, in ; is TENG the original voltage value generated, in .
In order to solve this problem, it is necessary to select a device or circuit with a higher input impedance to match the high output impedance of TENG. Among the active devices, the integrated operational amplifier, as an active device widely used in analog circuits, adopts a common-collection amplifier circuit, which is suitable for the signal processing circuit of TENG.