Self-powered Photodetecting Systems Based On Pulsed Triboelectric Nanogenerator

The rapid development of the Internet of Things(Io Ts),big data,artificial intelligence(AI),and etc.requires billions of sensors to obtain accurate and reliable physical information.As one of the most important sensors,photodetectors are widely used in automatic control,photometric measurement,laser stabilization,infrared imaging and other fields.Most of the current photodetectors rely on external power supply,which not only waste resources but also increases the volume of the photodetection system and limits the mobility and independence of photodetectors.Battery is a common alternative in scenarios where it is difficult to lay power lines.But the usage of batteries not only limits the service life of photodetectors,but also brings problems such as high maintenance costs and difficulty in recycling.In addition,improper recycling may cause environmental pollution.Therefore,it is urgent to develop self-powered photodetection systems that do not rely on external power supply.The existing self-powered photodetection systems are mainly based on impedance matching effect between triboelectric nanogenerator(TENG)and photodetector.In other words,the change of photodetector impedance caused by the change of light intensity can lead to a significant change of TENG output voltage/current,which can be used to characterize the light intensity.However,the output voltage/current of TENG are not only affected by load impedance,but also affected by working frequency of TENG.Due to the mechanical stimuli are random in amplitude and frequency in actual working environment,TENG cannot maintain constant frequency,which causes the inaccuracy of light detection results and limits the practical application of self-powered photodetection systems.In addition,as a kind of invisible light with short wavelength and high frequency,ultraviolet(UV)radiation at close range and high intensity will cause damage to human body,so it is urgent to develop self-powered wireless ultraviolet sensor system.However,the serious impedance mismatch between TENG and LC resonator leads to the inability of LC resonator to obtain sufficient energy to emit electromagnetic waves,which limits the development of self-powered wireless UV detector system.In order to solve the problem that the self-powered photodetector based on the impedance matching effect between traditional TENG and loaded photodetector cannot guarantee the accuracy of the photodetection results in the environment of random mechanical energy.It is found that the traditional TENG is equivalent to the series of a voltage source and a variable capacitor,and the change of working frequency will lead to the change of capacitance equivalent impedance(equivalent internal impedance of TENG),resulting in the change of output voltage/current.Different from conventional TENG,Pulsed-TENG is equivalent to the series of a voltage source,a constant capacitor and a synchronous trigger switch.Its equivalent internal resistance is zero,so it can maintain maximum output voltage regardless of load resistance and mechanical energy frequency.In chapter 2,a self-powered photodetection system based on Pulsed-TENG is developed,where a rotating freestanding triboelectric-layer mode Pulsed-TENG(RF-Pulsed-TENG)is used as the power supply,a resistive-type photodetector as the sensor,and several LEDs as alarms.The measured performances of a self-powered photodetector have verified that same detection results could be obtained for various rotation frequencies of a rotating Pulsed-TENG.Two self-powered detection modes,current mode and voltage mode,have been developed.In the current detection mode,the output current increased linearly with light intensity,and the detectable range of light intensity is 0～1 W/m~2.In the voltage detection mode,the output voltage is inversely proportional to the light intensity,and the detectable range of light intensity is 9～403 W/m~2.Finally,a self-powered photodetection system with visual display function has been developed,in which the light intensity can be displayed intuitively by the number of lighted LEDs.The self-powered photodetector is suitable for the actual working environments with random mechanical stimuli.In order to solve the impedance mismatch problem between TENG and LC resonant circuit,some researchers have used mechanical switch or electronic switch to control TENG to generate pulsed voltage to drive LC resonant circuit.However,the jitter at the moment when the mechanical switch is closed and the wear after long-term use will introduce high frequency components in the initial stage of the oscillating signal,which will affect the signal quality.The electronic switch is restricted by the response and recovery speed of the device,which limits the frequency of electromagnetic wave emitted by the LC circuit and ultimately affects the signal transmission distance.In chapter 3,a self-powered wireless UV detector system based on TENG induced tip-tip air discharge is developed.A soft contact TENG(SC-TENG)with long-term stable output performance is the power supply.The tip-tip air discharge switch is used to detect UV light and control the discharge state.The wireless transmission of the signal is realized through the magnetic induction coupling between two LC resonant circuits.When the discharge state is regulated to corona discharge,the energy output from TENG is almost completely consumed by air discharge,so the LC circuit is in a silent state without electromagnetic emission.At this time,if the tip-tip air discharge switch irradiated by UV light that reached the threshold intensity will change the discharge state into arc discharge.As the energy consumed by arc discharge is very small,LC circuit can obtain sufficient energy to produce oscillation and emit electromagnetic waves.After the signal is captured by the LC circuit at the receiving terminal,the same frequency resonance will occur,then the self-powered wireless detection of UV light is realized.For UV light with wavelength of 365 nm and intensity of 200 m W/cm~2,the response time of the self-powered wireless UV detector system is 5 s,the recovery time is 10 s,and the signal wireless transmission distance can reach 3 m.This system provides a solution for the detection of high intensity UV light which is harmful to human health and this is a new method to realize self-powered wireless sensing through TENG driven LC circuit.In this thesis,A self-powered photodetector based on Pulsed-TENG is developed.The photodetection results are not affected by Pulsed-TENG frequency,so the mechanical energy of random frequencies in the environment can be collected and used for the self-powered photodetector.A self-powered wireless UV detector system based on TENG induced tip-tip air discharge is developed,which provides a new self-powered wireless sensor scheme for detecting high intensity UV light that is harmful to human health.