| Surface acoustic wave devices have been widely used in communications.Meanwhile,researchers are also exploring their sensing applications.For many cases in practical situation,SAW devices are required to be mounted on non-planar surfaces for operation,while conventional surface acoustic wave devices are mostly fabricated on rigid substrates(silicon,common glass,etc.)or piezoelectric bulk materials(Lithium,quartz,etc.),limit its application in specific areas.Therefore,the study of flexible SAW devices based sensors can open up a new path for SAW in real life.As one of the most fundamental part of Internet of Things,-the sensor network will consist of trilloions of idependent sensors,which will be distributed worldwide.Powering up such a horreendous sensor network using traditional battery technology is clearly unrealistic,because people has to find the sensor,setup or replace the batteries and check the proper operation of batteries from time to time.One possible solution is to utlize passive or self-powered devices.In this reaearch,we have designed and fabricared the passive and self-powered devices based on piezoelectric and triboelectric effect,and then explored their sensing applications.The content and main achievements of this thesis are listed as follows,(1)Transparent flexible surface acoustic wave devise based on Corning Willow glass has been fabricated.The flexible glass based SAW devices exhibited similar power transmission performance,but have a better optical transmittance than those on rigid glass.These flexible and transparent strain sensors worked well under various applied strains up to ±3000 ?? with fast response time,and showed excellent linearity of resonant frequency with the change of strain with a sensitivity of?34 Hz/??.(2)We have made some improvements on flexible SAW strain sensors.Firstly,according to the theoretical results about the strain sensiti-vity under different strain angles,we have enhanced the sensitivity of the SAW strain sensor experimentally.And we also fabiricated SAW strain sensors with thicker ZnO piezoelectric thin film,which will also improve the strain sensitivity.The following cyclic bending test at a strain from zero to 2000 ?? shows very excellent mechanical stability and reliability of the SAW strain sensors.Besides,we have also measured the frequency shift of strain sensor under various environment disturbance(Temperture,humidity and ultraviolet light),which also demonstrates our SAW strain sensors have excellent mechanical stability and reliability.(3)Triboelectric nanogenerator can be used as energy harvestor as well as self-powered sensors.A transparent triboelectric nanogenerator(5cmx5cm)based on commercially available glasses and PDMS plates is proposed and fabricated to harvest mechanical energy.Using flat glass and PDMS plates,an open voltage up to 850 V,20.6 ?A short circuit current and 3.13 mW power are achieved.An improved model has been proposed for the TENG with excellent agreement with experiments.The TENGs also showed stable performance after 10000 times cyclic contact tests.(4)We explored the feasibility of using glass single electrode mode TENG as self-powered sensor.An open circuit voltage,short circuit current and power up to 318 V,8.3 pAand 427 ?W are obtained for a TENG of 5×5 cm2 size.Based on the study,a tracking sensor array consisting of nine 5×5 mm2 TENGs is proposed and developed.A Lab VIEW based automatic measurement system is also developed to record,process and display the real-time output voltages of the sensing array.(5)We propose a novel instantaneous force-driven self-powered self-identified wireless sensor based on triboelectric effect to meet the huge demand of true self-powered wireless sensors.The device consists of a microswitch controlled TENG in parallel with a capacitor-inductor oscillating circuit,and a wireless transmitter.The system is fully powered by the output of the TENG to generate a resonant frequency containing sensing and device identity information,which is then coupled to the transmitter for realizing a long-range wireless communication.The device,with the impressive functions of energy harvesting,sensing,identity generation and wireless signal transmission,is a standalone device,which responds to each trigger without losing sensing information.It eliminates the requirement of electric components for traditional wireless communication,such as rectification circuit,energy storage units,microprocessor,wireless communication chip,etc.Thus,we developed a true self-powered identifiable wireless sensor with great potential for widespread applications. |
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