Development Of A Nanocrack-Based Seismic Sensor

Using sensors to monitor seismic vibration has a wide range of applications in many fields.Strain sensors have the advantages of low manufacturing cost and convenient device integration.However,traditional strain sensors have low sensitivity and are difficult to use for seismic vibration monitoring.The strain sensor based on nanocracks proposed in recent years has ultra-high sensitivity and is expected to realize the monitoring of seismic vibration.This paper studied two nanocrack patterning methods,designed and fabricated a cantilever beam nanocrack strain sensor for seismic vibration monitoring,and tested its performance.A nanocrack patterning method based on V-shaped grooves was proposed.The V-shaped grooves on the surface of the polydimethylsiloxane(PDMS)substrate are used as the stress concentration structure.When the PDMS substrate is bent,the gold film deposited on the surface of PDMS will produce long and straight nanocracks at the bottom of V-shaped grooves.Another photolithography-assisted nanocrack patterning method was proposed.Photoresist stripes were fabricated on the surface of the gold film by photolithography.When the PDMS substrate is bent,due to the protection of the photoresist,a long and straight nanocrack will appear on the gold film only in the middle area of two adjacent photoresist stripes.Using these two methods respectively,film structured nanocrack strain sensors were fabricated,and each sensitivity was tested.In the strain range of 0-1.2%,the gauge factor of the sensor fabricated by the method of V-shaped grooves is 4814,and the gauge factor of the sensor fabricated by the photolithography process is 19883.The characteristics of the seismic vibration signal were analyzed,and it was concluded that the seismic sensor needs to collect low-frequency vibration(<100 Hz)signals in the direction perpendicular to the ground surface.Accordingly,a seismic sensor composed of a glass pedestal,a PDMS cantilever beam substrate and a gold film with nanocracks was designed.Firstly,the structure of the sensor was theoretically analyzed,and the result shows that the PDMS cantilever beam should have a lower natural frequency,and the maximum strain on the upper surface of the cantilever beam generated by its own weight should be less than the maximum strain that the sensor can withstand.Secondly,the cantilever beam structure was analyzed by numerical simulation,and finally the structural parameters of the cantilever beam were determined to be 2 mm in width,10 mm in length,and 0.5 mm in thickness.In this state,the natural frequency of the cantilever beam is 22 Hz.The maximum strain on the upper surface of the cantilever beam generated by its own weight is 1%,which meets the design requirements of the sensor.Firstly,the PDMS cantilever beam substrate was fabricated by a casting process.Then a gold film with nanocracks was fabricated by the photolithography process on the surface of the PDMS cantilever beam.Finally,the PDMS and the glass pedestal were bonded together to form a seismic sensor based on nanocracks.The vibration exciter was used to provide sinusoidal excitation for the seismic sensor,and its amplitude-frequency response performance in the 50-100 Hz frequency band was verified.The result shows that the seismic sensor has good frequency resolution and stable amplitude-frequency response characteristics in the tested frequency band.The seismic sensor was used to monitor the seismic vibration signals caused by human jumping and ball bouncing,which verifies the feasibility of applying the sensor to seismic vibration monitoring.