Design And Experimental Study Of Two-dimensional Ultrasonic Sensing Array Based On Graphene Film

With the characteristics of good energy clustering,strong penetrating power and no radioactivity,ultrasound waves are widely applied in medical ultrasound imaging,industrial non-destructive testing,and underwater sonar detection.As the core component of ultrasound system,ultrasonic sensors act as a carrier for transmitting and receiving ultrasonic waves.The two-dimensional ultrasonic array based on multisensor elements has the characteristics of fast acquisition speed and wide application range.The structure of traditional piezoelectric array is mostly a simple stack of sensing units,which has many limitations in array size and sensitivity.In this paper,a capacitive two-dimensional acoustic sensing array based on graphene film is proposed,which utilizes the excellent vibration characteristics of graphene to improve the sensitivity of the acoustic array.The main work includes the following aspects:(1)Sensing unit physics field coupling and array design options: The physics field coupling relationship of the ultrasonic sensing unit is analyzed by three sensing unit models.Comparing the differences of arrays in three dimensions,the two-dimensional array is selected as the design subject of this paper.The distribution of array elements,as well as the target requirements of array design,and plan the process of array design are determined.(2)Simulation analysis of capacitive ultrasonic sensing unit: This paper constructs the receiving and transmitting model of ultrasonic sensing unit,and analyzes the transmitting efficiency of capacitive and piezoelectric ultrasonic sensing unit by finite element simulation.Based on the receiving mode of the ultrasonic sensing unit,the vibration characteristics and output sensitivity of silicon nitride and graphene films were compared,and the feasibility and superiority of graphene as the vibrating film of the acoustic sensing unit are determined.(3)Design and fabrication of graphene two-dimensional acoustic sensing array: Through the finite element simulation results,the parameters of the array elements are determined,and the structure of the two-dimensional array is designed,which consists of a 16×16 acoustic sensing unit array.The structure of the upper and lower plates,the signal wiring layer were designed,and the process of transferring the graphene film to the upper plate is introduced.Comparing the size of the graphene-based twodimensional acoustic array with the piezoelectric array of the laboratory,the area is only 11.4% of the piezoelectric sensing array,which improves the array integration.(4)Graphene two-dimensional acoustic array receiving characteristic test: The array receiving characteristic test system is built,and the dynamic response of the array to 35k~45kHz ultrasonic wave is tested by piezoelectric transmitting probe.The sensitivity of the piezoelectric array over its operating frequency range was tested and 40 kHz was chosen as the contrast frequency point for the two arrays.At an ultrasonic excitation frequency of 40 kHz,the sensitivity of the graphene array was measured to be-60.7 dB,which is about 10 dB larger than that of the piezoelectric array.The characteristics of the single-channel and dual-channel receiving ultrasonic waves of the graphene array are tested.The waveforms of the array elements are classified,and the defect rate is 10.9%.The results of the dual-channel receiving characteristics test shows that the arrays has a good consistency.