Design And Fabrication Of Flexible Ultrasonic Transducer For Multi-mode Imaging

The application of ultrasonic has already spread to all walks of life,such as medical ultrasonic imaging diagnosis,ultrasonic cleaning machine,intelligent ranging,nondestructive testing and evaluation,ocean exploration and development,etc.Ultrasonic testing is widely used in medical ultrasonic imaging diagnosis by its advantages of non-invasive,real-time,dynamic and low cost.The core of ultrasonic imaging is ultrasonic transducer,whose performance is directly related to the effect of ultrasonic imaging.However,the traditional rigid ultrasonic transducer has poor fitting effect on the uneven surface of human body,and its application is limited.Secondly,in the traditional ultrasonic imaging test,the ultrasonic transducer needs to be controlled continuously by the sonographer.Long-term use will lead to shoulder and wrist strain.Finally,the traditional ultrasonic transducer needs to be coated with a large amount of coupling agent during detection,which makes the detection comfort of patients poor.Flexible electronic devices have the advantages of flexibility,thinness,tensile resistance,corrosion resistance,transparency,etc.,and are widely used in the field of medical devices.In order to make up for the shortcomings of traditional rigid ultrasonic transducers and promote the development of "Healthy China" and "overall health",this paper integrates flexible electronic devices into the field of ultrasonic transducers,and designs a flexible ultrasonic transducer that can fit well on the surface of different curvature radii of the human body,can continuously monitor the deep tissue of the human body,and can realize multi-mode imaging.The research content of this paper includes:(1)Based on the sandwich structure,a 4×10 array flexible ultrasonic transducer was designed by stacking the flexible electrode,flexible substrate and piezoelectric layer,and the flexible ultrasonic transducer was prepared based on the micro-electronic machining technology.Among them,the flexible electrode adopts one to one addressing design,which can accurately switch each oscillator,reduce the power consumption of the flexible ultrasonic transducer,and the joint work of CAD and laser marking machine to produce the flexible electrode.The flexible substrate was prepared by high speed spinning coating technology.1-3 piezoelectric composites were prepared by cutting-filling method.The flexible ultrasonic transducer was bonded to piezoelectric composite material by welding the flexible electrode with low temperature solder and Ecoflex00-30 package.(2)The resonant response frequency of 1-3 piezoelectric composites with different piezoelectric phase volume ratios was simulated by COMSOL Multiphysics 5.6simulation software.The electromechanical coupling coefficients of the composites with different piezoelectric phase volume ratios were calculated by impedance frequency diagram,and the optimal volume ratio of piezoelectric phase was 65%.The sound field distribution of the flexible ultrasonic transducer in the water tank is simulated,and the sound field distribution law of the flexible ultrasonic transducer in water is obtained.The sound pressure level is 208.7dB when the Y-axis coordinate is0 mm and 108 d B when the Y-axis coordinate is 500 mm.(3)The basic performance of the whole and each part of the flexible ultrasonic transducer is tested.The ultrasonic permeability of the flexible substrate was tested.The test results showed that Ecoflex00-30 was a better material to prepare the flexible substrate,and the thinner the flexible substrate was,the better the ultrasonic permeability was.The conductivity test and tensile and fatigue test of the flexible electrode show that the electrical conductivity of the flexible electrode is good under normal condition and tensile condition,and the tensile property can meet the maximum displacement required by human skin.The 1-3 piezoelectric composites with different volume ratio of piezoelectric phase were prepared,and the electromechanical coupling coefficients were tested by impedance analyzer.The test results show that the optimal volume ratio of piezoelectric phase is 62%,and the electromechanical coupling coefficient is 0.7.The bandwidth of the flexible ultrasonic transducer is measured by the spectrum analyzer.The results show that the bandwidth of the flexible ultrasonic transducer is 40%.(4)The fit degree and comfort degree of the flexible ultrasonic transducer were tested.Thirty volunteers were recruited to test the fit degree and comfort degree of the flexible ultrasonic transducer.The test results showed that the flexible ultrasonic transducer fitted well with various complex surfaces of the human body.With strong adhesion;The visual analog scale was used to evaluate the wearable comfort level.The higher the number,the better the comfort level was.The test results showed that the average comfort level of the three positions was 7.93,8.83 and 7.7,respectively,which verified the potential of the flexible ultrasonic transducer with wearable continuous vital sign monitoring.(5)The ultrasonic imaging system is used to verify that the flexible ultrasonic transducer has the characteristics of multi-mode imaging,and the ultrasonic imaging of A mode,B mode and Doppler mode is realized.Mode A imaging clearly shows the ultrasonic echo signal returned by human wrist tissue.B-mode imaging obtained a twodimensional plane image of the plexiglass plate at a depth of 50 mm inside the tank.The results of Doppler mode imaging are in good agreement with those of commercial ultrasonic transducers.It is proved that the flexible ultrasonic transducer has the potential of continuous monitoring of deep tissue signals in human body.