The Ultra Broadband Ultrasonic Sensors Used In Partial Discharge Be Detected

JPFYX piezoelectric thin film(we are replace it with new piezoelectric thin film in the following paper)is one of the new polymer materials,which has both fundamental characteristics such as oxidation resistance,chemical corrosion resistance,radiation resistance,high temperature resistance,weather resistance etc and individual properties such as thermoelectricity,dielectric properties,piezoelectricity etc.Researchers all around the world take advantage of its excellence performance to produce the devices like sensor,which is applied to various fields.Producing the ultra broadband ultrasonic sensors in this paper is dependent on its piezoelectric property,which also has higher piezoelectric coefficient comparing to the quartz crystal and piezoelectric ceramics.Therefore it is widely used in the production of sensors.In this paper,taking advantage of its excellent piezoelectric property,the ultra broadband ultrasonic sensors was produced based on the new piezoelectric thin film and then it was applied in partial discharge detection.To begin with,the reason why the new piezoelectric thin film has excellent piezoelectric property was studied in principle.Besides,the theory of ultrasonic reflection at the interface of single-layer or multi-layer as well as the sound pressure and intensity of eventual transmission ultrasonic was presented.Next,based on the study of refraction and reflection,the materials of sensors such as protective layer,coupling layer and the backing were determined and then internal structure design of sensor was completed.Besides,combined with the study on acoustic impedance of material and refraction and reflection of ultrasonic at the multi-layer interface,the rationality of material selecting was verified in principle.In addition,after preparing various materials,the producing of sensor was completed successfully.Meanwhile,the theory and production of pre-amplifier,matched with sensor,was presented.After that,the basic properties such as amplitude-frequency characteristic and phase frequency characteristics were detected successfully.The result showed that the bandwidth of ultra broadband ultrasonic sensors was from 20 kHz to 1 MHz and response of within this band frequency does not exceed 50 degree and with the higher frequency,the phase shift is less.The bandwidth range of amplifier exceeds the sensor and within 20 kHz-1 MHz,the phase shift is no more than 10 degree.Finally,the principle classification of time-frequency figure was introduced.Through three types of ultrasonic signals which we detected,combined with classification of time-frequency figure at the same time,the T-F figure was finished.In this T-F figure,classification of different types of partial discharge can be realized.And then we can use the detection system which we produced by ourselves,including ultrasonic sensor,amplifier,filter and oscilloscope to detect and record three types of ultrasonic signals including needle plate discharge in SF6 gas,creeping discharge in SF6 gas and background noise.