Ultrasonic Principle And Device For Thickness Measurement Of Radar Absorbing Coating

With the rapid development of detection technology and modern guidance technology, the development and application of radar absorbing materials is an important method to improve the survival ability of weapon and enhance defense capability. So countries around the world pay more and more attention on the development of radar absorbing materials. Due to the characteristics of simple process, convenient construction and adaptability of target, coated radar absorbing coating (CRAC) become one of the key development directions of stealth technique at present. In the process of development, depositing and quality control on CRAC, thickness is an important factor to affect the physical properties of the coating. Therefore, the non-destructive characterization of the coating thickness is vital to the research and application of CRAC. Measuring of the thickness of CRCA based on ultrasonic pulse echo method (UPEM) in painting process, traditional methods of time domain ultrasonic thickness measurement is difficult to obtain accurate result of coating thickness on the influence of factors, such as acoustic attenuation, stochastic noise and laminated coating structure and so on. This study puts forward a method which is based on UPEM combined with ultrasonic reflection coefficient (URC) to measure the thickness of CRAC and develops an instrument for thickness measurement of CRAC.According to ultrasonic propagation characteristic in coatings, we can derive the formula of the ultrasonic reflection coefficient power spectrum (URCPS)、the ultrasonic reflection coefficient autocorrelation function (URCAF) and the ultrasonic reflection coefficient cepstrum (URCC). Besides, we pick up the characteristic parameters that reflect the thickness of coatings. Based on the URCPS, URCAF and URCC, main parameters of thickness gauge are determined as follow; the bandwidth (-6dB) of probe must be wider than7.5MHz and the length of wedge must be longer than30.6mm. Finally, we use Olympus5072pulse generator, probe whose nominal frequency is15MHz, the wedge length with30.6mm and TDS2012C oscilloscope as hardware. All those are used to constitute the device of thickness measurement system.Based on.NET platform, the software which is matching the hardware of thickness gauge is constructed and signal processing modules consisted of URCPS, URCAF and URCC are developed. Assembly which can control TDS2012oscilloscope is developed with the use of VISA standard. Finally, according to P/Invoke technology of.NET platform, the software can invoke the assembly exactly.We measure the thickness of the outmost layer of5pieces of different radar absorbing coating sample using the ultrasonic thickness measurement device. Compared with the results of metallographic method, we can get96.25%of all tests to meet the requirement that error is less than0.03mm.