| Our society is entering a stage of severe aging,and the care of the elderly,widowed,and disabled population has become a very important social issue.To effectively deal with the above problems and maintain the dignity of life,it is urgent to combine advanced imaging technology with privacy protection.Compared with imaging methods such as cameras,millimeter-wave radar,and infrared,ultrasonic imaging has the advantages of green health,high confidentiality,low cost,and high precision.However,in air-coupled ultrasound imaging,there are problems such as low signal-to-noise ratio(SNR)of long-distance echoes and poor image quality.Based on the conventional air-coupled ultrasonic transducer,this thesis adopts two-dimensional transmit-receive synthesis and Total Focus Method(TFM)to solve the above problems,studies the theoretical relationship and key algorithms,and builds a prototype system to carry out Experimental verification.The main research contents are as follows:First of all,aiming at the low SNR of the echo signal when the two-dimensional ultrasonic phased array is used for indoor long-distance imaging,a method of full synthesis of the transmitting array and receiving array is proposed,and the working frequency,size,spacing,and number of ultrasonic transducers are analyzed.And the relationship between the deflection angle and the size of the imaging area,imaging quality,artifacts,etc.Then,based on the above relationship,a two-dimensional air-coupled ultrasound array was designed,and key algorithms such as the transmit subarray synthetic aperture focusing(SAFT)and receive total focusing were proposed,specifically including full matrix capture(FMC),interpolation filtering,scanning of the imaging area,true time delay and focusing,amplitude image acquisition,etc.Set 5 target points with equal intervals of 10 mm in a circular area with a radius of 0.5m at a distance of 2m from the indoor array,and simulate and verify the key algorithm.Simulation results show that the algorithm can perform clear imaging and can clearly distinguish 5 target points.Finally,on the basis of the aforementioned system design and key algorithms,the realization of the array,key modules,key algorithms,and control timing was completed,and a set of indoor ultrasonic imaging prototype verification system was built.In the shape area,the imaging quality of the key algorithm is verified.The verification results show that the ultrasonic imaging system can restore a higher resolution twodimensional image based on the synthetic aperture total focusing algorithm,and its pixel resolution can reach 140×140.The above theoretical analysis and experimental verification show that based on the conventional low-voltage air-coupled ultrasonic transducer,the two-dimensional transmitting synthetic aperture focusing and receiving full focusing algorithms can solve the imaging problem of indoor long-distance effects,with high imaging quality and high pixel resolution.140×140. |
