Research On Ultrasonic Bone Density Detection Method Based On PZT Piezoelectric Ceramics

With the rapid development of economy and society,the process of population aging in China is further intensified,and the health of the elderly has become one of the hot issues of social concern.The bone health status of the elderly is an important factor affecting the health and quality of life of the elderly.Human bones usually produce inevitable physiological degenerative lesions with age,resulting in bone loss,decreased bone mineral density,and degradation of bone microstructure,which leads to osteoporosis.Osteoporotic bones are prone to fracture,even life-threatening,due to their inability to withstand external pressure and torsion.Therefore,regular examination of bone status and prevention of osteoporosis in advance are necessary measures to ensure life and health.Clinical diagnosis of osteoporosis usually uses a dual-energy X-ray detector,but due to the large scale of the instrument,it is not convenient to screen for early osteoporosis.Ultrasound bone mineral density detection has obvious advantages in the early screening of osteoporosis.This method can not only reflect the bone mineral density of the human body,but also make relevant evaluation of the mechanical properties of the bone,so as to prevent the occurrence of osteoporosis.At present,the ultrasonic bone density detector currently used on the market still has problems such as large volume,single transducer form and inability to achieve position adjustment,poor adaptability to human skin deformation,inability to perform multi-point detection,and lack of information obtained by non-array sensors.In view of the above problems,the ultrasonic bone density detection method based on PZT piezoelectric ceramics was studied to make up for the shortcomings of current ultrasonic bone density detection.Firstly,the ultrasonic transmission characteristics of human soft tissue and bone are analyzed.Considering the soft and changeable characteristics of human skin,a new type of linear array flexible ultrasonic transducer is proposed and fabricated by combining the simulation analysis of the structural parameters of the piezoelectric sensitive element of the transducer.The performance indexes such as the conductivity of the device,the resonant frequency and anti-resonant frequency of the transducer,the electromechanical coupling coefficient,the uniformity of the array,the bandwidth and the sensitivity are tested.The deformation and stretching ability of the transducer and the position adjustment ability of the transducer unit in multiple scenes are tested,and the transmission effect of the soft tissue and bone of the human heel is tested.At the same time,according to the transducer transceiver mode,a suitable hardware transceiver circuit is designed to collect and process the ultrasonic signal at the receiving end.The evaluation indexes of bone ultrasonic velocity and broadband ultrasonic attenuation bone mineral density are calculated and compared with the clinical diagnosis results of the dual-energy X-ray detector to achieve the purpose of detection.The structure arrangement and main research contents of the thesis are as follows:(1)The common bone mineral density detection methods and their advantages and disadvantages in the diagnosis of osteoporosis are summarized.The progress of ultrasonic bone mineral density detection at home and abroad and the shortcomings of ultrasonic bone mineral density detection methods and transducers at this stage are emphatically analyzed.The structural characteristics and preparation process of flexible ultrasonic transducers and flexible electrodes are summarized and analyzed.A flexible transmission linear array ultrasonic transducer with adjustable unit based on PZT-5H piezoelectric ceramic was proposed.(2)The detection mechanism of human quantitative ultrasound detection technology and the evaluation index and calculation method of bone mineral density parameters are studied.The rules of ultrasonic reflection,refraction,absorption and attenuation in multiple structures of human tissue are analyzed and summarized.The ultrasonic scattering phenomenon under the cylindrical scattering and spherical scattering models of cancellous bone is analyzed.The ultrasonic transducer acoustic matching theory under the KLM transmission line model is studied and the thickness parameters of the acoustic impedance matching layer are determined.(3)The working principle of linear array ultrasonic transducer is introduced.The material and structure of each component of ultrasonic transducer are determined,and the overall structure and bonding form of the array are designed.The piezoelectric equation model of PZT-5H piezoelectric material is established and the finite element simulation analysis is carried out.The structure size of piezoelectric wafer suitable for human bone detection is determined.The influence of multi-layer structure of transducer on resonance frequency is analyzed.The mechanical properties of flexible electrode structure are analyzed and the stress distribution of serpentine electrode under tension is simulated.(4)According to the results of theoretical analysis,the transducer is prepared,and the conductivity of the electrode structure and the whole device of the finished transducer is tested.Several performance indexes of the transducer are tested and compared with the simulation results.At the same time,the uniformity of the array and the deformation and stretching ability of the transducer in multiple scenes and the position adjustment ability of the transducer unit are verified.The prepared transducer is used to conduct transmission tests on different points at the heel of the human body.The test results show that the transducer can effectively penetrate human skin tissue and bones under excitation.(5)A four-way independent transceiver circuit suitable for human bone ultrasonic detection and adapted to the transducer is designed.The NE555 chip is used to generate a repetitive square wave pulse signal with adjustable duty cycle and frequency.The low-voltage power supply transmitting circuit is used to generate an instantaneous highvoltage sharp pulse signal to excite the transducer and the corresponding echo processing circuit is designed.Finally,the circuit is debugged and the performance is tested.An ultrasonic bone mineral density detection device was set up to perform transmission detection on the left heel of many volunteers and calculate the parameters of speed of sound(SOS)and broadband ultrasound attenuation(BUA).The detection results were statistically analyzed and compared with the clinical diagnosis results.The results showed that the detection accuracy of the ultrasonic bone mineral density detection device prepared in this paper using SOS parameters as bone mineral density evaluation indicators was about 81.5 %.The detection accuracy of BUA parameters as bone mineral density evaluation index was about 85.2 %.