| With the ageing of social population structure in China,the problems faced by the elderly are becoming increasingly prominent.Falling,hitting or even bad posture can cause fracture of limbs and spine for the elderly.The traditional way of fracture treatment is to fix the fracture part through gypsum and other materials.This method is based on the healing function of human self skeleton.But this method of treatment for fracture takes usually three months or longer for the elderly.At present,studies have shown that stimulation of fracture site through a certain intensity of ultrasound can accelerate fracture healing and reduce fracture healing cycle.However,the traditional ultrasonic treatment equipment is rigid and can not fit closely with the skin of the human body.It is both uncomfortable and inconvenient in the process of long-term bone injury adjuvant treatment.The flexible piezoelectric ultrasonic transducers for bone injury have been developed on this demand.In order to provide long-term assistance for the treatment of bone injury,a flexible piezoelectric ultrasonic transducer is designed in this paper.First,the overall design of the flexible piezoelectric ultrasonic transducer is based on the combination of rigid components and flexible substrates used by most flexible electronic devices at present.The parts of device were fabricated by MEMS technology.In this paper,the tensile properties of flexible electrodes,the resonant frequency and amplitude of the piezoelectric ultrasonic module and underwater acoustic field distribution of the whole device are simulated and tested.It is helpful to further explore the application of the auxiliary treatment for bone injury.The main contents of this paper are listed as follows:(1)The problems in the current flexible piezoelectric ultrasonic transducer are studied by reading a lot of documents about rigid ultrasonic transducers,flexible electronic devices and flexible piezoelectric ultrasonic transducers.Based on the characteristics of rigid ultrasonic transducer and flexible electronic device,the structure of flexible piezoelectric ultrasonic transducer are defined.(2)According to the design of flexible piezoelectric ultrasonic transducer structure,the MEMS technology including photolithography,magnetron sputtering,etching and plasma vapor deposition is introduced in detail.Flexible substrates based on PDMS,flexible electrodes based on copper layer and PI protection layer,and piezoelectric ultrasonic module based on PZT are fabricated.Then,the whole device was completed by packaging.(3)The tensile properties of flexible electrodes were simulated to ensure that the designed flexible electrodes meet the needs of applications.The size of piezoelectric ceramic block is selected and the maximum average amplitude of a piezoelectric ceramic is obtained by the simulation of resonant frequency of piezoelectric ultrasonic module.The distribution of acoustic field in the water tank is simulated and the normal working state of the equipment under water can be clearly understood.(4)In order to ensure the conduction performance of the device,the flexible electrodes and the bonded piezoelectric ceramics were tested.The measurement of the resonant frequency and the amplitude were carried out to identify the characteristic parameters of the device.In this paper,a high-precision hydrophone has been used to carry out the experiment of ultrasonic underwater launching and ultrasonic penetration of pork tissue.When the excitation signal frequency is 357 kHz and the amplitude is 100 V,the hydrophone got the ultrasonic intensity is about 5.533mW/ at 5 cm from the device.The experimental study shows that the flexible piezoelectric ultrasonic transducer designed in this paper can produce low intensity ultrasound(less than 30mW/)for the human body,and has the potential to assist in the treatment of bone injury. |
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