| BackgroundThe focused ultrasound transducer is at the core of the High Intensity Focused Ultrasound tumor treatment system.The design of the transducer is the key to HIFU technology,and its stable work is the prerequisite for safe and effective HIFU treatment.Usually,the resonant frequency of the transducer is in a frequency range,which is the bandwidth of the transducer,which is simply referred to as the bandwidth,and the effective conversion between the electrical signal and the acoustic signal can be performed only within the bandwidth.Increasing the bandwidth of the transducer reduces frequency selectivity while also improving transducer output stability.As an important part of the transducer,the matching layer is well designed to enable efficient transmission of sound energy between human tissue and the transducer,reducing distortion and increasing the bandwidth of the transducer.PurposeThe theoretical analytical model of the 1-3 type piezoelectric composite matching layer transducer is constructed.The conductance characteristics of the transducer are analyzed.The effects of the acoustic impedance and thickness of the matching layer on the bandwidth of the 1-3 piezoelectric transducer are studied.It serves as a theoretical basis for the design of 1-3 piezoelectric composite matching layer transducers.Methods1.Based on the equal strain model of 1-3 piezoelectric composites,combined with the propagation characteristics of acoustic waves,a theoretical analytical model of a single matching layer transducer is established,and the analytical solution of the conductance of the matching layer transducer is derived.The acoustic impedance and thickness of the matching layer were changed respectively,and the influence of the change of the matching layer parameters on the conductance of the transducer was analyzed.2.Using the PZFlex software,the finite element model of the 1-3 piezoelectric composite matching layer transducer in water was constructed.The finite element simulation analysis of the model was carried out to obtain the conductivity curve of the transducer in the water.The acoustic impedance and thickness of the matching layer were changed respectively,and the influence of the change of the matching layer parameters on the performance of the transducer was analyzed.3.The 1-3 type piezoelectric composite material was fabricated by a cutting-filling method,and the matching layer of the transducer was prepared by a watering method,and the impedance curve and the conductance curve of the transducer were measured using an impedance analyzer.Compare the conductivity characteristics of the matching layer and compare the results obtained by the three methods.Result1.Through theoretical analysis,the theoretical analytical model of the 1-3 piezoelectric composite matching layer transducer is established,and the analytical solution of the conductivity of the matching layer transducer is obtained.The acoustic impedance of the matching layer is changed.With the increase of acoustic impedance,the conductance curve of the transducer has a double peak,and the valley between the double peaks is gradually deepened.When the acoustic impedance is 3.5 MRayl,the fluctuation between the double peaks of the conductance curve is small.Changing the thickness of the matching layer,when the thickness of the matching layer is ?/4,the bimodal height of the conductance curve is the same,and the conductance-3 dB bandwidth is the largest.The analytical parameters are obtained by the analytical model: the acoustic impedance is 3.5 MRayl and the thickness is ?/4,and the conductance bandwidth is approximately 401 kHz.2.Through theoretical analysis,the theoretical analytical model of the 1-3 piezoelectric composite matching layer transducer is established,and the analytical solution of the conductivity of the matching layer transducer is obtained.With the increase of acoustic impedance,the conductance curve of the transducer has a double peak,and the valley between the double peaks is gradually deepened.When the acoustic impedance is 3.5 MRayl,the fluctuation between the two peaks of the conductance curve is small.When the matching layer thickness is 48.0 l,the bimodal height of the conductance curve is the same,and the conductance-3 dB bandwidth is the largest.The best matching layer parameters are obtained by analytical model: the acoustic impedance is 3.5 MRayl,the thickness is 48.0 l,and the conductance bandwidth is about 401 kHz.3.A 1-3 type piezoelectric transducer is fabricated.In the absence of a matching layer,the conductance bandwidth is about 57 kHz.In the case of a matching layer,the conductance bandwidth is about 388 kHz.Increasing the transducer matching layer conductance bandwidth by about 7 times.Comparing the results of the two theories and the measured results,the impedance curves and conductance obtained by the three methods are in good agreement,and the resonant frequency and anti-resonant frequency obtained by the theoretical analytical model and the finite element model are compared with the actual results.And the rate of change of the conductance bandwidth is less than 5%,which confirms the accuracy of the analytical model and the finite element model.Conclusion1.The theoretical analytical model and finite element model of the matching layer of 1-3 piezoelectric composite transducer were constructed.The effects of acoustic impedance and thickness of the matching layer on the conductance characteristics of the transducer were studied by analytical method and finite element method.2.The 1-3 type piezoelectric composite transducer was prepared.The effect of increasing the matching layer on the conductance bandwidth of the transducer was compared.The results show that the matching layer with the appropriate parameters can significantly increase the conductance bandwidth of the transducer.3.The results obtained by theoretical,finite element simulation and experimental methods were compared.The results show that the results obtained by the three methods are in good agreement.Compared with the actual measurement,the rate of change of the conductance bandwidth is less than 5%,which confirms the validity of the analytical model.Therefore,the analytical model can provide a theoretical basis for the design of the 1-3 type piezoelectric composite transducer matching layer.Comparing the best matching layer parameters of the three methods,in the electrical case,due to the existence of lateral coupling,the actual optimal thickness of the matching layer is not ?/4. |
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