Research On Preparation And Performance Of 2.5 MHz Medical Ultrasonic Transducer

In modern medical diagnosis,ultrasound imaging has become one of the most commonly used diagnostic methods,which can provide rich image information for clinical diagnosis.In the components of ultrasonic transducers,a matching layer needs to be added between piezoelectric components and external loads,which plays a very important role in improving the sensitivity and bandwidth of the transducer.However,the acoustic impedance of single-phase matching layer materials often fails to meet the requirements of acoustic matching.The research shows that adding filler particles into the polymer can produce matching layer materials that meet the impedance matching.piezoelectric ceramic PZT has been widely studied as a piezoelectric material with excellent performance,but it has the disadvantages of high acoustic impedance(36 MRayls)and low mechanical strength.Therefore,composite materials with different volume fractions were prepared by composite method of piezoelectric ceramics and epoxy resin,and the properties of the composite materials with different volume fractions were characterized.Finally,single-layer and doublelayer matched layer medical phased array ultrasonic transducers with a center frequency of 2.5 MHz were designed based on the prepared composite materials and matched layer materials.The main research contents:(1)The equivalent circuit of the piezoelectric element is deduced and analyzed,and the equivalent circuit of the matching layer is also analyzed,and the optimal thickness of the matching layer is determined as λ/4.Finally,the calculation formula of the impedance value satisfying the impedance matching is given,Calculate the impedance values of the high impedance matching layer to be 3-7.6 MRayls,and the impedance values of the low impedance matching layer to be 2-2.5 MRayls,which provides a theoretical basis for the subsequent transducer design(2)Using epoxy resin Quick EPOXY as a polymer,hollow glass beads as fillers for low acoustic impedance matching layer materials,and aluminum nitride and tungsten powder as fillers for high acoustic impedance matching layer materials,matching layer samples with different mass fractions were prepared.The results indicate that the addition of hollow glass microspheres reduces the acoustic impedance of the matching layer sample.The matching layer sample of hollow glass beads with a mass fraction of 5.53% has the lowest acoustic impedance,which is 2.05 MRayls.When aluminum nitride is added,the acoustic impedance of the matching layer sample gradually increases,and the acoustic impedance of the matching layer sample of 60% aluminum nitride powder is 5.57 MRayls.To further improve the acoustic impedance of the matching layer sample,tungsten powder was added on the basis of 60% aluminum nitride.When the mass fraction of tungsten powder reached45%,it had the maximum acoustic impedance of 7.54 MRayls.(3)Selecting TJ-60 HD piezoelectric ceramic and EPO-TEK301-2 epoxy resin,1-3 type piezoelectric composite materials with different volume fractions were prepared using a cutting filling method.Research has shown that composite materials can reduce the acoustic impedance of low-voltage electrical components(13～19MRayls),and as the volume fraction increases,the piezoelectric properties,acoustic impedance,and electromechanical properties of composite materials show a linear growth state.When the volume fraction is 55%,kt is higher,and d33 uniformity is also good.(4)The acoustic impedance values of the matching layer required for the singlelayer matching layer and the double-layer matching layer are calculated according to the KLM model.The thickness of the matching layer is λ/4.Taking 55% volume fraction of 1-3 piezoelectric composite materials as active components,and 60%aluminum nitride-epoxy resin is used as the backing material to prepare the medical ultrasonic transducer with the operating frequency of 2.5 MHz.The results show that the center frequency of the single-layer matched layer ultrasonic transducer is 2.66 MHz,the bandwidth of-6 d B is 44.94%,and the relative sensitivity is-51 d B.The center frequency of the double-layer matched layer ultrasonic transducer is 2.70 MHz,the bandwidth of-6 d B is 60.37%,and the relative sensitivity is-42 d B.The increase in the number of matching layers effectively improves the sensitivity and bandwidth of the transducer.