Basic research of ultra-miniature medical ultrasound transducer by hydrothermal method

对水热法合成的PZT多晶薄膜的材料性能进行了测试，研究了沉积次数与晶体尺寸、薄膜厚度、组成比之间的关系。晶体尺寸和薄膜厚度随沉积次数的增加而成比例增长。用水热法制备了宽35μm、长4 mm、单元间距70μm的8个阵列型超声探头。可以证实，这些探头没有任何声学匹配层，具有很高的距离分辨率。由测量的方向性发现，同时驱动8个单元时，单元因子为+1-65°，群因子约为+/-10°。利用相控阵技术对超声波束进行扇形扫描。通过在直径为0.2~1.0 mm的钛丝上沉积PZT薄膜制备了针型微型水听器，实验证明该水听器可以在1~20 MHz频率范围内使用。然而，在频率特性中可以观察到峰和谷。峰峰和峰谷的频率取决于钛丝的直径。采用锥形钛丝制作水听器，以抑制钛丝端部频率特性的峰谷和回波。此外，我们还尝试用水热法制备了以细钛丝为声导的导管式超声换能器。

Material properties of hydrothermally synthesized PZT poly-crystalline films were measured and relationships between number of deposition and crystal sizes, thickness of films, composition rates were investigated. Crystal size and film thickness grew up proportionally with number of deposition. PZT crystals grew up about 2 μm per one deposition and grew up about 30 μm with 15 times of deposition and film thickness increased to 50 μm. Array type ultrasound probes including 8 elements with 35 μm width, 4mm length, element pitch of 70 μm were fabricated by using hydrothermally synthesized PZT films. It could be confirmed that the probes had high distance resolution without any acoustic matching layer. It was found by measured directivity that element factor was +1-65°, group factor was about +/-10° by driving 8 elements simultaneously. The ultrasound beam could be sector scanned with phased array technique. Needle type miniature hydrophones were fabricated by deposition of PZT film on titanium wires with diameter from 0.2 to 1.0 mm and it was proved that fabricated hydrophone could be used from 1 to 20 MHz. However, peaks and dips could be observed in the frequency characteristics. The frequency of peaks and dips depend on diameter of titanium wire. The hydrophone was fabricated by using tapered titanium wire to suppress the peaks and dips in the frequency characteristics and back echo from the end of titanium wire. Furthermore, we tried to fabricate catheter type ultrasound transducer with thin titanium wire as acoustic wave guide by hydrothermal method.