超声电缆与探头的最佳匹配方法

超声波采油和管道清洗施工均需要特殊的长距离电缆．为使激励源产生的高频电能量能够有效地经电缆长距离传输到探头上，必须首先解决电缆与探头间的匹配问题．利用探头的集总参数和电缆的分布参数模型研究了电缆输入阻抗随频率和电缆长度的变化规律．在探头的谐振频率处，电缆的特征阻抗与探头的动态阻抗相等时，电缆与探头是最佳匹配；不相等时，电缆的输入阻抗或导纳均随频率变化，具有一系列的峰值．导纳的峰值对应1／2波长，阻抗的峰值对应1／4波长．用4294A阻抗分析仪测量到了这些峰值，频率越高其峰值越小．电缆接探头后，这些峰值向低频移动．考虑到大功率超声电源内阻较小，电缆与探头匹配时，应使电缆长度为1／2波长附近，导纳的极大值位于探头的谐振频率处．并联匹配电感用于抵消探头导纳的虚部．

Optimal Match Method of Ultrasound Cable and Piezoelectric Transducer

Special ultrasound cable is designed to meet the demand of ultrasonic oil extraction and pipeline cleaning for the propagation of high-frequency ultrasonic power over a great distance to transducer located underground. Cable input impedance versus frequency and length curve was studied by making use of the transducer lumped-parameter model and the cable distributed-parameter model. As a conclusion, when the characteristic impedance of the cable and the impedance of the transducer are equal at transducer resonant frequency, they achieve the best match; if they are not equal, the impedance or admittance of the cable varies with frequency, and both real and imaginary parts have a series of peaks. Admittance peak corresponds to half wave length, and impedance peak to quarter wave length. 4 294 A impedance analyzer was used to measure these peaks, and it was found that the higher the frequency, the smaller the peak value. After the cable and the transducer were connected, these peaks were found to move to the low-frequency region. Considering the small inner resistance of ultrasound power source, the cable length should be the half of wave length, and the maximum admittance of the cable should be within the resonant frequency of the transducer for an optimal design. Matching inductor is used to offset the imaginary part of transducer admittance in practical application.