Piezoelectric transducer impedance matching
Sonic transmitter need to provide a sufficiently large transducer excitation signal, otherwise the receiver will be unable to detect the probe from the formation of the back reflection acoustic signals, the maximum of the excitation pulse voltage of up to several RV. Moreover, it should be between the driving circuit and the transducer impedance matching, the energy of the excitation pulse can be effectively transmitted to the transducer.
Under such a high voltage, is difficult to directly join directly between the signal source and the electrical transducer consisting of an impedance matching network reactance element. Therefore exploring how to use pulse transformer impedance matching network consisting of a method. The test results show that the method has achieved significant results.
I. impedance matching principle
Acoustic logging, in order to ensure effective incentives for transmitting transducer, the impedance matching network should be set up between the signal source and the transducer impedance matching of the general principles include two aspects:. A tuned piezoelectric transducer There is a certain reactance at the operating frequency causes a phase difference exists between the output voltage and current, so that the output power of less than the desired maximum output of the signal source needs to parallel or in series with a signal source to reverse reactance becomes purely resistive load.
b. impedance conversion, impedance matching in accordance with the principle, when the load is purely resistive, the internal resistance of the signal source and the load can be obtained with the same rated power of the load, between the signal source can be added to the transformer and the load transducer method the resistance of the signal source is converted into a resistance equal to the resistance. Therefore, to achieve impedance matching between the signal source and the transducer can be a use of capacitors and inductors W b transformer matching circuit consisting of two ways. This paper discusses the method b.
A pulse signal through the pulse step-up transformer boosting the direct excitation transducer, the transducer can be represented by the equivalent impedance network C0, C1, R1, L1 composition, C0 is a static capacitance of the transducer, C1 dynamic capacitance, R1 is dynamic resistance, L1 dynamic inductance. The input impedance of the transducer, R0 + jx0 output signal representative of the source impedance, the input impedance of the transducer representative of the impedance matching circuit is added after. Set signal source resistance is purely resistive, according to the principle of maximum power output, impedance matching can be obtained ideal conditions: R0 = Rc, X0 = 0.
