| Ultrasonic transducer is one of the most basic and important acoustic devices, which plays an important role in ultrasound application. In ultrasonic devices, transducer should work in a resonant frequency in order to achieve high efficiency of energy transmission. However, the equivalent impedance of transducer would change by the variation of working status. For the purpose of protecting device and improving efficiency of energy transmission, impedance matching in resonant frequency is needed. For the moment, the existing methods of impedance matching can be divided into two major categories of static matching and dynamic matching. According to the impedance of the load, the corresponding inductance and capacitance of the transducer should be figured out for the static matching, which is suitable for the application of invariable impedance. While for the application of time-varying impedance, dynamic matching method should be applied. Based on real-time detection of system matching status, dynamic matching can be conducted by adjusting the variable inductance and capacitance, which is still limited by its disadvantages of low precision and high complexity. In this paper, based on the study of current matching technologies, a transformer-inductance matching model is proposed with improved matching accuracy, convenience and instantaneity, and then real-time signal detection and feedback control circuit is also presented for further design of impedance matching.In this paper, with the analysis the impedance characteristic of ultrasonic transducer, the principle of the proposed matching model is analyzed with the adjustments of inductance and transformer. The voltage and current signals are first detected on both ends of the matching circuit by a real-time detecting circuit. Then through phase analysis for the voltage and current signals, the matching status can be achieved. When the impedance does not match, control circuit to adjust the primary winding of the transformer and the turns of the inductance to realize real part and image part of impedance matching. The hardware of the matching system consists of three parts of impedance matching network, phase detection circuit and display circuit. The impedance matching network is designed to control the parameters of the transformer and inductance. Phase detection circuit includes voltage and current sampling circuits and shaping circuit, and the parameters of frequency, phase and amplitude are detected by a FPGA device. Feedback control circuit is launched with the purpose of stepper motor control for impedance adjustment. The software of the system is composed of system initialization, data acquisition, data feedback and parameter display, which are all executed by STC89C52. Finally, to validate the performance of the system, several tests are carried out for the measurements of phase, amplitude and efficiency of energy transmission using the devices of functional signal generator, digital oscilloscope, impedance analyzer and power amplifier. The theoretical and experimental results prove the high precision of the proposed impedance matching and suggest the prosperous application potential in impedance matching of ultrasonic transducer. |
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