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Principle of Ultrasonic Transducer

The ultrasonic transducer is the heart of the ultrasonic welding machine, just like the engine of a car. The ultrasonic transducer converts the high-frequency electric energy or magnetic energy output by the ultrasonic generator into mechanical vibration of the same frequency. There are two types of ultrasonic transducers. One is a magnetostrictive transducer, and the other is a piezoelectric ceramic transducer. Magnetostrictive transducers, due to low efficiency and low cost performance, require an external DC polarization magnetic field, so ultrasonic welding machines are rarely used at present. Nowadays, ultrasonic welding machines use piezoelectric ceramic transducers. The basic principle is the piezoelectric effect of crystal materials. This material is piezoelectric crystal material. When this material deforms in a mature place, the piezoelectric ceramic crystal surface There will be electric charges, and an electric field will be generated inside the crystal. On the contrary, when the crystal is subjected to an external electric field, the gold sheet will deform. This situation is called the piezoelectric effect. The former is called the positive effect or the reverse current effect.

Ultrasonic transducer classification

The ultrasonic transducer is the heart of the ultrasonic welding machine. The design of the ultrasonic transducer is directly related to the performance, stability and life of the welding machine. Most piezoelectric ceramic transducers used in the market are based on vibration There are many different types of forms, such as radial vibration mode, longitudinal compound vibration mode, shear vibration mode, thickness vibration mode, etc. Ultrasonic plastic welding machine uses longitudinal high frequency vibration when welding plastic workpieces. The upper mold and the lower mold of the workpiece are melted under high-frequency vibration and friction, and then welded under pressure to achieve the welding effect.

Piezoelectric ceramic transducer

1. Structure

The structure of the piezoelectric ceramic transducer is composed of piezoelectric ceramic wafers, electrode sheets, front and rear covers, etc. The rear cover is generally made of steel with a larger mass. The front cover is made of light, high-strength aluminum alloy or titanium alloy. It uses the longitudinal effector of piezoelectric ceramics and the polarization direction of ceramic components. The electric field direction and the mechanical vibration direction are the same.

2. Advantages

1. Most ceramic components have greater compressive strength, which will increase when the environmental strength changes, and the stability of the transducer will change. The disadvantage of ceramic materials is that the allowable tensile stress is small. Configure an overload system to prevent damage to the transducer when overload occurs.

2. Because the central assembly part is composed of a set of electrode shafts on the axially polarized rings at both ends, the maximum effective coupling coefficient k33 can be used.

3. There are options for the number of rings and the connection method, so that the transducer can be designed with a wider impedance and frequency range.

4. Changing the material size of the head and tail metal cover can control the bandwidth of the transducer, the front-to-back vibration speed ratio and the effective electromechanical coupling coefficient.