structure of piezoelectric ultrasonic transducer

The ultrasonic transducer is a sound pressure-electrical conversion device that can convert the surface acoustic energy and electrical energy.Since 1917, the French scientist Paul Langevin discovered the inverse piezoelectric effect, it is using quartz crystals as piezoelectric materials.The first practical sandwich quartz crystal ultrasonic transducer was successfully developed by clamping two steel plates.Although the transducer has been developed into a multi-vibration element line array, a square matrix, a convex array according to the number of vibration elements.Phased array of sound beam characteristics also evolved from the original non-focusing type to one-dimensional and two-dimensional electronic focusing and acoustic focusing, the shape has also developed into a variety of geometric transducers, but the basic unit structure has not changed greatly. The figure shows the structure of the basic piezoelectric tube sensor, it can be seen that the basic part of the ultrasonic transducer is composed.

(2) Acoustic matching layer and backing

Matching can be divided into an electrical matching network, an acoustic matching layer and impedance matching.The purpose is to increase the output power of the transducer, and the equivalent impedance inside and outside is required to be as close as possible or equal.Reducing energy loss due to mismatch in the propagation process. In the transmitting piezoelectric disc element due to the input impedance.Not as high as the receiving transducer, in order to transmit as much ultrasonic energy as possible into the tissue, electricity is required Impedance network matching.

In the electrical matching network, assuming that the impedance of the transducer is gas and the electrical impedance of the source is gas,The ratio of the primary transformers can be expressed according to the ratio between the primary and secondary of the transformer, and the P5A materials piezoelectric sensor.The equivalent capacitance CO is obtained by finding the capacitance which is  corresponding to the tuning circuit, which can be expressed as matching circuit resonance frequency in the middle of the transducer.It is known that the heart frequency is known. In the RLC tuning circuit, a suitable matching inductance can be determined by calculation.

The acoustic impedance matching layer is also known as the material or protective layer of the transducer, which is designed to reduce the acoustic energy reflection loss.Improving the efficiency of sound wave transmission. There is a big difference in the acoustic impedance between the piezoelectric ring crystal material and the load material, in order to improve the transmission of sound waves between the piezoelectric wafer and the load (tissue, water or acoustic lens).The introduction of the acoustic matching layer is the upper layer of appropriate thickness, and the acoustic impedance and acoustic attenuation characteristics,Improving the sensitivity and bandwidth of the transducer is of great help.it is the common acoustic matching layer and backing material acoustics.

(3) Other structures: wires and casing

A wire is a carrier that collects piezoelectric material to generate electric charge and conduct electrical signals.Electrical impedance is often also electrically matched as a piezoelectric disc generator material. Therefore, the conductivity of the material has electrical characteristics have certain requirements. The outer casing acts as a structural member of the transducer and generally determines the size of the final transducer. Therefore, the housing is often selected according to different application requirements. In some special applications,It is often necessary to design the mechanical structure according to the application requirements. In addition, the outer casing also protects the internal components.The role of the design is not only the design of the shape structure, but also the characteristics of the material.