Views: 0 Author: Site Editor Publish Time: 2023-06-09 Origin: Site
1. The dielectric constant should be moderate
Usually the dielectric constant is 10 to 1000. If the dielectric constant is too large, it will cause direct coupling between the interdigital electrodes; if the dielectric constant is too small, the impedance will be too large and it will not be easy to match. A connection between a circuit and a device. Among the single-component piezoelectric ceramics, except for BaTiO3, which has a dielectric constant of 1700, the PbTiO3 system and PbNb2O6 are both small, about 200, and can be well used as piezoelectric materials on the surface of ultrasonic transducers. The dielectric constant of other binary and multi-component piezoelectric ceramic materials ultrasonic range transducer is 200-1000, which just meets the requirement of medium dielectric constant.
2. Through processing, a good surface suitable for making interdigital electrodes can be obtained.
Single crystal materials are very dense and the surface is ideal after subsequent processing such as cutting and polishing. piezoelectric ceramics transducers are usually made of powdered materials with different compositions. After a series of treatments, it is sintered at high temperature, so its grain size and pore size are the main indicators of piezoelectric ceramic materials used in ultrasonic surface wave devices. It not only determines the smoothness of the material, but also determines the operating frequency of the device.
The operating frequency of the ultrasonic surface wave device depends on the width of the interdigital rod of the interdigital transducer, which requires that the L dimension of the surface of the ultrasonic instrument is at least smaller than the width of the interdigital transducer. In order to reduce the reflection of sound waves, a sub-finger transducer is used, that is, each finger is λ/8, and the width of each finger is only 51um. In order to prevent the pores and grains of the material from affecting the metal finger rods, the size of the pores and grains is required to be at least less than 3 μm. Therefore, in order to obtain a good surface suitable for making interdigitated electrodes, the crystal grains and pores of piezoelectric ceramic materials are required to be as small as possible.
3. The transmission attenuation of ultrasonic surface wave should be small
The attenuation of ultrasonic surface wl ave transmission is related to the physical properties and surface state of the piezoelectric ceramic material itself. If the pores and grains are too large, scattering losses will be induced, while attenuation will also be caused by frictional losses during vibration between grains. Therefore, in addition to the process treatment, it must also be determined by the selection of materials.
4. The electromechanical coupling coefficient needs to be as high as possible to improve the electromechanical conversion efficiency
The electromechanical coupling coefficient reflects the conversion efficiency between mechanical energy and electrical energy of piezoelectric materials. This is a very important indicator. It is not only closely related to the elasticity, dielectric properties and piezoelectric properties of materials, but also has a close relationship with different vibration modes. In order to improve the conversion efficiency, the larger the electromechanical coupling coefficient, the better. This also reduces energy losses during signal processing. Generally, the electromechanical coupling coefficient of piezoelectric ceramic materials is relatively large, so this is easy for piezoelectric ceramics.
5. Better consistency and repeatability
When the device is mass-produced, the performance difference between the same material or local areas of the same batch of material should be small so that the device can work properly. This has little effect on piezoelectric single crystals because of the better consistency and repeatability of piezoelectric single crystal materials, but the influence is greater on piezoelectric ceramic materials. The main factors affecting the dispersion of materials are the dispersion of raw materials, the weighing deviation of ingredients, the control of sintering temperature and time. When the deviation of key characteristics (such as the speed of sound) reaches 1%, it is already unacceptable for the mass production of equipment, so it is more stringent to be less than 0.1%.
