A composite material is a material made from two or more constituent materials. Piezoelectric composite materials are generally made with piezoelectric ceramic and polymer (for example: epoxy resin). Possessing both the advantages of piezoelectric ceramics and polymers, the composite has good physical toughness and processing flexibility. In application, the acoustic impedance of piezoelectric composite material is relatively closer to that of common media, such as water, air and biological tissues, leading to higher frequency bandwidth in its piezoelectric characteristics. With the incorporation of polymer, the piezoelectric composite material operates better in single direction with reduced interference.
Piezoelectric composite materials have the following characteristics:
- Single vibration mode in thickness, lower lateral vibrational interference
- Large electromechanical coupling coefficient
- Large bandwidth
- Low acoustic impedance
- Each piezoelectric pillar on the composite can be individually connected through electrode segmentation technology
The designation for composite material is defined according to the connectivity of each constituent material. For example, in the 1-3 composite material, the ceramic pillars are connected in one direction while the polymer is connected in three directions. (As shown in Fig.1)
By varying the ceramic filling rate (VF), acoustic impedance and electromechanical efficiency of piezoelectric composite materials can be varied. The ceramic filling ratios are defined as shown in Fig.2.
Design principles for piezoelectric composite material:
With the structure of the 1-3 piezoelectric composite, Lamb wave propagating in the horizontal direction will be generated when the piezoelectric pillar is oscillating in the vertical direction. The interference of these resonances will reduce the thickness resonance, thus reducing the piezoelectric performance of the transducer. When the wavelength of the Lamb wave is close to half the wavelength of the shear wave of the filler, the first stop-band edge resonance occurs. This resonance will cause other oscillational interference, which in turn interferes with the sensitivity and piezoelectric performance.
When designing the composite, Unictron will select the appropriate frequency and wavelength of the piezoelectric composite material to match with those of the piezoelectric ceramics and polymers to avoid interference caused by Lamb waves. (As shown in Fig.3)
The main applications of piezoelectric composites are as following:
- Scouting: sonar, sensor
- Medical: phased array imaging ultrasound probe
- Detection: flaw detection probe, high resolution ultrasonic prob
Unictron has more than 25 years of experience in the development and production of piezoelectric ceramic products. With a sound foundation in piezoelectric ceramic formulation and process capabilities, coupled with the designing capability for composite material filling ratio, plastic material selection, electrode fabrication with various materials, we can provide different types of piezoelectric composite materials. We can also develop and produce customized piezoelectric composite materials according to customer specific needs.