Piezoelectret, also known as ferroelectrets, are thin films of polymer foams exhibiting piezoelectric properties after electric charging, and are new kinds of artificial functional materials. Researchers show great interest on piezoelectret materials since the normal polypropylene (PP) was found to exhibit excellent piezoelectric activity around 20 years ago.

Figure 2 shows the formation of piezoelectret materials. Cellular polymer foam materials exhibit piezoelectric activity after polarization (corona charging or contact charging).

Figure 2. Schematic view of formation of piezoelectrets

Piezoelectrets have many advantages, such as large piezoelectric activity, softness, light, flexibility, low acoustic impedance, and are suitable for application in wearable device, smart home, micro energy harvesting, non-contact ultrasonic imaging, non-destructive testing, electro-acoustic transducers, etc. Figure 3 shows application fields of piezoelectret.

Figure 3. Schematic of application fields of piezoelectrets