Large and broadband piezoelectricity in smart polymer-foam space-charge electrets

Abstract

Charged closed-cell microporous polypropylene foams are shown to exhibit piezoelectric resonance modes in the dielectric function, coupled with a large anisotropy in the electromechanical and elastic material properties. Strong direct and converse dynamic piezoelectricity with a piezoelectric d33 coefficient of 140 pC/N at 600 kHz is identified. The piezoelectric d33 coefficient exceeds that of the ferroelectric polymer polyvinylidene fluoride by a factor of 5 and compares favorably with ferroelectric ceramics. Applications of similar concepts should provide a broad class of easily fabricated “soft” piezoelectric materials.

Microstorms in Cellular Polymers: A Route to Soft Piezoelectric Transducer Materials with Engineered Macroscopic Dipoles

“…The anisotropy of the elliptically shaped voids in the plane is also reflected in the piezoelectric-like d 31 and d 32 coefficients, as shown, for example, in refs. [8] and [25]. This finding is illustrated in Figure 11, where piezoelectric resonances of PP foam samples are depicted, cut along and perpendicular to the machine direction during biax- Piezoelectric resonances are an excellent experimental tool for determining several elements of the piezoelectric tensor of such polymers; they are therefore widely used in the quest for better piezoelectric polymers.…”

“…Large values up to several hundred pC/N are commonly achieved for d 33 , more than one order of magnitude larger than in conventional ferroelectric polymers. [6,8,12,16,25,27] In comparison to the rather weak dipole-density piezoelectricity of conventional polymers, the strong intrinsic piezoelectricity of foams is caused by the large deformation of the macroscopic dipoles under mechanical load. The anisotropy of the elliptically shaped voids in the plane is also reflected in the piezoelectric-like d 31 and d 32 coefficients, as shown, for example, in refs.…”

“…[6,8,25,26] The piezoelectric tensor of cellular polymers is similar to that of ferroelectric polymers and consists of the shear coefficients d 15 …”

Energy harvesting from vibration with cross-linked polypropylene piezoelectrets

“…In the present study, the complex capacitance spectraC( f ) of IXPP samples, with a mechanically free thickness excitation, were measured. Under free boundary conditions,C( f ) is given by 29,30 …”

Ceramic Based Intelligent Piezoelectric Energy Harvesting Device

“…From the application point of view, it is important to take into account that if the metal coating or the glue is too rigid, the piezoelectric response of the film (a charge) will be small, causing a shift of the piezoelectric resonance peak (74) . In summary, ferroelectrics polymers have some advantages compared to conventional piezoelectric materials based on ceramics or polar polymers.…”