For decades, organic polymers were important only as insulators in the electornic industries. Research on electroactive properties was confined mainly to inorganic materials such as barium titanate, lead zirconate titanate, quartz, silicon, cadmium sulfide, and gallium arsenide. In the 198s, organic polymers emerged as a new class of electronic materials and challenged earlier technologies based on inorganic materials. The superiority of organic polymeric materials lies in their versatility and in the possibility of tailoring materials for a particualr end-use. Organic polymers offer several advantages over inorganic materials: They are lighweight, flexible, and tough. They can be obtained in the form of ultrathin films, fiber, and even liquid crystals. They can be easily transformed into the desired configuartion. Their physical properties can be controlled over a wide range by appropriate chemical modifications. Some of them are biocompatible and hence can be utilized in biological processes.

Recent developments in ferroelectric polymers

The piezoelectric and pyroelectric polymer poly(vinylidene fluoride) (PVF2) was recently classified as a polymeric ferroelectric. The physical properties of PVF2 are reviewed to justify this definition. Applications are classified on the basis of transduction mechanism including electrical to mechanical, mechanical to electrical, thermal to mechanical, thermal to electrical, and optical to mechanical. Applications in each of these classifications are surveyed, and advantages and disadvantages of using polymeric ferroelectrics rather than more conventional materials are described.

Ferroelectric polymers and their applications

Good response, in particular high sensitivity, of polyvinylidene fluoride (PVDF) attracts a lot of research works on its manufacturing process and applications. Polarization is an important factor that is influential to the performance of PVDF. In this article, a new polarization method using ITO (Indium Tin Oxide) glass is proposed. Different from the conventional poling method using metal eletrode coated onto PVDF film, ITO glass is used as electrode to transmit the electric field voltage into PVDF film for poling. With the advantage of applying higher electric field in the process of polarization and eliminating the occurrence of flashover and arcing efficiently, this approach can thus make PVDF film gain better electric output response. Also, thinner film is constructed would be another advantage of sensitivity improvement. Comparison with conventional method for regular polarization area is carried out by using both FTIR and DSC equipment. Piezoelectric charge constant d33 and electricity output resp...

A New Approach of Polyvinylidene Fluoride (PVDF) Poling Method for Higher Electric Response

A rotary pulse generator is disclosed which generally includes a wheel rotatable about an axis. The wheel has a plurality of protrusions which deflect a piezoelectric element in a deflection zone. Several embodiments are shown. The various features include a thumbwheel in which the turning surface has teeth on it serving as the protrusions, a thumbwheel in which the teeth are directed radially inwardly, a push/pull knob which places the wheel in alignment with a selected one of three piezoelectric elements, and a wheel held in selected positions by an indent/detent mechanism with rods extending out of the side of the wheel to deflect the piezoelectric element. Yet another embodiment provides for the combination of linear and rotary pulse generation. Another form provides four sets of indicator locations with a location from each of the sets forming an aligned row of indicator locations. The protrusions are disposed selectively in the indicator locations to give each row a unique binary code when sensed by four associated piezoelectric elements.

Piezoelectric pulse generator

Lamb wave propagation in thin films of polyvinylidene fluoride PVF2 is examined as a function of temperature. Results are presented for frequencies from 10 to 70 MHz and temperatures from −50 to −175 °C. Lamb waves were excited in the 28.4‐μm‐thick films by interdigital transducers with a center frequency wavelength of 92 μm. At the fundamental wavelength, the first five Lamb modes were observed, while at the third harmonic of the transducer only the first two branches of the dispersion curves could be detected. The observed velocities of the seven modes are compared to the theoretical dispersion curves to obtain stiffness constants for the PVF2 film as a function of temperature. The results obtained for constants c33 and c55 are in agreement with previous literature. Values for the constants c11 and c13 are presented for the first time.

Low‐temperature Lamb wave propagation in PVF2

The usefulness of the piezoelectric polymer, poly(vinylidene) fluoride, for sensors in coin operated devices is demonstrated. Features such as high sensitivity, low cost, and ease of handling and processing make this material extremely attractive for these applications.

G.R. Crane

Papers

Poly (vinylidene) fluoride used for piezoelectric coin sensors