Properties of piezoelectric thin films

Piezoelectric thin film is a kind of flexible, lightweight, high toughness plastic film and can be made into a variety of thickness and large area. As a sensor, its main characteristic parameters are as follows:

- 0.001 Hz~109, broadband, Hz.

Wide dynamic range (10-8~106Psi or mu torr~Mbar)

Close - low acoustic impedance with water, human tissue and adhesive system

High flexibility and flexibility

High - voltage output on the same stress condition, 10 times higher than that of piezoelectric ceramics

Without delay of using of high dielectric strength can withstand strong electric field (75V/ m) most of the piezoelectric ceramic depolarization

High mechanical strength and impact resistance (109 ~010Pascal modulus)

High stability moisture (moisture <0.02%), most of the chemicals, oxidant, strong ultraviolet radiation and nuclear radiation

• can be machined to a specific shape

Without delay of on using commercially available adhesive for can

One of the main advantages of a piezoelectric film is that it has a low acoustic impedance, and its acoustic impedance is closer to the water, the human tissue and the acoustic impedance of other organic materials than the piezoelectric ceramics. For example, the acoustic impedance of the piezoelectric film (Z0= p V) is only equivalent to 2.6 times of water, and the acoustic impedance of piezoelectric ceramics are usually more than 11 times that of water. A close impedance match facilitates the more effective transduction of sound signals in water and human tissues.

However, there are some restrictions on the application of the piezoelectric film. Compared with the piezoelectric ceramics, the electrical transmitter is relatively weak, especially in the resonance and low frequency applications. The maximum use / storage temperature of the copolymer film can be as high as 135 degrees C. Moreover, if the electrode on the membrane is exposed, it is also sensitive to electromagnetic radiation. Good shielding technology is used in the environment of electromagnetic interference and radio frequency interference.

The typical characteristic parameters of the piezoelectric film are listed in Table 1. The piezoelectric properties of the PVDF polymer and the characteristics of the two commonly used piezoelectric ceramic materials are compared in Table 2.

The optical transmission properties of piezoelectric films refer to figure 1, which has strong absorbability to infrared energy at 7~20 wavelength and make it an ideal choice for intrusion detection and energy management devices.

PVDF thin film is usually thin, soft, low density, excellent sensitivity and mechanical toughness. The flexibility of piezoelectric film is 10 times higher than that of piezoceramic. When piezoelectric polymer is extruded into thin film, it can be directly attached to the surface of the machine without affecting the mechanical movement of the parts. Piezoelectric films are very suitable for strain sensing applications requiring large bandwidth and high sensitivity. As an actuating device, the low acoustic impedance of the polymer enables it to be effectively used to transmit energy into the air and other gases.

Table 1, typical characteristic parameters of a piezoelectric film

Symbol parameter PVDF copolymer unit

T thickness 9,28,52110 all kinds of UM (micron, 10-6)

D31 piezo strain constant 2311

D33 -33 -38

G31 piezo stress constant 216162

G33 -330 -542

K31 electric one coupling constant 12% 20%

Kt 14% 25-29%

C capacitor 380 (28 mu m) 68 (100 mu m) PF/cm2@1kHz

Y Young modulus 2-4 3-5 109N/m2

V0 sound speed

stretching

Thickness 1.5 2.3

103m/s

2.2 2.4

P thermoelectric coefficient 3040 1