Polyvinylidene fluoride (PVDF) piezoelectric film

Characteristics and Applications of Polyvinylidene Fluoride (PVDF) Piezoelectric Thin Films

Polyvinylidene fluoride (PVDF), abbreviated as PVDF, mainly refers to a homopolymer of polyvinylidene fluoride or a copolymer of polyvinylidene fluoride and other small amounts of fluorine-containing monomers. It combines the characteristics of fluororesin and general-purpose resin. Its resin itself has good chemical corrosion resistance, high temperature resistance, oxidation resistance, weather resistance, and radiation resistance. In addition, it also has special properties such as piezoelectricity, dielectric properties, and thermoelectric properties. Therefore, it is widely used in high-end functional films such as piezoelectric films, solar backsheet films, and lithium battery separators. With the rise of wearable devices, the demand for piezoelectric sensors in devices continues to grow. Therefore, this article will focus on the application of PVDF films in the field of piezoelectricity.

Optoelectronic properties of PVDF piezoelectric thin film

PVDF piezoelectric film, also known as polyvinylidene fluoride piezoelectric film, is a new type of polymer piezoelectric material that was introduced in Japan in the 1970s. Due to its complex polarization treatment process, only a few advanced countries in the world have produced it so far. PVDF piezoelectric film is a soft, lightweight, and high toughness plastic film that can be made into various shapes and thicknesses of components according to needs. Combined with microelectronics technology, it can support multifunctional sensing elements.

PVDF piezoelectric films have unique dielectric, piezoelectric, and thermoelectric effects. Compared with traditional piezoelectric materials such as ceramic piezoelectric sheets, it has the characteristics of wide frequency response, large dynamic range, high sensitivity to force point conversion, good mechanical properties, high mechanical strength, and easy matching of acoustic impedance. It also has the advantages of light weight, softness and non brittleness, impact resistance, resistance to water and chemical pollution, and easy production of sheet or pipe materials of any shape and area. It is widely used in technical fields such as mechanics, acoustics, optics, electronics, measurement, infrared, security alarm, healthcare, military, transportation, information engineering, office automation, ocean development, geological exploration, etc. The products mainly come in three varieties: gold, silver, and aluminum. The film thickness ranges from 30-500 μ m, and the shape and area size of the product can be determined according to user needs. It is a new type of transducer material for producing improved pressure dynamic sensors, ultrasound, and intelligent detection. Among them, piezoelectric films with a thickness of over 200um can be applied in military and high-tech fields, and are currently banned by developed countries.

Advantages of PVDF piezoelectric film

PVDF piezoelectric film has high chemical stability, low moisture absorption, high thermal stability, high resistance to ultraviolet radiation, high impact resistance, and fatigue resistance. Its chemical stability is 10 times higher than that of ceramics, and it can be used for a long time below 80 ℃. PVDF piezoelectric film has a soft texture, light weight, similar acoustic impedance to water, good matching state, and high application sensitivity; The resonant frequency of PVDF piezoelectric film's stretching vibration in the thickness direction is very high, and a wide flat response can be obtained, with a frequency response width better than that of ordinary piezoelectric ceramic transducers; The advantages of PVDF piezoelectric thin film are as follows:

Good processability can be processed using existing equipment

Capable of producing large-area sensitive components

Wide frequency band response (0-500MHz);

The acoustic impedance is close to that of human tissue and water, so it can be used in sensitive device structures for medical diagnosis

Has high impact strength (can be used in shock wave sensors); ·

Corrosion resistance (this property is necessary when used in active media);

The relatively low dielectric constant corresponds to a higher piezoelectric constant value d33 (approximately one order of magnitude higher than other piezoelectric materials) and thermal signal sensitivity (ρ/ε)

Compared with piezoelectric ceramics, it has lower thermal conductivity; And it can produce thinner films;

The flexibility coefficient of PVDF, which is soft and tough, is about 30 times that of PZT, and it is lightweight (with a relative density of only about 1/4 of PZT); It can support various complex shapes required (prototypes, dome shapes, etc.) and can be used in components that require special orientation.

Overall, PVDF piezoelectric films have the characteristics of higher piezoelectric constant, wider frequency response, good mechanical strength, impact resistance, light weight, flexibility, easy matching of acoustic impedance, easy processing into large areas, less susceptibility to water and general chemical pollution, and lower price compared to quartz, PZT, etc. It can not only replace piezoelectric ceramic materials in many fields, but also be applied in situations where piezoelectric ceramic materials cannot be used. Therefore, it is a highly promising transduction polymer sensitive material.

Application of PVDF piezoelectric film

Due to the wide range of applications of PVDF piezoelectric films, from consumer electronics to automotive electronics, small household appliances, medical equipment, instrumentation, as well as military and high-tech fields, we have summarized the main applications of PVDF piezoelectric films in some civilian fields.

category

performance

Application scope

ultrasonic sensor

Piezoelectric dynamic response exhibits linearity over a wide range

Wearable devices include pedometers, heart rate and pulse counters.

Audio transducer

Utilizing the transverse piezoelectricity of PVDF piezoelectric film

Microphone, noise and laughter microphone, telephone transmitter, piezoelectric transducer, headphones, speaker, accelerometer, medical sensor.

Electromechanical transducers and devices

Utilizing the transverse piezoelectricity of PVDF piezoelectric molds

Electric record player pickup, non-contact switch, telephone dial, typewriter and computer keyboard, blood pressure monitor, optical shutter, fiber optic switch, zoom lens, tactile sensor, display, displacement sensor.

Ultrasonic and underwater transducers

Utilizing the longitudinal piezoelectricity of PVDF piezoelectric film

Ultrasonic transmitter and receiver, non-destructive testing transducer, imaging array, hydrophone, delay line, optical modulator, variable focus transducer, ultrasonic microscope, ultrasonic diagnostic instrument.

Infrared and optical components

Utilizing the thermoelectric properties of PVDF piezoelectric molds

Infrared detector, camera, infrared visible light converter, photocopier, reverse detector, laser power meter, fire detector, anti-theft alarm

Overall, PVDF piezoelectric films have good flexibility and impact resistance, and compared to ceramic piezoelectric sheets, they have a higher service life, higher product stability, and adaptability for backend applications. There will be great development prospects in the future.