Last Updated on April 23, 2023 by You Ling
Piezoelectric composite material is a piezoelectric material composed of two or more materials. 1-3 type piezoelectric composite materials can be used for ultrasonic testing in various fields. They have good acoustic impedance matching with media such as water, plastic, inorganic materials, composite materials, and air, thereby improving the penetration rate of sound waves. We have produced many ultrasonic probes based on piezoelectric composite materials, so we would like to share relevant experiences with everyone.
1、What is an ultrasonic probe?
An ultrasonic probe is a device that emits and receives ultrasonic waves during ultrasonic testing. It is mainly composed of sound-absorbing materials, shell, damping block, and piezoelectric chip. The sound-absorbing material absorbs ultrasonic noise, and the shell plays a role in supporting, fixing, protecting, and shielding electromagnetic waves. The damping block can reduce chip ringing and noise and improve resolution.
The piezoelectric chip is the key component for generating ultrasonic waves in the probe. It can emit and receive ultrasonic waves. Generally, piezoelectric chips are made of materials such as quartz and piezoelectric ceramics that have piezoelectric effects. The ultrasonic probe is used for ranging and is the front end of the ultrasonic sensor, which is used to emit ultrasonic waves and receive sound waves reflected back from the object surface. Specifically, it is a part of the ultrasonic sensor.
In other words, the ultrasonic probe generally refers to the transducer inside the sensor, which is only an electro-acoustic conversion device that does not output standard signals. The ultrasonic transducer uses piezoelectric ceramic materials to convert electrical energy into mechanical energy. Generally, ultrasonic waves are generated by an ultrasonic generator, which is converted into mechanical vibration by the transducer, and then exported as ultrasonic waves through the export device.
A single ultrasonic transducer cannot work alone and needs a driving circuit to give it a driving voltage to make it work. The ultrasonic probe mainly uses the reverse piezoelectric effect of the piezoelectric crystal to emit ultrasonic waves. When a high-frequency voltage is applied to the crystal, the piezoelectric crystal is excited to propagate ultrasonic waves in adjacent media at the same frequency, completing the conversion of electrical energy into mechanical vibration.
The receiving probe mainly uses the piezoelectric effect of the piezoelectric crystal to receive ultrasonic waves. When ultrasonic waves propagate in different media, they reflect at the interface of the media. The reflected ultrasonic waves act on the piezoelectric crystal, generating electrical energy with the same frequency as the mechanical vibration and completing the conversion of mechanical vibration into electrical energy.
2、Working principle of ultrasonic probes
Ultrasonic probes emit and receive ultrasonic waves through the piezoelectric effect. A 640V alternating voltage is applied to the silver layer of the piezoelectric chip, causing two metal electrodes with the same area and a certain distance between them to carry equal amounts of opposite charges to form an electric field. An electric field creates an electric field force, and the piezoelectric chip undergoes deformation under the action of the electric field force. Under the action of the alternating electric field force, a deformation effect occurs, which is called the inverse piezoelectric effect and is the process of emitting ultrasonic waves.
Ultrasonic waves are mechanical waves, which are generated by vibrations. Ultrasonic waves detect defects and cause them to vibrate, and a part of them returns along the original path. Due to the energy of ultrasonic waves, they act on the piezoelectric crystal again, causing the piezoelectric crystal to produce alternating electric fields under the action of alternating tension and pressure. This effect is called the direct piezoelectric effect and is the process of receiving ultrasonic waves. The direct and inverse piezoelectric effects are collectively called the piezoelectric effect.
3、Application of Piezoelectric Composite Materials in Ultrasonic Probes
Piezoelectric composite materials are made up of two or more materials combined to create a piezoelectric material. Common piezoelectric composite materials are two-phase composites of piezoelectric ceramics and polymers such as polyvinylidene fluoride and epoxy resin. This type of composite material has the advantages of both piezoelectric ceramics and polymers, with good flexibility and processing performance, as well as low density and ease of achieving acoustic impedance matching with air, water, and biological tissue.
Advantages:
Weak lateral vibration, low crosstalk pressure
Low mechanical quality factor Q
Wide bandwidth (60% to 100%)
High Kt value
High sensitivity of probes processed from the material, with signal-to-noise ratio better than ordinary PZT probes
Can be processed into complex probe shapes
Easy to change sound velocity, acoustic impedance, relative dielectric constant, and electromechanical coefficient (as these parameters depend on the volume ratio of the ceramic material)
Easy to match with materials of different acoustic impedance (such as transmitting ultrasonic waves to liquids or non-metallic materials)
Sensitivity of transducer can be adjusted by changing the ceramic volume ratio
Piezoelectric composite materials are made by combining piezoelectric ceramic elements with polymers such as epoxy resin or other polymers. They are classified according to their connectivity (such as 1-3, 2-2, 0-3, etc.). The most widely used type is the 1-3 type. 1-3 piezoelectric composite materials can be used for ultrasonic detection in various fields. They have good acoustic impedance matching with media such as water, plastics, inorganic materials, composite materials, and air, which improves the penetration of sound waves. Piezoelectric composite materials are a new type of material, and He-Shuai company has many years of experience in designing and manufacturing them.
Most of our ultrasonic probe products are based on the design and processing of 1-3 piezoelectric composite materials. With the excellent performance of 1-3 piezoelectric composite materials, we can produce high-quality ultrasonic probes. After years of exploration, we have accumulated rich material and process experience to meet the different needs of customers for ultrasonic probes. In the past few years, we have customized ultrasonic probes for many customers, solving many of their problems and receiving good evaluations.
