Main performance parameters of piezoelectric materials

(1) Dielectric constant ε

The dielectric constant is a reflection of the dielectric properties of a material, or the nature of polarization, and is usually expressed . Piezoelectric ceramic components for different purposes have different dielectric constant requirements for piezoelectric ceramics. For example, an audio component such as a piezoelectric ceramic speaker requires a piezo ceramic which is having a large dielectric constant. The high-frequency piezoelectric ceramic component requires a material of having a low dielectric constant. The relationship between the dielectric constant and the capacitance of the component, the electrode area A and the inter-electrode distance t is ε=C·t/A, where C is the capacitor capacitance; A is the capacitor plate area; t—— Capacitor electrode spacing .When the distance and area of the capacitor plate are constant, the larger dielectric constant ε, the larger the capacitance C, that is, the more power the capacitor stores. Since the required detection frequency is low, ε should be larger. Because ε is large, C is correspondingly large, capacitor charging and discharging time is long, and the frequency is correspondingly low.

(2)Piezoelectric strain constant: The piezoelectric strain constant indicates the magnitude of strain generated when a unit voltage is applied to the piezoelectric crystal: t = dmVU. Where U is the piezoelectric applied to both sides of the piezoelectric wafer, Δt - the deformation of the wafer in the thickness direction. The piezoelectric strain constant 33d is an important parameter to measure the emission properties of piezo tube piezoceramic transducer. The value is large, the emission performance is good, and the emission sensitivity is higher. (3) The piezoelectric voltage constant is 33 g, and the piezoelectric voltage constant indicates the magnitude of the piezoelectric gradient generated by the unit stress acting on the piezoelectric crystal: 31 (m/N) PUgVP. In the middle.

(3) Mechanical quality factor

The mechanical quality factor is also an important parameter for measuring piezoelectric ceramics. It represents the degree of energy consumption inside the material during vibration conversion. The cause of the loss is internal friction. Value has a greater impact on resolution. The larger the mechanical quality factor, the smaller the energy loss, the longer the vibration of the wafer, the larger the pulse width and the lower the resolution. (4) Frequency constant From the standing wave theory, the condition that the piezoelectric wafer resonates under the excitation of the high-frequency electric pulse is known. This means that the product of the thickness of the piezoceramic ceramics crystal and the natural frequency is a constant, and this constant is called a frequency constant. Therefore, it is the same material, when making a high-frequency probe, the thickness of the piezoelectric wafer is small; when is making a low frequency probe, the thickness of the wafer is large.

(4)Electromechanical coupling coefficient K

The electromechanical coupling coefficient K is a parameter that comprehensively reflects the performance of the piezoelectric material, and it represents the coupling effect between the mechanical energy and the electrical energy of the piezoelectric material. The electromechanical coupling coefficient can be defined as K is the energy of the conversion. The input capability is that when the probe wafer vibrates, both the thickness direction and the radial direction are generated. Therefore, the electromechanical coupling coefficient is divided into the thickness direction tK and the radial direction pK. The tK is large, the detection sensitivity is high; the pK is large, the low-frequency resonance wave is increased, and the emission pulse is widened, which is resulting in a decrease and an increase in a blind spot. (7) Curie temperature CT and piezoelectric materials, like magnetic materials,which has a piezoelectric effect that is temperature dependent. It can only be produced within a certain temperature range. When the temperature exceeds a certain temperature, the piezoelectric effect will disappear. The temperature at which the piezoelectric effect of the piezoelectric material disappears is called the curie temperature of the piezoelectric material piezoceramic ceramics transducer. The general requirements of the probe are used for the wafer: