Ultrasonik Piezoelektrik Seramiklerin Özellikleri

Ultrasonik piezoelektrik seramikler, piezoelektrik özelliklere sahip bir elektronik seramik malzeme sınıfıdır. Ferroelektrik bileşenler içermeyen tipik piezoelektrik kuvars kristallerinden temel farkı, ana bileşenlerini oluşturan kristal fazlarının hepsinin ferroelektrik tanecikler olmasıdır. odaklı. Seramiklerin makroskobik piezoelektrik özellikler sergileyebilmesi için piezoelektrik seramiklerde pişirilmesi gerekir. Oluşturulduktan ve uç yüzdeki kompozit elektrot ile birleştirildikten sonra, polarizasyon işlemi için güçlü bir DC elektrik alanı altına yerleştirilir, böylece orijinal düzensiz oryantasyonun ilgili polarizasyon vektörleri, tercihen elektrik alanının yönü boyunca yönlendirilir. Elektrik alan iptal edildikten sonra, polarizasyon işleminden sonra piezoelektrik seramikler, seramiğin belirli piezoelektrik özelliklere sahip olması için belirli bir makroskopik kalıcı polarizasyon korunacaktır.

Dielektrik ve elastik özellikler:

Piezoelektrik seramiklerin dielektrik özelliği, genellikle dielektrik sabiti ε0 ile temsil edilen, seramik malzemenin harici bir elektrik alana tepki derecesini yansıtır. Dış elektrik alan çok büyük olmadığında, dielektrikin elektrik alana tepkisi için doğrusal bir ilişki kullanılabilir:

Piezoelektrik seramikler için P polarizasyon kuvvetidir, ε0 vakum geçirgenliğidir, E elektrik hassasiyetidir ve E uygulanan elektrik alanıdır. Piezoelektrik seramik bileşenlerin farklı kullanımları, piezoelektrik seramiklerin dielektrik sabiti için farklı gereksinimlere sahiptir. Örneğin, piezoelektrik seramik hoparlörler gibi ses bileşenleri, seramiğin büyük bir dielektrik sabitini gerektirirken, yüksek frekanslı piezoelektrik seramik bileşenleri, malzemenin küçük bir dielektrik sabitini gerektirir.

Piezoelektrik seramiğin elastik katsayısı, seramiğin deformasyonu ile uygulanan kuvvet arasındaki ilişkiyi yansıtan bir parametredir. Diğer elastomerler gibi, piezoelektrik seramik malzemeler de Hooke yasasına uyar: Xmn=cmnpqxmnpq, burada cmnpq elastomerin elastik sertlik sabiti olarak adlandırılır, X gerilmedir ve x gerilmedir. Piezoelektrik cisimler için, piezoelektriklikten dolayı, elastik katsayısının değeri elektriksel sınır koşullarıyla ilişkilidir.

Piezoelektrik Seramiklerin Piezoelektrikliği:

The biggest characteristic of piezoelectric ceramics is piezoelectricity, including positive piezoelectricity and inverse piezoelectricity. Positive piezoelectricity refers to the relative displacement of the positive and negative charge centers in some dielectrics under the action of mechanical external force, which causes polarization, which leads to the appearance of bound charges with opposite signs on the surfaces of the dielectrics. In the case where the external force is not too large, its charge density is proportional to the external force, following the formula:

where δ is the surface charge density, d is the piezoelectric strain constant, and T is the tensile stress. Conversely, when an external electric field is applied to a piezoelectric dielectric, the positive and negative charge centers inside the dielectric undergo relative displacement and are polarized, and the displacement causes the dielectric to deform. This effect is called inverse piezoelectricity. When the electric field is not very strong, the deformation has a linear relationship with the external electric field, following the formula:

dt is the inverse piezoelectric strain constant, that is, the transposed matrix of d, E is the applied electric field, and x is the strain. The strength of the piezoelectric effect reflects the degree of coupling between the elastic properties and dielectric properties of the crystal, which is represented by the electromechanical coupling coefficient K, which follows the formula:

where u12 is piezoelectric energy, u1 is elastic energy, and u2 is dielectric energy.

Physical Mechanisms of Piezoelectric Properties:

The two ends of the polarized piezoelectric ceramic sheet will have bound charges, so a layer of free charges from the outside world is adsorbed on the electrode surface. When an external pressure F is applied to the ceramic sheet, discharge occurs at both ends of the sheet. On the contrary, if it is pulled, the charging phenomenon will occur. The phenomenon in which this mechanical effect is transformed into an electrical effect belongs to the positive piezoelectric effect.

In addition, piezoelectric ceramics have the property of spontaneous polarization, and the spontaneous polarization can be transformed under the action of an external electric field. Therefore, when an external electric field is applied to a piezoelectric dielectric, the change as shown in the figure will occur, and the piezoelectric ceramic will be deformed. However, the reason why piezoelectric ceramics deform is because when the same external electric field as spontaneous polarization is applied, it is equivalent to enhancing the polarization strength. The increase of the polarization strength makes the piezoelectric ceramic sheet elongate in the polarization direction. On the contrary, if the reverse electric field is applied, the ceramic sheet shortens along the polarization direction. This phenomenon, which is converted into a mechanical effect due to an electrical effect, is the inverse piezoelectric effect.

Other features:

Piezoelectric ceramics have sensitive characteristics and can convert extremely weak mechanical vibrations into electrical signals, which can be used in sonar systems, weather detection, telemetry environmental protection, household appliances, etc. The sensitivity of piezoelectric ceramics to external forces makes it even possible to sense the disturbance of the air caused by flying insects flapping their wings more than ten meters away. Using it to make piezoelectric seismometers can accurately measure the intensity of earthquakes and indicate the azimuth and distance of earthquakes. This has to be said to be a great feat of piezoelectric ceramics.

The deformation of piezoelectric ceramics under the action of the electric field is very small, at most no more than one ten-millionth of its own size. Don't underestimate this small change. Control of precision instruments and machinery, microelectronics technology, bioengineering and other fields are a great boon.

Frequency control devices such as resonators and filters are key components that determine the performance of communication equipment. Piezoelectric ceramics have obvious advantages in this regard. It has good frequency stability, high precision, wide applicable frequency range, small size, no moisture absorption, and long life. Especially in multi-channel communication equipment, it can improve the anti-interference performance, which makes the previous electromagnetic equipment unable to look back and faced with the problem of being overwhelmed. Alternative destiny.