Bending vibration mode of piezoelectric ceramics vibrator

Views: 13 Author: Site Editor Publish Time: 2018-10-30 Origin: Site

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If two thick PZT5 material piezo disks sheets having the same thickness and polarized electrodes are bonded together, when an externally applied exciting electric field can elongate one of the sheets and the other piece is shortened, bending vibration can be generated. For the sheets bonded in the opposite directions of polarization, the power is connected in series, and the sheets bonded in the same direction of polarization are connected in parallel to the power source. When the upper electrode of the applied voltage is positive and the lower electrode is negative, the applied electric field of the upper sheet is opposite to the polarization direction, the sheet is elongated, the polarization direction of the lower sheet is the same as the direction of the applied electric field, and the sheet is shortened to produce a convex curved shape; Then a concave curve is produced. When an alternating electric field is applied, bending vibration is generated.

When bending vibration of the upper part is to be elongated (shortened), the lower part of wiring piezoceramic disks is shortened (elongated), and there must be a surface that is neither elongated nor shortened in the middle. For a sheet of the same thickness, this side is the bonding surface. On the adhesive surface does not stretch and shorten, there are two points a and b that remain stationary during vibration. These two points are called nodes. In the two adhesive sheets, the electric field only excites one of them to generate bending vibration. Similarly, if two piezoelectric ceramic sheets are bonded to a thin metal sheet, or a piezo ceramic sheet is bonded to a thin metal sheet, bending vibration can be generated.

The relationship between the resonant frequency of the thickness bending vibration mode and the length of the film and the total thickness of the bonded sheet is:

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Here the frequency constant, which is the coefficient related to the wave number, y is the Young's modulus, and ρ is the piezo ceramic density. The relative bandwidth of the bending vibration of the strip thickness is 0.25-3%, and the applicable frequency range is 500 Hz to 20 kHz. The size of such vibrators is generally: l=(6~10)w, w≥3.5t.

Second, the strip width bending vibration mode:

By dividing the electrode, a single ceramic piece of piezoelectric ultrasonic transducer can be subjected to bending vibration in the width direction (or a bending vibration mode), and the electrode is divided into two parts along the center line of the electrodes of the two sides of the long piece of ceramic piece, which is equivalent to two ultrasound piezoelectric ceramic sheets are bonded together. If an alternating electric field is applied to the divided pairs of electrodes, bending vibration in the width direction can be generated. Since the surface electrode of one piezo ceramic piece is divided into two pairs of electrodes, there are two ways of exciting the bending vibration:

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Resonance frequency of long strip width bending vibration mode:

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w is the width of the ceramic sheet; l is the length of the ceramic sheet; y is the Young's modulus; k is the wave number; ρ is the density of the ceramic.

Third, the thickness of the disk bending vibration mode:

If the two wafers in the radial vibration mode are bonded together and polarized and excited in the same manner as the long strips, the thickness vibration of the wafer is obtained. The resonant frequency of this bending vibration is

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Thickness shear vibration mode:

The thickness shear vibration mode of ultrasonic piezoelectric disk pickup is characterized in that the electrode faces are parallel to the polarization direction. Under the action of an alternating electric field, the piezo ceramic sheet produces a thickness shear vibration. This vibration is the relative sliding deformation along the length and thickness directions of the two opposing surfaces of the piezoelectric body parallel to the direction of polarization. The particle is displaced along the length and thickness directions, while the wave propagates along the thickness.The resonant frequency of the thickness shear vibration mode is

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trap vibration mode:

When the electrode area of the piezoceramic materials piezoelectric discs is small relative to the area of the ceramic sheet, a proper electrode area and its metal mass load can cause a so-called trapping phenomenon. After the trap occurs, the excitation energy is confined below the spot electrode and decays exponentially around. At this point the spot electrode area and the nearby edge form an independent vibration system.The trapping vibration is actually a thickness stretching vibration. Since the electrode of this vibrator is small, it is also called a point vibrator or a point electrode vibrator. The fundamental resonant frequency of this oscillator is

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