Characteristic curve and drive piezoelectric ceramics
Piezoelectric ceramics, commonly known as the buzzer is an electronic pronunciation components. Based on the principle of the piezoelectric effect, in the middle of two pieces of copper circular electrode placed piezoelectric ceramic dielectric material, when the above two electrodes connected to AC audio signal, the size of the piezoelectric film will signal frequency of vibrations generated according to the corresponding voices.
Because of simple structure and low cost, is widely used in electrical and electronic aspects, such as toys, pronunciation electronic watches, electronic equipment, electronic watches and clocks, timers and so on.
When given by two piezoelectric ceramic vibrator or a piezoelectric ceramic and a metal sheet consisting of the so-called called bimorph element, an electrical signal is applied, it will emit ultrasonic vibration due to bending. On the contrary, when applying ultrasonic vibration to the bimorph element, it will generate an electrical signal.
Frequency characteristics of piezoelectric ceramics curve as shown. When the piezoelectric material - the timing, the resonance frequency is proportional to h, and (D / 2) 2 is inversely proportional. The resonance frequency fo and the diameter D of the composite vibrating plate exponential relationship. Clearly D larger, low-frequency characteristics better. When piezoelectric ceramics for microphone use, the operating frequency of about 300Hz ~ 5kHz. Z impedance piezoelectric ceramics depends on ratio d / D of, seen from the figure, the impedance with d / D ratio increases and decreases.
There are two kinds of piezoelectric ceramics drive. The first is a self-oscillation type drive. The circuit principle is to provide a positive feedback transistor amplifier, constituting the piezoelectric crystal oscillator, the piezoelectric ceramic plate in the sound resonance frequency fo. At this point piezoelectric ceramics showed low impedance output volume by the input current control, and therefore also known as current-driven.
The second is he excited oscillating drive, using a square wave (or short-wave) oscillator to excite sound. Then piezoelectric ceramics generally work on a frequency fo outside, so the higher the impedance, the input current is small, it is living in the voltage-driven. The advantage is that a wide range. Sounds better.
