These converters belong to a subgroup of generators, they are based on mechanically accumulated electrical charges. As a result, the following relationship is distinguished: Q=d P. In this case, d is the piezoelectric modulus, and P is the force. As a rule, the material is quartz, tourmaline, annealing mixtures, barium, lead. To design a piezoelectric transducer, it is necessary to use load patterns: compression, bending, shear, tension.
Direct and reverse piezoelectric effect
The direct effect is characterized by the following: the crystalline material used forms a lattice due to charged ions arranged in a certain order. In the process, dissimilar particles alternate and mutually compensate, resulting in electrical neutrality. Crystals have features that are indicated as follows:
- symmetry with respect to the axis;
- considering the previous view, a lattice appears with ions that alternate and compensate.
If the material used in the process is directed to the force Fx, then itis deformed, the distance between the positive and negative charges changes, and the direction in the given axis is electrified. All this is expressed in the formula q=d11Fx and is proportional to force. The coefficient is associated with the substance and its state, it has a name - the piezoelectric module. Indexes are determined by strength and edge, but if you change direction, the effect will be different.
The piezoelectric transducer in the direct process electrifies the crystals under the influence of external forces. This effect occurs under the influence of substances that are electricians. To make measuring instruments, you will need quartz crystals. That is, the principle of operation of the piezoelectric transducer is as follows: with a direct effect, the action is carried out through mechanics, and with the reverse, crystals are deformed.
Additional piezo effects
Crystal can be polarized when the plate is subjected to forces on the X, Y axes. Fy – transverse, with Fz no charges arise. The quartz crystal is located on three coordinate axes. In order to use piezoelectric transducers, it is necessary to cut a plate that indicates the effect. It has the following description:
- high strength;
- voltage allowed up to 108 N/m2, thus large measurable forces are possible;
- rigidity and elasticity;
- minimal friction inside;
- stability,which does not change;
- Maximum quality factor of the fabricated material.
Quartz plates are used only in transducers that measure pressure and force. Given the hardness of the material, it is difficult to process, so a simple shape is created from it. The modulus is constant at a constant temperature. If it increases, then in this case there is a decrease in the module. The piezoelectric properties disappear at 573 degrees Celsius.
Description of the device and measurement circuits
Piezoelectric pressure transducer has the following structure:
- membrane, which is the bottom of the case;
- the outer lining is grounded, and the middle one is insulated with quartz;
- plates have high resistance, connected in parallel;
- the foil and the inner core of the cable are fastened in a hole closed by a lid.
The output power is minimal, in this regard, an amplifier with a large resistance is provided. Essentially, the voltage depends on the capacitance of the input circuit. The characteristics of the transducer indicate sensitivity and capacitance. Basically, this is the charge and the device's own indicators. If calculated in total, then the following output power will be obtained: Sq =q/F or Uxx=d11 F/Co.
To expand the frequency range, it is necessary to increase the measured low variables towards a constant time circuit. It is easy to do this by turning oncapacitors that are located in parallel with the device. In this case, however, the output voltage will decrease. The resistance that has been increased will expand the range without loss of sensitivity. But to increase it, improved isolation qualities and amplifiers with a high-resistance input are needed.
Description of measurement circuits
Specific and surface resistance determine their own, and the main component for quartz is higher, so the piezoelectric transducer must be sealed. As a result, the quality is improved and the surface is protected from moisture and dirt. Sensor measurement circuits were created as high-resistance amplifiers, which were based on a field-effect transistor output stage and a non-inverting amplifier with an operational device. Voltage is supplied to the input and output.
However, this outdated piezoelectric transducer had flaws:
- dependence of output voltage and sensitivity in relation to sensor volume;
- unstable capacity that changes due to temperature conditions.
The voltage of the amplifier and the sensitivity are determined by the permissible error, if the included stable volume is supplemented with C1. Formula: ys=(ΔCo + ΔCk)/(Co+Ck +C1). After transformation we get: S=Ubx/F. If the coefficient increases, respectively, and these variables increase. The measuring circuit is characterized by:
- constant timeline;
- resistance R is determined by input gain, isolation of sensors, cables, and R3;
- MOS transistors are stronger than field devices but have a high noise level;
- R3 stabilizes the voltage, its value is calculated as ~ 1011 Ohm.
Analyzing the last variable, we can assume that the constant time line is as follows: t ≦ 1c. Devices today can use piezoelectric sensors with voltage amplifiers to charge.
Device Advantages
The piezoelectric transducer has the following advantages:
- easy structural assembly;
- dimensions;
- reliability;
- conversion of mechanical voltage into electric charge;
- variables that can be measured quickly.
In the case of a material like quartz, which is close to the ideal state of the body, the transformation of mechanics into an electrical charge is possible with a minimum error of -4 to -6. However, the development of high-precision technology has improved the ability to realize lossless accuracy. As a result, we can conclude that these piezoelectric transducers are the most suitable for measuring forces, pressure and other elements.
PET acceleration has the following structure:
- all materials are attached to the titanium base;
- two simultaneously turned on piezoelectric elementsfrom quartz;
- high-density inertial mass designed for minimum dimensions;
- signal removal with brass foil;
- she, in turn, is connected to a cable that is soldered;
- sensor covered by a cap screwed into the base;
- to fix the meter on the object, cut the thread.
Despite the mass, the sensor is quite stable and dense. Operates at 150 m/s2.
Design features of converters
If it is necessary to fabricate an accelerometer sensor, it is important to correctly attach the piezo-sensing plates to the base. This action is carried out by soldering. The cable must meet the following requirements:
- insulation resistance should be high;
- the screen is placed next to the living room;
- anti-vibration;
- flexibility.
That is, the cable should not be shaken at the input of the amplifier. The measuring circuit is created symmetrically so that interference does not occur. In the sensor, the connection is asymmetric, the resistance of the leads and the case is connected in such a way that the insulation of the outer plates is obtained. To achieve the desired result, the meter is required to be made from an odd number of materials that are used in the process. The elements are pressed against the amplifier through holes in the central part and through insulators that are screwed to the case.
Features of vibration measuring instruments
To increase the sensitivity of the measuring device, it is necessary to use high modulus piezoelectric elements. Thisthe material is laid in parallel in a row and connected with metal gaskets and plates. For a similar effect, substances that work on bending can still be used. However, they are low frequency and inferior to compression mechanics.
Material can be bimorph, it is usually collected in series or in parallel, it all depends on the positively located axes. As a rule, these are two plates. If the neutral layer is taken into account, an overlay made of metal with an average thickness can be used instead of a piezoelectric element.
To measure signals that move slowly enough, do the following:
- piezoelectric transducer included in the oscillator;
- crystal is at resonant frequency;
- as soon as the load occurs, the indicators will change.
Today, piezo accelerometers are advanced devices that can be high frequency, with strong sensitivity.
Alternative energy source through converters
One of the famous and inexhaustible means of generating electricity is wave energy. Such stations are mounted directly in the aquatic environment. This phenomenon is associated with the sun's rays, which heat up the mass of air, due to which waves arise. The shaft of this phenomenon has an energy intensity, which is determined by the strength of the wind, the width of the air fronts, the duration of the gusts.
The value may fluctuate in shallow water or reach 100 kW per meter. The piezoelectric wave energy converter works according to a certain principle. The water level rises by means of a wave, in the process the air is squeezed out of the vessel. The flows are then passed through by a reversing turbine. The unit rotates in a certain direction, regardless of the movement of the waves.
This device has a positive characteristic. Until today, the improvement of the design is not predicted, because the efficiency and principle of operation have been proven in all existing ways. In the process of technological progress, floating stations may be built.
Ultrasonic piezoelectric transducer
This device is designed in such a way that it does not require additional settings. It is equipped with a memory block, which gives the technical result. Refers to control and measuring devices. Such devices differ in type, technical characteristics, which are compiled on the basis of design and purpose data with minimal errors. All requirements are considered based on design.
For all such devices, a standard creation scheme is provided: a flaw detector, a housing, electrodes, the main element that is fastened to the base, a core, foil and other materials. An ultrasonic piezoelectric transducer is a utility model. It allows you to receive data directly using the sound installed on the base of the device.
Piezo transducer applications
Devices withdirect effect are used in instruments that measure force, pressure, acceleration. They have a high level of frequency and harshness. Apparatuses with feedback are used in ultrasonic vibrations, the transformation of stress into deformation, balancing. If both effects are taken into account at the same time, then this option is suitable for piezoresonators that convert one type of energy into another rather quickly.
Positive devices, connected in the opposite direction, operate on automatic oscillations and are used in generators. The scope of their application is extensive, as they have high stability when properly created. Often, several piezo resonators are used to achieve the desired effect and obtain the correct information.
Disadvantages of converters
These devices have a huge number of positive aspects. However, they also have negative features:
- output resistance - maximum;
- measuring circuits and cables must be created based on strict requirements and guidelines.
Calculation of the piezoelectric transducer initially derives the equation formula for the resonant frequency: Fp =0.24 ·c·. Plate thickness: h=Fp a2 / 0.24 c=35 103 25 10-6/ 0.24 2900=1.257 10-3m. Energy characteristics are calculated as follows: Wak =Wak.ud S=40 4.53 10-3.
