These converters belong to a subgroup of generating ones, in their basis electric charges are accumulated by means of mechanics. As a result, the following relationship is distinguished: Q = d · P. In this case, d is a piezoelectric module, and P is a force. As a rule, the material is quartz, tourmaline, annealing mixtures, barium, and lead. In order to design a piezoelectric transducer, it is necessary to use load schemes: compression, bending, shear, tension.
Forward 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 specific order. In the process, unlike particles alternate and produce mutual compensation, resulting in electrical neutrality. Crystals have features that are indicated as follows:
- symmetry with respect to the axis;
- taking into account the previous form, a lattice with ions appears, which alternate and compensate.
If the material used in the process is directed to the force F x , then it is deformed, the distance between positive and negative charges changes, and the direction is electrified in a given axis. All this is expressed in the formula q = d 11 F x and is proportional to the force. The coefficient is associated with the substance and its state, has a name - a piezoelectric module. Indexes are determined by force and facet, but if you change direction, the effect will be different.
In a direct process, a piezoelectric transducer electrifies crystals under the influence of external forces. This effect occurs with the influence of substances that are electricians. To make measuring instruments, you need quartz crystals. That is, the principle of operation of the piezoelectric transducer is as follows: with the direct effect, the action is carried out through mechanics, and with the opposite, the crystals are deformed.
Additional piezoelectric effects
The crystal can polarize when the plate is subjected to forces on the X, Y axes. If the force F x , then the longitudinal effect is manifested, and when F y is transverse, at F z no charges arise. A quartz crystal is located on three coordinate axes. To use piezoelectric transducers, it is necessary to cut out a plate that will indicate the effect. It has the following description:
- high strength;
- voltage is allowed up to 10 8 N / m 2 , due to this, large measured forces are possible;
- stiffness and elasticity;
- minimal friction inside;
- stability that 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, the material is difficult to process, so a simple form is created from it. The module is constant at a constant temperature. If it increases, then in this case the module decreases. Piezoelectric properties disappear at a temperature of 573 degrees Celsius.
Description of device and measurement circuits
The piezoelectric pressure transducer has the following structure:
- a membrane that is the bottom of the body;
- the outer lining is grounded, and the middle is quartz insulated;
- plates have high resistance, are connected in parallel;
- the foil and 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 high resistance is provided. In fact, the voltage depends on the capacity of the input circuit. Transducer specifications indicate sensitivity and capacitance. This is mainly the charge and the device’s own performance. If we calculate in total, we get the following output power: S q = q / F or U xx = d 11 · F / C o .
To expand the frequency range, it is necessary to increase the measured low variables in the direction of a constant time chain. Such an action is easily carried out by switching on capacitors, which are located in parallel with the device. True, the output voltage will decrease. The resistance, which has been increased, will expand the range without loss of sensitivity. But to improve it, improved insulation qualities and amplifiers with a high-impedance input are needed.
Description of measurement circuits
The specific and surface resistances determine their own, and the main component for quartz is higher, therefore, the piezoelectric transducer must be sealed. As a result, quality is enhanced and the surface is protected from moisture and dirt. The sensor measurement circuits were created as high-resistance amplifiers, which were based on an output stage on a field-effect transistor and a non-inverting amplifier with an operating device. Voltage is applied to the input and output.
However, this obsolete piezoelectric transducer had drawbacks:
- dependence of output voltage and sensitivity with respect to the volume of the sensor;
- unstable capacity, which changes due to temperature conditions.
The amplifier voltage and sensitivity are determined by the permissible error, if the included stable volume C 1 is supplemented. Formula: y s = (ΔC o + ΔC k ) / (C o + C k + C 1 ). After the conversion, we get: S = U bx / F. If the coefficient increases, respectively, and these variables increase. The measuring circuit is characterized by:
- constant time line ;
- resistance R is determined by input gain, isolation of sensors, cables, and R 3 ;
- MIS transistors are stronger compared to field devices, but they have a high noise level;
- R 3 stabilizes the voltage, its value is calculated as ~ 10 11 Ohms.
Analyzing the last variable, we can assume that the constant time line is as follows: t ≤ 1c. Today, devices can use piezoelectric sensors to charge with voltage amplifiers.
Preferred device features
The piezoelectric transducer has the following advantages:
- simplicity of structural assembly;
- dimensions;
- reliability;
- conversion of mechanics voltage into electric charge;
- variables that can be quickly measured.
In the case of a material like quartz, which is close to the ideal state of the body, the conversion of mechanics into an electric charge is possible with a minimum error of -4 to -6. However, the development of precision engineering has improved the ability to realize precision without loss. As a result, it can be concluded that these piezoelectric transducers are most suitable for measuring force, pressure, and other elements.
Acceleration probe has the following design:
- all materials are attached to a titanium base;
- two simultaneously included piezoelectric elements from quartz;
- high-density inertial mass is designed for minimum dimensions;
- signal pickup by means of brass foil;
- it, in turn, is connected to a cable that is soldered;
- the sensor is closed by a cap screwed on the base;
- to fix the meter on the object, cut the thread.
Despite the mass, the sensor is quite stable and dense. Works in the range of 150 m / s 2 .
Constructive features of converters
If it is necessary to fabricate an accelerometer sensor, it is important to correctly attach the piezo-sensitive 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 core;
- 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 no interference occurs. In the sensor, the connection is asymmetric, the resistance of the terminals and the housing is connected in such a way that the insulation of the external plates is obtained. To achieve the desired result, the meter is required to be made from an odd amount of materials that are used in the process. Elements are pressed to the amplifier through holes in the central part and through insulators, which are screwed to the housing.
Features of vibration measuring instruments
To increase the sensitivity of the measuring device, it is necessary to use piezoelectric elements with a high modulus. This 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 also be used. However, they have a low frequency and are inferior to compression mechanics.
The material can be bimorphic, 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 you take into account the neutral layer, then over it, instead of a piezoelectric element, an overlay of metal with an average thickness can be used.
To measure signals that move slowly enough, you must do the following:
- the piezoelectric transducer is included in the oscillator;
- the crystal is at the resonant frequency;
- as soon as the load occurs, the indicators will change.
Today piezoelectric accelerometers are advanced instruments that can be high-frequency, with strong sensitivity.
Alternative energy 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 a 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 gusts.
The value can fluctuate in shallow water or reach 100 kW per meter. A piezoelectric wave energy converter works according to a certain principle. The water level rises by means of a wave, in the process air is squeezed out of the vessel. Then the flows are passed through a reversing turbine. The unit rotates in a certain direction, regardless of the movement of the waves.
This unit has a positive characteristic. Until today, the improvement of the design is not predicted, because the efficiency and principle of operation are proved by 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 does not require additional settings. It is equipped with a memory unit that produces a technical result. Refers to instrumentation. Such devices differ in type, technical characteristics, which are compiled on the basis of data on the design and purpose with minimal errors. All requirements are taken into account on the basis of 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, core, foil and other materials. An ultrasonic piezoelectric transducer is a useful model. It allows you to receive data directly using sound installed on the basis of the device.
Piezoelectric Transducer Applications
Devices with a direct effect are used in devices that measure force, pressure, acceleration. They have a high level of frequency and rigidity. Feedback devices are used in ultrasonic vibrations, converting stress to deformation, balancing. If both effects are taken into account at the same time, then this option is suitable for piezoresonators, which convert one type of energy to another quite quickly.
Positive devices included 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 piezoresonators are used to achieve the desired effect and obtain the correct information.
Converters disadvantages
These devices have a huge number of positive aspects. However, they have negative features:
- output resistance - maximum;
- measuring circuits and cables must be created based on stringent requirements and recommendations.
The calculation of the piezoelectric transducer initially derives the equation for the resonant frequency: F p = 0.24 s Plate thickness: h = F p · a 2 / 0.24 · c = 35 · 10 3 · 25 · 10 -6 / 0.24 · 2900 = 1.257 · 10 -3 m. Energy characteristics are calculated as follows: W ak = W ak.ud · S = 40 · 4.53 · 10 -3 .