The radiation flux varies in time (t) according to the exponential law:
where: A is a constant coefficient corresponding to the initial value of the exponential pulse amplitude, N is the number of pulses from the beginning of the exponent to the moment of change of the photoelectric signal.
At the moment of equality of the radiation fluxes and we obtain that
from which it follows that:
where: te is the exponential time constant.
In the alarm sensor for geothermal energy facilities, LEDs with radiation spectra of 3.2 microns (reference) and LEDs with radiation spectra of 3.4 microns (working) are used.
Figure 1 shows a block diagram of an alarm sensor for geothermal energy facilities, which consist of a power supply unit 1, a generator 2, a frequency divider 3, a singlevibrator 4, an exponential function modulator 5, an emitter repeater 6, electronic keys 7 and 8, light-emitting diodes (9 and 10), gas chamber 11, photodiode 12, first differentiating device 13, threshold device 14, matching circuit 15, second differentiating device 16, counter 17.
The alarm sensor for geothermal energy facilities works as follows:
The rectangular pulse generator 2 generates pulses with the required repetition rate. These pulses from the antiphase outputs go to the input of the divider 3 frequencies and to the control inputs of the keys 7 and 8. Rectangular pulses from the output of the divider 3 frequencies go to the input of the single vibrator 4. Rectangular pulses with the required duration from the output of the single vibrator 4 enter the input of the exponent modulator 5, the output of which is connected via an emitter repeater 6 to the input of the electronic key 8, where a discrete exponential current pulse is formed, which flows through the emitting diode 9, causing a radiation flux according to the same law. The electronic key 7 switches to the pulses that fill the exponent in an antiphase manner.
Figure 3 shows the transfer function of the alarm sensor for geothermal energy facilities.
A current pulse flowing through a light-emitting diode 10 causes a luminous flux, the amplitude of which is constant. The radiation streams of LEDs that have passed through the gas chamber 11 are received by the photodiode 12. This signal is fed to the input of the first differentiating device 13, from the output of which the differentiated photoelectric signal enters the input of the threshold device 14.
Next, the signal from the output of the threshold device 14 is fed to one of the inputs of the matching circuit 15. A signal is sent to the other input of the coincidence circuit 15 from the output of the second differentiating device 16. From the moment of comparison, a number of pulses appear at the output of the coincidence circuit 15, which arrive at the counting input of the counter 17. At the beginning of the next exponent, the counter 17 receives rectangular pulses from the output of the singlevibrator 4 at the input "Zero setting" and the counter 17 is prepared for the next cycle.
Comparison of the amplitudes of the reference and measuring radiation fluxes using a threshold device ensures the accuracy of measurement of a geothermal gas monitoring device based on semiconductor emitters.
Literature
1. Akhmedov G. Ya. Protection of geothermal systems from carbonate deposits. M.: Scientific World, 2012.
2. Kiseleva S. V., Kolomiets Y. G., and O. S. Popel, «Assessment of solar energy resources in Central Asia,» Appl. Sol. Energy (English Transl. Solar Engineering), 2015, doi: 10.3103/S0003701X15030056.
PHOTOVOLTAIC EFFECT IN a-QUARTZ
UDC 548.1.024.5
Karimov Boxodir Xoshimovich
Candidate of Physical and Mathematical Sciences, Associate Professor of the Department of "Technological Education" of the Faculty of Physics and Technology of Fergana State University
Ferghana State University, Ferghana, Uzbekistan
Annotation. The anomalous photovoltaic effect observed earlier for LibO 3:Fes ferroelectrics is a special case of a more general FE existing in crystals without a center of symmetry and described by the third ai j k tensors.
Keywords: photovoltaic effect, ferroelectrics, tensor, tensor components.
Аннотация. Аномальный фотовольтаический эффект, наблюдавшийся ранее для сегнетоэлектриков Li bO3:Fe SbSJ, является частным случаем более общего ФЭ существующего в кристаллах без центра симметрии и описываемого тензорам третьего a
i j k
Ключевые слова: фотовольтаический эффект, сегнетоэлектрики, тензор, компоненты тензора.
The components of the aij tensor are nonzero for 20 acentric point symmetry groups. With uniform illumination by linearly polarized light of a homogeneous piezo crystal and ferroelectrics, a photovoltaic current arises in it. The sign and magnitude of the photovoltaic current depends on the orientation of the polarization vector of light with its components and Ul*, the direction of its propagation and the symmetry of the crystal.
In accordance with (I) and the symmetry of the point group, it is possible to write an expression for the photovoltaic current. Comparison of the experimental criminal dependence with (β) makes it possible to determine the photovoltaic tensor aajk or photovoltaic coefficients
(a* is the light absorption coefficient).
If the electrodes of the crystal are opened, the photovoltaic current generates a photovoltaic voltage of 103-105 B. the value of which can be several orders of magnitude greater than the band gap of piezo or ferroelectrics. There is no FE in centrosymmetric crystals.
We studied a-quartz, one of the more common crystalline forms of silica (SiO2). At tempratures up to 573o, there is a so-called "low-temperature" a-quartz. A-quartz crystals belong to the trigonal trapezohedral class of the trigonal system (point group of symmetry 32) and are often found in two known forms: right and left crystals. At normal pressure and temperature of 573o With a quartz turns into a hexagonaltrapezohedral class of the hexagonal system (point symmetry group 622).
The thirdorder axis in quartz is the optical axis of the crystal. One of the axes of the second order is the electric axis and the normal to both of these axes is the mechanical axis.
The symmetry of the quartz structure determines the symmetry of the properties of this crystal.
Quartz has the need to rotate the plane of the field, not only along the optical axis, but also in a direction perpendicular to it. It has been experimentally established that the ratio remains constant for wavelengths from 545 to 565 Nm and is equal to 054, i.e. the rotation of the plane in the directions perpendicular to the optical wasp is immeasurably two times less than that of the optical wasp. Despite all the "popularity" of quartz, both its properties have not yet been studied in detail.
In this paper, the results are presented, the effect of the polarization of light on
Af effect in natural crystal -quartz with natural coloring.
Figure 1 shows the angular instability of the photovoltaic current in a native a-quartz crystal with a natural color. The crystals were suspended in the impurity spectral region (l- 300500 nm, a2 = 2cm -1) at room temperature. Figure 1 shows two orientational angular dependence Jx (b) when illuminated in the direction of the a-z axis, while for a-quartz K11 = (13). 1013 A. cm (W) -1.
The illumination in the Zdirection reveals a noticeable deviation of Jx(b) from the theory. Perhaps this is due to the difference in the values of the optical activity coefficient of quartz for the Z and Ydirections. Attention is drawn to the very low value of the photovoltaic coefficient K11 in a-quartz. It characterizes the impurity centers responsible for the natural coloring of natural crystals and does not reflect the asymmetry of their own transitions. Unfortunately, a-quartz impurity centers have not been specifically investigated; this provides an independent task.