Develop and usage virtual schemes of remote acoustic laser microphones with visible and invisible waves

. This article developed and investigates the operation of remote acoustic laser microphones in virtual and practical circuits. Various simulation processes were studied and mainly the circuit of an open optical transmitter and receiver were simulated. Another aspect of the work are the introduction and use of a laser in the invisible light range into the system, the essence of which is explained by not causing inconvenience to the environment. The invisible wave may be ultraviolet or infrared light ranges.


Introduction
Remote acoustic laser microphones are widely used to solve the problem of remote data controllers.It is possible to use them mainly when there are no transmitting devices.Thus, they allow to organize simplex communication channel communication [1,2].Because the laser microphone is affected by changes in the coordinates signals of a fixed surface, it can be used, for example, to detect movement or activity on the surface of an object.There are other potential uses for this type of communication, if some kind of reflective surface is attached to the body of the reflector, even for human heart, vascular warfare, respiration detection [6], or for detecting buildings within its vibrations.It can be used in tasks such as monitoring the objects.The advantages of such systems are speed (because information is transmitted through optical radiation, and its speed is close to the speed of light and is limited only by the speed of information processing) and the possibility of remote access from the location of information collection.Its working principle is shown in figure one.The light of the laser beam is directed from the source to the surface (reflector) on which the light beam is reflected.The angle of reflection of the laser beam changes when the reflector vibrates.Thus, the light flux is intensively modulated by information of object.The returned light (reflected) is received by an optical receiver phototransistor placed at the point of light reception.Changes in the direction of the reflected light during the oscillations of the reflector lead to corresponding changes in the state of the light potential in the photosensitive element of the optical receiver (photodiode or phototransistor) [7][8][9][10][11][12][13][14][15].

Materials and methods
Therefore, a remote acoustic laser microphone should include several blocks that perform the appropriate functions.A constant-power laser diode light flux must be maintained.Since the laser radiation has a very wide dispersion pattern (aperture), it is directed through a collimator to focus the beam.Then, the reflected collimated beam falls on the receiving unit.Its input has an optical filter with a bandwidth that includes the wavelength of the laser diode.Such a filter allows you to select the light from the incoming light sources.Moreover, only laser radiation reaches the photodiode (or phototransistor) [3].In this case, the light beam falling on its photosensitive area turns into an electric current.Then the photodiode current is converted into a voltage through a variable dynamic resistance (trans impedance) [4,5,12], because all amplifiers amplify this signal first.It is important factor.In addition, the first modified signal goes to a low-frequency amplifier that increases the voltage to the desired level.Based on the above, the structural diagram of the laser microphone shown in Fig. 2 is constructed.The electrical part of the laser disk drive is supplied with power that provides a stable current supply to the laser diode (emitter).It is known that the laser diode is very " damageable " and the current passing through it slightly different from the norm can burn it.The most common application of a laser diode is optical drives (disc drives).DVD-RW used lasers that emit at a wavelength of 650 nm.The higher the writing speed on such disc drives, the more current the laser consumes and the more power it has, for example: -if the speed is 16x -the current will be 250-260 mA, the power will be 200 mW; -if the speed is 20x -the current is 400-450 mA, the power is 270 mW; -if the speed is 22x -the current will be 450-500 mA, the power will be 300 mW.

Results and discussion
Based on this, a sufficiently high-power laser diode can be removed from unnecessary optical disk drives.This distant laser microphone uses a 50 mW laser at a wavelength of 630 nm wavelength.But for long-term service, you should not apply a current higher than 50 mA to it, because when heated, the direct current flowing through the laser increases and it can "damage".As a power limiter, the resistor connected to it is a voltage regulator.And since the voltage is stabilized, so is the current (limited only by the resistor) [3][4][5][6][7][8][9][10]. The main factors affecting the range are determined by the power of the transmitter and the sensitivity of the receiver.At the same time, the focus of the beam, that is, the minimum value, must be provided by the collimator.Divergence also has a big impact on this cases.Both atmospheric change and attenuation significantly affect range.Multisim 141 modeling software package was used to test the performance of this scheme.Figure 3 shows the transmitter circuit modeled in the Multisim 141 program in general view (top) and during performance testing (bottom).The ammeter shows a stabilized current of 44.4 mA flowing through the laser diode U7.Therefore, the operation of the current stabilizer for the laser diode was checked.The main criterion for choosing a phototransistor for a receiver is its spectral sensitivity, and for an amplifier, the trans impedance (variable resistance) coefficient (the ratio of the output voltage to the input current) is the factor [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20].The following scheme was used to check the performance of the designed receiver.The electrical circuit is shown in Figure 4

Fig. 1 .
Fig. 1.General structure and principle of operation of remote acoustic laser microphones.

Fig. 2 .
Fig. 2. Block diagram of the remote acoustic laser microphone under investigation.

Figure 5
Figure5shows the input and output signals of the receiver [6].It can be built and simulated by Micro-Cap and Electronic Workbench software tools.We obtained this through the Electronic Workbench software tools.Thus, according to the results of the performed work and simulation, the amplitude of the output voltage should be 3.89 In the work performed, the operation of the laser microphone was analyzed, structural and schematic diagrams were developed, and the operation of the transmitting device was simulated[7][8][9][10].