RU2649056C2 - Method of creating a microphone based on selective absorption of infrared radiation by carbon dioxide in atmospheric air - Google Patents

Abstract

FIELD: acoustics.

SUBSTANCE: invention relates to acoustics, especially to microphones. Method of creating a microphone based on the selective absorption of infrared (IR) radiation by carbon dioxide. In this case, the IR emitter is used in the wavelength range λ_{by a pose} = 2.64÷2.87 mcm at the emitter power, which provides the ratio of the number of generated quanta of light λ_{by a pose} to the number of molecules of carbon dioxide

within the volume of the emitting beam on the path, the emitter-receiver in the form of an inequality

the detectability of the IR receiver is not worse than 5⋅10⁹W^-1⋅Hz^1/2⋅cm. Interference filter with a bandwidth of 40 nm and an emission factor of at least 0.7 is set at the input of the IR receiver. By the zero of the measurement readout a signal is usually received. This signal is recorded at normal atmospheric pressure and under the conditions that pressures above atmospheric are measured at a transmitter-receiver distance of not more than 1 cm, and the pressure below atmospheric is measured at a distance of not less than 10 cm, and the IR emitter is provided with a focusing lens.

EFFECT: technical result is an increase in efficiency, expansion of the range of measured pressures.

1 cl, 3 dwg, 4 tbl

Description

A new type of microphone is proposed based on the selective absorption of infrared (IR) radiation by carbon dioxide (CO ₂ ) air, which can be used in measurement technology for recording high and low sound pressure levels.

Currently, the world uses a variety of microphone models, which are the primary converters of acoustic sound pressure into an electrical signal [1, 2, 3, 4, 5, 6, 7]. All known models consist of a serial connection of subsystems (links), which are:

- an acoustic antenna, in which the sound pressure acts on the acoustic input of the microphone, which forms a mechanical force on the moving mechanical element of the microphone - a membrane, a diffuser;

- an acoustic-mechanical link in which, in accordance with the vibrational velocity of air particles, the membrane is displaced in condenser microphones or diffusers are oscillated in dynamic microphones;

- an electromechanical link, which is an electromechanical converter of mechanical vibrations into electromotive force, while the conversion efficiency is characterized by an electromechanical coupling coefficient (using the Lenz electromagnetic law, the piezoelectric effect, changes in the voltage on the capacitance when the electric charge changes);

- an electrical link (circuit), which provides the formation of the output electrical signal of the microphone, equivalent to the input acoustic signal, in a form convenient for its subsequent use in transmission over communication channels, for storage, amplification and reproduction.

As an analogue (prototype), any known microphone consisting of the above elements can be used.

The disadvantages of the analogue include:

- low efficiency (not more than 5%);

- maximum values of pressure levels for known microphones [3, 6, 7] not more than 130-140 dB;

- microphones for recording high pressure levels [3, 6, 7] up to 180 dB have a frequency range of 10-120 Hz.

In the proposed microphones, according to the authors, the listed disadvantages of analogues will be eliminated, which is a new technical solution.

к числу молекул углекислого газа в пределах объема излучающего луча

на трассе ИК излучатель-ИК приемник в виде равенстваIn the method of creating a microphone based on the selective absorption of IR radiation by carbon dioxide molecules of air, in accordance with the proposal, an IR emitter is used in the wavelength range λ _dpi = 2.64 ÷ 2.87 μm with an IR emitter power that provides a ratio of the number of generated quanta

to the number of carbon dioxide molecules within the volume of the emitting beam

on the path of the IR emitter-IR receiver in the form of equality

,

moreover, the detecting ability of the receiver is not worse than 5⋅10 ⁹ W ^-1 ⋅Hz ^1/2 ⋅cm. At the input of the IR receiver, an interference filter is installed with a bandwidth of the spectrum of 40 nm relative to the average value of the absorption wavelength range and with a transmittance of at least 0.7, while a signal that is recorded at normal atmospheric pressure is taken as a zero point when measuring the output signal of the IR receiver and provided that pressures above atmospheric are performed at a transmitter-receiver distance of not more than 1 cm, and pressures below atmospheric are performed at a transmitter-receiver distance of not less than it is 10 cm, and the emitter is provided with an additional focusing lens for focusing radiation on the receiver.

Further explanations of the text will be illustrated by the following drawings.

FIG. 1 - spectral distribution of the intensity of IR emitters depending on the concentration of CdSe in the initial solid solution;

FIG. 2 - spectral detection ability of infrared photodetectors of the RD-36 type;

FIG. 3 is a functional diagram of a microphone with two pulsed IR emitters of the IL151A-e type, a photodetector of the RD 36-m type, and a timing diagram of the microphone's operation in pulsed mode.

From the course of general physics it is known that carbon dioxide CO ₂ is part of the atmospheric air of the Earth in an amount of 0.03%. Since the total number of molecules in 1 cm ^{3 of} air at normal atmospheric pressure is 27⋅10 ¹⁸ mol, the number of CO ₂ molecules in this volume will be 8.1⋅10 ¹⁵ mol.

Suppose that the transverse beam size of an IR emitter with selective CO ₂ absorption is 1 × 1 mm, then the beam volume over a length of 1 cm will be 10 ^-2 cm ³ and the number of CO ₂ molecules in this volume will be

, поглощаемых CO₂, будет много больше расчетного числа молекул CO₂ 8,1⋅10¹³ мол.Implementation of the proposed method for creating a new type of microphone is possible only if the number of photons generated by the IR emitter

absorbed by CO ₂ will be much larger than the calculated number of CO ₂ molecules 8.1⋅10 ¹³ mol.

в объеме луча на длине волны λ_погл=2,64÷2,87 мкм для того, чтобы выполнить измерение давления.Determine the required power of the IR emitter at

in the beam volume at a wavelength λ _pogl = 2.64 ÷ 2.87 microns in order to perform a pressure measurement.

The energy of a quantum of light is determined from the expression [9]

where h is Planck's constant; c is the speed of light; λ _sweep in microns, ε _λ in [eV] from [9].

Power P _rad radiator can be calculated using the expression

where e is the electron charge of 1.6⋅10 ^-19 kul.

при исходной величине

.Table 1 shows the calculated values of P _rad depending on the ratio

at the initial value

.

From the table it follows that at a power value of the IR emitter ~ 6⋅10 ^-3 W, pressure measurements up to 160 dB are possible (100 dB corresponds to normal atmospheric pressure). Also, the calculated values of P _rad can serve as a guide when choosing the type of emitter for a microphone.

на молекулах CO₂ установлена экспериментально на Фурье-спектрометре [10] и составляет 0,085 см^-1⋅атм^-1. Селективное поглощение на СO₂ подчиняется действию закона Бугера-Беера [11] видаAbsorption coefficient

on CO ₂ molecules was established experimentally on a Fourier spectrometer [10] and amounts to 0.085 cm ^-1 ⋅atm ^-1 . Selective absorption on CO ₂ is subject to the action of the Bouger-Beer law [11] of the form

where P and P ₀ - respectively, the power of the infrared emitter and its power at a distance L from the emitter.

As an IR emitter, the authors propose the products of the company of St. Petersburg Girikond OJSC - small-sized high-speed semiconductor IR emitters of the IL151A series based on fractally structured nanocomposite films of lead selenide in solid solutions based on it (Pb _1-x Cd _x Se).

In FIG. Figure 1 shows the spectral distribution of the intensity of the emitters depending on the concentration of CdSe, which determine the wavelengths of the emitters. From FIG. 1 it follows that for the proposed microphone, it is possible to recommend a radiator of the IL151A-e type with a concentration of CdSe, providing λ _dop = 2.64 ÷ 2.87 μm.

Table 2 shows the main technical parameters of the IR emitter.

From Tab. 2 follows:

- the maximum radiation power of the emitter IL151A - e is achieved in a pulsed mode of operation (1.2⋅10 ^-3 W);

- the width of the radiation spectrum at λ _pogl is 500 nm, while the width of the absorption spectrum is 20 ÷ 60 nm.

Thus, the authors propose:

1. use the pulse mode of operation of the emitter IL151A - e;

2. The IR receiver installed on inlet interference filter with a bandwidth of 40 nm and λ _abs transmittance of not less than 0.7 (such filters also produces JSC "Girikond").

The emission angle of the IL151A emitters is 30 ° -40 °, therefore, at a small distance, the emitter-receiver (not more than 1 cm), for example 7 mm, with a receiving pad diameter of 2 mm, the disclosure of the radiation beam will be ~ 4 mm in diameter. This means that without focusing the measuring beam at a transmitter-receiver distance of ~ 7 mm, the power of the acting radiation will be reduced by 60%.

The authors propose using photodetectors of the company AIBI LLC (IBSG Co.Ltd), which works in collaboration with the IR Optoelectronics Laboratory of the Physicotechnical Institute named after A.F. Ioffe St. Petersburg. At present, photodiodes of the RD 36-30-TES series [12] will find greater application in the proposed method for the spectral range of 1.5-3.8 μm. The detection ability of such receivers (photodiodes) is (1 ÷ 5) ⋅10 ¹⁰ W ^-1 ⋅Hz ^1/2 ⋅cm. In FIG. 2, the required photodiode is indicated by the letter m among the presented curves of the detecting ability of the series of photodiodes of AIBI LLC.

In FIG. 3 shows a functional diagram of the proposed microphone and a timing diagram of its operation in a pulsed mode. In the presented scheme, two IR emitters 1 were used, the emission axes of which are directed to the center of the radiation detector RD 36 - m2. A filter 3 is placed at the input of the receiver. The output signal of the receiver (photodiode) 2 is amplified by an amplifier 4. Then, the amplified signal is supplied to an indicator-measuring system 5. The pulse operation of both emitters 1 is provided by a generator 6, and the second emitter is launched through a delay line 7. The generator 6 provides a pulsed inclusion of emitters 1 and 2 with a duration of t _u = 100 μs with a duty cycle of 200 μs, and the delay line 7 delays the start of the second emitter, for example, by 150 μs, that is, 1.5 t _u .

The use of two emitters increases the acting power due to a change in the duty cycle, which, when the radiation is switched on for 100 μs, forms a time between them (duty cycle) of 50 μs.

Thus, the power P _Σ acting on the photodetector can be written as

- коэффициент, учитывающий превышение пятна излучения размера чувствительной площадки приемника

при наличии на излучателе фокусирующей линзы.where γ _p = 0.7 - transmittance filter, γ _wells - coefficient taking into account the duty cycle pulse mode (with two emitters γ _borehole ≅0,7),

- coefficient taking into account the excess of the radiation spot size of the sensitive area of the receiver

in the presence of a focusing lens on the emitter.

на расстоянии излучатель-приемник

. Расчетные данные при Р_Σ=1,2⋅10^-3 с учетом перечисленных значений коэффициентов γ отражены в таблице 3.When measuring high pressures, using expressions (3) and (4), we determine the power P _Σ acting on the receiver, taking

at a distance emitter-receiver

. The calculated data at Р _Σ = 1.2⋅10 ^-3 taking into account the listed values of the coefficients γ are shown in table 3.

при условии снабжения излучателей фокусирующими линзами с размещением их фокуса на входной поверхности приемника.When measuring low sound pressures, the need to increase the distance L _{due to others} is obvious. Table 4 shows the calculated values of P _{output signal} for L _from-pr ≅15 cm and

subject to the supply of emitters with focusing lenses with the placement of their focus on the input surface of the receiver.

The calculated values of the output power of the photodetector presented in tables 3 and 4 show reliable detection and measurement of pressures arising in the atmosphere.

It is proposed to take measurements from a conditional quasi-zero signal value corresponding to normal atmospheric pressure, that is, at ΔP = 1.0. If we assign atmospheric pressure equal to 1.0 Pa, the value of the level counted from the threshold of human hearing (10 ^-5 Pa and equal to 100 dB), then when measuring the proposed microphone in the frequency band of sound (see table. 3) high pressure measurement up to ~ 150 dB, and when measuring low pressures - from quasi-zero to 50 dB.

The authors are sure that the range of measurement of sound pressure can be expanded for large levels of values up to 180 dB, and for small levels of values - up to 10 dB due to:

- increasing the power of IR emitters in a pulsed mode up to (20 ÷ 40) ⋅10 ^-3 W;

- the use of amplifiers of the output signal, the gain of which varies according to the inverse logarithmic law (see expression (3).

It should be noted that in the proposed microphone there are no mechanical elements such as membranes and diffusers, the presence of which leads to a decrease in efficiency in analogs due to the presence of reflection of sound pressure from the sensitive input surface and similar reflections already in the capsule of microphones. Therefore, the authors believe that the proposed microphone will have an efficiency due only to the efficiency of IR receivers and IR emitters.

Thus, according to the authors, a method is proposed for creating a new type of microphone, which can be in demand in the problems of measuring pressure in a wide range with subsequent spectral analysis in a wide frequency range.

Also, the proposed microphones can provide a pressure measurement of one of the components of aqueous media, for example, the marine environment, due to the selective absorption of infrared radiation of the desired component. In this case, a microphone with an appropriate selection of the radiation wavelengths of the desired component is placed in waterproof cases with windows of emitters and receivers.

It is possible to use the proposed microphones for measuring pressure both at infrared and at ultrahigh frequencies.

References

1. Sapozhkov M.A. "Electroacoustics". - M.: Communication, 1978

2. Vakhitov Y. Sh. "Theoretical foundations of electroacoustics and electro-acoustic equipment." - M .: Art, 1982

3. Vakhitov Sh. Ya. “Modern microphones. Theory, design. " - St. Petersburg: ed. St. Petersburg GUK and T, 2003

4. Vakhitov Y. Sh., Vakhitov Sh. Ya. "Electromechanical converters and dynamic microphones" - St. Petersburg: ed. St. Petersburg GUK and T, 2004

5. "Acoustics." Directory edited by Sapozhkova M.A. - M .: Radio and communications, 1989.

6. GOST 16123-88 “Microphones. Measurement Methods ”- M .: 1989

7. Audio-technical Corporation (always listening), Japan, Product Catalog 2013-2014

8. USB Bass Meter - sound pressure meter, 2005. Measuring and Android.

9. P. Lynch, A. Nicholas. "Tasks on physical electronics." - M .: Mir, 1975

10. Alexandrov S.E., Gavrilov G.A., Kapralov A.A. et al. “Modeling sensors based on diode optocouplers of the mid-IR range” - M .: “Technical Physics”, Volume 79, Issue 06, 2009

11. Kriksunov L.Z. "Guide to the basics of infrared technology" - M .: Soviet radio, 1978

Claims (3)

A method of creating a microphone based on the selective absorption of infrared (IR) radiation by carbon dioxide of atmospheric air, characterized in that they use an infrared radiation emitter in the wavelength range λ _damp = 2.64 ÷ 2.87 μm with an emitter power that provides a ratio of the number of generated quanta _abs λ light to the number of carbon dioxide molecules

within the scope of the emitting beam on the path of the emitter-receiver in the form of inequality

moreover, the detecting ability of the IR receiver is not worse

and an interference filter is installed at the input of the IR receiver with a bandwidth of the spectrum of 40 nm relative to the average value of the absorption wavelength range and with a transmittance of at least 0.7, while a signal recorded at normal atmospheric pressure is received by the measurement zero of the output signal of the IR receiver and under conditions that pressures above atmospheric are measured at a distance of the emitter-receiver of not more than 1 cm, and pressures below atmospheric are measured at a distance of not less than 10 cm, and the IR emitter They are equipped with an additional focusing lens with focus on the input area of the receiver.

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