SU1642596A1 - Microphone - Google Patents

Abstract

The invention relates to communication technology, electroacoustics. The purpose of the invention is to improve the accuracy, which is provided by expanding the low-frequency range of operation, and increasing the overall sensitivity of the eddy current (electrodynamic) microphone by reducing the damping effects. The microphone contains a housing 1, a cover 2, an elastic membrane 3 with an insulated non-ferromagnetic conductive disk 4, an auto-oscillator 8. A flat helix-shaped inductance coil 7 connected to an auto-oscillator 8 mounted on a dielectric plate 5. New in the device is that in an elastic membrane 3, a conductive, non-ferromagnetic and electrically insulated disk is installed on the surface of its central part introduced into the high-frequency field of a flat spiral-shaped inductance coil 7, with the gap size between the conductive disk 4 and the plane of the spiral-shaped inductance coil 7 is determined by the impedance of the oscillating circuit, and the dielectric plate 5 is made in the form of a gas-permeable grid with a central hole 6 equal to the diameter of the inner turn of the flat spiral-shaped inductance coil 7, 1 mud. sl S th rd th Os

Description

The invention relates to communication technology, electro-acoustics, and can also be used in measurement technology for recording low and infra-low frequency sound vibrations.

The purpose of the invention is to improve accuracy by expanding the low frequency range of operation and increasing the overall sensitivity of the microphone by reducing the damping effects on the membrane, eliminating parasitic electrical connections between the membrane and the flat spiral coil inductance, and determining the optimum size ratios of the microphone elements,

The drawing shows a microphone, a slit.

The microphone includes a housing 1, a protective cover 2, an elastic membrane 3 with an electrically insulated conductive center (disk) 4, a gas-permeable dielectric plate 5 with a central hole 6, a flat spiral inductor 7 and an auto-oscillator 8.

The device works as follows.

Acoustic pressure P acts on an elastic membrane 3 with an insulated conductive disk 4 through a grid cover 2. The power supply and removal of the signal is carried out through the outputs of the oscillator 8. Connected to the oscillator 8, a flat spiral inductor 7, having its own inductance LL, and the capacitance CL form oscillating circuit LL € L, having an impedance Z °. The introduction of the conductive electrically isolated center 4 of the membrane 3 into the surrounding inductance 7 of the high-frequency field reduces its inductance C. and the impedance Z ° to the residual values LL - LOCT;

Z ° - 7OST

which leads to an increase in the oscillation frequency of the oscillator 8 and a decrease in the amplitude of the generated high-frequency voltage.

Thus, the acoustic pressure perceived by an elastic membrane with a conductive electrical insulated center 4 is converted into a change in the frequency and amplitude of oscillations of the oscillator 8. To reduce the damping and expansion of the frequency range of the microphone, the dielectric plate 5 and the flat inductance coil 7 mounted on it are in the form of a gas-permeable grid with a central hole 6, the diameter of which is equal to the diameter of the inner turn of the spiral inductance 7. At the same time, the diameter is in external coil DBH flat spiral

the inductor determines the overall dimensions of the conductive electrically isolated non-ferromagnetic disk 4 on the surface of the elastic membrane 3, and the thickness of the disk 4 b is determined by the ratio

l (s-5) and

where d is the depth of penetration of the high-frequency current into the disk body:

five

0

five

0

five

0

five

2

Soo / i / o

where (d is the frequency of the current of the oscillator in a flat coil, Hz;

i - relative magnetic permeability of the disk material;

y is the conductivity of the disk material;

jUQ is the magnetic constant, equal in the SI 4n GN / m system.

With an increase in the diameter of the central hole 6 larger than the diameter of the inner coil of the DDH inductance 7, its mechanical rigidity decreases, and with a decrease in the diameter, the damping effect on the membrane increases.

When the conductive area 4 of membrane 3 is enlarged, the parasitic capacitance Cm and microphone sensitivity decrease, and the pad diameter decreases to a value smaller than the outer coil diameter DBH of the spiral inductor, reducing the screen effect, as well as the microphone sensitivity. Selection of the thickness b of a non-ferromagnetic metal of a conductive isolated site within the ratio b (3-5) d of the depth of penetration of the high-frequency current

t-provides the minimum mass of the membrane at the maximum sensitivity of the microphone. The size of the gap h between the conductive area of the membrane and the plane of the spiral coil

The inductance is determined by the value of ZOCT — the residual impedance of the oscillator circuit of the oscillator, which is defined as the ratio 2 ° Cte (0i2-0.5) Z °.

where Z ° is the initial impedance of the oscillating circuit with a spiral-shaped flat inductance coil.

When reducing the gap h to the value at which the residual impedance Htw of the oscillating circuit ZOCT becomes

less than 0.22 °, the generator operation becomes unstable and the generation can be broken, and as the gap h increases, corresponding to the residual impedance of the oscillating circuit, above 0.5Z °, the sensitivity of the microphone decreases.

With a fluoroplast membrane of 5 µm thickness with a diameter of 16 mm, a diameter of the conductive part equal to the diameter of the outer coil coil Lvn 10 mm and a plate opening diameter equal to the diameter of the inner coil coil 0Vn 2 mm, generator frequency 24 MHz and voltage A supply of 30 V was obtained at a pressure sensitivity of 240 MV / bar, which is 5–8 times higher than the sensitivity of known industrial microphones at a frequency of 5 Hz.

Claims (1)

Invention Formula A microphone comprising a housing with a protective cover, a dielectric plate mounted in the housing, a flat spiral inductor placed on the side of the dielectric plate facing the protective cover and connected to an oscillator, and an elastic a membrane mounted in the housing parallel to the dielectric plate with a gap relative to the inductance coil, characterized in that, in order to improve accuracy, a disk made of electrically conductive non-ferromagnetic material is inserted into it, fixed on the side of the membrane facing the spiral coil and electrically isolated from the membrane; through holes are made in the center and on the periphery of the dielectric plate, and the diameter of the central hole is equal to the diameter of the inner turn of the spiral coil inductively minute, and the diameter D and the thickness b satisfy the condition of the disc D (1.0-1.1) -DBH. where DBH is the diameter of the outer coil of the spiral coil; b (3 -5), where w - the frequency of the current of the oscillator; p is the relative magnetic permeability of the disk material; y is the conductivity of the disk material; / Ae magnetic constant.