RU151224U1 - ACTIVE ECHO-PULSE LOCATOR - Google Patents

Abstract

An active echo-pulse locator containing a control unit connected to the control inputs of the processing and display unit, the generator and receiving paths, consisting of series-connected amplifier units and a frequency filtering unit, the output of which is connected to the signal input of the processing and display unit, acoustic transducer unit, connected to the output of the generator and the input of the amplifier unit, characterized in that it additionally includes a coefficient calculation unit, the control input of which is connected to the control unit, the additional control input is connected to the output of the processing and display unit, and the output is connected to the control input of the frequency filtering unit, the complex frequency response K (jω) of which changes in time in accordance with the expression where B is a constant factor; is the interference spectral density; is the function complex conjugate of the spectral density of the signal, defined by the expression where the spectral density of the initial probe signal radiated into the location medium; is a factor its attenuation of the probe signal during its propagation in the location medium; t is the countdown time from the beginning of the location cycle; β is the absorption coefficient, and c is the acoustic signal propagation velocity in the location medium; the complex reflection coefficient of the probe signal from the location object.

Description

The utility model relates to location-based devices designed to detect objects located in various environments. The inventive locator can be used in sonar systems for various purposes - echo sounders, sonars, profilographs, as well as in ultrasonic flaw detectors, ultrasound medical devices, level gauges and other active location systems. The preferred area of use is sonar.

Active echolocation systems are known, the description of which is given in numerous literature [1-7] and patent [8-10] sources. As a rule, they contain an acoustic transducer block connected to the output of the generator and input of the receiving paths, a control unit connected to the control inputs of the processing and display unit, generator and receiving paths, and the output of the receiving path connected to the signal input of the processing and display unit. The receiving paths of these location systems contain, in various combinations, series-connected amplifiers and frequency selective filters. The processing and display unit in various combinations may contain blocks with a time-varying transmission coefficient, a detector, threshold elements, an analog-to-digital converter, and other auxiliary blocks.

The work of these location systems is as follows. In the control unit, at specified time intervals T, clock signals are generated that determine the beginning of duty cycles for the remaining locator blocks, as well as other signals that determine the operation modes of these blocks [1-7]. In the generator channel, a radio-pulse sounding signal is generated with a duration of yew with a filling frequency f, which arrives at the block of acoustic transducers emitting an acoustic signal into the location medium, which propagates in the location medium and is reflected from objects located in the location channel. The reflected acoustic echo signals are received by the elements of the block of acoustic transducers, and the corresponding electrical signals are fed to the input of the receiving path. The values of the parameters T, τ, and f depend on each specific and case on the location conditions and are calculated according to well-known expressions [1-7].

In the receiving path, the echo signals are processed according to the specified algorithms - this is, as a rule, amplification and frequency filtering, and then they are sent to the processing and display unit, where they are detected, processed in the “Cutoff”, “VARU” - “VCR” blocks, digitization and others [1-7]. Then, the parameters of the detected objects are determined (distances to them, sizes, and others), followed by an indication of the location results.

All of these location systems use narrow-band probing signals of a simple form. Therefore, filtering is carried out in their receiving paths, which is realized by conventional active or passive narrow-band frequency-selective systems with unchanged parameters.

These locators have limited performance due to the low signal to noise ratio at the output of their receiving paths. This is due to the fact that when acoustic signals are reflected from objects for which there is a change in the distance between the locator carrier and the object itself, the frequency of the echo signals changes by the value of the Doppler shift. Therefore, the passband of the frequency filters of the receiving paths of the locators is chosen more by the magnitude of the Doppler shift, which increases the noise level at the output of the receiving path. As a result of this, the location range is reduced, and such locators cannot detect small objects at the maximum location ranges. Locators with narrowband probing signals allow obtaining limited information about detected objects, usually their removal in the direction of location and target strength.

In patents [11-15], hydroacoustic location systems are proposed in which a receiving path is used to receive narrow-band echo signals whose frequency changes as a result of the Doppler effect, in which frequency filtering is implemented by a unit consisting of several circuits connected in parallel, each of which contains a series-connected narrow-band filter, a threshold element, and a block allowing the passage of only those frequency components of the signal whose levels exceed the threshold level determined by the level The noise component for the same frequency range. The use of several parallel chains of frequency filtering increases the signal-to-noise ratio at the output of the receiving path, however, it does not allow obtaining additional information about the detected objects.

A further increase in the range of location and obtaining additional information about the objects of location became possible when using in the location systems broadband probing signals with a complex structure, frequency-modulated, phase-shifted and others [16-18]. Subsequent correlation processing of such signals or their optimal filtering in the receiving path allows one to obtain a higher signal-to-noise ratio compared to using narrow-band signals, increase the range of location, and obtain additional information about the detected objects [19-20]. However, in these systems, the processing of echo signals does not take into account the change in the spectra of sounding signals that occurs when they propagate in real-world location media having a frequency dependence of the attenuation coefficient. Changing the spectra of the probing signals, and after their reflection from the objects - the echo signals violates the optimality conditions for processing the echo signals in the receiving paths of such locators. This does not allow to obtain an achievable value of increasing the signal-to-noise ratio at the output of the receiving path of the locator, which limits its operational capabilities.

In [19], it was shown that in the case of frequency filtering of the additive sum of the signal and noise in order to obtain the maximum signal / noise ratio at the output of the linear filter for time t0, its complex frequency response K (jω) should correspond to the expression

where B is a constant factor, S * (jω) is the complex complex conjugate function of the signal spectral density S (jω), S _p (jω) is the noise spectral density. If the probe signal emitted into the location medium has an initial spectral density S ₁ (jω), then when it propagates in the location medium and when reflected from the object, its spectrum will change in accordance with the expression

where the factor A (jω) characterizes the complex reflection coefficient of the probe signal from the object, and the factor exp (-2βr) is the attenuation of the level of the probe signal as a result of absorption during propagation in the location medium, β is the absorption coefficient, and r is the distance to the detected object.

For the case of hydroacoustics, the absorption coefficient β for the frequency range of acoustic signals f = (5-100) kHz can be determined using the empirical formula of Shea and Helly [1 p. 71]

where the frequency of the signal f is expressed in kHz.

In accordance with expressions (2-3), it follows that, due to the dependence of the attenuation coefficient β on frequency, the spectrum of the echo signal will depend on the distance r to the detected located object. With increasing distance r due to greater absorption of high-frequency components of the signal spectrum, its envelope will shift to the low-frequency region. In accordance with expression (1), for optimal reception of echo signals, the frequency response of the linear filter K (jω) should also have a different form for objects located at different distances r.

This applies to all hydroacoustic location systems, including specialized ones, such as profilographs, echo-meters, and other systems in which the sounding signal propagates not only in the aquatic environment, but also in other environments - bottom sediments or in the ice mass. So in [21] graphs are given (Fig. 1) for changes in the spectrum of the LFM-probe signal during its propagation in the bottom sediment, which show a significant distortion of the spectrum of the probe signal with increasing distance r. The graphs show that when receiving echoes transmitted in sedimentary soils, a distance of up to 3-5 m should have a filter bandwidth of about 10 kHz at a filter center frequency of about 10 kHz, and if a distance of more than 10 m is passed, the filter’s central frequency will shift to 5 kHz, and its bandwidth is reduced by more than half. Thus, in this case, to obtain the maximum signal-to-noise ratio at the output path of the location system, it is necessary to change in time the parameters of the linear filter installed in the receive path of the profilograph. This conclusion applies to other location systems using broadband signals.

The purpose of this utility model is to expand the operational capabilities of an active echo-pulse locator.

The technical result consists in the implementation in the receiving path of the locator of the optimal filtering condition for broadband echo signals from all objects, regardless of their removal, which allows the maximum value of the signal-to-noise ratio to be obtained at the output of the receiving path.

The technical result is achieved by the fact that in the active echo-pulse locator according to the patent [11], which contains a control unit connected to the control inputs of the processing and indication unit, generator and receiving paths, consisting of series-connected amplifier unit and frequency filtering unit, the output of which is connected to the signal input of the processing and display unit, the unit of acoustic transducers connected to the output of the generator and the input of the amplifier unit, an additional unit for calculating the coefficients is introduced, I control whose input is connected to the output of the control unit, the additional control input is connected to the output of the processing and display unit, and the output is connected to the control input of the frequency filtering unit, the complex frequency response of which K (jω) changes in time in accordance with the expression

K (jω) = Bexp (-jωt) S * (jω) / S _p (jω),

where B is a constant factor, S _p (jω) is the interference spectral density, S * (jω) is the complex conjugate function of the spectral density S (jω) of the signal, defined by the expression

,

,

where S ₁ (jω) is the spectral density of the initial probe signal radiated into the location medium, exp (-2βct) is the factor characterizing the attenuation of the probe signal during its propagation in the location environment, t is the reference time from the beginning of the location cycle, β is the absorption coefficient, c is the propagation velocity of the acoustic signal in the location medium, A (jω) is the complex reflection coefficient of the probe signal from the location object.

The utility model is illustrated by drawings. In FIG. 1 shows graphs for the envelope of the LFM spectrum of the probe signal during its propagation in bottom sediments, FIG. 2 shows a structural diagram of the inventive locator, and in FIG. 3 is a structural diagram of one embodiment of a frequency filtering unit.

The active echo-pulse locator contains a control unit 1 connected to the control inputs of the processing and display unit 2, the coefficient calculation unit 3, the generator path 4 and the amplification unit 5 entering the receiving path 7 with the frequency filtering unit 6, the acoustic transducer unit 8 connected to the generator output path 4 and the input of the amplification unit 5, connected in series with the frequency filtering unit 6, the processing and indication unit 2; the additional control input of the coefficient calculation unit 3 is connected to the output of the processing and display unit 2, and the output of the coefficient calculation unit 3 is connected to the control input of the frequency filtering unit 6, whose complex frequency response K (jω) changes in time in accordance with the expression

K (jω) = Bexp (-jωt) S * (jω) / S _p (jω),

where B is a constant factor, S _p (jω) is the interference spectral density, S * (jω) is the complex conjugate function of the spectral density S (jω) of the signal, defined by the expression

,

,

where S ₁ (jω) is the spectral density of the probe signal radiated into the location medium, exp (-2βct) is the factor characterizing the attenuation of the probe signal during its propagation in the location environment, β is the absorption coefficient, t is the reference time from the start of the location cycles, c is the propagation velocity of the acoustic signal in the location medium, A (jω) is the complex reflection coefficient of the probe signal of the location object.

The operation of the echo-pulse locator is as follows.

In the control unit 1, at predetermined time intervals T, clock signals are generated that determine the beginning of duty cycles for the remaining locator blocks. In the generator path 4, a broadband probing signal of duration τ is generated, which arrives at the block of acoustic transducers 8 that emit an acoustic signal into the location medium, which propagates in the location medium and is reflected from objects located in the location channel. The reflected acoustic echo signals are received by the elements of the acoustic transducer unit 8, and the corresponding electrical signals are fed to the input of the amplification unit, and then to the input of the frequency filtering unit 6 of the receiving path 7. The values of the parameters T, τ, the spectral and temporal parameters of the probe signal depend on the specific conditions of location and are calculated according to well-known expressions [1-7].

In the receiving path 7, the signals are processed according to the given algorithms - this is, as a rule, amplification and frequency filtering, and then they are sent to the processing and display unit, where detection, processing in the “Cut-off” and “VARU” - “VCR” blocks, conversion to digital form and others [1-7]. After that, the determination of the parameters of the detected objects (distance to them, sizes and others) is carried out with the subsequent indication of the location results.

To obtain the maximum value of the signal-to-noise ratio in block 6, linear frequency filtering of the additive sum of the signal and interference is performed. The control signals received from the coefficient calculation unit 3 to the additional input of the frequency filtering unit 6 change in time its complex frequency response K (jω) in accordance with the condition

where B is a constant factor, S _p (jω) is the interference spectral density, S * (jω) is the complex conjugate function of the spectral density S (jω) of the signal, which is

where S ₁ (jω) is the spectral density of the probe signal radiated into the location medium, A (jω) is the complex reflection coefficient of the probe signal from the location object, the factor exp (-2βct) characterizes the attenuation of the probe signal as a result of absorption during its propagation in the location environment , t is the reference time from the beginning of the location cycle, β is the absorption coefficient, and c is the propagation velocity of the acoustic signal in the location environment.

The parameters of the coefficient A (jω) for various types of objects from which the probe signal can be reflected for the considered locator, as well as the values of the remaining parameters S ₁ (jω), β, c, f are stored in block 3 and are used to calculate the signals received by the control the input of block 6 and the complex transfer coefficient changing it in accordance with expressions (4) - (5). Moreover, the coefficients β, c can be given and used sequentially for several different locations, for example, for a profilograph — these can be water and various sedimentary rocks. The choice of certain values of the coefficients is determined by the commands received at the additional control input of block 3 from the processing and display unit 2.

There are various options for the structural construction of block 2, where analog signals can be processed (detection, conversion in the “Cutoff”, “VARU” - “VCR” blocks), and their conversion to digital form with subsequent software processing according to specified algorithms.

Various construction options for the frequency filtering unit 6 are also possible. FIG. 3 shows one of the options for constructing block 6. It contains n parallel-connected circuits, each of which contains a series-connected narrow-band filter 10, an amplifier with an adjustable gain 11 and a phase shifter 12. The inputs of all n filters are connected to the output of the amplification block 5, the outputs of n phase shifters connected to n inputs of the adder 13, the output of which is connected to the input of the processing and display unit 2. The control inputs of n amplifiers and n phase shifters are connected to the outputs of the coefficient calculation unit 3.

The signals from the output of the amplification unit 5 are fed to the inputs of n narrow-band filters 10, which pass the individual frequency components of the signals. The number of filters 10 and their passband are determined by the width of the spectrum of the processed echo signals. From the outputs of the filters, these frequency components are amplified by amplifiers 11 and fed to the inputs of the phase shifters 12. The transmission coefficients of the amplifiers 11 and the phase changes of the frequency components of the signals in the phase shifters 12 are set by supplying control signals from block 3 to their control inputs so that the conditions of the expressions are satisfied (4 ) and (5) for individual frequency components of the processed signals. The frequency components of the signals are then fed to the inputs of the adder 13, at the output of which a signal is formed with a maximum signal-to-noise ratio, then fed to the input of block 2.

Simulation of the locator with the proposed frequency filtering unit, performed for various location conditions, confirmed the operability of its frequency filtering unit when processing real wideband echo signals obtained when using location systems for various purposes. All blocks of the proposed echo-pulse locator are implemented using common analog and digital elements of varying degrees of integration.

Information sources

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Claims (1)

An active echo-pulse locator containing a control unit connected to the control inputs of the processing and display unit, the generator and receiving paths, consisting of series-connected amplifier units and a frequency filtering unit, the output of which is connected to the signal input of the processing and display unit, acoustic transducer unit, connected to the output of the generator and the input of the amplifier unit, characterized in that it additionally includes a coefficient calculation unit, the control input of which is connected to swing control unit, third control input connected to the output of the processing and display unit, and an output connected to the control input of the frequency filtering unit, complex frequency response K (jω) which varies in time in accordance with the expression

where B is a constant factor;

- spectral density of interference;

is a complex conjugate spectral density function

signal defined by

Where

- spectral density of the initial probe signal radiated into the location medium;

- a factor characterizing the attenuation of the probe signal during its propagation in the location medium; t is the countdown time from the beginning of the location cycle; β is the absorption coefficient, c is the propagation velocity of the acoustic signal in the location medium;

complex reflection coefficient of the probe signal from the location object.

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