阅读说明：本技术 激光致声发射相控阵聚焦系统 (Laser-induced acoustic emission phased array focusing system ) 是由 宗思光 刘涛 梁善永 曹静 黄鑫 于 2020-12-01 设计创作，主要内容包括：本发明提供一种激光致声发射相控阵聚焦系统,包括发射时延模块和发射相控阵；所述发射相控阵包括至少两个激光声相控阵单元,所述激光声相控阵单元包括光纤激光器和激光声换能器,所述激发延时器与光纤激光器通信连接；所述发射时延模块,用于将各路控制信号在激光发射控制模块的控制下,分别延时预设时延后送至光纤激光器；所述光纤激光器,用于根据收到的控制信号产生激光；所述激光声换能器,用于根据光纤激光器产生的激光产生激光声信号。本发明可提高激光声的声源级以及声利用率；同时通过改变光纤激光器和相控阵的参数,可提高激光声的距离分辨率和角度分辨率。(The invention provides a laser-induced emission phased array focusing system, which comprises an emission delay module and an emission phased array, wherein the emission delay module is used for delaying the emission of a laser; the transmitting phased array comprises at least two laser acoustic phased array units, each laser acoustic phased array unit comprises a fiber laser and a laser acoustic transducer, and the excitation delayer is in communication connection with the fiber laser; the transmitting time delay module is used for respectively delaying the preset time delay of each path of control signal under the control of the laser transmitting control module and then transmitting the control signal to the optical fiber laser; the optical fiber laser is used for generating laser according to the received control signal; the laser acoustic transducer is used for generating laser acoustic signals according to laser generated by the fiber laser. The invention can improve the sound source level and the sound utilization rate of the laser sound; meanwhile, the distance resolution and the angle resolution of the laser can be improved by changing the parameters of the fiber laser and the phased array.)

1. A laser-induced acoustic emission phased array focusing system is characterized in that: the system comprises a transmitting time delay module and a transmitting phased array; the transmitting phased array comprises at least two laser acoustic phased array units, each laser acoustic phased array unit comprises a fiber laser and a laser acoustic transducer, and the excitation delayer is in communication connection with the fiber laser;

the transmitting time delay module is used for respectively delaying the preset time delay of each path of control signal under the control of the laser transmitting control module and then transmitting the control signal to the optical fiber laser;

the optical fiber laser is used for generating laser according to the received control signal;

the laser acoustic transducer is used for generating laser acoustic signals according to laser generated by the fiber laser.

2. The laser-induced acoustic emission phased array focusing system of claim 1, wherein: laser emitted by the fiber laser expands and focuses laser beams through a diffusion focusing lens group of the laser acoustic transducer, and breaks down a liquid medium to generate laser acoustic signals.

3. The laser-induced acoustic emission phased array focusing system of claim 1, wherein: the transmitting phased array is formed by arranging at least two laser acoustic phased array units according to a certain shape and size, the laser acoustic phased array units are excited and triggered at different moments by controlling the optical fiber lasers in the laser acoustic phased array units according to a set time delay sequence, laser acoustic signals are generated by excitation of the laser acoustic phased array units, laser acoustic coherent sub-beams at different phases are overlapped and interfered in space, and the generated synthesized beam has the effect of deflection or focusing.

4. The laser-induced acoustic emission phased array focusing system of claim 1, wherein: the laser acoustic transducer adopts rectangular piston type array elements.

Technical Field

The invention relates to the field of underwater target detection, in particular to a laser-induced acoustic emission phased array focusing system.

Background

In the preparation of military combat for ocean development and utilization and win-win informatization war, the capabilities of detection, confrontation and the like of the traditional sonar sound source meet severe challenges in a plurality of fields. The traditional sonar has a narrow sound frequency band, and if a wide frequency band signal needs to be generated, a plurality of sonars with different structure sizes are required to be combined for use, so that the structure cost is complex. In the face of the fields of small target detection and identification of the frogman, underwater acoustic countermeasure of ships, submarine topography and landform surveying and mapping and the like, signals of wide frequency bands are sometimes needed, and therefore the design and manufacture of a novel sonar transducer is the key place for solving the problems.

The inventor of the present application has found through research in the process of implementing the present invention that: when laser irradiates a liquid medium, when the laser energy and the power density of an acting area exceed an energy breakdown threshold and a power breakdown threshold required by a breakdown medium at the same time, optical breakdown is caused to generate an underwater laser induced acoustic signal. The laser sound as a novel sonar sound source has the advantages of wide frequency spectrum, high sound source level and high distance resolution of an explosion sound source, and has the advantage of repeatability of a traditional sonar transducer. Specifically, the method has the following advantages in five aspects: firstly, the laser audio frequency spectrum is wide, and the distance resolution is high; secondly, the master frequency is adjustable, the noise interference resistance is strong, and the sonar detection method is suitable for sonars with various different purposes; thirdly, obtaining laser acoustic signals with good repeatability by using repeatable laser pulses and transparent liquid with stable physical properties; fourthly, the phase of the laser light is stable; fifthly, in the field of underwater communication, the laser acoustic signal can be modulated by modulating the laser parameters, and the modulated laser acoustic signal is used for realizing the confidential and rapid underwater communication.

Disclosure of Invention

The invention aims to provide a laser-induced acoustic emission phased array focusing system, which has the characteristics of controlled deflection and focusing of an acoustic beam and can improve the acoustic source level and the acoustic utilization rate of laser and sound; meanwhile, the distance resolution and the angle resolution of the laser can be improved by changing the parameters of the fiber laser and the phased array.

A laser-induced acoustic emission phased array focusing system comprises an emission time delay module and an emission phased array; the transmitting phased array comprises at least two laser acoustic phased array units, each laser acoustic phased array unit comprises a fiber laser and a laser acoustic transducer, and the excitation delayer is in communication connection with the fiber laser;

the transmitting time delay module is used for respectively delaying the preset time delay of each path of control signal under the control of the laser transmitting control module and then transmitting the control signal to the optical fiber laser;

the optical fiber laser is used for generating laser according to the received control signal;

the laser acoustic transducer is used for generating laser acoustic signals according to laser generated by the fiber laser.

Furthermore, laser emitted by the fiber laser expands and focuses laser beams through a diffusion focusing lens group of the laser acoustic transducer, and breaks down a liquid medium to generate laser optical signals.

Furthermore, the transmitting phased array is formed by arranging at least two laser acoustic phased array units according to a certain shape and size, the laser acoustic phased array units are excited and triggered at different moments by controlling the optical fiber lasers in the laser acoustic phased array units according to a set time delay sequence, laser acoustic signals are generated by excitation of the laser acoustic phased array units, laser acoustic coherent sub-beams at different phases are overlapped and interfered in space, and the generated synthesized beam has the effect of deflection or focusing.

Furthermore, rectangular piston type array elements are adopted in the laser acoustic transducer.

The invention has the following beneficial effects:

1. achieving directivity control of laser induced acoustic signals

Triggering time sequence control by using a transmitting signal of an optical fiber laser to control the excitation time sequences of different laser sound source arrays, and forming directivity control of a laser direct signal by using an underwater sound signal synthesis technology;

2. realizing the enhancement effect of laser induced acoustic signals

By using an underwater acoustic phased array synthesis technology, laser acoustic signals are subjected to spatial interference synthesis, and the sound source level of the laser acoustic signals in a specified direction is improved;

3. the laser-induced acoustic phased array system has high maneuverability

The laser-induced acoustic phased array system has low power consumption, small volume, light weight and high reliability by using the optical fiber laser, can be conveniently installed on an underwater platform, and improves the communication maneuverability of each unit;

4. strong universality and usability

And aiming at different underwater platforms, the type and design of the applicable laser are selected, so that the effective adaptation among different underwater platforms is met.

Drawings

FIG. 1 is a schematic diagram of the structure of one embodiment of a laser-induced acoustic emission phased array focusing system of the present invention;

FIG. 2 is a schematic diagram of the arrangement of laser acoustic phased array elements in a transmit phased array according to the present invention;

FIG. 3(a) is a schematic diagram of the transmitting phased array transmitting deflection of the present invention, and FIG. 3(b) is a schematic diagram of the transmitting phased array focusing of the present invention;

FIG. 4 is a schematic diagram of a matrix wavefront coordinate system of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.

Referring to fig. 1, a laser-induced acoustic emission phased array focusing system according to an embodiment of the present invention includes a transmission delay module and a transmission phased array; the transmitting phased array comprises at least two laser and acoustic wave phased array units, each laser and acoustic wave phased array unit comprises an optical fiber laser and a laser acoustic transducer, and the excitation delayer is in communication connection with the optical fiber laser.

The transmitting time delay module is used for respectively delaying the preset time delay of each path of control signal under the control of the laser transmitting control module and then transmitting the control signal to the optical fiber laser;

the optical fiber laser is used for generating laser according to the received control signal;

the laser acoustic transducer is used for generating laser acoustic signals according to laser generated by the fiber laser, and specifically, laser emitted by the fiber laser firstly widens and then focuses laser beams through a diffusion focusing lens group of the laser acoustic transducer, and breaks down a liquid medium to generate the laser acoustic signals.

The transmitting phased array structure is shown in fig. 2 and is formed by arranging at least two laser acoustic phased array units according to a certain shape and size, by controlling the optical fiber laser in the laser acoustic phased array units and exciting and triggering according to a set time delay sequence, each transmitting array element (namely the laser acoustic phased array unit) is excited at different time to generate laser acoustic signals, laser acoustic coherent sub-beams with different phases are superposed and interfered in space, and the generated synthetic beam has the effect of deflecting or focusing, as shown in fig. 3(a) and fig. 3 (b).

The multi-channel laser acoustic phased array unit is arranged through the laser emission control module, and the working time sequence of each laser-induced emission array element is controlled by the aid of the excitation delayers to synthesize laser acoustic signals with directivity.

The principle of laser optical signal emission focusing is as follows:

a single vibration source arranged in a uniform medium, a radiation sound field can be generally used as a velocity potential functionTo solve for:

in the formulaIs the spatial position vector of the field point. Assuming that the vibration amplitude and phase of each point on the surface of a piston array element are the same, then any excitation v (t) is given to the field pointThe resulting velocity potential function can be obtained by:

where v (t) is the excitation function and represents the convolution operator. Wherein the integration:

called space impulse response, which represents the field point after the transducer receives unit impulse signal delta (t) excitationThe response can be regarded as the impulse response of a linear system at a point in space.

With a spatial impulse response, the radiated acoustic field can be given by:

the above convolution model can calculate the radiated acoustic field of the transducer under arbitrary excitation. Because the model adopts the theory of a linear system, the radiation sound field of the transducer with any surface vibration velocity amplitude distribution can be described. Therefore, the radiation sound field model based on the space impulse response can describe the sound field distribution of the transducer or the transducer array with any shape, any size and any surface vibration velocity amplitude distribution when being excited arbitrarily, and can describe the sound field distribution of continuous waves.

Assuming that a piston transducer with any shape and size is placed in a uniform medium and is excited by a waveform with a single frequency, so that the vibration amplitude and the phase of each point on the surface of the transducer are the same, namely a sound source vibrates in v (t), and a radiation sound field model can obtain a continuous radiation sound field as follows:

in the formula: rho₀Is the density of the medium, c₀Is the acoustic velocity, k is the wavenumber, u₀For the vibration amplitude, R is the bin-to-field point distance, where e^j(ωt-α)The representation is a function of time.

In laser acoustic transducers, generally rectangular piston-type array elements are used, and the radiation sound field of the array elements can be obtained by the above formula. The rectangular piston array element is divided into a series of rectangular units which are large enough relative to a point source but small enough as shown in fig. 4, and after the division, the sound pressure amplitude distribution of the rectangular array element is the sum of the sound pressure amplitude superposition of each unit:

wherein N is the number of rectangular units, u₀The vibration amplitude of the excitation function is the same as that of all rectangular array elements, and A is the area of the rectangular unit.

In fig. 4, it is assumed that the center coordinate of the nth rectangular cell is (x)_n,y_n) Define one to (x)_n,y_n) New coordinate system x as origin₀，y₀Thus, the sound pressure amplitude of a rectangular array element can be expressed as:

in the formulaA suitable approximation needs to be made. The smaller Δ w and Δ h are chosen so that the rectangular elements are at a much greater distance from the field point than the size of the elements, the field point being located in the far field region of the rectangular elements.

For a single tiny rectangular transducer, if its length a and width b are already small enough, the radiated acoustic field produced by the transducer, under far field conditions, is:

wherein R is the distance from the field point to the center of a single vibration source, theta₁Is the angle between R and the plane yoz, theta₁Is the angle of R from plane xoz.

The radiation sound field distribution of the single rectangular array element transducer is obtained through calculation, and the radiation sound field of the linear array transducer consisting of the rectangular array elements can be obtained by superposing the radiation sound fields generated by all array elements in the array.

The above formula is the distribution of the synthetic radiation sound field generated when all array elements of the acoustic array vibrate in the same frequency, phase and amplitude. The directivity refers to the property of ultrasonic directional emission and propagation, reflects the ability of the ultrasonic transducer to concentrate beams in one direction, and is an important property of the ultrasonic transducer to radiate a sound field. The directivity function substantially represents the ratio of the sound pressure at a point on an arc at a distance r from the sound source in the sound field to the maximum sound pressure, reflecting the quality of beam propagation.

The invention discloses a laser-induced acoustic emission phased array focusing system, which is based on the point explosion sound source effect generated by laser focusing breakdown, utilizes the acoustic reflection characteristic of a paraboloid of revolution to adjust and control a laser sound beam to generate a narrow beam, completes high-speed scanning under the condition that a single laser-induced acoustic source is not moved by a phased array technology, has the characteristics of controlled deflection and focusing of the sound beam, and improves the sound source level and the sound utilization rate of laser sound; meanwhile, the distance resolution and the angle resolution of the laser can be improved by changing the parameters of the fiber laser and the phased array.

The above description is only an embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Those skilled in the art will appreciate that the invention may be practiced without these specific details.