Optoacoustic effect solid-state ice moving sound source for air-underwater communication

Abstract

This invention relates to the field of marine wireless communication technology, and more particularly to a photoacoustic effect solid ice mobile sound source for air-to-underwater communication. It utilizes a combination of laser communication and underwater acoustic communication technologies to construct an air-to-underwater signal transmission mechanism across an ice-covered medium. This is achieved through the photoacoustic effect of the solid ice layer covering the sea surface. Specifically, an airborne laser is incident on the ice layer in an atmospheric space channel. The interaction between the laser pulse and the solid ice generates a laser ultrasonic source, which rapidly penetrates the ice layer and transmits to the communication target in the water below. Finally, an optical / acoustic communication link is established across the ice layer to achieve information transmission from air to underwater. The purpose of this invention is to address the problem that in extremely cold and polar regions where the sea surface is covered by ice, traditional single radio waves, light waves, and sound waves cannot penetrate the ice layer using non-contact methods, making air-to-underwater communication difficult.

Description

Technical Field

[0001] This invention relates to the field of marine wireless communication technology, and in particular to a photoacoustic effect solid ice moving sound source for air-to-underwater communication. Background Technology

[0002] Trans-oceanic communication relies primarily on both the atmosphere and the water. Due to the complexity of the marine environment, communication depends mainly on radio waves, light waves, and sound waves. With the continuous advancement of marine exploration, integrated air-space-land-sea communication has become an inevitable trend in modern communication development. The anticipated 6G network will provide seamless global connectivity from space to underwater. However, air-sea trans-medium communication remains a critical challenge, especially in extremely cold regions and polar areas covered by ice and snow year-round. Ice severely hinders information transmission between the air and sea, making it impossible to establish communication independently using the aforementioned three technologies in such environments. Currently, communication in ice-covered waters often involves icebreaking and deploying active relay communication equipment on ships or buoys submerged in water to establish communication links above and below the surface. However, this method is difficult to deploy, costly, lacks concealment and flexibility, and is unsuitable for rapid response in emergency situations such as search and rescue operations. Summary of the Invention

[0003] The purpose of this invention is to provide a photoacoustic effect solid ice mobile sound source for air-to-underwater communication, aiming to solve the technical problem of difficulty in establishing communication links between atmospheric and underwater space when the sea surface is blocked by ice in extremely cold and polar regions.

[0004] To achieve the above objectives, the present invention provides a photoacoustic effect solid ice mobile sound source for air-to-underwater communication, comprising an airborne laser and a solid ice medium covering the sea surface, wherein the airborne laser is a pulsed laser carrying information encoding and modulation, which is incident on the solid ice medium through the atmospheric space to form a laser sound source;

[0005] The laser sound source consists of narrow pulse-induced waveforms, including longitudinal waves, transverse waves, and surface waves. Longitudinal waves can propagate in solids, liquids, and gases, and the particle vibration direction of the longitudinal wave is parallel to the wave propagation direction. Transverse waves can only propagate in solids, and the particle vibration direction is perpendicular to the wave propagation direction. Surface waves only propagate on the surface of a semi-infinite solid medium with a thickness much greater than its wavelength, and the particles vibrate and propagate along an elliptical trajectory.

[0006] The pulse width of the coded modulated laser ranges from nanoseconds to picoseconds, and the laser acoustic frequency can vary from Hz to GHz.

[0007] The laser sound source is an elastic sound wave that expands and contracts, and the size of the laser sound source region is determined by the crystal structure of the solid ice medium and the output energy of the pulsed laser.

[0008] The laser sound source is excited non-contactly, and the signal intensity increases with the energy of the incident pulse laser. The corresponding excitation mechanism changes from thermoelastic effect to ablation effect.

[0009] The airborne laser is carried by either a high-altitude airborne or spaceborne system, and the solid ice medium is thick and opaque to ensure that the airborne laser cannot penetrate the solid ice medium to reach underwater.

[0010] The signal type of the photoacoustic effect solid ice mobile sound source used for air-to-underwater communication is light wave in the atmospheric space channel and sound wave in the solid ice medium and liquid water medium channel.

[0011] This invention provides a photoacoustic effect solid ice mobile sound source for air-to-underwater communication. It utilizes a combination of laser communication and underwater acoustic communication technologies to construct an air-to-underwater signal transmission mechanism across an ice-covered medium. This is achieved through the photoacoustic effect of the solid ice layer covering the sea surface. Specifically, an airborne laser is incident on the sea surface ice layer via an atmospheric space channel. The interaction between the laser pulse and the solid ice generates a laser ultrasonic source, which rapidly penetrates the ice layer and transmits to the communication target in the water below. Finally, an optical / acoustic communication link is established across the ice layer to achieve information transmission from air to underwater. The purpose of this invention is to address the obstacle-prone environmental conditions of ice-covered sea surfaces in extremely cold and polar regions, where traditional single radio waves, light waves, and sound waves cannot penetrate the ice layer using non-contact methods, making air-to-underwater communication difficult. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is a schematic diagram of a laser-excited solid medium model during the excitation of the thermoelastic effect mechanism of the present invention.

[0014] Figure 2 This is a schematic diagram of the rectangular pulse action medium during the excitation of the thermoelastic effect mechanism of the present invention in a solid medium.

[0015] Figure 3This is a schematic diagram of an application model of a photoacoustic effect solid ice moving sound source for air-to-underwater communication according to the present invention.

[0016] Figure 4 This is a schematic diagram of an experimental testing system according to a specific embodiment of the present invention. Detailed Implementation

[0017] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0018] This invention proposes a photoacoustic effect solid ice mobile sound source for air-to-underwater communication, comprising an airborne laser, a pulsed laser encoding and driving module, and a solid ice medium covering the sea surface. The airborne laser is a pulsed laser that carries information encoding and modulation, which is incident on the solid ice medium through the atmospheric space to form a laser sound source.

[0019] The laser sound source consists of narrow pulse-induced waveforms, including longitudinal waves, transverse waves, and surface waves. Longitudinal waves can propagate in solids, liquids, and gases, and the particle vibration direction of the longitudinal wave is parallel to the wave propagation direction. Transverse waves can only propagate in solids, and the particle vibration direction is perpendicular to the wave propagation direction. Surface waves only propagate on the surface of a semi-infinite solid medium with a thickness much greater than its wavelength, and the particles vibrate and propagate along an elliptical trajectory.

[0020] The present invention will be further described below with reference to relevant terminology and background technology:

[0021] Since White proposed using light radiation to excite sound waves in solids in 1963, the technology of signal detection by laser sound wave propagation in solid media has been effectively applied. In the 1990s, laser ultrasonics was formed, and great progress has been made in the excitation, reception, propagation and application of laser ultrasonic signals.

[0022] This invention employs an airborne laser and explains the formation process of a laser sound source through the photoacoustic effect mechanism of the interaction between a pulsed laser and a solid ice medium. The photoacoustic effect is a physics term referring to the phenomenon where a material generates mechanical waves when irradiated with periodically modulated light. When light irradiates a medium, the absorption of light causes a change in its internal temperature, resulting in structural and volume changes in certain regions of the medium. When a pulsed or modulated light source is used, the temperature rise and fall of the medium causes its volume expansion and contraction, thus radiating mechanical elastic waves outwards. When laser energy is absorbed by an object and converted into heat, it causes internal expansion and contraction. If the object is a solid, the sound source region can be approximated as a cylindrical region inside the solid where laser energy is absorbed at a certain depth, causing the temperature to rise. The diameter of the sound source formed in this region depends on the diameter of the laser beam. The absorption of laser pulse energy inside the solid causes thermoelastic expansion, which in turn generates tension and forms elastic waves. The sound waves excited by this sound source propagate radially outward from the center point of the sound source, causing the volume of the region to expand rapidly and then contract slowly. This process of volume expansion and contraction forming elastic sound waves is the photoacoustic effect.

[0023] Furthermore, gases, liquids, and solids all exhibit photoacoustic effects when excited by pulsed lasers, generating laser-ultrasonic signals. Various applications can be achieved by utilizing the propagation of laser-induced acoustic waves within the medium. Solid media have relatively stable structures and superior acoustic signal transmission capabilities compared to gases and liquids. In extremely cold regions and polar environments, ice layers covering water surfaces are suitable for acoustic wave propagation applications. Based on the communication environment and the characteristics of the ice material, the laser output energy can be appropriately selected to obtain the desired laser-induced acoustic level and the size of the laser spot (beam) reaching the medium surface can be controlled, thereby inducing the generation of corresponding ultrasonic signals. The laser-induced ultrasonic signal is related not only to the spatiotemporal characteristics of the laser beam itself but also to the properties and surface characteristics of the solid material. Generally, the mechanisms of laser-induced ultrasonic waves in solids can be divided into two types: thermoelastic effects and ablation effects.

[0024] The thermoelastic effect occurs when the power density of the incident laser beam does not reach the melting threshold of the solid surface (typically 2–3 J / cm² for ice). 2When a solid surface is subjected to pulsed laser light, the temperature of the irradiated area rises due to the absorption of light energy. The laser energy is converted into heat energy, and the high concentration of heat energy in the irradiated area causes thermal expansion. This part of the medium deforms due to thermal expansion, and the periodic deformation causes stress pulses to form in the surrounding medium. Local photoacoustic energy conversion causes tangential pressure on the surface of the solid medium, thereby exciting periodically varying pulsed ultrasonic waves that propagate inside the solid or along the surface. Under the thermoelastic effect, due to the lower excitation light power, the local temperature rise does not cause a phase change in the medium material, but longitudinal waves, transverse waves, and surface waves can be excited. In contrast, the longitudinal waves and surface waves obtained under the ablation mechanism have much larger amplitudes, and their conversion efficiency is much higher than that of the thermoelastic mechanism.

[0025] When a rectangular pulsed laser with a pulse width of t0 is incident perpendicularly on the free surface of a semi-infinite medium (with optical absorption coefficient, thermal conductivity, and thermal diffusivity of β, K, and α, respectively), the medium absorbs the light energy and forms a corresponding heat source, the heat power density g(z,t) of which is:

[0026] g(z,t)=g0 -βz [H(t)-H(t-t0)] (1)

[0027] In the formula, g0 is the heat source intensity, H(t) is the step function, and represents the rectangular laser pulse function.

[0028] Solid ice media exhibits weak absorption; the stress pulse intensity (signal) generated by laser ultrasound can be expressed as:

[0029] u1=u0{[sh(βct)-sh[βc(t-t0)]]H(t-t0)}e -βz

[0030]

[0031] In the formula, u0=-αg0α T E / Kβc(1-2ν), where β is the light absorption coefficient, E is Young's modulus, K is thermal conductivity, α is thermal diffusivity, ν is Poisson's ratio, and c is the ultrasonic velocity.

[0032] In practical applications, laser ultrasonic pulses are bipolar vibration instantaneous signals in the time domain. Due to the different characteristics of the medium structure, they are accompanied by relaxation oscillations and show a propagation delay attenuation trend.

[0033] like Figure 1 and Figure 2 The diagram shows an acoustic signal excited in a solid medium by the thermoelastic effect mechanism. When the solid surface is subjected to... Figure 2When a laser with a pulse width of t0 is applied, the temperature of the affected area rises due to the absorption of light energy. The laser energy is converted into heat energy, and the high concentration of heat energy in the irradiated area causes a thermal expansion effect. This part of the medium deforms due to thermal expansion, and the periodic deformation causes stress pulses to form in the surrounding medium. Local photoacoustic energy conversion causes tangential pressure to be generated on the surface of the solid medium, thereby exciting periodically changing pulsed ultrasonic waves, such as... Figure 1 It propagates inside a solid or along its surface.

[0034] Solid ice has the following characteristics: the propagation speed of sound signals is related to the type of medium and temperature. Generally, the propagation speed increases with the increase of medium temperature and density, and the propagation characteristics of the same substance differ in different states. Water differs from ordinary substances in that it expands when cold and contracts when hot. In its liquid state, its density is 1 (at 4℃), but when it freezes into a solid, its volume expands and its density decreases to 0.9 (at 0℃). Water molecules in ice are less mobile than in liquid water, with smaller intermolecular distances and stronger forces, thus ice has a special crystal structure. The propagation speeds of sound waves in water and ice are 1450 m / s and 3160 m / s, respectively, indicating that sound waves travel faster in solid ice. The ice layer on the surface of polar waters has a certain thickness and is opaque, preventing lasers from penetrating to the underwater environment. Currently, acoustic communication is the most reliable technology for underwater applications. Laser sound sources achieve remote, non-contact excitation via airborne means, offering excellent flexibility and concealment. Furthermore, the crystal structure of solid ice is relatively stable, and its position on the water surface is relatively fixed. The solid ice layer at the location of the laser pulse is equivalent to a moving sound source placed on the water surface, experiencing minimal interference from seawater fluctuations. Relying on the bridging effect of sound wave transmission through the ice layer, ultrasonic signals can penetrate the covering sea ice and rapidly transmit to the water below, making it the most effective method for achieving communication between airborne and underwater targets.

[0035] In summary, laser sound sources excited by pulsed lasers have the following characteristics:

[0036] 1) Laser acoustic excitation is a non-contact method, and the resulting photoacoustic source is fully coupled with the solid sound transmission medium, making it a portable laser acoustic source.

[0037] 2) The signal intensity of laser acoustics will change from weak to strong as the energy of the incident laser pulse increases. The corresponding excitation mechanism changes from thermoelastic effect to ablation mechanism. Depending on the different laser acoustic mechanisms, the conversion efficiency ranges from 3% to 30%.

[0038] 3) When the incident laser power density is low, the transverse and longitudinal waves excited by the thermoelastic effect mainly propagate along the hollow conical surface symmetrically distributed with 0° as the central axis. The maximum energy of the longitudinal wave is distributed at about ±60°, while the maximum energy of the transverse wave is about ±30°, and it has a sharp directionality. The energy of both the transverse and longitudinal waves at the central axis 0° is the minimum.

[0039] 4) Laser sound sources have high-resolution broadband characteristics in both space and time. Depending on the laser pulse width, which varies from ns to ps, the laser sound frequency can vary from Hz to GHz, which is beneficial for target communication and detection.

[0040] The photoacoustic solid ice mobile sound source for air-to-underwater communication described in this invention is an interdisciplinary technology integrating optics and acoustics. It is suitable for environments where the sea surface is covered by ice in extremely cold and polar regions, and where single-form signals such as radio waves, light waves, and sound waves cannot penetrate the ice medium, making air-to-underwater communication difficult.

[0041] Please see Figure 3 , Figure 3 The diagram illustrates an application model of this invention. In the air, an airborne laser can be used to emit a laser beam towards the ice layer covering the ocean. At the first moment, a laser beam is emitted downwards towards a designated area from position A, generating a laser-sound source on the ice surface. The sound wave signal rapidly penetrates the ice layer and propagates into the water below, reaching the underwater target. Following the planned flight path, a laser can be emitted again at position B at the next moment, effectively moving the sound source floating on the ocean ice within the designated communication area. Both solid ice and liquid water media have excellent transmission capabilities for the sound wave signal from the laser-sound source. As long as the communicating parties follow a certain encoding protocol and utilize the fusion mechanism of light and sound wave technologies, long-range, non-contact communication across the ice layer can be achieved through photoacoustic radiation generated by the photoacoustic effect.

[0042] Furthermore, the present invention also proposes a specific embodiment for experimental testing system verification, such as... Figure 4 The diagram illustrates the system's principle. A certain thickness of ice layer covers the surface of a laboratory pool. Using a specific encoding and modulation technique at the transmitter, a pulsed laser emits laser pulses that are reflected by a mirror onto the ice layer, completing the photoacoustic signal conversion. The laser-acoustic signal generated in the ice layer propagates underwater. As shown in the diagram, the experiment involves placing an underwater acoustic transducer below the ice layer and moving it up and down in the direction of the arrow to establish communication across the ice layer from the atmosphere to underwater. The detection device can detect acoustic signals by placing it anywhere within the laser-acoustic radiation area and then send the signals to the backend for processing.

[0043] In summary, the advantages of the photoacoustic effect solid ice mobile sound source for air-to-underwater communication proposed in this invention in cross-medium communication environments are as follows:

[0044] (1) Traditional methods of using active relays for ice breaking lack flexibility, are costly and difficult. This invention uses a remote induced acoustic wave mechanism based on the interaction between laser and solid ice medium. By forming an autonomous, mobile, passive solid sound source to replace the bulky active relay placed on the water surface, it integrates the advantages of optical and acoustic communication to achieve the goal of communication between the air and underwater. This provides an effective method for in-depth research on the application of laser acoustic technology in communication across ice layers in polar regions.

[0045] (2) By utilizing the bridging effect of the solid ice layer covering the water surface on the transmission of sound waves, the problem of the ice layer is effectively solved in terms of the isolation of radio waves and light waves in the transmission of communication signals from the air to the water. The underwater acoustic transducer in the form of a buoy can flexibly acquire the laser acoustic signal transmitted from the solid ice layer to the water at any underwater location. In the relatively stable water body within the area covered by the ice layer, the transmission loss, multipath and propagation speed caused by water surface undulation can be reduced, effectively improving the communication efficiency between air and underwater targets.

[0046] The above description discloses only one preferred embodiment of the present invention, and should not be construed as limiting the scope of the present invention. Those skilled in the art will understand that all or part of the processes of the above embodiments can be implemented, and equivalent changes made in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A photoacoustic effect solid ice moving sound source for air-to-underwater communication, characterized in that, It includes an airborne laser and a solid ice medium covering the sea surface. The airborne laser is a pulsed laser that carries information encoding and modulation, which is incident on the solid ice medium through the atmospheric space to form a laser sound source. The pulse width of the encoded modulated laser ranges from the nanosecond level to the picosecond level, and the laser acoustic frequency can vary from the Hz level to the GHz level. The laser sound source consists of narrow pulse-induced waveforms, including longitudinal waves, transverse waves, and surface waves. Longitudinal waves can propagate in solids, liquids, and gases, and the particle vibration direction of the longitudinal wave is parallel to the wave propagation direction. Transverse waves can only propagate in solids, and the particle vibration direction is perpendicular to the wave propagation direction. Surface waves only propagate on the surface of a semi-infinite solid medium with a thickness much greater than its wavelength, and the particles vibrate and propagate along an elliptical trajectory. The laser sound source is an elastic sound wave that expands and contracts. The size of the laser sound source region is determined by the crystal structure of the solid ice medium and the output energy of the pulsed laser. The airborne laser is carried by either high-altitude airborne or spaceborne systems. The solid ice medium is thick and opaque, ensuring that the airborne laser cannot penetrate the solid ice medium to reach underwater.

2. The photoacoustic effect solid ice moving sound source for air-to-underwater communication as described in claim 1, characterized in that, The laser sound source is excited in a non-contact manner, and the signal intensity increases with the energy of the incident pulse laser. The corresponding excitation mechanism changes from thermoelastic effect to ablation effect.

3. The photoacoustic effect solid ice moving sound source for air-to-underwater communication as described in claim 2, characterized in that, The signal type of the photoacoustic effect solid ice mobile sound source used for air-to-underwater communication is light wave when transmitted in the atmospheric space channel, and sound wave when transmitted in the solid ice medium and liquid water medium channel.

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