An acoustic non-reciprocal device, method and application based on magnetofluid motion

Abstract

This invention discloses an acoustic non-reciprocal device, apparatus, and application based on magnetohydrodynamic motion, relating to the field of non-reciprocal acoustic device technology, and particularly to an acoustic non-reciprocal device, method, and application based on magnetohydrodynamic motion. It solves the problems of complex structure and difficult manufacturing of existing acoustic non-reciprocal devices. The device includes a magnetic field generator for providing a magnetic field; a magnetohydrodynamic driving device for driving the magnetohydrodynamic motion; a laser for providing a light source to control the velocity of the magnetohydrodynamic motion; a magnetohydrodynamic cavity for constraining the magnetohydrodynamic fluid to form a channel and providing an ultrasonic propagation channel; and an ultrasonic transmitting and receiving component for transmitting and receiving ultrasonic signals propagating through the magnetohydrodynamic fluid. This invention provides an acoustic non-reciprocal device with low waveform distortion, simple structure, easy manufacturing, and convenient application.

Description

Technical Field

[0001] This invention relates to the field of non-reciprocal acoustic devices, and particularly to an acoustic non-reciprocal device, method, and application based on magnetohydrodynamic motion. Background Technology

[0002] Acoustic non-reciprocity refers to the fact that when the positions of the sound source and receiver are exchanged, the amplitude and phase of the received signal are different. Acoustic non-reciprocal devices ensure that no acoustic signal is reflected back to the sound source, guaranteeing unidirectional signal propagation. As an extremely important acoustic device, acoustic non-reciprocal devices have enormous application potential in ultrasonic imaging, energy flow control, topological acoustics, and surface acoustic wave devices. Acoustic non-reciprocal devices with high isolation can achieve unidirectional sound wave transmission, much like diodes in electrical systems. Incorporating such devices as part of an acoustic system effectively isolates reflected sound signals.

[0003] Currently, such isolation devices typically consist of nonlinear acoustic materials, moving media, time-controlled media, and bi-anisotropic devices.

[0004] Nonlinear materials and non-reciprocal acoustic devices introduce frequency harmonics into sound waves as they pass through nonlinear media, causing distortion in the time response of the sound waves. Simultaneously, due to the variation in effective material properties with amplitude, the amplitude response of the sound waves is also distorted. Sound waves generate second harmonics through nonlinear materials, which then pass through phononic crystals or resonators that block the fundamental frequency and the second harmonics. In the reverse direction, they are completely blocked, achieving a high degree of isolation.

[0005] However, such non-reciprocal devices always produce large waveform distortion, their performance degrades when both positive and negative waves are present, and good non-reciprocity can only be obtained at large amplitudes.

[0006] Non-reciprocal acoustic devices in moving media break the time symmetry in sound wave propagation by introducing momentum. The sound wave velocity differs in the upstream and downstream directions, thus introducing non-reciprocity. However, non-reciprocal devices require a large motion speed or a long motion distance, which has a significant disadvantage in terms of integration.

[0007] Temporally controlled dielectric acoustic non-reciprocal devices use piezoelectric sensors and other devices to modulate the effective bulk modulus of the acoustic cavity, introducing an effective angular momentum to break the reciprocity between ports and achieve a larger isolation coefficient. However, such devices often suffer from problems such as complex structure, high manufacturing difficulty, and high cost.

[0008] Bitropic non-reciprocal devices can exhibit extreme acoustic non-reciprocity through Willis coupling. The transmission and reflection of bent waves within the device can be independently controlled through an active mechanical Willis metamaterial layer, breaking the reciprocity. However, such devices also suffer from structural complexity, fabrication difficulties, and challenges in large-scale manufacturing.

[0009] It is evident that existing acoustic non-reciprocal devices suffer from drawbacks such as complex structure and difficult manufacturing. Summary of the Invention

[0010] The purpose of this invention is to solve the problems of complex structure and difficult manufacturing of existing acoustic non-reciprocal devices.

[0011] To achieve the above objectives, the present invention specifically adopts the following technical solution:

[0012] An acoustic non-reciprocal device based on magnetohydrodynamic motion includes: a magnetic field generator for providing a magnetic field; a magnetohydrodynamic driving device for driving the magnetohydrodynamic motion; a laser for providing a light source to control the speed of the magnetohydrodynamic motion; a magnetohydrodynamic cavity for constraining the magnetohydrodynamic fluid to form a channel and providing an ultrasonic propagation channel; and an ultrasonic transmitting and receiving component for transmitting and receiving ultrasonic signals propagating through the magnetohydrodynamic fluid.

[0013] Furthermore, the magnetohydrodynamic driving device includes a semiconductor heating element, a semiconductor cooling element, and a laser reflector located in the output optical path of the laser. The semiconductor heating element and the semiconductor cooling element are used to create a temperature difference at both ends of the magnetohydrodynamic cavity, and the laser reflector is used to reflect the laser light from the laser onto the magnetohydrodynamic surface and adjust the irradiation position.

[0014] Furthermore, the magnetic fluid cavity channel includes a magnetic fluid, a resin cavity, and a permanent magnet, with the magnetic fluid disposed within the resin cavity and the permanent magnet disposed below the resin cavity.

[0015] Furthermore, the semiconductor heating element and the semiconductor cooling element are provided with a temperature feedback adjustment module, which is used to adjust the temperature of the semiconductor heating element and the semiconductor cooling element.

[0016] Furthermore, the temperature adjustment range of the semiconductor cooling chip is 0 to 10°C, and the temperature adjustment range of the semiconductor heating chip is 30 to 120°C.

[0017] Furthermore, the light source wavelength of the laser is 400nm to 700nm.

[0018] Furthermore, the ultrasonic transmitting and receiving assembly includes an ultrasonic transducer and a needle hydrophone or transducer.

[0019] The present invention also provides a method for acoustic non-reciprocity, comprising the following steps:

[0020] S1. Provides a magnetic field generating device, a magnetofluid cavity, a magnetofluid driving device, and a magnetofluid, wherein the magnetofluid driving device includes a semiconductor heating element, a semiconductor cooling element, a laser reflector, an ultrasonic transducer, and a needle hydrophone;

[0021] S2. The semiconductor cooling chip and the semiconductor heating chip are placed at both ends of the channel of the magnetic fluid cavity. The magnetic fluid cavity is filled with magnetic fluid. An ultrasonic transducer is placed at one end of the magnetic fluid, and a needle hydrophone is placed at the end of the magnetic fluid that is away from the ultrasonic transducer.

[0022] S3. Turn on the magnetic field generator, ultrasonic transducer and needle hydrophone, adjust the magnetohydrodynamic drive device to locally heat the magnetohydrodynamic fluid, so that the magnetohydrodynamic fluid flows, change the parameters of the magnetic field and thus change the acoustic isolation.

[0023] Furthermore, the change in acoustic isolation by altering the magnetic field parameters in S3 includes: accelerating the magnetic fluid when the magnetohydrodynamic drive device irradiates one end near the semiconductor heating element; and decelerating or stopping the magnetic fluid when the magnetohydrodynamic drive device irradiates one end near the semiconductor cooling element.

[0024] The present invention also provides an application of an acoustic non-reciprocal device based on magnetohydrodynamic motion.

[0025] Compared with the prior art, the advantages of the present invention are as follows:

[0026] 1. The acoustic non-reciprocal device based on magnetohydrodynamic motion provided by this invention can be manufactured using methods such as 3D printing, resulting in a simple structure and low manufacturing difficulty. The magnetohydrodynamic fluid and neodymium iron boron magnets are inexpensive and readily available, and the heating and cooling equipment used is also inexpensive, making the device easy to construct. The laser source used has a wide range of wavelengths, covering ultraviolet, visible, and near-infrared light, and requires relatively low power, achieving manipulation of magnetohydrodynamic fluid and sound without the need for a high-power laser.

[0027] It does not require the introduction of mechanical driving devices such as fans, air pumps, and water pumps, and has the characteristics of simple structure, high reliability, good stability, and low cost. Moreover, the self-generated fluid motion does not introduce noise, and the output signal is more stable and cleaner.

[0028] It can achieve contactless and non-destructive precise operation. It can not only be used as a non-reciprocal switch, but also control the degree of acoustic non-reciprocal isolation by controlling the flow rate. The device is highly flexible.

[0029] This enables the miniaturization of devices, eliminating the need for decimeter- or even meter-long cavities or ring resonators, and making integration with other acoustic devices more convenient.

[0030] 2. The acoustic non-reciprocal method provided by this invention has a simple structure and is easy to operate, with low equipment manufacturing difficulty; the preparation materials are inexpensive and easy to obtain.

[0031] 3. The application of an acoustic non-reciprocal device based on magnetohydrodynamic motion provided by this invention features repeatability, controllable fluid motion direction, wide applicability, great application potential, high energy conversion efficiency, long motion duration, and environmental friendliness and energy saving. The provided device has a simple structure, high photothermal conversion efficiency, high reliability, good stability, and low cost, providing a new option for the application of photo-controlled fluids. This invention has universal applicability and promising application prospects. Attached image description:

[0032] Figure 1 This is a schematic diagram of the structure of an acoustic non-reciprocal device based on magnetohydrodynamic motion provided by the present invention.

[0033] Figure 2 The image shows a side view of the structure of an acoustic non-reciprocal device based on magnetohydrodynamic motion, provided by the present invention.

[0034] Figure 3 This is a schematic diagram illustrating the principle and effect of laser-induced deceleration and stopping of magnetohydrodynamic motion, provided in an embodiment of the present invention.

[0035] Figure 4 This is a schematic diagram illustrating the principle and effect of laser-assisted acceleration of magnetohydrodynamic motion provided in an embodiment of the present invention.

[0036] Figure 5 A reference diagram showing the relationship between the temperature of the heating element and the velocity of the magnetohydrodynamic fluid provided in an embodiment of the present invention.

[0037] Figure 6 The reference figure provided by the present invention shows the relationship between laser power, magnetofluid velocity, and surface temperature when the magnetofluid motion is stopped.

[0038] Figure 7 The figure shows a method for droplet transport on a long-range self-circulating magnetofluid 4 according to an embodiment of the present invention.

[0039] Figure 8 This is a schematic diagram of the frequency response according to an embodiment of the present invention.

[0040] Figure 9 This is a schematic diagram of the magnetic field involved in Embodiment 5 of the present invention.

[0041] Figure 10 This is a schematic diagram of the motion of the magnetofluid involved in Embodiment 5 of the present invention.

[0042] Figure 11. Laser; 2. Laser reflector; 3. Ultrasonic transducer; 4. Resin magnetohydrodynamic cavity; 5. Needle hydrophone; 6. Semiconductor heating element; 7. Semiconductor cooling element; 8. Long strip neodymium iron boron magnet. Figure 2 3. Ultrasonic transducer; 4. Resin magnetohydrodynamic cavity; 5. Needle hydrophone; 6. Semiconductor heating element; 7. Semiconductor cooling element.

[0043] Figure 3 , Figure 4 1. Laser; 2. Laser reflector; 4. Glass substrate; 6. Heating end; 7. Cooling end; 9. Laser irradiation point.

[0044] To make the objectives, 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. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0045] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Detailed Implementation

[0046] Existing acoustic non-reciprocal devices suffer from difficulties in manufacturing and complex structures.

[0047] An acoustic non-reciprocal device based on magnetohydrodynamic motion includes: a magnetic field generator for providing a magnetic field; a magnetohydrodynamic driving device for driving unidirectional motion of the magnetohydrodynamic fluid; a laser for providing a light source to control the motion speed of the magnetohydrodynamic fluid; a magnetohydrodynamic cavity for constraining the magnetohydrodynamic fluid to form a channel and providing an ultrasonic propagation channel; and an ultrasonic transmitting and receiving component for transmitting and receiving ultrasonic signals propagating through the magnetohydrodynamic fluid.

[0048] Understandably, the magnetic field generator provides the magnetic field, and the magnetofluid within the magnetofluid cavity begins to move under the combined effects of thermomagnetic convection and the Marangoni effect. Due to the surface tension gradient and demagnetization, the magnetofluid forms a unidirectional flow from the heating end to the cooling end on the surface, and then recirculates back to the heating end from the low-temperature region under the action of magnetic volume force. Therefore, as long as a temperature gradient exists, the magnetofluid will continue to move. This unidirectional surface movement breaks the time symmetry of sound propagation, resulting in a Doppler frequency shift. The sound waves generate different frequency shifts in the direction of flow and against the flow direction. Therefore, after exchanging the transmitter and receiver, the received signal phase and amplitude are different, producing a large isolation at a specific frequency. That is, sound wave propagation exhibits non-reciprocity; exchanging the positions of the sound source and receiver results in different received signal amplitudes and phases, with a certain isolation ratio, achieving unidirectional isolation of sound waves, i.e., achieving unidirectional transmission of sound waves. This invention provides a device for non-reciprocal sound propagation, with low waveform distortion, simple structure, easy manufacturing, and convenient application.

[0049] Furthermore, the acoustic non-reciprocal device of the present invention can be manufactured using methods such as 3D printing, resulting in a simple structure and low manufacturing difficulty. The magnetohydrodynamic fluid and neodymium iron boron magnets are inexpensive and readily available, and the heating and cooling equipment used is inexpensive, making the device easy to construct. The laser source used has a wide range of wavelengths, covering ultraviolet, visible, and near-infrared light, and requires relatively low power, eliminating the need for high-power lasers to manipulate magnetohydrodynamic fluids and sound.

[0050] Without the need for mechanical driving devices such as fans, air pumps, or water pumps, this device features a simple structure, high reliability, good stability, and low cost. Furthermore, the self-generated fluid motion does not introduce noise, resulting in a more stable and cleaner output signal. It enables contactless and non-destructive precise manipulation, serving not only as a non-reciprocal switch but also allowing for control of acoustic non-reciprocity isolation by adjusting flow rate, making the device highly flexible. It achieves miniaturization, eliminating the need for decimeter- or even meter-long cavities or ring resonators, thus facilitating integration with other acoustic devices.

[0051] In some embodiments of the present invention, the magnetohydrodynamic driving device includes a semiconductor heating element, a semiconductor cooling element, and a laser reflector located in the output optical path of the laser. The semiconductor heating element and the semiconductor cooling element are used to form a temperature difference at both ends of the magnetohydrodynamic cavity, and the laser reflector is used to reflect the laser light from the laser onto the magnetohydrodynamic surface and adjust the irradiation position.

[0052] In some embodiments of the present invention, the magnetofluid cavity channel includes a magnetofluid, a resin cavity, and a permanent magnet, wherein the magnetofluid is disposed within the resin cavity, and the permanent magnet is disposed below the resin cavity.

[0053] In some embodiments of the present invention, the permanent magnet includes, but is not limited to, neodymium iron boron magnets.

[0054] In some embodiments of the present invention, the laser is provided with a power adjustment module, which is used to adjust the power of the laser, thereby controlling the speed of the magnetohydrodynamic motion.

[0055] The power adjustment range of the power adjustment module is preferably 0 to 1250 mW.

[0056] In some embodiments of the present invention, the semiconductor heating element and the semiconductor cooling element are provided with a temperature feedback adjustment module, which is used to adjust the temperature of the semiconductor heating element and the semiconductor cooling element.

[0057] It is understandable that when the temperature feedback regulation module adjusts the temperature of the semiconductor heating element and the semiconductor cooling element, the temperature affects the magnetic fluid, thereby regulating the flow rate of the magnetic fluid.

[0058] In some embodiments of the present invention, the temperature adjustment range of the semiconductor cooling chip is 0 to 10°C, and the temperature adjustment range of the semiconductor heating chip is 30 to 120°C.

[0059] In some embodiments of the present invention, the light source wavelength of the laser is 400nm to 700nm.

[0060] In some embodiments of the present invention, the ultrasonic transmitting and receiving assembly includes an ultrasonic transducer and a needle hydrophone or transducer. The ultrasonic transducer is used to transmit ultrasonic signals, and the needle hydrophone or transducer is used to receive ultrasonic signals.

[0061] The preferred range for the ultrasonic transducer's emitted ultrasonic frequency is 300-700kHz.

[0062] The present invention also provides a method for acoustic non-reciprocity, comprising the following steps:

[0063] S1. Provides a magnetic field generating device, a magnetofluid cavity, a magnetofluid driving device, and a magnetofluid, wherein the magnetofluid driving device includes a semiconductor heating element, a semiconductor cooling element, a laser reflector, an ultrasonic transducer, and a needle hydrophone;

[0064] S2. The semiconductor cooling chip and the semiconductor heating chip are placed at both ends of the channel of the magnetic fluid cavity. The magnetic fluid cavity is filled with magnetic fluid. An ultrasonic transducer is placed at one end of the magnetic fluid, and a needle hydrophone is placed at the end of the magnetic fluid that is away from the ultrasonic transducer.

[0065] S3. Turn on the magnetic field generator, ultrasonic transducer and needle hydrophone, adjust the magnetohydrodynamic drive device to locally heat the magnetohydrodynamic fluid, so that the magnetohydrodynamic fluid flows, and change the magnetic field parameters to change the acoustic isolation.

[0066] In some embodiments of the present invention, changing the acoustic isolation by changing the parameters of the magnetic field in S3 includes: accelerating the magnetic fluid when the magnetic fluid driving device irradiates one end near the semiconductor heating element; and decelerating or stopping the magnetic fluid when the magnetic fluid driving device irradiates one end near the semiconductor cooling element.

[0067] It is understandable that changing the magnetic field parameters in S3 alters the acoustic isolation. When the laser irradiates one end of the semiconductor heating element, the magnetofluid on the surface of that region is heated, its temperature rises, and its surface tension decreases, thus accelerating the magnetofluid's movement. When the laser irradiates one end of the semiconductor cooling element, the magnetofluid on the surface of that region is heated, its temperature rises, and the temperature difference between the two surfaces decreases, causing the surface movement speed to decrease or even stop. Acceleration of the magnetofluid increases the acoustic isolation, while deceleration decreases it. The main reason is that increased magnetofluid velocity leads to increased frequency shift.

[0068] The non-reciprocal isolation theory of sound signal generation states that the motion of the magnetofluid, which serves as the sound propagation medium, breaks the time symmetry of sound propagation. Due to the Doppler effect, the sound waves generate different frequency shifts in the direction of flow and in the direction of flow. Therefore, after switching the transmitter and receiver, the phase and amplitude of the received signals are different, resulting in a large degree of isolation at a specific frequency.

[0069] The present invention also provides an application of an acoustic non-reciprocal device based on magnetohydrodynamic motion.

[0070] It is understood that the device of this invention features repeatability, controllable fluid movement direction, wide applicability, great application potential, high energy conversion efficiency, long movement duration, and environmental friendliness and energy saving. The device has a simple structure, high photothermal conversion efficiency, high reliability, good stability, and low cost, providing a new option for the application of photocontrolled fluids. It has universal applicability and promising application prospects.

[0071] Example 1

[0072] This embodiment provides an acoustic non-reciprocal device based on magnetohydrodynamic motion. Please refer to [link to relevant documentation]. Figure 1 It includes a magnetohydrodynamic drive device, a magnetohydrodynamic cavity, and an ultrasonic transmitting and receiving device.

[0073] Magnetohydrodynamic (MHD) drive device: The temperature difference gradient at both ends is formed by a semiconductor cooling chip 7 with temperature feedback control and a semiconductor heating chip 6, which provides the power for the movement of the MHD. A 532nm continuous semiconductor laser provides the light source, which is reflected by the laser reflector 2 onto the surface of the MHD, thereby generating a local heat source and realizing the control of the MHD.

[0074] Magnetofluid cavity: The magnetic field is provided by a long strip neodymium iron boron magnet 8 of 60*20*10mm, and the 3D printed resin magnetofluid cavity 4 is filled with a sufficient amount of magnetofluid.

[0075] Please see Figure 2 The cavity consists of two 10*20*5mm cooling and heating ends and a 40*5*5mm flow channel.

[0076] Ultrasonic transmitting and receiving equipment: It consists of an ultrasonic transducer 3 and a needle hydrophone 5. The ultrasonic transducer 3 transmits ultrasonic signals with a frequency of 300-700kHz, which are received by the needle hydrophone 5 through the magnetic fluid contained in the resin magnetic fluid cavity 4.

[0077] The movement of the magnetofluid in the magnetofluid cavity 4 is the result of the combined effects of thermomagnetic convection and the Marangoni effect. Due to the surface tension gradient and demagnetization, the magnetofluid forms a unidirectional flow from the heating plate end to the cooling plate end on the surface, and under the action of magnetic volume force, it recirculates from the low temperature zone back to the heating zone.

[0078] Therefore, as long as a temperature gradient exists, the magnetohydrodynamic fluid will continue to move. This unidirectional surface motion breaks the time symmetry of sound propagation, resulting in a Doppler frequency shift, which makes the sound wave propagation non-reciprocal. That is, if the positions of the sound source and receiver are exchanged, the amplitude and phase of the received signals will be different, resulting in a certain isolation ratio and achieving unidirectional isolation of the sound waves.

[0079] The device has a very simple structure. It only requires a semiconductor heating element and a semiconductor cooling element to provide a temperature difference. The neodymium iron boron magnet, the simple resin acoustic cavity, and the internal magnetic fluid form a transport channel. Convection will be generated under the influence of the Marangoni effect and thermomagnetic effect. Then, due to the Doppler effect, the time symmetry of sound wave propagation is broken, and acoustic non-reciprocal isolation is formed.

[0080] Example 2

[0081] In this embodiment, an acoustic non-reciprocal method is provided, comprising:

[0082] Step 1: A magnetic field is provided by a long strip of neodymium iron boron magnet, and a semiconductor cooling plate and a semiconductor heating plate are placed at both ends of the cavity channel.

[0083] Step two: Fill the cavity with magnetic fluid, and start the semiconductor heating and cooling plates to make the bottom of both ends of the magnetic fluid reach the set temperature.

[0084] Step 3: The movement of the magnetofluid is the result of the combined effects of thermomagnetic convection and the Marangoni effect. Under the temperature gradient generated by the semiconductor heating and cooling plates, the magnetofluid forms a unidirectional long-distance movement from the hot end to the cold end on the surface due to the surface tension gradient and thermal demagnetization, and then recirculates back from the low-temperature region under the action of volume force.

[0085] Step four involves emitting ultrasonic signals via an ultrasonic transducer positioned at one end of the magnetofluid, while a needle-type hydrophone at the other end records the ultrasonic signals after passing through the long-range unidirectional moving magnetofluid surface. Switching the positions of the transducer and hydrophone alters the characteristics of the received signal compared to the forward transmission, creating acoustic isolation.

[0086] Step five: The laser beam is emitted by the laser generator and incident parallel to the laser reflector, which reflects the beam onto the magnetofluid. By adjusting the laser power, localized heating of the magnetofluid can be achieved, thereby controlling the flow velocity and even acting as a flow switch. Changing the flow velocity can alter the acoustic isolation.

[0087] Example 3

[0088] This embodiment analyzes the relationship between the magnetohydrodynamic velocity and the hot-end heating temperature. Based on laboratory experiments, the results are shown below. Figure 5 and Figure 6 ,Discover:

[0089] Please see Figure 5 As the temperature at the heating end of the magnetofluid increases, the velocity of the magnetofluid increases significantly.

[0090] Because lasers have excellent monochromaticity and collimation, and magnetofluids absorb 400-700nm wavelength lasers significantly, lasers can be used to create local heat sources on the surface of magnetofluids, change the temperature gradient, and thus manipulate the movement of the magnetofluid. This also enables manipulation of acoustic non-reciprocity, and can be used as a non-reciprocal switch.

[0091] The device for achieving non-reciprocity laser control is very simple, requiring only a mirror to reflect the laser emitted by the laser onto the surface of the magnetofluid within the magnetofluid cavity. By changing the laser power and the position of the laser beam, the motion on the magnetofluid surface can be accelerated, decelerated, or stopped.

[0092] Please see Figure 3 When the laser irradiates the surface of the channel on one side of the cooling chip, it creates a local heat source, which reduces the temperature difference between the cooling end 7 and the heating end 6, thereby reducing the surface velocity of the magnetofluid.

[0093] Please see Figure 6Experiments have shown that the higher the laser power, the higher the surface heat source temperature it creates, which in turn reduces the surface velocity of the magnetofluid and can even stop the movement of the magnetofluid. When the movement of the magnetofluid stops, the reciprocity of sound wave propagation can be restored.

[0094] Please see Figure 4 When the laser irradiates the surface of the channel on one side of the heating element, it increases the temperature difference between the surfaces of the cooling end 7 and the heating end 6, thereby accelerating the surface velocity of the magnetofluid within a certain time. The flow velocity is related to the acoustic non-reciprocity isolation; when the flow velocity accelerates, the non-reciprocity frequency shift also increases, thus increasing the isolation within a certain range.

[0095] Example 4

[0096] Please see Figure 7 This invention provides a method for droplet transport on a long-range self-circulating magnetofluid 4, comprising:

[0097] S101 is provided with a magnetic field by a long strip neodymium iron boron magnet, and a semiconductor cooling chip and a semiconductor heating chip are located at both ends of the cavity channel.

[0098] S102, fill the cavity with magnetic fluid, so that the semiconductor heating element and cooling element start working and the bottom of both ends of the magnetic fluid reach the set temperature.

[0099] S103, the movement of the magnetofluid is the result of the combined action of thermomagnetic convection and the Marangoni effect. Under the temperature gradient generated by the semiconductor heating and cooling plates, the magnetofluid forms a unidirectional long-distance movement from the hot end to the cold end on the surface due to the surface tension gradient and thermal demagnetization, and then recirculates back from the low temperature region under the action of volume force.

[0100] S104 uses an ultrasonic transducer located at one end of the magnetofluid to emit ultrasonic signals, while a needle-type hydrophone at the other end records the ultrasonic signals after passing through the long-distance unidirectional moving magnetofluid surface. By switching the positions of the transducer and the hydrophone, the characteristics of the received signal change compared to the forward transmission, resulting in acoustic isolation.

[0101] In S105, a laser beam is emitted from a laser source and incident parallel to a laser reflector, which reflects the beam onto the magnetofluid. By adjusting the laser power, localized heating of the magnetofluid can be achieved, thereby controlling the flow velocity and even acting as a flow switch. Changing the flow velocity can alter the acoustic isolation.

[0102] The ferrofluid 4 is a commercially available ferrofluid 4 (EFH1) purchased from Ferrotec. Its absorption coefficient at a laser wavelength of 532 nm reaches 86000 μm. -1 The transmission depth is 11 μm. The thermal diffusivity of ferrofluid 4 is 9.2 × 10⁻⁶.-4 cm 2 The surface tension of the magnetohydrodynamic fluid 4 is only half that of pure water, with a temperature coefficient of 0.31 × 10⁻⁶ / s. Strong light absorption and low thermal diffusivity are the reasons for the high temperature difference at the liquid surface. -3 Nm -1 K -1 The viscosity is more than twice that of pure water. High light absorption and a large surface tension temperature coefficient generate a considerable surface tension gradient, driving the surface liquid outwards. During temperature increases, the viscosity of the ferrofluid 4 decreases rapidly, thus intensifying Marangoni convection. The combined effects of a high surface tension temperature coefficient, strong light absorption, low thermal diffusivity, and low viscosity cause the Marangoni coefficient to rise to 6.1 × 10⁻⁶. 4 It is as large as the Marangoni coefficient of molten metal and NaNO3 crystals.

[0103] Example 5

[0104] In this embodiment, see Figure 9 and Figure 10 ( Figure 10 In this context, "sound source" refers to an ultrasonic signal source, and "hydrophone" refers to a hydrophone. Under the vertical magnetic field generated by a cylindrical magnetic field generator, due to Rosen-Sweig instability, the magnetohydrodynamic fluid generates a magnetovolute composed of two or more peaks. Within the stationary magnetovolute, sound transmission remains reciprocal. When a focused laser spot irradiates a specific location on the inner side of the magnetovolute, the surface tension and magnetic susceptibility of that location decrease due to the photothermal effect. This results in localized Marangoni convection and thermomagnetic convection, which in turn induces a large-scale rotation of the magnetovolute, generating a rotating flow field. This flow field breaks the time-reversal symmetry of sound wave transmission, thus exhibiting a certain degree of acoustic non-reciprocity and creating isolation between forward and reverse transmission.

[0105] Example 6 Performance Verification

[0106] 6.1 Test Setup

[0107] In this embodiment, the performance of the acoustic non-reciprocal device of the present invention is verified. Sound waves are generated by a transducer and received by a needle hydrophone; the frequency response of the sound waves is measured. The measurement results are shown below. Figure 8 .

[0108] 6.2 Results Analysis

[0109] Please refer to this document. Figure 8The dotted line represents the frequency response of sound wave transmission in stillness, while the dashed line represents the frequency response of sound wave transmission in flow. It can be seen that a large sound pressure difference can be observed at specific frequencies, achieving a sound pressure isolation exceeding 40 dB. Therefore, the acoustic non-reciprocal device involved in this invention possesses high sound pressure isolation.

[0110] The above embodiments are merely one implementation of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. An acoustic non-reciprocal device based on magnetohydrodynamic motion, characterized in that, include: A magnetic field generator is used to provide a magnetic field; a laser provides a light source for controlling the speed of the magnetohydrodynamic fluid. Magnetohydrodynamic (MHD) drive device for driving the motion of magnetohydrodynamic fluids; A magnetohydrodynamic cavity constrains the formation of a magnetohydrodynamic channel and provides an ultrasonic propagation channel; the magnetohydrodynamic driving device includes a semiconductor heating element, a semiconductor cooling element, and a laser reflector located on the output optical path of the laser; the semiconductor heating element and the semiconductor cooling element are used to create a temperature difference at both ends of the magnetohydrodynamic cavity to drive the movement of the magnetohydrodynamic fluid. An ultrasonic transmitter-receiver assembly for transmitting and receiving ultrasonic signals propagating through a magnetohydrodynamic medium.

2. An acoustic nonreciprocal device based on the motion of magnetic fluid according to claim 1, characterized in that, The laser reflector is used to reflect the laser light from the laser onto the magnetohydrodynamic surface and adjust the irradiation position.

3. An acoustic nonreciprocal device based on the motion of magnetic fluid according to claim 1, characterized in that, The magnetic field generating device includes a permanent magnet, and the magnetofluid cavity channel includes a magnetofluid and a resin cavity, with the magnetofluid disposed within the resin cavity and the permanent magnet disposed below the resin cavity.

4. An acoustic nonreciprocal device based on the motion of magnetic fluid according to claim 2, characterized in that, The semiconductor heating element and the semiconductor cooling element are provided with a temperature feedback adjustment module, which is used to adjust the temperature of the semiconductor heating element and the semiconductor cooling element.

5. A non-reciprocal acoustic device based on the motion of magnetic fluid according to claim 2 or 4, characterized in that, The temperature adjustment range of the semiconductor cooling chip is 0~10℃, and the temperature adjustment range of the semiconductor heating chip is 30~120℃.

6. The acoustic non-reciprocal device based on magnetohydrodynamic motion according to claim 1, characterized in that, The laser has a light source wavelength of 400nm to 700nm.

7. The acoustic non-reciprocal device based on magnetohydrodynamic motion according to claim 1, characterized in that, The ultrasonic transmitting and receiving assembly includes an ultrasonic transducer and a needle hydrophone.

8. An acoustic non-reciprocal method based on the acoustic non-reciprocal device according to any one of claims 1-7, characterized in that, Includes the following steps: S1. Provides a magnetic field generating device, a laser, a magnetohydrodynamic cavity, a magnetohydrodynamic driving device, and an ultrasonic transmitting and receiving assembly, wherein the magnetohydrodynamic driving device includes a semiconductor heating element, a semiconductor cooling element, and a laser reflector; S2. The semiconductor cooling chip and the semiconductor heating chip are placed at both ends of the channel of the magnetic fluid cavity. The magnetic fluid cavity is filled with magnetic fluid. An ultrasonic transducer is placed at one end of the magnetic fluid, and a needle hydrophone is placed at the end of the magnetic fluid that is away from the ultrasonic transducer. S3. Turn on the magnetic field generator, ultrasonic transducer and needle hydrophone, adjust the magnetohydrodynamic drive device to locally heat the magnetohydrodynamic fluid, so that the magnetohydrodynamic fluid flows, and change the magnetic field parameters to change the acoustic isolation.

9. An acoustically non reciprocal method according to claim 8, wherein, The change in acoustic isolation by altering the magnetic field parameters in S3 includes: when the laser is irradiated by the laser reflector of the magnetohydrodynamic driving device at one end near the semiconductor heating element, the magnetohydrodynamic fluid is accelerated; when the laser is irradiated by the laser reflector of the magnetohydrodynamic driving device at one end near the semiconductor cooling element, the magnetohydrodynamic fluid is decelerated or brought to a standstill.

10. The application of an acoustic non-reciprocal device based on magnetohydrodynamic motion according to any one of claims 1 to 7.

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