Research On Photothermally Controlled Ferrofluidic Nonreciprocal Acoustic Devices

As one of the most important components in electronic circuits,diodes have become an indispensable part of modern life by ensuring non-reciprocal transmission of electric currents.Acoustic non-reciprocal devices,as diode-like acoustic devices,also play an irreplaceable role in acoustics,with important applications in ultrasonic communications,ultrasound imaging,energy rectification,and acoustic calculations.However,the size and complexity of current acoustic non-reciprocal devices present significant challenges for their integration with other equipment or systems,particularly in underwater acoustics.To overcome this challenge,this thesis proposes a compact,simple,and mechanical noise-free acoustic non-reciprocal device that can be tuned by temperature gradients and lasers.The device is based on self-driven ferrofluid self-circulation flow and has the ability to effectively achieve acoustic non-reciprocity can acoustic Zeeman splitting.With the introduction of laser,the magnetic fluid self-circulating motion can be accelerated,decelerated,stopped and even reversed and can further realize the manipulation of acoustic Zeeman splitting and non-reciprocal phenomenon.Through simulations and experiments,the existence and principle of magnetofluid flow motion,self-circulation,acoustic mode splitting,and non-reciprocity have been demonstrated.This controllable flow motion allows for effective and non-reciprocal manipulation of acoustic modes,and has potential applications in acoustic signal processing and other fields.The main contents of this thesis are as follows:(1)By combining thermomagnetic convection and Marangoni convection enhanced by a magnetic field,optimizing cavity design,and regulating parameters such as magnetic field strength and temperature difference,up to 29 mm/s high-speed magnetofluid motion driven by heat has been achieved.(2)Non-contact manipulation of long-range fast ferrofluid motion by laser is achieved.The acceleration,deceleration,stopping and motion reversal of the magneto-fluid surface motion can be realized by different laser power.(3)An acoustic non-reciprocal switch based on magnetofluid motion has been implemented.The long-distance self-circulating motion of the magnetofluid breaks the time-reversal symmetry of sound wave transmission.By laser-controlled fluid motion,manipulation of the sound wave transmission characteristics has been achieved.The device has demonstrated the heat and laser induced frequency shift and Zeeman-like splitting of acoustic resonant modes in a rectangular resonant cavity,and has confirmed the non-reciprocity with a non-reciprocal isolation of 17 dB.The optically controlled acoustic mode switch in the device has achieved a switching difference of 15 dB.