Focused Ultrasound Based Heat Dissipation Strategy For Small Heat Sources

In recent years,with the rapid increase of miniaturization degree and integration level,the temperature rise of electronic devices has become a critical factor which limits their highest performance.It is known that the acoustic streaming,which is a vortex flow resulting from the spatial gradient of the Reynolds' stress in ultrasonic field,can be employed for the cooling by enhancing the forced convection around a heat source.As a new approach for thermal management,it has advantages of no moving parts,no noise,simple system structure and so on.The main demerit of this cooling method is its weak cooling effect,which limits its practical application.In this work,to overcome this problem,we proposed and developed a cooling strategy based on the acoustic streaming generated by the focused ultrasound.In the strategy,the strong acoustic streaming around the focal point was utilized to cool small-size electronic devices.The main contents and achievements are as follows:1.Design method of the cooling device,which is based on the focused ultrasound,was proposed.The device includes a Langevin ultrasonic transducer and an aluminum acoustic lens.The vibration characteristics and acoustic streaming field was primarily calculated by the the finite element method.2.The experimental platform was set up.Using the platform,the feasibility of the cooling strategy was proved,and the cooling characteristics and principles were discussed.The results show that the optimal position of the cooled device is near the focal point.When the input power of the ultrasonic transducer is 1W,an ellipsoidal heat source with heating power of 0.17 W,initial temperature of 80°C and the axis lengths of 0.92 mm ×0.62mm×0.61 mm can be cooled down to39°C.It is also confirmed that this device can also be used to cool the heat sources of different shapes and sizes.3.The acoustic and vibration characteristic of the cooling device were simulated by the finite element method.It is proved that the acoustic streaming is the main reason for the temperature decrease.The relationships between some parameters and cooling effect were found and the way to improve cooling effect were discussed.