Design And Experiment Research Of Equipment For Ultrasonic Standing Wave Levitation And Transportation

As the disciplines are developing rapidly, such as physics, chemistry, biology, pharmacy, materials and mechanics, the ways that the samples are dealed with are more and more strictly required. The traditional ways can hardly separate samples from contacting with walls of containers, which can cause lots of interferences. For example, the vessel wall can cause pollution to the samples, it’s absorbability will affect composition tests of the micro-scaled samples, and the container itself can lead an interference on the signal tested by optical machines. The technology of ultrasonic standing wave levitation can deal with the samples in an contactless way. This way has many advantages. For example, it can avoid the defects produced by the vessel wall in the samples analysis, and makes it possible to transmit, mix and extract without contact. The ultrasonic transducer and transducer array are the equipments that can make the ultrasonic standing wave levitation and transportation come true.Firstly, this paper analyzes the wave equation in the ultrasonic standing wave acoustic field, and on the basis of the equation, the paper gets the distribution of sound pressure and the distribution of the velocity of the medium particles in the planar standing wave acoustic field. Then combined with the theory of time average potential, this paper gets the acoustic radial force which acts on the spheres that are levitated in the planar standing wave acoustic field. According to the relationship of the acoustic radial force and the gravity, this paper gets the theoretical levitated position of the levitated spheres.Secondly, on the basis of the acoustic radial force equation above, this paper theoretically calculates the amplitude of ultrasonic transducer radiator, which is the transducer’s design requirement. This paper requires that the single-axis acoustic levitator can levitate a steel sphere. And the transducer array can realize contactless transport of a polystyrene sphere, this requires every transducer in the transducer array can levitate a polystyrene sphere. To meet the requirements above, the amplitude of the single-axis transducer radiator should be 66.08μm, and the amplitude of every transducer radiator in the transducer array should be 7.5μm. The radiation amplitudes are this paper’s design goal. According to the longitudinal vibration equation of one-dimensional variable cross-section rods, this paper uses analytical method to design the single-axis transducer and the transducer array. This paper also does the mission of modal analysis for the designed transducer with ANSYS software.Thirdly, the frequency of every transducer in the transducer array is different. In order to reduce the impacts of frequency difference on the transport, this paper adopts flexible support for the transducer array elements. And this paper designs a support mean for the designed acoustic levitator. The equipment can realize that the cavity height varies in micron level. Then this paper performs experiments to verify the single-layer and multi-layer levitation and transportation capabilities of the transducer array elements, the transducer array and the single-axis acoustic levitator. Finally, this paper verifies the impacts of acoustic radial force on the cohesive force of molecules of the levitated water droplets with the single-axis cascaded transducer.