Application Cases

Experiment Name: Optimization Design and Dynamic Control of the Electrostatic Levitation Process

Experiment Purpose:

Through various technical means, the existing electrostatic levitation system has been optimized in multiple aspects. Considering the morphology and size of the levitation electrodes and the positioning light path, stable levitation of solid metallic materials with a diameter of 10mm has been achieved. By improving the control algorithm, the shape and positional stability of the molten sample during the levitation process have been enhanced. The functions of triggering nucleation and liquid quenching have been added, enriching the means for studying the solidification process of materials. Moreover, by coupling laser heating and temperature measurement, precise control of the levitated sample's temperature has been realized.

Testing Equipment: High-voltage amplifier, position-sensitive detector, computer, etc.

Figure 1: Schematic Diagram of the Electrostatic Levitation Device

Experiment Process:

In electrostatic levitation, for samples with a diameter of around 3mm, to increase the stability of levitation, the vertical direction generally uses a hemispherical upper electrode and a concave lower electrode, with the lower electrode diameter larger than the upper electrode. The spacing between the upper and lower electrodes is usually set at 10mm. Thus, for a sample with a density of 7g·cm−3 and a diameter of around 3mm, the experiment found that its take-off voltage is approximately 25kV. If the diameter of the levitated sample increases to 10mm, the spacing between the upper and lower electrodes needs to be stretched to more than 15mm, and the take-off voltage will be above 45kV. Additionally, for the same sample, the experiment found that the take-off voltage for the upper large and lower small electrode combination is lower than that for the upper small and lower large electrode combination. Therefore, to maximize the system's levitation capability, an upper large and lower small electrode combination should be used. Moreover, for the upper large and lower small electrode combination, the charge distribution at the top of the sample is more dispersed, effectively avoiding discharge between the sample and the upper electrode due to excessive charge concentration.

Figure 2: Improvement of the Electrostatic Levitation Power Distribution Method

This paper adopts the method of powering both the upper and lower electrodes simultaneously, as shown in Figure 2, and experiments have shown that connecting the lower electrode to a positive charge can reduce the voltage of the upper electrode while successfully levitating the sample. This is equivalent to connecting two high-voltage amplifiers in series to provide voltage between the upper and lower electrodes. Figure 3 shows the experimentally determined take-off voltage and levitation voltage of the upper electrode for levitating the same sample as a function of the voltage applied to the lower electrode. As the lower electrode voltage increases from 0 to 5kV, the upper electrode take-off voltage decreases from 9.5kV to 5.8kV, and the levitation voltage decreases from 8.2kV to 3.3kV. Therefore, applying a positive voltage to the lower electrode and a negative voltage to the upper electrode has the same effect. Additionally, since the sample take-off is a relatively random process, the linearity of the take-off voltage is not as good as that of the levitation voltage.

Figure 3: Variation of Upper Electrode Take-off Voltage and Levitation Voltage with Lower Electrode Voltage: (a) Take-off Voltage; (b) Levitation Voltage

Another key point in achieving levitation of large-scale samples is the improvement of the positioning light path. The currently used position-sensitive detector (PSD) has a photosensitive surface size of 11mm, and the diameter of the positioning parallel laser beam is 10mm. This combination is impossible for levitating a 10mm diameter sample. The diameter of the positioning laser beam required for levitating a 10mm sample and the spacing between the upper and lower electrodes in the vertical direction are both 15mm. Therefore, to match the positioning laser with the position-sensitive detector, the beam diameter needs to be adjusted using a lens.

Figure 4: Improvement of the Positioning Laser Light Path in the Electrostatic Levitation System

Experimental Results:

As shown in Figure 4, when the positioning laser passes through the sample, placing two convex lenses with a focal length ratio of 3:2 in its light path can transform a 15mm beam into a 10mm beam, and correspondingly, the projection diameter of the sample on the photosensitive surface of the position-sensitive detector (PSD) is also reduced by 1.5 times. Figure 5 shows the stably levitated 10mm Ti and Fe spheres, with the Ti sphere having a mass of 2.36g and the Fe sphere having a mass of 4.12g.

Figure 5: Levitation of 10mm Diameter Samples: (a) Ti; (b) Fe

In the experiment, the electrostatic levitation process was optimized by changing the positioning light path and power distribution method, significantly enhancing the electrostatic levitation capability and successfully achieving stable levitation of large-sized metallic materials with a diameter of 10mm for the first time.

Voltage Amplifier Recommendation: ATA-7050

Figure: Specification Parameters of the ATA-7050 High-Voltage Amplifier

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