mi14061267.pdf - 第16页

Micromachines 2023 , 14 , 1267 16 of 17 viscosity will reduce the difﬁculty of injection, increase the droplet outlet velocity and droplet volume and impr ove the injection efﬁciency of the device, but the control accura…

Micromachines 2023, 14, 1267 15 of 17

device gradually decreases due to the entry of bubbles until the device almost fails. Based

on the above and experimental results, it can be seen that the nozzle-driven piezoelectric

micro-jet device proposed in this work has good stability and control accuracy compared

with the traditional piezoelectric micro-jet device.

Micromachines 2023, 14, x FOR PEER REVIEW 25 of 28

The nozzle-driven piezoelectric micro-jet device proposed in this work is not like the

traditional piezoelectric micro-jet device; due to the entry of bubbles, the stability of the

device will gradually decline as the work progresses. Once the bubbles are entrapped, the

air bubble grows via rectiﬁed diﬀusion and results in a malfunction [13]. In addition to

excellent stability, the piezoelectric micro-jet device proposed in this paper also has good

accuracy and ejection speed. The device has a maximum drop outlet velocity of 29.056 m/s

at a voltage amplitude of 200 V and a maximum drop accuracy of 13.864 nL at a nozzle

diameter of 0.2 mm. A piezoelectric micro-jet device with a pin joint designed by Deng et

al. is a typical traditional piezoelectric micro-jet device. Under the condition of an operat-

ing frequency of 100 HZ and voltage amplitude of 100 V, 1 Pa.s adhesive is sprayed, and

its maximum control accuracy can reach about 35 nL [24]. The piezoelectric micro-jet de-

vice proposed by Li et al. can obtain the injection speed of 4.7 m/s under the voltage am-

plitude of 130 V, and the control accuracy can reach 4.7 nL under the signal of a 50% duty

cycle [25]. In summary, compared with the traditional piezoelectric micro-jet device, the

nozzle-driven piezoelectric micro-jet device proposed in this work performs well in terms

of control accuracy and ejection speed, while in terms of stability, the nozzle-driven pie-

zoelectric micro-jet device is beer because it is not aﬀected by bubbles.

In order to prove the stability of the proposed nozzle-driven piezoelectric micro-jet

device, a traditional piezoelectric micro-jet device is fabricated in this work, and its inter-

nal structure is shown in Figure 24a. The cavity structure and experimental seings of the

two sets of experimental devices are the same, and the experimental system built is shown

in Figure 24b. The comparison experiment steps are as follows: under the seings of a

voltage amplitude of 100 V, signal frequency of 8090 Hz, nozzle diameter of 0.4 mm and

oil viscosity of 200 cs, the same continuous pulse signal is applied to the two sets of devices

through a signal generator and power ampliﬁer, and the volume of droplets ejected by

the devices under multiple pulses is measured. The experimental results are shown in

Figure 25. The analysis shows that both sets of devices have good ejection conditions in

the initial few cycles, and both have high control accuracy. However, with the increase in

the total working time, the ejection performance of the traditional piezoelectric micro-jet

device gradually decreases due to the entry of bubbles until the device almost fails. Based

on the above and experimental results, it can be seen that the nozzle-driven piezoelectric

micro-jet device proposed in this work has good stability and control accuracy compared

with the traditional piezoelectric micro-jet device.

Cavity

Piezoelectric

vibrator

Nozzle

Signal generator

Power amplifier

Traditional

device

Proposed

device

Figure 24. The internal structure of the traditional piezoelectric micro-jet device and the comparison

experimental system: (a) The internal structure of the traditional piezoelectric micro-jet device; (b)

the comparison experimental system.

Figure 24.

The internal structure of the traditional piezoelectric micro-jet device and the comparison

experimental system: (

) The internal structure of the traditional piezoelectric micro-jet device; (

) the

comparison experimental system.

Micromachines 2023, 14, x FOR PEER REVIEW 26 of 28

0T 2T 4T 6T 8T 10T 12T 14T 16T

100

150

200

Droplet volume (nL)

Time

The proposed device

The traditional device

Figure 25. The experimental results of the comparison experiment.

5. Conclusions

In this work, a piezoelectric micro-jet device is proposed. Its unique nozzle driving

mode makes the device have many outstanding advantages that traditional piezoelectric

micro-jet devices do not have: (1) The external nozzle is diﬀerent from the traditional cav-

ity vibration type, which avoids the problem that the bubble enters the cavity and reduces

the injection performance. (2) The external nozzle makes the structure of the device more

compact, and the cavity cannot consider the assembly of the vibrator and the problem of

an outlet wire. (3) The external nozzle has strong interchangeability, which can be re-

placed and repaired from time to time without remanufacturing and assembling the de-

vice.

Based on the brief description of the structure of the device and the process of micro-

jet, ANSYS two-phase, two-way ﬂuid–structure coupling analysis is carried out, and the

mechanism of the piezoelectric micro-jet is elaborated upon in detail. On the basis of de-

termining the optimal working frequency, the inﬂuence of voltage amplitude, input signal

frequency, nozzle diameter and oil viscosity on the injection performance of the proposed

device is studied, and a set of control methods is proposed based on this. A small range

of frequency adjustment has lile inﬂuence on the injection performance. Increasing the

voltage amplitude, decreasing the nozzle diameter and decreasing the oil viscosity will

reduce the diﬃculty of injection, increase the droplet outlet velocity and droplet volume

and improve the injection eﬃciency of the device, but the control accuracy of the droplet

will decrease. In addition, when the oil viscosity is greater than 100 Pa.s, it has lile inﬂu-

ence on the volume of droplets, namely, the control accuracy, while the inﬂuence on the

diﬃculty of injection and the outlet velocity of droplets still exists. This work proved the

correctness of the piezoelectric micro-jet mechanism and the feasibility of the proposed

nozzle-driven piezoelectric micro-jet device through experiments and carried out the in-

jection performance test experiment, which mainly investigated the eﬀects of voltage am-

plitude, signal frequency, oil viscosity and nozzle diameter on the droplet outlet velocity

and droplet volume. The experimental results showed that the piezoelectric micro-jet de-

vice has a maximum droplet outlet velocity of 29.056 m/s and a maximum droplet volume

of 86.45 nL at a voltage amplitude of 200 V, while the device can achieve a maximum

droplet accuracy of 13.864 nL at a nozzle diameter of 0.2 mm. From the above mentioned,

it can be seen that the device combines high precision and high eﬃciency excellently. The

experimental results coincide with the ANSYS simulation results, which conﬁrms the cor-

rectness of the simulation experiment. Finally, a comparation experiment is carried out in

this work, and the stability and superiority of the proposed device are veriﬁed by the ex-

periment with the traditional piezoelectric micro-jet device.

Figure 25. The experimental results of the comparison experiment.

5. Conclusions

In this work, a piezoelectric micro-jet device is proposed. Its unique nozzle driving

mode makes the device have many outstanding advantages that traditional piezoelectric

micro-jet devices do not have: (1) The external nozzle is different from the traditional cavity

vibration type, which avoids the problem that the bubble enters the cavity and reduces

the injection performance. (2) The external nozzle makes the structure of the device more

compact, and the cavity cannot consider the assembly of the vibrator and the problem of

an outlet wire. (3) The external nozzle has strong interchangeability, which can be replaced

and repaired from time to time without remanufacturing and assembling the device.

Based on the brief description of the structure of the device and the process of micro-

jet, ANSYS two-phase, two-way ﬂuid–structure coupling analysis is carried out, and the

mechanism of the piezoelectric micro-jet is elaborated upon in detail. On the basis of

determining the optimal working frequency, the inﬂuence of voltage amplitude, input

signal frequency, nozzle diameter and oil viscosity on the injection performance of the

proposed device is studied, and a set of control methods is proposed based on this. A

small range of frequency adjustment has little inﬂuence on the injection performance.

Increasing the voltage amplitude, decreasing the nozzle diameter and decreasing the oil

Micromachines 2023, 14, 1267 16 of 17

viscosity will reduce the difﬁculty of injection, increase the droplet outlet velocity and

droplet volume and improve the injection efﬁciency of the device, but the control accuracy

of the droplet will decrease. In addition, when the oil viscosity is greater than 100 Pa.s,

it has little inﬂuence on the volume of droplets, namely, the control accuracy, while the

inﬂuence on the difﬁculty of injection and the outlet velocity of droplets still exists. This

work proved the correctness of the piezoelectric micro-jet mechanism and the feasibility

of the proposed nozzle-driven piezoelectric micro-jet device through experiments and

carried out the injection performance test experiment, which mainly investigated the effects

of voltage amplitude, signal frequency, oil viscosity and nozzle diameter on the droplet

outlet velocity and droplet volume. The experimental results showed that the piezoelectric

micro-jet device has a maximum droplet outlet velocity of 29.056 m/s and a maximum

droplet volume of 86.45 nL at a voltage amplitude of 200 V, while the device can achieve a

maximum droplet accuracy of 13.864 nL at a nozzle diameter of 0.2 mm. From the above

mentioned, it can be seen that the device combines high precision and high efﬁciency

excellently. The experimental results coincide with the ANSYS simulation results, which

conﬁrms the correctness of the simulation experiment. Finally, a comparation experiment

is carried out in this work, and the stability and superiority of the proposed device are

veriﬁed by the experiment with the traditional piezoelectric micro-jet device.

Supplementary Materials:

The following supporting information can be downloaded at: https:

//www.mdpi.com/article/10.3390/mi14061267/s1, Video S1: experiment demo.

Author Contributions:

Conceptualization, T.-Y.S. and X.-S.W.; methodology, T.-Y.S. and X.-S.W.;

software, Y.-W.H.; validation, X.-D.L. and D.-F.S.; formal analysis, T.-Y.S. and D.-F.S.; investiga-

tion, T.-Y.S.; resources, X.-S.W.; data curation, Y.-W.H.; writing—original draft preparation, T.-Y.S.;

writing—review and editing, T.-Y.S. and X.-S.W.; visualization, X.-S.W.; supervision, X.-S.W.; project

administration, X.-S.W. All authors have read and agreed to the published version of the manuscript.

Funding:

This work was supported by the Professional technical service platform of Shanghai

Committee of Science and Technology (19DZ2291103).

Data Availability Statement: Data sharing is not applicable to this article.

Conﬂicts of Interest: The authors declare no conﬂict of interest.

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