Three-dimensional printing techniques

Acoustic levitation uses acoustic radiation forces to counteract gravity and suspend objects in mid-air. Although acoustic levitation was first demonstrated almost a century ago, for a long time, it was limited to objects much smaller than the acoustic wavelength levitating at fixed positions in space. Recent advances in acoustic levitation now allow not only suspending but also rotating and translating objects in three dimensions. Acoustic levitation is also no longer restricted to small objects and can now be employed to levitate objects larger than the acoustic wavelength. This article reviews the progress of acoustic levitation, focusing on the working mechanism of different types of acoustic levitation devices developed to date. We start with a brief review of the theory. Then, we review the acoustic levitation methods to suspend objects at fixed positions, followed by the techniques that allow the manipulation of objects. Finally, we present a brief summary and offer some future perspectives for acoustic levitation.

Review of Progress in Acoustic Levitation

Continuous flow synthesis of ultrasmall gold nanoparticles in a microreactor using trisodium citrate and their SERS performance

A review of recent studies on piezoelectric pumps and their applications

Review of digital printing technologies for electronic materials

A piezoelectric impinging jet valve is used as a study object to investigate the effect of the ball needle in the existing impinging jet and nozzle structure of the valve on the performance of the jet. First, FLUENT software is used under different ball needle and nozzle structural parameters to simulate the pressure distribution that the ball needle and nozzle in the pressure cavity form when the ball needle hits the nozzle, by arranging the structure model of the ball needle and impact valve nozzle. The piezoelectric impact injection valve and the experiment test system are then designed. Test results show that the ball needle and nozzle structural parameters are closely related to the injection performance of the impact valve. Under certain conditions, a greater needle radius corresponds to a smaller nozzle aperture and taper. Moreover, high-viscosity liquid jetting is easily achieved. By using a ball needle with a radius of 1.5 mm, a taper angle of 60°, and a nozzle diameter of 0.1 mm, we can realize the industrial viscosity of 58 000 cps in glue spray, and the injection plastic fluid volume is 0.62 μl.

http://iopscience.iop.org/article/10.1088/0964-1726/24/10/105023/pdf

Nozzle and needle during high viscosity adhesive jetting based on piezoelectric jet dispensing

To compensate for the insufficiency and instability of solder paste dispensing and printing that are used in the SMT (Surface Mount Technology) production process, a noncontact solder paste jetting system driven by a piezoelectric stack based on the principle of the nozzle-needle-system is introduced in this paper, in which a miniscule gap exists between the nozzle and needle during the jetting process. Here, the critical jet ejection velocity is discussed through theoretical analysis. The relations between ejection velocity and needle structure, needle velocity, and nozzle diameter were obtained by FLUENT software. Then, the prototype of the solder paste jetting system was fabricated, and the performance was verified by experiments. The effects of the gap between nozzle and needle, the driving voltage, and the nozzle diameter on the jetting performance and droplet diameter were obtained. Solder paste droplets 0.85 mm in diameter were produced when the gap between the nozzle and needle was adjusted to 10 μm, the driving voltage to 80 V, the nozzle diameter to 0.1 mm, and the variation of the droplet diameter was within ±3%.

Design and Experiment of a Solder Paste Jetting System Driven by a Piezoelectric Stack.

Many scholars have conducted in-depth analysis on relevant factors that affect the accuracy of jet dispensing. However, research on the influence of needle impact velocity on jetting performance is limited. Thus, a piezoelectric needle-collision dispenser for micro-droplet jetting is designed in this study, and the influence of the needle impact velocity on jetting effect is deeply analyzed. Initially, the principle of droplet formation and injection is analyzed by Fluent simulation. Thereafter, the mathematical model of the droplet velocity in the nozzle orifice is derived, and the influence of the needle impact velocity on the jetting performance is simulated and analyzed. Results show that the needle impact velocity has an influence on the jetting effect. A prototype of the jetting dispenser is subsequently fabricated, and the needle impact velocity is tested with laser micrometer. The relationship between the needle impact velocity and droplet weight and its corresponding ejected effect are obtained through experimental research. Finally, a UV glue with viscosity of 5,000 cps can be ejected with a minimum average diameter of 272.1 μm by using a needle with a radius of 0.5 mm, a nozzle with a diameter of 50 μm, a taper angle of 90°, a supply pressure of 0.2 Mpa, and a needle impact velocity of 0.13 m/s. The variation of the droplet diameter is within ±2.5%.

/pdf/influence-of-needle-impact-velocity-on-the-jetting-effect-of-3k2e2pgvm7.pdf

Influence of needle impact velocity on the jetting effect of a piezoelectric needle-collision jetting dispenser

To prepare the gold nanoparticles (AuNPs) with uniform sizes, fine morphology, and good monodispersity, a pulsed mixing microfluidic system based on PZT actuation was presented. The system includes PZT micropump and Y type micromixer. By adjusting voltage (entrance flow rate), pulsed frequency, phase, and other parameters, a variety of mixing modes can be achieved, so as to realize the controllable synthesis of nanoparticles in a certain range. By numerical simulation and analysis, the channel section size, entrance angle, and pulse frequency were optimized. Based on the optimized structure and working parameters, the test prototype has been manufactured in lab, and the related synthesis tests of AuNPs were carried out. The test results indicate that AuNPs with uniform morphology and good monodispersity can be synthesized using the system with the section size (0.4 mm × 0.4 mm), the entrance channel angle (60°) under condition of the pulsed frequency (300 Hz), and the entrance flow rate (4 mL/min). The average diameter and its standard deviation of AuNPs synthesized were 21.6 nm, 4.83 nm, respectively. The research work above can be applied to the fields such as the controlled synthesis of noble metal nanoparticles, biomedicine, and microchemical system.

/pdf/continuous-flow-controlled-synthesis-of-gold-nanoparticles-2stjkohtwn.pdf

Continuous Flow Controlled Synthesis of Gold Nanoparticles Using Pulsed Mixing Microfluidic System

A low driving voltage, low cost, high performance insulin delivery system based on PZT actuation is presented in this paper, which consists of two functional units, namely, micropump unit and electronic control unit. The PZT micropump is the core of micropump unit and is the key base to ultimately realize insulin precision delivery of the whole system. The electronic control unit is the important auxiliary unit for the realization of the whole system function. To obtain a higher working performance under low voltage, a serial structure with two chambers and three check valves is adopted in the design of PZT micropump. In place of silicon and glass, main parts of micro-pump unit are manufactured using the polymers which have good biocompatibility, stability and low cost. Through the systematic experimental test for the prototype of PZT insulin delivery system in lab, the maximum backpressure of 14.64 kPa is recorded at applied voltage of 36 V and working frequency of 160 Hz, the maximum flow rate of 5.74 ml/min is obtained in the condition of 36 V and 300 Hz. Under the voltage of 36 V and working frequency of 200 Hz, the micro-dosage pumped by PZT micro-pump displays a good linear characteristic with the number of driving impulses. The minimum resolution of insulin delivery can obtain 3 × 10?4 ml (0.03 U insulin at the concentration of 100 U).

Jianfang Liu

Papers

Nozzle and needle during high viscosity adhesive jetting based on piezoelectric jet dispensing

Design and Experiment of a Solder Paste Jetting System Driven by a Piezoelectric Stack.

Influence of needle impact velocity on the jetting effect of a piezoelectric needle-collision jetting dispenser

Continuous Flow Controlled Synthesis of Gold Nanoparticles Using Pulsed Mixing Microfluidic System

A low cost, high performance insulin delivery system based on PZT actuation