The squeeze mode PIJ was invented by Steven Zoltan in 1972 (US patent 3,683, 212, 1972). The actuator in this mode consists of a hollow tube of piezoelectric material with electrodes on its inner and outer surface. The tube is radially polarised, and this causes a contraction of the transducer when a driving voltage is applied.
The sudden displacement of the enclosed volume causes a drop of ink to be ejected from the nozzle. Some of the ink is moved backward in the tube, but this is not significant because of the high acoustic impedance of the long and narrow channel of the tube.
The print head consists of a glass capillary surrounded by a piezoelectric material. When an electric voltage is applied to the piezoelectric material, it squeezes or expands the glass capillary, which results in an ejection of a drop. An integrated orifice and wetted surfaces that are predominantly glass make this inkjet device suitable for many liquids. Able to dispense drops of both aqueous and solvent based fluids at up to 50 °C, the print head can be used to print fluids with viscosity of < 20 mPa s and surface tension between 20 and 70 mN m-1. This type of single-nozzle print head is widely used for material testing and small prototype fabrication of organic semiconductor devices because it has advantages over multinozzle designs. Controlling the driving electronics and supplying the fluid are very simple as this is only one nozzle. In addition, it is tolerant to nozzle clogging because of the ease of cleaning the nozzle chamber. The glass nozzle also makes it possible for the user to observe the movement of the meniscus inside the nozzle. But, the low throughput is the major disadvantage of such a single jet system.
Ref: PhD Thesis - Fluid characterisation and drop impact in inkjet printing for organic semiconductor devices, Sungjune Jung, St John’s College, 2011
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