Screen-printing processes offer advantages in producing directly patterned and integrated piezoelectric elements, and fill an important technological gap between thin film and bulk ceramics. However, several existing problems in the screen-printed piezoelectric thick films, such as the poor reliability and the required high sintering temperature, are significantly limiting their applications. In this work, lead zirconate titanate (PZT) ceramic films of 30 μm in thickness were deposited on Pt-coated silicon substrates by the screen-printing process, in which the ceramic pastes were prepared through a chemical liquid-phase doping approach. Porous thick films with good adhesion were formed on the substrates at a temperature of 925°C. Stable out-of-plane piezoelectric vibration of the thick films was observed with a laser scanning vibrometer (LSV), and the piezoelectric dilatation magnitude was determined accordingly. Our piezoelectric measurements through the areal displacement detection with LSV exhibited distinct advantages for piezoelectric film characterization, including high reliability, high efficiency, and comprehensive information. The longitudinal piezoelectric coefficients of the thick films were calculated from the measured dilatation data through a numerical simulation. High piezoelectric voltage constants were obtained due to the very low dielectric constant of the porous thick films. The application potentials of our screen-printed thick films as integrated piezoelectric sensors are discussed.
For effective pulmonary drug delivery of insulin for example, drug particles must be in the range of 1 to 5 microns. A piezoelectrically actuated MEMS atomizer based on Rayleigh instability-driven breakup of filaments has been designed to produce drug particles in this range. Although the formation of droplets from jets have been used extensively in ink-jet printing, the currently presented mode of droplet formation has not yet been demonstrated by any MEMS device. Testing of the vaporiser reveals that the droplets generated lie primarily in the range of 1.0 through 3.0 microns, a range that covers the designed droplet size of 2.5 microns. We thus show that it is possible to implement this mode of droplet generation that will achieve better device efficiency.
This paper reports a process used for the microfabrication of an array of hollow microneedles. The purpose of the array is for painless transdermal drug delivery. The fabrication process uses wet bulk silicon technology and copper electroplating technology. First, a microneedle array mold on <100>-oriented silicon was fabricated by wet anisotropic etching using KOH solution, then the silicon mold was electroplated with copper. After which, the hollow copper microneedle array was released by a lift-off process or by etching off the silicon mold in KOH solution. The hollow copper microneedle array has been mounted on a polycarbonate platform, which consist of laser ablated cavities and channel for external connection to drug source. In consideration of the contour of human’s skin and the geometry of the microneedle tip, which has walls of sloping gradient corresponding to the (111)-planes, the height of the microneedle array is 200 μm. Two arrays of hollow copper microneedle were fabricated. They have square base of dimensions 390 μm and 400 μm and square tips of size 100 μm and 120 μm with square holes of size 88 μm and 94 μm respectively. Both arrays have microneedle tips at 1900 μm apart from one another and consist of 10 × 10 microneedle tips.
A 3D model of one type of micro pumps was supposed and analyzed using finite element method (FEM). The pump had square shape cavity and was driven by a square shape PZT component. The finite element analysis (FEA) took into consideration of the effects of PZT component dimensions, membrane thickness, pump chamber pressure and other geometric parameters. Modal analyses were also conducted. Compression ratio of the pump chamber was taken as the prime parameter for the analyses. It was found that the membrane thickness and the PZT plate thickness played major roles in determining the compression ratio. For each membrane thickness, there was always an optimum PZT plate thickness that gave the maximum compression ratio. Curves showing the relationship between the optimum PZT plate thickness and the membrane thickness at different chamber pressures were given, based on the FEA results. A set of optimum pump design parameters was proposed.
A methodology for the simulation of a reciprocating displacement micro-pump is presented. First a check valve model was analyzed using coupled FEM to obtain the characteristics relationship between flow rate and the pressure as well as the minimum valve opening pressure. Then a model for the micro-pump actuator driven by PZT disks is proposed and simulated. The pump model takes into account the effects of chamber pressure and geometrical parameters. The maximum downward deflection of the actuating membrane is taken as the target parameter to analyze. It was found that the maximum membrane deflection could reach over 10micrometers microns, much larger than the radial displacement. This 'displacement amplification' is the underlying working principle of this kind of micro-pump. Quantitative analyses of the effects of various factors on the deflection are conducted. It is found that the thickness of the membrane has the biggest influence on the deflection. For each membrane thickness, there exists an op[t9kum PZT disk thickness that gives the maximum deflection at a particular electric field. Other factors with less influence on the deflection are also investigated. An optimum set of design parameters for the micro-pump is obtained form the analyses.
In this paper, an electrochemical actuator was fabricated and tested. The good linearity relationship between the dosing rate and the electrolysis current has been achieved for the demonstrative electrochemical actuator in the selected electrolyte and electrode material cell from 50 micro-A to 1000 micro-A electrolysis current. The microflow rate less than the evaporation that can be obtained by an improved standard gravimetric method in situ. The error resulted from tested work liquid inevitable evaporation was also excluded by the improved approach at very low microflow testing. The on-line testing method can be used as very low microflow rate calibration. The lowest stable flow rate was 0.19 micro-liter/min (3.2nl/s). The response time was also shown by the means of on-line measurement.
In this paper, simulation studies to determine the feasibility of producing filaments using `drop and demand' techniques are presented. These filaments will break up into droplets due to the phenomena caused by Rayleigh instability. In the biomedical applications, for effective pulmonary drug delivery of insulin, for example, the drug particles must be in the range of 1 to 5 microns in size. This stringent requirement is also encountered in gas flow seeding for Laser Doppler Velocimetry studies. A piezoelectrically actuated MEMS atomizer based on Rayleigh instability-driven break-up of filaments has been designed to meet this requirement. Although the formation of droplets from jets has been used extensively in ink-jet printing, the currently presented mode of droplet formulation has yet to be demonstrated in a MEMS device.
In this paper, the feasibility of a self-oscillating anemometer is examined. A 2D numerical study of a novel self-oscillating anemometer that can be fabricated using micromachining techniques is performed. The device is essentially a square cylinder suspended in the fluid flow by a fixed beam. The flow velocity can be easily measured by determining the frequency of oscillation obtained from capacitance sensing. Anemometer with different length scales can be fabricated to enable different ranges of velocities to be measured.
This paper reports an experimental investigation on the statistical properties of laser speckle recorded by using a CCD camera under different F numbers. Statistical properties such as the probability density function of the intensity of the laser speckle varies with the F number of the optical set-up for different m parameters were analyzed and compared with the theoretical prediction.