Parameter extraction from BVD electrical model of PZT actuator of micropumps using time-domain measurement technique

To minimize the power consumption of the piezoelectric micropumps utilized in the microfluidics field, suitable models are required to enable the optimization of the lead zirconate titanate (PZT) actuator driving circuits. The recent research shows that the electromechanical parameters of piezoelectric materials can be obtained from Butterworth Van-Dyke (BVD) model. The current study presents a novel time-domain measurement technique for extracting the parameters of a BVD electrical model describing a PZT actuator of the micropump excited by a square pulse with a relatively high voltage and low frequency. The validity of the BVD model is evaluated by using MATLAB software to solve the ordinary differential equations of the electrical model and then comparing the numerical results obtained for the current response of the PZT actuator with the experimentally-observed results. The BVD model has been found to be valid for this specific application of piezo actuators. A good agreement is observed between the two sets of result, and thus the validity of the BVD model and the proposed time-domain measurement technique is confirmed.     

MEMS-based micropumps in drug delivery and biomedical applications

This paper briefly overviews progress on the development of MEMS-based micropumps and their applications in drug delivery and other biomedical applications such as micrototal analysis systems (μTAS) or lab-on-a-chip and point of care testing systems (POCT). The focus of the review is to present key features of micropumps such as actuation methods, working principles, construction, fabrication methods, performance parameters and their medical applications. Micropumps have been categorized as mechanical or non-mechanical based on the method by which actuation energy is obtained to drive fluid flow. The survey attempts to provide a comprehensive reference for researchers working on design and development of MEMS-based micropumps and a source for those outside the field who wish to select the best available micropump for a specific drug delivery or biomedical application. Micropumps for transdermal insulin delivery, artificial sphincter prosthesis, antithrombogenic micropumps for blood transportation, micropump for injection of glucose for diabetes patients and administration of neurotransmitters to neurons and micropumps for chemical and biological sensing have been reported. Various performance parameters such as flow rate, pressure generated and size of the micropump have been compared to facilitate selection of appropriate micropump for a particular application. Electrowetting, electrochemical and ion conductive polymer film (ICPF) actuator micropumps appear to be the most promising ones which provide adequate flow rates at very low applied voltage. Electroosmotic micropumps consume high voltages but exhibit high pressures and are intended for applications where compactness in terms of small size is required along with high-pressure generation. Bimetallic and electrostatic micropumps are smaller in size but exhibit high self-pumping frequency and further research on their design could improve their performance. Micropumps based on piezoelectric actuation require relatively high-applied voltage but exhibit high flow rates and have grown to be the dominant type of micropumps in drug delivery systems and other biomedical applications. Although a lot of progress has been made in micropump research and performance of micropumps has been continuously increasing, there is still a need to incorporate various categories of micropumps in practical drug delivery and biomedical devices and this will continue to provide a substantial stimulus for micropump research and development in future.     

Equivalent electrical network for performance characterization of piezoelectric peristaltic micropump

Utilizing an electronic–hydraulic analogy, this study develops an equivalent electrical network of a piezoelectric peristaltic micropump which has not been modeled the whole system operation completely by computational fluid dynamics (CFD) or equivalent electrical network so far due to its excessive complicated structure. The validity of the proposed model is verified by comparing the simulation results obtained using the SPICE (simulation program with integrated circuit emphasis) software package for flow rate spectrum and its maximum state of a typical micropump with the experimental observations for two working fluids, namely DI water and blood. The simulation results predict a maximum flow rate frequency and flow rate of 280 Hz and 43.23 μL/min, respectively, for water, and 210 Hz and 24.12 μL/min for blood. The corresponding experimental results are found to be 300 Hz and 41.58 μL/min for water and 250 Hz and 23.75 μL/min for blood. The relatively poorer agreement between the two sets of results when using blood as the working fluid is thought to be the result of the non-Newtonian nature of blood, which induces a more complex, non-linear flow behavior within the micropump. Having validated the proposed model, the equivalent network is used to perform a systematic analysis of the correlation between the principal micropump design parameters and operating conditions and the micropump performance. The results confirm the validity of the equivalent electrical network model as the first microfluidic modeling tool for optimizing the design of peristaltic micropumps and for predicting their performance.     

Parametric characterization of piezoelectric valveless micropump

Experimental investigations are performed to determine the influence of electrical excitation and geometrical parameters on the performance of piezoelectric valveless micropumps fabricated on printed circuit board substrates. Strain gauges and shunt resistor are used in conjunction with a data acquisition system to form an effective transducer, capable of providing magnitude and phase response information pertaining to fluid–structure interaction. Effect of conical diffuser geometry on the displacement response and pressure flow characteristics are studied. With suitable variations in the design of the diffuser element and input excitation parameters, the ability of the valveless micropump can be extended to include forward, reversed and bidirectional flow features. The characteristic signatures of single and two peaks in flowrate or pressure data are captured in the displacement phase response. System identification approach is proposed to model and predict the performance of valveless micropumps.     

An experimental and numerical investigation into the effects of the PZT actuator shape in polymethylmethacrylate (PMMA) peristaltic micropumps

Utilizing a solvent-assisted bonding process, two diffuser-type polymethylmethacrylate (PMMA) peristaltic micropumps are fabricated with a linear array of circular microchambers with a depth and diameter of 15 m and 7 mm, respectively, actuated using either square or circular PZT actuators. Experimental trials are performed to characterize the performance of the two micropumps under driving frequencies ranging from 80 to 150 Vpp and actuation frequencies in the range of 10 Hz to 1 kHz. The results reveal that the micropump with square PZT actuators generates a maximum pumping rate and back pressure of 217 l/min and 9.2 kPa, respectively, while the micropump with circular actuators generates a maximum flow rate of 131 l/min and a back pressure of 2.7 kPa. ANSYS finite element simulations demonstrate two events. First, given an equivalent surface area, the circular actuators undergo a greater displacement than the square actuators under given actuation conditions. In other words, the circular actuator design is more efficient to represent a higher ratio of the displacement to the actuation area (d/A). However, the circular actuators with the surface area of 38.47 mm² are smaller than the square actuators (49 mm²). In addition, it is inferred that the relatively poorer performance of the circular actuators is due in part to thermal damage of the PZT patches during their removal from the bulk PZT chip using a laser cutting device in the pump fabrication process. Secondly, when the shape of the effective working area for the actuation is rectangular which is usual in a MEMS design, the rectangular actuator with length of 7 mm has significantly higher displacement (0.71 m) than that of the circular actuator with diameter of 7 mm (0.396 m). Consequently, a rectangular actuator design presents a more practical solution for higher performance of micro-actuators.     

Thin-film shape-memory alloy actuated micropumps

Micropumps capable of precise handling of low-fluid volumes have the potential to revolutionize applications in fields such as drug delivery, fuel injection, and micrototal chemical analysis systems (μTAS). Traditional microactuators used in micropumps suffer from low strokes and, as a result, are unsuitable for achieving large fluid displacement. They also suffer low-actuation work densities, which translate to low forces. We investigate the use of the shape-memory effect (SMA) in sputter-deposited thin-film shape-memory alloy (SMA) titanium nickel (TiNi) as an actuator for microelectromechanical systems (MEMS)-based microfluidic devices, as it is capable of both high force and high strains. The resistivity of the SMA thin film is suitable for Joule heating, which allows direct electrical control of the actuator. Two micropump designs were fabricated-one with a novel complementary actuator and the other with a polyimide-biased actuator-which provided thermal isolation between the heated microactuator and the fluid being pumped. A maximum water flow rate of 50 μl/min was achieved     

Flow characterization of valveless micropump using driving equivalent moment: theory and experiments

A valveless micropump, actuated by a PZT disk bonded to a glass plate, can generate positive flow. In order to estimate flow characteristics of micropumps, it is necessary to theoretically analyze the radial expansion (more specifically, the equivalent moment) of the PZT disk according to the voltage input. Using the equivalent moment, deflection equations are derived for the tri-layer disk (PZT, epoxy bonder and glass plate) and are confirmed to match well with experiments. The flow rate of the valveless micropump is also theoretically and experimentally investigated in terms of input voltage and oscillation frequency. The flow increased at a rate of 0.1 μL/min/V, and the maximum flow rate was obtained at the driving frequency of around 225 Hz.     

A multifunction and bidirectional valve-less rectification micropump based on bifurcation geometry

In this paper, we introduce a novel valve-less rectification micropump based on bifurcation geometry. Three micropumps based on three different bifurcation configurations were designed, fabricated and experimentally investigated. These designs demonstrate the potentials of developing bidirectional micropumps and multifunction microfluidic devices (combined functions of micro pumping and mixing). Polydimethylsiloxane (PDMS) was employed to fabricate the micropumps. Circular piezoelectric transducers (PZT) were used as flow actuators. Detailed fabrication procedures are illustrated. The micropumps were tested against two ranges of actuator frequencies. The first test was conducted in a frequency range between 0 and 100 Hz with small increments of 5 Hz, while the second test was conducted in a frequency range between 0 and 300 Hz with increments of 50 Hz. Ethanol was used as the working fluid in all experiments. A new dimensionless parameter was introduced to evaluate the efficiency of valve-less rectification micropumps and determine the optimum operational frequency. The flow rate and maximum back pressure were measured. Results of experiments confirmed and demonstrated the feasibility of valve-less rectification micropumps based on bifurcation geometry at a low frequency range. Additionally, results showed the potentials of multifunctional, bidirectional, and self-priming micropumps.     

Dynamic simulation of thermopneumatic micropumps for biomedical applications

A model simulation of dynamic behavior of thermopneumatic micropump is presented. The model uses conservation of energy, mass, and momentum to predict the behavior of existing thermopneumatic micropumps. Applied to existing micropumps, simulation predicts trends similar to those reported experimentally. Dynamic simulation of effect of design parameters on performance of micropump is, then, carried out through the article. Results suggest that increasing operating frequencies results in higher volume flow rates until a critical frequency is reached. At higher frequencies volume flow rates decrease. Critical frequencies are dependent on damping. The higher the damping coefficient the lower the critical frequency becomes. For high frequency operation the performance of the micropump is dominated by both damping and heat capacity of micropump components. For low frequency operation the performance is dominated by heat losses from walls of air-chamber. The model provides general guidelines for building and operating the micropump.     

一种用于生化传感检测的压电式行波微流泵的研究

为了减少生化传感器中样品的消耗,基于行波原理,本文设计了一种新型的压电式微流泵.首先,理论证明了行波的产生机理,并用流体仿真软件Fluent进行了验证;其次,设计并制作了锯齿沟道和直沟道两种结构的微流泵,在压电双晶片阵列的驱动下,测量了这两种微流泵在不同频率和电压下的特性.结果表明锯齿形沟道结构的压电式行波微流泵性能更...     

A push–pull multi-layered piggyback PZT actuator

 To increase the recording density of hard disk drives (HDDs), we developed a push–pull multi-layered piggyback PZT actuator that enables fine positioning by a dual-stage servo system. This PZT actuator consists of 31-mode push–pull multi-layered PZT strips and a head suspension. It generates a 1.4-μm effective radial head displacement at 5 V. This displacement is twice that of conventional piggyback actuators. The main resonance frequency of the actuator is higher than 9 kHz, its lifetime is longer than five years, and it has a self-latch property. These features mean that the developed actuator can meet all the requirements for implementation in HDD servo systems, including a track density of 100 kTPI (kilo-tracks per inch). The actuator was implemented in two types of HDDs (A-type and B-type), which reduced the repeatable and non-repeatable positioning errors (by 40 to 45% and 28 to 34%, respectively). Received: 25 July 2001/Accepted: 11 December 2001     

Self-assembly of PZT actuators for micropumps with high process repeatability

In this paper, we report a novel capillary-driven self-assembly technique which proceeds in an air environment and demonstrate it by assembling square piezoelectric transducer (PZT) actuators for 28 diffuser valve micropumps on a 4-inch pyrex/silicon substrate: on the substrate, binding sites are wells of 24 /spl mu/m in depth and the only hydrophilic areas; on the bonding face of the PZT actuator, the central hydrophilic area is a square identical in size to the binding site, and the rim is hydrophobic; acrylate-based adhesive liquid is dispensed across the substrate and wets only the binding sites; the hydrophilic areas on the introduced PZT actuators self-align with the binding sites to minimize interfacial energies by capillary forces from the adhesive droplets; the aligned PZT actuators are pressed to contact the gold coated substrate by their rims and the adhesive is polymerized by heating to 85 /spl deg/C for half an hour, so permanent mechanical and electrical connections are established, respectively, at the center and rim of each PZT actuator. These pumps perform with high uniformity, which is indicated by a small standard deviation of their resonant frequencies to pump ethanol: the average resonant frequency is 6.99 kHz and the standard deviation is 0.1 kHz. Compared with the conventional bonding process with highly viscous silver epoxy, this assembly method has several major advantages: highly accurate placement with self-alignment, controllable adhesive thickness, tilt free bonding, low process temperature and high process repeatability.     

A micropump using amplified deformation of resilient membranes through oil hydraulics

Toward the development of micropumps that operate under low external air pressures, a new polydimethylsiloxane (PDMS), pneumatic micropump using amplified deformation of resilient PDMS membranes through oil hydraulics was presented in this study. The new micropump employed oil-hydraulic chambers with pre-filled mineral oil to amplify the deformation of flexible PDMS membranes; it therefore delivered a higher pumping rate and withstood a greater back pressure while requiring a significantly lower external air pressure for actuation. The optimized pumping rate and back pressure of the oil-hydraulic micropump compared favorably to previous pneumatic micropumps. Characterization of the micropump revealed that the oil hydraulics amplified the deformation of PDMS membranes by approximately threefold and improved the pumping rate and the back pressure by 77 and 21 %, respectively. With high pumping performances and the capability to be driven with only a low air pressure, this new micropump may therefore become a key component in future microfluidic devices and lab-on-a-chip systems.     

Fully coupled modeling and design of a piezoelectric actuation based valveless micropump for drug delivery application

The precise control over the drug delivery involved in several vital applications including healthcare is required for achieving a therapeutic effect. For such precise control/manipulation of the drugs, micropumps are used. These micropumps are basically of two types viz. check valve-based and valveless micropumps. The valveless micropumps are preferable due to the congestion-free operation of diffuser/nozzle valves. In this paper, design optimization of a valveless piezo-electric actuation based micropump is carried out using COMSOL Multiphysics 5.0 by coupling two Multiphysics interface modules namely fluid–structure interaction and piezoelectric physics modules. Using simulation studies, the influence of pump design parameters including diffuser angle, diffuser length, neck width, chamber depth, chamber diameter and diaphragm thickness on net flow rate is studied. An optimal set of design parameters for the proposed micropump is identified. Further, the influence of actuation frequency on the flow rate is analysed. It is found that the proposed micropump is capable to deliver a net flow rate of 20 µl/min and a maximum back pressure attainable is 200 Pa.

     

A study of PZT valveless micropump with asymmetric obstacles

The results of a study on a new type of PZT valveless micropump with asymmetric obstacles are presented in this paper. The valveless micropump was made through a MEMS fabrication process by using simply only one photo mask. Asymmetric obstacles are used for the flow directing device instead of the diffuser/nozzle elements used in previous studies. In this study, numerical simulations were also carried out to evaluate the design and the performance of the new micropump. The main feature of the present micropump is that it has a uniform cross-section area across the micro-channel, which gives many advantages. The differential pressure head and the pumping flow rate can be adjusted easily by using obstacles of different shapes and changing the PZT operating frequency without changing the dimensions of the micro-channel. In this experiment, the performance of the micropump was evaluated by measuring the pressure head difference and the flow rate as the input voltage ranged from 20 to 40 V, a range much lower than those in previous studies. The pumping pressure can reach a maximum of 1.2 kPa, and the maximum net volume flow rate is 156 μl/min. These test data indicate that this micropump fulfills the demands for most micro-fluidic systems. Moreover, the present device can be easily applied to complex systems with combinations of several pumps and microchannels in the future.     

Design and control of a single-stage dual-actuator system for high-precision manufacturing

This paper proposes a design for the linear state feedback control of the dual-actuator system, which is a dual-input single-output system for the high-precision manufacturing stage. The proposed control prevents saturation or reduces the unnecessary movement of the piezoelectric (PZT) actuator at the transient response by tracking the error between the estimated and actual positions of the coarse-actuator system at each control sample. Also, a new mechanism of the single-stage dual actuator is introduced. The axes of the stepper motor and the PZT actuator are co-axial. The coupling effects between the stepper motor and the PZT actuator are considered. Both the simulation and experiment results show that the proposed algorithm successfully prevents unwanted motions of the PZT actuator at the transient response. The experiment results show that the settling time and overshoot were enhanced by 45.7 and 95.9 %, respectively, for the proposed algorithm when the reference distance was 10 μm, which exceeds the stroke of the PZT actuator.     

基于MEMS的微泵研究进展

主要介绍了基于MEMS的微泵 10年来的研究成果和研究现状。微泵是微电子机械系统(MEMS)中重要的执行器件 ,在系统中占有很重要的地位。微泵可以分为有阀泵和无阀泵两大类 ,一般来说 ,有阀泵的制造工艺和应用技术比较成熟 ,但存在加工尺寸限制和使用寿命的问题 ;无阀泵的原理新颖 ,结构相对简单 ,更适合微型化发展 ,是目前研究的热点。     

Peristaltic micropump system with piezoelectric actuators

This work presents a driving system for a peristaltic micropump that is based on piezoelectric actuation. The effects of the actuation sequence on pump performance are also considered. A valveless peristaltic micropump based on piezoelectric actuation is designed and fabricated using microelectromechanical system technology. The pump has three parts––silicon, Pyrex glass and commercially available bulk PZT (lead zirconate titanate) chips. The peristaltic micropump actuated by PZT chips comprises three chambers that are in series. The driving system consists of an ATmega 8535 microprocessor, a high voltage power supply, three differential amplifiers, a phase controller, an A/D converter, a 555 oscillator and an LCD module. It is supplied via a 110 Vrms 60-Hz AC line and is programmable. The system can produce step-function signals with voltages of up to 100 V_pp and frequencies ranging from 10 Hz to 1 kHz, as the inputs for the pump. Fluid pumping with air is successfully demonstrated. Additionally, 3-, 4- and 6-phase actuation sequences for the pump are designed and used to study the effects on pump performance, as revealed by the flow rate and the displacement of a pump diaphragm. The experimental results show that the flow rate and the displacement of the diaphragm actuated by the 4-phase sequence exceed those actuated by the 3- and 6-phase sequences. A flow rate of 17.6 μl min⁻¹ and a displacement of 2.91 μm (peak-to-peak) in 4-phase peristaltic motion are achieved at 100 Hz and 100 V_pp. The results demonstrate that the pump actuated in the 4-phase sequence is the most efficient. Consequently, the actuation sequences can affect the pump performance.     

Study on a piezoelectric micropump for the controlled drug delivery system

We present the design of a new controlled drug delivery system potential for in vitro injection of diabetics. The system incorporates some integrated circuit units and microelectromechanical system devices, such as micropump, microneedle array and microsensor. Its goal is to achieve safer and more effective drug delivery. Moreover, a valveless micropump excited by the piezoelectric actuator is designed for the drug delivery system, and a simple fabrication process is proposed. A dynamic model is developed for the valveless micropump based upon the mass conservation. To characterize the micropump, a complete electro-solid-fluid coupling model, including the diffuser/nozzle element and the piezoelectric actuator, is built using the ANSYS software. The simulation results show that the performance of micropump is in direct proportion to the stroke volume of the pump membrane and there is an optimal thickness of the piezoelectric membrane under the 500 V/mm electric field. Based on this simulation model, the effects of several important parameters such as excitation voltage, excitation frequency, pump membrane dimension, piezoelectric membrane dimension and mechanical properties on the characteristics of valveless micropump have been investigated.     

Numerical analysis of non Newtonian fluid flow in a low voltage cascade electroosmotic micropump

In microfluidic devices, many fluids have non-Newtonian behaviors, especially biofluids. The viscosity of these fluids mostly depends on the shear rate. Sometimes the non-Newtonian fluids should be transferred by micropumps in lab-on-chip devices. Previous researchers investigated the flow rate in simple electroosmotic flow micropumps which have a simple channel geometry. In the present study, the effects of non-Newtonian properties of fluid in a low voltage cascade electroosmotic micropump are numerically investigated using the power law model. The micropump is modeled in two dimensional with one symmetric step and has a more complex geometry than previous studies. The numerical results show that, the non-Newtonian behavior of fluid affects flow rate in the micropump. The flow rate decreases if the fluid is dilatant. Also, it increases if the fluid is pseudoplastic. Moreover, the pressure which is needed to stop the electroosmotic flow rate in the micropump is calculated. Results show that, the back pressure has a slight change as the fluid has non-Newtonian behavior.