In recent research, there has been a growing interest in the analysis of flow through microdiffusers and micropumps in order to characterize and optimize the performance of these devices. In this review, the recent advances in the numerical and experimental analysis of the steady and pulsating flows through microdiffusers and valveless micropumps are surveyed. The differences between the performance of microdiffusers and micropumps in steady and unsteady flow regimes are described. Qualitative and quantitative discussions of the effects of different design parameters on the performance of microdiffusers and valveless micropumps in both steady and unsteady flow regimes along with the contradictory results reported in the literature in this regard are provided. In addition, a summary of the latest micropump technologies along with the advantages and disadvantages of each mechanism with the emphasis on the innovative and less-reviewed micropumps are presented. Two important types of fixed microvalves, as part of valveless micropumps are described in details. Experimental flow visualization of steady and pulsating flows through microdiffusers and micropumps as a useful tool for better understanding the underlying micro-fluid dynamics is discussed. The present review reveals that there are many possible areas of research in the field of steady and unsteady flows through microdiffusers and micropumps in order to understand the effects of all important design parameters on the performance of these devices.

Steady and unsteady flow analysis in microdiffusers and micropumps: a critical review

The importance of understanding the six-degrees-of-freedom kinematics of the knee during ambulatory activities was examined in the context of the function of total knee arthroplasty. Studies of knee kinematics during walking, stair climbing, and a deep flexion squat indicate that knee kinematics is activity-dependent. A comparative study of patients and healthy subjects during stair climbing indicates the importance of maintaining the function of the posterior cruciate ligament. A second study used walking kinematics derived from patient testing as input to a wear simulator. There was increased wear relative to standard simulator input that was related to the slip velocity at the contact surface. Finally, results from a study of deep flexion indicate that substantial femoral rotation is required during deep flexion activities. The current study shows the importance of studying in vivo knee kinematics for future enhancement in the treatment of the arthritic knee.

The use of functional analysis in evaluating knee kinematics : Knee kinematics and total knee replacement design

A Surface Acoustic Wave (SAW) resonator operating at a frequency of 99.50 MHz using piezoelectric ST-cut quartz has been fabricated. The resonator device has been successfully integrated with ZnO sensing layer for detection of NO 2 gas. The fabricated sensor device is found to be detecting trace level concentration of NO 2 gas (400 ppb to 16 ppm) efficiently and selectively. The ZnO/Quartz SAW sensor is useful for wireless detection of NO 2 gas.

ZnO/ST-Quartz SAW resonator: An efficient NO2 gas sensor

A review of recent studies on piezoelectric pumps and their applications

We have designed and characterized a surface acoustic wave (SAW) fluid actuation platform that significantly improves the transmission of sound energy from the SAW device into the fluid in order to obtain enhanced performance. This is in distinct contrast to previous SAW microfluidic devices where the SAW substrate is simply interfaced with a microchannel without due consideration given to the direction in which the sound energy is transmitted into the fluid, thus resulting in considerable reflective and dissipative losses due to reflection and absorption at the channel walls. For the first time, we therefore demonstrate the ability for continuous fluid transfer between independent reservoirs driven by the SAW in a miniature device and report the associated pressure–flow rate relationship, in which a maximum flow rate of 100 μl min−1 and pressure of 15 Pa were obtained. The pumping efficiency is observed to increase with input power and, at peak performance, offers an order-of-magnitude improvement over that of existing SAW micropumps that have been reported to date.

https://users.monash.edu/~lyeo/Dr_Leslie_Yeo/SAW_Microchannel_Pumping_files/Dentry_LOC.pdf

Continuous flow actuation between external reservoirs in small-scale devices driven by surface acoustic waves

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.

Equivalent electrical network for performance characterization of piezoelectric peristaltic micropump

This study develops a diffuser micropump and characterizes its output flow rates, such as the parabola shape on the frequency domain and the affecting factors. First, an equivalent circuit using electronic–hydraulic analogies was constructed. Flow rate analysis results were then compared to experimental results to verify the applicability of the circuit simulation. The operational frequency was 800 Hz for both cases and maximum flow rates were 0.078 and 0.075 μl/s for simulation and experimental results, respectively. Maximum flow rate difference between simulation and experiment was 3.7%. The circuit was then utilized to analyze inertial effects of transferred fluid and system components on output flow rates. This work also explained why the flow rate spectrum has a parabolic shape. Analysis results demonstrated that without inertial effects, micropump flow rates are linearly proportional to operational frequency; otherwise flow rate spectrum has parabolic shape. The natural frequency of the actuator-membrane structure was identified using the finite element method to verify whether this parameter affects flow rate characteristics. Experimental and simulation results demonstrated that the frequency of the maximum pumping flow rate was 800 Hz and the first mode natural frequency of actuator-membrane structure was 91.4 kHz, suggesting that the structure natural frequencies of the actuator-membrane structure do not play any role in micropump operations.

Inertial effects on flow rate spectrum of diffuser micropumps

Utilizing micro-electromechanical systems (MEMS) techniques and a solvent-assisted bonding process, this study fabricates two peristaltic polymethylmethacrylate (PMMA) micropumps In the first micropump, the actuation chambers are connected via straight microchannels with a uniform width and depth of 500 μm and 200 μm, respectively, while in the second micropump, the chambers are connected via tapered microchannels, which function as diffuser valves and yield a net one-way fluid flow The experimental results indicate that the conventional and diffuser-type micropumps yield maximum flow rates of 2624 μl/min and 1148 μl/min, respectively Furthermore, it is shown that the back pressure in the conventional micropump is 39 kPa, while that in the diffuser-type pump is 92 kPa The flow rate spectra of the two micropumps are modeled numerically using an electronic–hydraulic analogy The results obtained for the resonant excitation frequency of the two micropumps are consistent with those observed experimentally (400 Hz) However, the flow rate predictions are slightly lower than the experimental values Furthermore, the experimental flow rate spectrum has a broader bandwidth than the numerical equivalent The discrepancy between the two sets of results is attributed to the overly simplistic modeling of the actuator–membrane mechanism in the equivalent circuit used to simulate the micropumps

An experimental and numerical investigation into the effects of diffuser valves in polymethylmethacrylate (PMMA) peristaltic micropumps

This paper used the theoretical calculation to simulate the response of surface acoustic wave (SAW) delay-line on quartz substrate and then compared to the experimental results. The coupling coefficients affected by operation frequency as well as aperture length were built up by experimental data analysis. Based on the experimental values of these two parameters, the device-coupling coefficient was defined. This method is new and we has not found in other document. In addition, it improves the simulation results and helps the analysis process more comprehensive. This study developed ST-cut quartz SAW delay-lines with gold inter-digital transducer (IDT) operating at 39.5 and 78.9 MHz corresponding to 80 and 40 μm of the wavelength. The differences of aperture length in IDT designs were investigated to help understand the effects of this parameter on SAW sensor response. The maximum error of operating frequency is 1%; of insertion loss is 4.25 and 3.13% for bandwidth. The larger of the insertion loss error is expected owing to the result of mathematical approximation and the quality of quartz substrate. The simulation results agree with the experimental results shows that the simulation method can apply to quartz-based SAW delay-line as well as for other material based SAW delay-line applications. The results help understand more about the parameters which effect the insertion loss, operating frequency and bandwidth. It should be very useful for IDT design in specific, SAW sensor and SAW filter design in general.

Coupling coefficient determination based on simulation and experiment for ST-Cut quartz saw delay-line response

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.

Ngoc-Bich Le

Papers

Equivalent electrical network for performance characterization of piezoelectric peristaltic micropump

Inertial effects on flow rate spectrum of diffuser micropumps

An experimental and numerical investigation into the effects of diffuser valves in polymethylmethacrylate (PMMA) peristaltic micropumps

Coupling coefficient determination based on simulation and experiment for ST-Cut quartz saw delay-line response

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