Actuation Pulse Research Articles

Effects of different working parameters on the turbulent drag reduction regulated by annular plasma synthetic jet actuators

Reduction of turbulent drag force is one of important works in the design of airplanes and hypersonic aircrafts. The annular plasma synthetic jet (APSJ) has become an interesting and popular flow control method in reducing the drag of turbulent boundary layers. In this paper, a comprehensive experimental study is carried out on the turbulent drag reduction regulated by an array of annular plasma synthetic jet actuators. The effects of the operating parameters such as the actuation voltage, the pulse frequency and the incoming wind speed on the drag reduction rate are studied and discussed in detail. The performances of the plasma actuator array are evaluated and summarized at multiple working conditions. Finally, the coherent structures of turbulence and the hairpin-like vortices are depicted and discussed. The results show that the optimal drag reduction rate is achieved, as the actuation voltage, pulse frequency and incoming wind speed are Vpp = 7 kV, fp= 50 Hz, and U∞ = 7 m/s, respectively. A resonant coupling phenomenon is observed when the pulse frequency of the actuators approaches the characteristic frequency of the coherent structure. The upward sweep flow induced by APSJ actuators may lead to a reduction of the turbulent drag force, but the downward wash flow leads to an increase in the drag. Present study could provide solid experimental data and a helpful guidance for the drag reduction of an airplane.

Numerical Research on the Effects of Process Parameters on Microdroplet Jetting Characteristics by Piezoelectric Printhead

The precision and consistency of the microdroplet jetting procedure are crucial for the casting sand mold’s performance during binder injection. The generation and jetting of microdroplets in piezoelectric printheads were examined in this study in relation to changes in specific jetting process parameters. Using finite element analysis and a simplified physical model of a microdroplet jetting device, an electromechanically coupled model of a microdroplet jetting device was created in order to study the characteristics of microdroplet jetting. A volume-of-fluid model was also created in order to study the microdroplet jetting process and perform repeatability tests. The effects of altering nozzle radius, actuation pulse width, intake velocity, and fluid viscosity on microdroplet jetting properties were then investigated using the models. We were able to control the development of satellite droplets thanks to the knowledge we gained about how each process parameter affected droplet status. This study demonstrates how the radius of the nozzle and the pulse width of the piezoelectric actuation signal have a significant impact on the jetting properties of piezoelectric printheads and the production of microdroplets. The quantitative correlations between process factors and jetting characteristics can be used to optimize microdroplet production and reduce droplet size. Finally, this study will help create control systems for microdroplet jetting operations and enhance the precision of 3D printed casting sand molds.

Frequency-dependent stimulated and post-stimulated voltage control of magnetism in transition metal nitrides: towards brain-inspired magneto-ionics.

Magneto-ionics, which deals with the change of magnetic properties through voltage-driven ion migration, is expected to be one of the emerging technologies to develop energy-efficient spintronics. While a precise modulation of magnetism is achieved when voltage is applied, much more uncontrolled is the spontaneous evolution of magneto-ionic systems upon removing the electric stimuli (i.e., post-stimulated behavior). Here, we demonstrate a voltage-controllable N ion accumulation effect at the outer surface of CoN films adjacent to a liquid electrolyte, which allows for the control of magneto-ionic properties both during and after voltage pulse actuation (i.e., stimulated and post-stimulated behavior, respectively). This effect, which takes place when the CoN film thickness is below 50 nm and the voltage pulse frequency is at least 100 Hz, is based on the trade-off between generation (voltage ON) and partial depletion (voltage OFF) of ferromagnetism in CoN by magneto-ionics. This novel effect may open opportunities for new neuromorphic computing functions, such as post-stimulated neural learning under deep sleep.

Energy-saving actuation signal for magnetorheological valve train by leveraging hysteresis effect

• Analysis of electromagnetic hysteresis effect in magnetorheological valve train. • Customized pulse actuation signal for leveraging the hysteresis effect in magnetorheological valve train. • Pulse signal optimization for energy saving operation of VVL that improves the engine efficiency. • Customized pulse signal saves actuation energy of magnetorheological valve train. Smart, adaptive, and effective magnetorheological (MR) technology-based devices are replacing conventional brakes, clutches, valves, and dampers. MR valve improves engine performance by enabling variable valve actuation. Constructing an MR valve train is simpler than other active valve systems. However, similar to other electromagnetic valves, the MR valve train consumes considerable electrical energy in controlling the resistance force of the MR fluid such that the valve can remain partially open or fully closed. Thus, an engine equipped with an MR valve expends additional fuel for the actuation of the valve system. In this study, instead of conventional direct current (DC) actuation, an energy-saving customized pulse (CP) signal is proposed for valve actuation by leveraging the electromagnetic hysteresis effect. The applied CP signal causes fluctuations in the generated magnetic flux, resistance force, and consequent valve position. Therefore, the variation in MR resistance force at various duty cycles and negative half cycles was investigated and compared with the required force to perform variable valve lift (VVL). Simulations indicated that a 35% duty cycle with 75% current during the negative half cycle was able to maintain the required force but results in negligible deviation in the resistance force which doesn’t affect the VVL operation. Therefore, the proposed method is advantageous over conventional DC input, conferring actuation energy-savings of approximately 28%.

Electrical and aerodynamic characteristics of sliding discharge based on a microsecond pulsed plasma supply

Plasma flow control technology has broad prospects for application. Compared with conventional dielectric barrier discharge plasma actuators (DBD-PA), the sliding discharge plasma actuator (SD-PA) has the advantages of a large discharge area and a deflectable induced jet. To achieve the basic performance requirements of light weight, low cost, and high reliability required for UAV (Unmanned Aerial Vehicle) plasma flight experiments, this work designed a microsecond pulse plasma supply that can be used for sliding discharge plasma actuators. In this study, the topology of the primary circuit of the microsecond pulse supply is determined, the waveform of the output terminal of the microsecond pulse plasma supply is detected using the Simulink simulation platform, and the design of the actuation voltage, the pulse frequency modulation function and the construction of the hardware circuit are achieved. Using electrical diagnosis and flow field analysis, the actuation characteristics and flow characteristics of sliding discharge plasma under microsecond pulse actuation are studied, the optimal electrical actuation parameters and flow field characteristics are described.

Chalcogenide Phase-Change Material Germanium Telluride for Radio-Frequency Applications: An overview

Chalcogenide phase-change materials (PCMs) have been widely used in optical storage media and nonvolatile memory devices applications. Over the past several years, there has been interest in exploiting PCM technology, especially germanium telluride (GeTe) and its alloys, for radio-frequency (RF) applications. The principle of operation of PCM-based RF devices is based on the ability of the material to transform from a high-resistivity (amorphous phase) to low-resistivity state (crystalline phase) and vice versa, with the application of a short, thermal pulse. Actuation pulses are applied to microheaters embedded with the PCM junction to switch between the two states. The PCM switch can exhibit more than five orders of resistance change between the two states. PCM-based RF switches are expected to bridge the gap between semiconductor switches and microelectromechanical systems (MEMS) switches as they combine the low insertion loss performance of MEMS technology and the small size and reliability performance of semiconductor technology. In addition to miniaturization, GeTe-based switches offer unique latching functionality and ease of monolithic integration with other RF circuits. This article presents an overview of PCM technology and its applications to RF circuits. A brief history of the technology is presented first, followed by a discussion of the basic characteristics of PCMs. The steps of a fabrication process of PCM RF devices are illustrated. A description of RF-PCM switch is presented in detail along with a comparison between RF performance of PCM switches and other existing commercial switches. As examples of application of the PCM technology to other RF circuits, the article concludes by presenting a crossbar switch matrix, phase shifter, and variable attenuator, realized using the PCM technology.

Phase Change Nanoelectromechanical Relay for Nonvolatile Low Leakage Switching

AbstractThe design, modeling, and experimental validation of a highly scalable phase change electromechanical relay are present. The Phase Change NEMS Relay (PCNR) is a nonvolatile mechanical relay actuated by the volumetric expansion of phase change material. GeTe is used as the active phase change material, and nonvolatile relay states are changed by converting it between amorphous and crystalline phases, which differ in volume by 10%. Phase conversion is induced by Joule heating an adjacent metal layer. Finite element analysis (FEA) models are developed to predict actuator temperature distributions and quench times for varied actuation pulses. Additional models are developed to simulate actuator deflection including reflow of molten phase change material during an actuation pulse. The smallest fabricated device has a heater footprint of 3 µm × 1 µm, with a 20 nm air‐gap. The FEA model, which calculates the actuation voltage, energy, and ON–OFF current ratio for this device to be 1.1 V, 42 nJ, and 108, respectively, are experimentally verified. A PCNR scaled down to a 15 nm × 5 nm heater footprint with a 2 nm air‐gap is predicted to actuate at 400 mV and 1.7 pJ.

Aerodynamic Control of a Dynamically Pitching Airfoil Using Pulsed Actuation

Transitory control and regulation of the aerodynamic loads on a static and dynamically pitching VR-12 airfoil is investigated in wind tunnel experiments. Actuation is enabled by a spanwise array of integrated combustion-based actuators that are triggered intermittently relative to the airfoil’s motion, producing high-impulse actuation jets on characteristic time scales that are an order of magnitude shorter than the airfoil’s convective time scale. Poststall transitory actuation leads to a momentary reattachment of the flow over the airfoil, and the effects of sequencing of actuation pulses on the aerodynamic characteristics of the airfoil are assessed using time-resolved measurements of the lift force and pitching moment coupled with particle image velocimetry that is acquired phased-locked to the airfoil motion. The present investigations show that the aerodynamic loading can be significantly altered by a number of actuation programs using strategically timed bursts during the pitch cycle. While actuation during the upstroke primarily affects the formation, evolution, and advection of the dynamic stall vortex, actuation during the downstroke accelerates flow reattachment. Superposition of such actuation programs can lead to enhancement of cycle lift and pitch stability, and reduced cycle hysteresis.

Flow separation control in S-shaped ∼inlet with a nanosecond pulsed surface dielectric barrier discharge plasma actuator

A nanosecond pulsed surface dielectric barrier discharge (nSDBD) plasma actuator is proposed to eliminate the complex 3D flow separation in an S-shaped ∼engine inlet. A set of wind tunnel experiments based on pressure measurements are conducted to verify the flow control effectiveness and obtain the influence laws of actuation voltage, pulse frequency, actuator layout and coverage area. The results show that nSDBD can effectively eliminate flow separation, leading to a noticeable improvement in the total pressure distribution at the outlet, manifested as a reduction in the low-pressure zone and an extension of the high-pressure zone. The spanwise layout nSDBD delivers a better flow control effect compared to the streamwise layout. For the same geometrical layout, the flow control effect improves with increasing voltage, and the optimal actuation frequency corresponds to a Strouhal number of approximately F + = 0.5. In particular, with a spanwise array of nSDBD plasma actuators operating at V p-p = 10 kV and F + = 0.5, the flow separation region is completely suppressed. The mechanism of flow separation with nSDBD can be ascribed to the mixing enhancement between the boundary layer and the main flow, which improves the boundary layer’s ability to resist the adverse pressure gradient.

Accelerated electrowetting-based tunable fluidic lenses.

One of the limitations in the application of electrowetting-based tunable fluidic lenses is their slow response time. We consider here two approaches for enhancing the response speed of tunable fluidic lenses: optimization of the properties of the fluids employed and modification of the time-dependent actuation voltages. Using a tubular optofluidic configuration, it is shown through simulations how one may take advantage of the interplay between liquid viscosities and surface tension to reduce the actuation time. In addition, by careful designing the actuation pulses, the response speed of both overdamped and underdamped systems may be increased by over an order of magnitude, leading to response times of several ten milliseconds. These performance improvements may significantly enhance the applicability of tunable optofluidic-based components and systems.

Designing a physical quantum agent

The concept of an embodied intelligent agent is a key concept in modern artificial intelligence and robotics. Physically, an agent is an open system embedded in an environment that it interacts with through sensors and actuators. It contains a learning algorithm that correlates the sensor and actuator results by learning features about its environment. In this article we present a simple optical agent that uses light to probe and learn components of its environment. In our scenario, the quantum agent outperforms a classical agent: The quantum agent probes the world using single photon pulses, where its classical counterpart uses a weak coherent state with an average photon number equal to one. We analyze the thermodynamic behavior of both agents, showing that improving the agent's estimate of the world corresponds to an increase in average work done on the sensor by the actuator pulse. Thus, our model provides a useful toy model for studying the interface between machine learning, optics, and statistical thermodynamics.

Cancer drug screening with an on-chip multi-drug dispenser in digital microfluidics.

Microfluidics has been the most promising platform for drug screening with a limited number of cells. However, convenient on-chip preparation of a wide range of drug concentrations remains a large challenge and has restricted wide acceptance of microfluidics in precision medicine. In this paper, we report a digital microfluidic system with an innovative control structure and chip design for on-chip drug dispensing to generate concentrations that span three to four orders of magnitude, enabling single drug or combinatorial multi-drug screening with simple electronic control. Specifically, we utilize droplet ejection from a drug drop sitting on a special electrode, named a drug dispenser, under high-voltage pulse actuation to deliver the desired amount of drugs to be picked up by a cell suspension drop driven by low-voltage sine wave actuation. Our proof-of-principle validation for this technique as a convenient single and multi-drug screening involved testing of the drug toxicity of two chemotherapeutics, cisplatin (Cis) and epirubicin (EP), towards MDA-MB-231 breast cancer cells and MCF-10A normal breast cells. The results are consistent with those screened based on traditional 96-well plates. These findings demonstrate the reliability of the drug screening system with an on-chip drug dispenser. This system with fewer cancer cells, less drug consumption, a small footprint, and high scalability with regard to concentration could pave the way for drug screening on biopsied primary tumor cells for precision medicine or any concentration-related research.

Inkjet printing platform for fabrication of uniform, excipient-free drug particles for pulmonary delivery in a preclinical setting

Drop on demand inkjet printing was applied to obtain excipient-free particles with a narrow size distribution. The objective of this work was to establish the general applicability of the process on a range of structurally different active pharmaceutical ingredients (APIs). Four APIs; fluticasone, budesonide, tiotropium and olodaterol were utilized. The droplet generation protocols could be established based on the solvent system, chosen with regard to stable printability and solubility of the APIs. Triple actuation pulse was applied to generate droplets of desired dimensions. Drying temperature and dispensing frequency were used to optimize the drying of the droplets. The particle size of the product was dictated by the concentration of the ink and the volume of the droplets. These parameters were used to obtain the particle diameters of 1–6 μm. Intra-tracheal instillation to rats of fluticasone in suspensions of polydisperse spray dried particles and print dried particles of 3 and 5 μm was performed. Amounts of residual drug content in the lung and systemic exposures differed depending on the total surface area. The developed methodology can improve the mechanistic understanding of pulmonary drug dissolution and absorption on the wide range of structurally diverse APIs in the preclinical setting.

Raman Spectroscopic Detection in Continuous Microflow Using a Chip-Integrated Silver Electrode as an Electrically Regenerable Surface-Enhanced Raman Spectroscopy Substrate

An electrochemical approach to enable surface-enhanced Raman spectroscopy (SERS) detection in continuous microflow is presented. This is achieved by the integration of a silver electrode as SERS substrate in a microfluidic chip device. By the application of actuation pulses of about 4 V, otherwise irreversibly adsorbed analytes are stripped off, which enables quasi-real-time SERS detection in a continuous microflow. The approach opens up a way for in situ SERS monitoring of compounds in microflow with high application potential in microseparation techniques like HPLC and lab-on-a-chip devices.

Investigation of Airfoil Flow Separation Control by Dielectric Barrier Discharge Plasma Actuators

The performance of dielectric barrier discharge (DBD) plasma actuators on controlling the flow separation of NACA0015 airfoil was investigated in a low-turbulence and low-speed wind tunnel. The smoke flow visualization was applied to reflect the modification of the flow over the airfoil controlled by the plasma actuators. Lift and drag were measured by the pressure distribution on airfoil surface with electronic pressure scanners to investigate the separation control effect of the pulse frequency and actuator position. The results show that the plasma actuators can effectively suppress the flow separation and make the flow reattach to the surface. The plasma actuation increases the angle of the attack of the flow reattachment by 5° at the free-stream velocity of 15m/s. With the same input power of the plasma actuators, the flow control effect will be better when the actuator pulse frequency increases.

A Self-Adaptive Stiffness Approach to Improving the Robustness of Electrostatic Switches Against Parameter Variations

The “soft-landing” effect during the closure of RF-MEMS switches is crucial for improving their reliability. However, the rebound suppression effectiveness has rather poor robustness against the dimension deviations and waveform distortions resulting from micro-fabrication tolerance, wear and tear, and circuit aging in the device’s life-cycle. In contrast to the traditional constant stiffness system, this letter proposes a novel self-adaptive stiffness approach, whereby the system’s stiffness increases markedly with increasing displacement so that its elastic potential energy against the electrostatic energy is mainly concentrated in the region near the closing position for a better rebound suppression. Our experiments show that, for an ensemble of fabricated devices subjected to the unified dual-pulse actuation waveform, the reliable working gap range of the new approach ( $1.4~\mu \text{m}$ ) in which the switches can be closed completely, is 4.6 times larger than that of the constant stiffness scheme ( $0.3~\mu \text{m}$ ). In addition, for the actuation voltage and pulse time with variations of up to ±10%, this new approach shows significantly reduced closure time and bounce.

Combustion-Powered Actuation for Transitory Flow Control

The susceptibility of wall-bounded and free shear flows to transitory, pulsed actuation having time scales that are significantly shorter than the flow’s characteristic convective time scale has been used for external and internal aerodynamic flow control. This approach, which exploits the disparity between the onset and relaxation time scales of the embedding flow response, requires brief, anharmonic high-impulse actuation that is difficult to achieve by conventional momentum-based electromechanical actuation. However, investigations over the past decade have demonstrated the utility of chemically based actuation in which controllable high-impulse jets are produced using small-scale combustion-powered actuation. The present paper comprises two parts. The beginning of the paper describes the development of this actuation technology. In the present implementation, high-speed pulsed actuation jets are engendered by the ignition of a mixture of gaseous fuel and air within a cubic-centimeter-scale combustion chamber. The dependence of the actuator’s performance and of the ensuing momentary actuation jet on the composition of the chemical species, the internal geometry, and the flow configuration are characterized using dynamic pressure measurements and flow measurements using particle image velocimetry. The latter part of the paper describes a few examples of aerodynamic flow control using combustion-based pulsed actuation for the mitigation of separated flows over external static and moving aerodynamic surfaces. A fundamental aspect of the receptivity to pulsed actuation is the disparity between the time scales of the attachment and relaxation processes such that a single actuation pulse having a characteristic time scale of 0.05 can lead to brief, partial collapse of the separated flow domain, coupled with a momentary increase in circulation on a time scale that is nearly 200 times longer; and that repetitive actuation results in sustained lift enhancement.

Flow separation control by dielectric barrier discharge plasma actuation via pulsed momentum injection

Control of a turbulent boundary layer separating on a half-cylinder mounted on a flat plate has been investigated using a Dielectric Barrier Discharge (DBD) plasma actuator placed along the apex of a cylinder. The main focus of the study has been to evaluate if the control ability of the actuator can be improved through pulsed actuation compared to its steady counterpart. Investigations of the electric wind induced by the DBD plasma actuator in still air, when mounted on the flat plate, revealed that while the steady actuation produces an electric wind similar to a wall jet, the pulsed actuation creates a train of co-rotating vortices. The vortices are the result of a starting vortex produced by the actuator at each actuation pulse. A parametric study showed a dependence of the size, shape and propagation velocity of the vortices on the pulse frequency and duty cycle. With the actuator mounted along the apex of the cylinder, Particle Image Velocimetry measurements of the uncontrolled and controlled flow with a free-stream velocity of 5 m/s showed a clear reduction of the recirculation region downstream the cylinder when using plasma actuation. An even higher control effect could be achieved with pulsed actuation compared to the steady actuation. Phase-locked measurements of the unsteady actuation showed that pulsed actuation periodically shifted the flow separation location resulting in the propagation of vortical structures in the recirculation region. The size of the vortical structures showed a dependence on the pulsed actuation timing parameters.

Operation of pneumatically-actuated membrane-based microdevices for in situ analysis of extraterrestrial organic molecules after prolonged storage and in multiple orientations with respect to Earth’s gravitational field

Pneumatically-actuated monolithic membrane microvalves are powerful microfluidic tools that can be integrated into programmable microfluidic architectures (PMAs) for multiple portable chemical analysis applications, including point-of-care (POC) diagnostics, environmental science, space exploration, etc…. However, these systems have not seen wide-scale deployment in industry or spaceflight due in part to (1) a concern that these systems may have a limited shelf-life and (2) a concern that performance depends on specific device orientation in a gravitational field. To address these concerns, we functionally tested a Mars Organic Analyzer microdevice fabricated in 2005 after 10 years of storage under ambient conditions. Using a square wave with a 500 millisecond (ms) actuation pulse width and a 1000 ms period and operating under vacuum at −980 millibar (mbar) from ambient pressure, all pneumatically-actuated valves opened in less than 1 h. The vacuum required to actuate an open valve ranged from −218 to −175 mbar from ambient pressure. The microvalves were then programmed to transfer fluid through the microdevice for flow rate characterization. Fluidic transfer occurred at a flow rate of 122 ± 8 microliters/minute (μL/min) right-side up in Earth’s gravitational field and 114 ± 14 μL/min upside down in Earth’s gravitational field, indicating likely successful implementation in an orbital microgravity environment. This demonstration that microdevices retain full functionality after over 10 years of storage combined with successful operation in multiple orientations in Earth’s gravitational field further validates the value of microdevices based on these microvalves for fluidic manipulation and sample handling in outer planetary missions.

Fast, repeatable and precise magnetic actuation in ambient environments at the micrometer scale

This work aims at increasing the velocity of micrometer scale particles controlled by non contact magnetic actuation systems. The particles are placed in an ambient environment (i.e. in air) to minimize the drag forces. However this approach raises two major issues: the repeatability and the precision of position are difficult to obtain in ambient environments due to the adhesion force between the substrate and the particle. This work proposes to use first a magnetic torque to provoke in-plane rotation of the particle to overcome adhesion between the particle and the substrate. Then a magnetic force is applied to induce the movement of the particle. To ensure that the static friction is broken and that the position of the particle can be controlled precisely a current pulse actuation mode is used. A dedicated closed loop control law which controls both the amplitude and the duration of the current simultaneously is proposed to ensure accurate positioning of the particle. Speed during pulse can reach 176 mm/s (more than 350 body lengths per second) in open loop on silicon substrates. Adhesion is overcome in 95% of the tests using the magnetic torque, compared to 66% using classical approaches. Precision of positioning of less than 20% of the size of the particle can be reached. The approach proposed in this paper is generic so that it can be easily transposed to other systems in the literature. The large number of experimental tests provides a deep understanding of the possibilities and challenges of magnetic actuation in ambient environments.