This work was supported by Chinese Civil Aircraft Project [No. MJ-2017-S49] and China Postdoctoral Science Foundation [No.2021M700331].

1. Simulation of pump flow characteristics
<ol>
	<li>Build the simulation model of the motor-pump assembly. Open the AMESim simulation platform and enter the SKETCH mode.
	<ol>
		<li>Build the simulation model for a single piston according to the kinematic mathematic model and the distribution curve (Figure 3). Encapsulate the single-piston model as a super component (Figure 4). 
		NOTE: The main kinematic mathematic model of the piston (Eq (1)) yields: 
		<img alt="Equation 1" src="/files/ftp_upload/63549/63549eq01.jpg" /> 
		<img alt="Equation 2" src="/files/ftp_upload/63549/63549eq02.jpg" />&#160;(1) 
		In this equation, x is the absolute displacement of the piston, &#946; is the swash plate incline angle, &#966; is the phase angle of the piston, Rf is the distribution radius of the cylinder block, df is the distribution diameter of the cylinder block.</li>
		<li>Build the pump model considering the leakage and friction of the valve plate (Figure 4). To build the valve plate module, mainly focus on the viscous friction and throttling effect of the piston/cylinder block interface and slipper/swash plate interface.</li>
		<li>Build the motor model via an ideal torque module (Figure 4). Use an ideal torque module to simulate the motor, ignoring the iron loss, copper loss, and stirring loss of the motor.</li>
	</ol>
	</li>
	<li>Set the main parameters of the motor-pump assembly model.
	<ol>
		<li>Set the parameters of the motor-pump assembly according to Table 1. Enter the PARAMETER mode and set the main parameters by double-clicking the specific component in the simulation model. Set the rotating speed and test pressure according to Table 2.</li>
		<li>Set the prerun parameters of the model : Start time: 0 s, Final time: 1 s, Print interval: 1 ms.</li>
		<li>Prerun the simulation to achieve the steady state.
		<ol>
			<li>Run the simulation and check whether the system will reach the steady state at the end of the simulation. If the system reaches the steady state, check the use old final values option in the Run Parameters window. If not, reset the Final time in step 1.2.1 to 2 s or even longer and repeat step 1.2.2 until the system reaches the steady state.</li>
		</ol>
		</li>
		<li>Set the run parameters of the model: Start time: 0 s, Final time: 0.2s, Print interval: 0.002 ms.</li>
	</ol>
	</li>
	<li>Run the simulation and save the simulation data. 
	NOTE: Repeat steps 1.2.1-1.2.4 for a specific working condition; save the data after the simulation.</li>
	<li>Export the simulation data and plot the flow characteristic contour of the motor-pump assembly in OriginPro. Calculate the value of the pump flow as the average of the pump flow recorded within 0.2 s.</li>
	<li>Determination of output flow characteristics
	<ol>
		<li>Plot the output flow curve of the motor-pump assembly at the maximum speed under different pressure conditions.</li>
		<li>Compute the required output flow rate of the pump according to the specific EHA maximum speed, and plot the required output flow rate curve at different pressure conditions.</li>
		<li>Ensure that the required flow rate curve of the EHA is enveloped by the output flow rate curve of the motor-pump assembly.</li>
	</ol>
	</li>
</ol>
2. Establishment of the experimental platform
<ol>
	<li>Establish the test bench.
	<ol>
		<li>Prepare hydraulic components of the test bench according to Table 3. Ensure that the key parameters of each component meet the requirements listed in Table 3.</li>
		<li>Design and manufacture the hydraulic valve blocks and build a hydraulic system according to the hydraulic schematic diagram (Figure 5). Ensure that the relative positions of components are the same as the schematic diagram shown, and the pressure sensors and temperature sensors are positioned as close to the test point as possible. 
		NOTE: This series of experiments was conducted on a dedicated high-speed and high-pressure pump load simulation test bench, as shown in Figure 6.</li>
		<li>Design and manufacture the tooling and test valve blocks. Ensure that design tooling is according to the specific interface of the tested pump and the test bench.</li>
	</ol>
	</li>
	<li>Installation of the mechanical interfaces (Figure 7)
	<ol>
		<li>Connect the end face of the motor-pump assembly with the test valve block. Use at least 4 screws to ensure a good sealing performance.</li>
		<li>Fix the motor-pump assembly and the test valve block on the workbench of the test bench (Figure 8). Connect the motor-pump assembly and the test valve block to the dedicated tooling with four screws and the tooling to the workbench with 2 screws. 
		NOTE: Make sure that the two screws are sufficiently strong so that no vibration appears while conducting the test.</li>
		<li>Install two groups of pressure and temperature sensors of port A and port B on the test valve block. Connect these sensors directly to the leakage port for leakage monitoring. 
		NOTE: It is necessary to design and manufacture different tooling for different tested motor pump assemblies to complete the experiment.</li>
	</ol>
	</li>
	<li>Connection of the hydraulic interfaces (Figure 7)
	<ol>
		<li>Connect the two high-pressure oil ports of the pump source with port A or B of the test valve block.</li>
		<li>Connect the pressurized oil port with the leakage oil port of the pump.</li>
	</ol>
	</li>
	<li>Air-exhausting of the motor-pump assembly
	<ol>
		<li>Make sure the relief valve of the oil supply system is in the unloading state. Run the oil supply motor for 3 minutes to exhaust the air of the testing system and warm it. 
		NOTE: The specific running time is determined according to the specific conditions of the test bench. The main purpose of this step is to ensure that the oil is fully flowing into each component of the testing circuit and the surface temperature of the tested pump is close to the oil temperature.</li>
	</ol>
	</li>
	<li>To check for leaks in the motor-pump assembly, shut off the relief valve of the oil supply system. Adjust the oil supply pressure to 2 MPa for more than 1 min. 
	NOTE: This will help find out if there is any obvious leakage in the testing system, such as the leakage caused by the failure of the O-ring.
	<ol>
		<li>Look for leakage in the motor-pump assembly. If it leaks, first, shut down the hydraulic system and replace the seal, and then repeat steps 2.3 and 2.4. If there is no leakage, open the relief valve of the oil supply system.</li>
	</ol>
	</li>
	<li>Connection of the electrical interfaces (Figure 9)
	<ol>
		<li>Connect the power supply interface and the rotary signal interface to the motor-pump assembly driver.</li>
		<li>Connect the driver to the controller via RS 442, working in full-duplex mode.</li>
		<li>Connect the driver to 270 VDC power.</li>
	</ol>
	</li>
	<li>No-load inspection of the motor-pump assembly
	<ol>
		<li>Run the oil supply pump and keep the relief valves of the oil supply and loading systems in the unloading state. Power on the driver and controller and check whether the motor-pump assembly can receive the control command normally. 
		NOTE: The inlet port of the motor-pump assembly can be pressurized via an oil supply pump, preventing the component from cavitation.</li>
		<li>Set an instruction of 2,000 rpm forward to the motor-pump assembly. Observe the working state of the motor-pump assembly and check whether there is leakage at the valve block (see step 2.5).</li>
		<li>Set an instruction of 2,000 rpm reverse to the motor-pump assembly. Observe the working state of the motor-pump assembly and check whether there is leakage at the valve block (see step 2.5).</li>
	</ol>
	</li>
</ol>
3. Pump flow and overall efficiency test of the motor-pump assembly
<ol>
	<li>Setting of the oil supply system
	<ol>
		<li>Run the oil supply pump and switch the relief valves of the oil supply system and loading system to the loading state.</li>
		<li>Adjust the oil supply relief valve to the minimum oil supply pressure psmin of 0.6 MPa. Follow steps 3.1.2.1-3.1.2.3 to select psmin. 
		NOTE: psmin is the pressure in the inlet port of the motor-pump assembly to avoid cavitation.
		<ol>
			<li>Adjust the oil supply pressure to 1 MPa or more, which is decided by the tested motor-pump assembly.</li>
			<li>Adjust the rotational speed of the tested motor-pump assembly to 9,000 rpm, making sure that the pump flow is equal to the theoretical pump flow. Otherwise, increase the oil supply pressure to avoid cavitation.</li>
			<li>Reduce the oil supply pressure slowly and record the change of the pump flow. Plot the relative pump flow versus oil supply pressure, and find the inflection point of the pump flow-the oil supply pressure of this point is the minimum oil supply pressure psmin.</li>
		</ol>
		</li>
		<li>Adjust the load relief valve to psmin.</li>
	</ol>
	</li>
	<li>Turn on the temperature control system and adjust the oil temperature to 30 &#176;C.</li>
	<li>Turn on the thermal imager to detect the surface temperature of the motor-pump assembly.</li>
	<li>Send control instructions to the motor-pump assembly to make it run continuously at a specific speed (Table 2).</li>
	<li>Adjust the load relief valve and gradually increase the load pressure to a specific value (Table 2). Hold for 4 s at each critical measured pressure. 
	NOTE: Pay close attention to the motor temperature during the experiment. Ensure the temperature of the motor-pump assembly surface is lower than 100 &#176;C.</li>
	<li>After the pressure reaches the specific value of the speed, adjust the load relief valve back to 1 MPa.</li>
	<li>Repeat steps 3.3 and 3.4 until the characteristics of all critical pressure measuring points are tested according to Table 2.</li>
	<li>Export the experimental flow data and plot the pump flow characteristic map of the motor-pump assembly.</li>
	<li>Calculate the overall efficiency &#951;o of the motor-pump assembly in different working conditions and plot the overall efficiency map. 
	NOTE: The overall efficiency of the motor-pump assembly is given by Eq (2): 
	<img alt="Equation 3" src="/files/ftp_upload/63549/63549eq03.jpg" />. (2) 
	Where Po is the output power of the motor-pump assembly, Pi is the input power of the driver, Qpump is the pump flow; &#916;p is the pump pressure difference; Upower is the power supply output voltage; Ipower is the power supply output current.</li>
</ol>

<ol>
	<li>Yu, B., Wu, S., Jiao, Z., Shang, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multi-objective+optimization+design+of+an+electrohydrostatic+actuator+based+on+a+particle+swarm+optimization+algorithm+and+an+analytic+hierarchy+process.">Multi-objective optimization design of an electrohydrostatic actuator based on a particle swarm optimization algorithm and an analytic hierarchy process.</a> Energies. 11 (9), 2426 (2018).</li><li>Chao, Q., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Load-sensing+pump+design+to+reduce+heat+generation+of+electro-hydrostatic+actuator+systems.">Load-sensing pump design to reduce heat generation of electro-hydrostatic actuator systems.</a> Energies. 11 (9), 2266 (2018).</li><li>Zhao, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Experimental+research+on+tribological+characteristics+of+TiAlN+coated+valve+plate+in+electro-hydrostatic+actuator+pumps.">Experimental research on tribological characteristics of TiAlN coated valve plate in electro-hydrostatic actuator pumps.</a> Tribology International. 155, 106782 (2021).</li><li>Zhao, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Review+of+cylinder+block/valve+plate+interface+in+axial+piston+pumps:+Theoretical+models,+experimental+investigations,+and+optimal+design.">Review of cylinder block/valve plate interface in axial piston pumps: Theoretical models, experimental investigations, and optimal design.</a> Chinese Journal of Aeronautics. 34 (1), 111-134 (2021).</li><li>Chao, Q., Zhang, J., Xu, B., Huang, H., Pan, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+review+of+high-speed+electro-hydrostatic+actuator+pumps+in+aerospace+applications:+challenges+and+solutions.">A review of high-speed electro-hydrostatic actuator pumps in aerospace applications: challenges and solutions.</a> Journal of Mechanical Design. 141 (5), 050801 (2019).</li><li>Fu, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Design+and+performance+analysis+of+position-based+impedance+control+for+an+electrohydrostatic+actuation+system.">Design and performance analysis of position-based impedance control for an electrohydrostatic actuation system.</a> Chinese Journal of Aeronautics. 31 (3), 584-596 (2018).</li><li>Alle, N., Hiremath, S. 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N., Emeneth, M., Schneegans, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+methodology+for+vehicle+and+mission+level+comparison+of+More+Electric+Aircraft+subsystem+solutions:+Application+to+the+flight+control+actuation+system.">A methodology for vehicle and mission level comparison of More Electric Aircraft subsystem solutions: Application to the flight control actuation system.</a> Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering. 229 (6), 1088-1102 (2014).</li><li>Zhang, T., He, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+reliability-based+robust+design+method+for+the+sealing+of+slipper-swash+plate+friction+pair+in+hydraulic+piston+pump.">A reliability-based robust design method for the sealing of slipper-swash plate friction pair in hydraulic piston pump.</a> IEEE Transactions on Reliability. 67 (2), 459-469 (2018).</li><li>Guo, S., Chen, J., Lu, Y., Wang, Y., Dong, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hydraulic+piston+pump+in+civil+aircraft:+current+status,+future+directions+and+critical+technologies.">Hydraulic piston pump in civil aircraft: current status, future directions and critical technologies.</a> Chinese Journal of Aeronautics. 33 (1), 16-30 (2020).</li><li>Habibi, S., Goldenberg, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Design+of+a+new+high-performance+electrohydraulic+actuator.">Design of a new high-performance electrohydraulic actuator.</a> IEEE/ASME Transactions on Mechatronics. 5 (2), 158-164 (1999).</li><li>Xu, B., Hu, M., Zhang, J., Mao, Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Distribution+characteristics+and+impact+on+pump's+efficiency+of+hydro-mechanical+losses+of+axial+piston+pump+over+wide+operating+ranges.">Distribution characteristics and impact on pump's efficiency of hydro-mechanical losses of axial piston pump over wide operating ranges.</a> Journal of Central South University. 24 (3), 609-624 (2017).</li></ol>

The authors declare that they have no conflicts of interest.

When conducting these experimental steps, it is important to make sure that the pressure measuring points are close enough to the oil port of the pump, which would greatly influence the experimental results. In addition, pay attention to the pressure of the inlet port of the motor-pump assembly to ensure that no cavitation exists, especially at high-speed working conditions.
This method enables a dynamic adjustment of oil supply pressure, realizing an accurate simulation of different working c...

Known as a typically integrated actuator with high power density, the EHA has broad prospects in areas such as aerospace, aviation, construction machinery, and robotics1,2. The EHA mainly consists of a servo motor, pump, cylinder, pressurized reservoir, valve block, mode control valves, module control valves, and sensors, constituting a highly integrated, pump-controlled, closed hydraulic system. The schematic diagram and physical model are shown in Figure 13,4,5,6,7. The motor-pump assembly is the core power and the control component, and it determines the static and dynamic performance of the EHA7.
The conventional motor-pump assembly consists of a separate motor and pump, whose shafts are connected by a shaft coupling8. This structure has significant negative effects on the performance and life of the EHA. First, both the motor and pump will bear a relatively large vibration due to the assembling accuracy, especially at high speed5. Vibration will not only affect the output characteristics of the pump but also accelerate the wear of the friction interfaces in the pump, leading to the failure of the motor-pump assembly9. Second, sealings must be set at the shaft ends of the pump, which cannot fundamentally prevent leakage. Meanwhile, the mechanical efficiency of the motor-pump assembly decreases with increasing friction resistance10. Third, the frequent reversing of the motor-pump assembly will accelerate the wear of the coupling and increase the possibility of fatigue fracture, reducing the system reliability of the EHA11,12.
Thus, a single-shaft coaxial motor-pump assembly within a shared housing was developed to avoid these shortcomings. The structure is shown in Figure 2. A no-coupling design is adopted in this component, which could simultaneously increase the dynamic performance and the lubricating status of the motor and pump. This single-shaft coaxial design ensures the alignment of the two rotors and improves dynamic balance under high-speed conditions. Moreover, shared housing fundamentally eliminates shaft end leakage.
Testing the output characteristics of the EHA motor-pump assembly is of great significance for the optimization and improvement of the EHA performance. However, there are relatively few studies on performance testing of the motor-pump assembly, especially for EHAs. Therefore, we conducted a testing method of combining simulation and experiments. This method is suitable for testing motor-pump assemblies with a wide range of operating conditions, especially EHA pumps.
There are two main challenges: the first is to build an accurate simulation model to analyze the output flow characteristics of the motor-pump and provide assistance for the optimal design of the motor-pump assembly. We have established a simulation model of the motor-pump assembly through hierarchical modeling and realized the simulation analysis of the output flow by changing different parameters. The second is the cavitation of the test element caused by high speed, which is the most important aspect that distinguishes it from ordinary pumps. Therefore, we focused more on the design of the oil supply system when designing the test system to realize the test under various working conditions.
In this protocol, a one-dimensional simulation model was established to simulate the pump flow characteristics initially, judging whether the pump flow characteristics meet the requirements of EHA. Then, the flow characteristics and the overall efficiency were experimentally tested on a dedicated test bench, obtaining the overall efficiency map that cannot be accurately simulated by simulation. Lastly, the pump flow characteristics were compared with the experimental results to verify the accuracy of the simulation results. Meanwhile, the overall efficiency map was obtained to evaluate the performance of the single-shaft coaxial motor-pump assembly.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>AmeSim simulation platform</td>
			<td>Siemens</td>
			<td>Amesim 16</td>
			<td></td>
		</tr>
		<tr>
			<td>DAQ card</td>
			<td>Advantech</td>
			<td>PCI1710</td>
			<td></td>
		</tr>
		<tr>
			<td>Flowmeter</td>
			<td>KRACHT</td>
			<td>VC0.04E1RS, 0.02-4 L/min</td>
			<td></td>
		</tr>
		<tr>
			<td>Flowmeter</td>
			<td>KRACHT</td>
			<td>VC0.4E1RS, 0.2-40 L/min</td>
			<td></td>
		</tr>
		<tr>
			<td>Industrial Computer</td>
			<td>Advantech</td>
			<td>610H</td>
			<td></td>
		</tr>
		<tr>
			<td>Oil supply motor</td>
			<td>Siemens</td>
			<td>1TL0001-1BB23-3JA5</td>
			<td></td>
		</tr>
		<tr>
			<td>Oil supply pump</td>
			<td>Kangbaishi</td>
			<td>P222RF01DT</td>
			<td></td>
		</tr>
		<tr>
			<td>OriginPro</td>
			<td>OriginLab Corporation</td>
			<td>OriginPro 2021 (64-bit) 9.8.0.200</td>
			<td></td>
		</tr>
		<tr>
			<td>Pressure sensor</td>
			<td>Feejoy</td>
			<td>PI131G(0-5 MPA)F4MCAH5C</td>
			<td></td>
		</tr>
		<tr>
			<td>Proportional relief valve</td>
			<td>Huade hydraulic</td>
			<td>DBE10-30B/50YV</td>
			<td></td>
		</tr>
		<tr>
			<td>Proportional relief valve</td>
			<td>Huade hydraulic</td>
			<td>DBE10-30B/315YV</td>
			<td></td>
		</tr>
		<tr>
			<td>Spindle motor</td>
			<td>HAOZHI</td>
			<td>DGZX-18020 / 22A2-KFHWVJLS</td>
			<td>Max speed: 18,000 rpm;&#160; Power: 22 kW</td>
		</tr>
		<tr>
			<td>Temperature sensor</td>
			<td>Feejoy</td>
			<td>TI-A42M1A180/30+F1</td>
			<td></td>
		</tr>
	</tbody>
</table>

modeling and experimental analysis of the single-shaft coaxial motor-pump assembly in electrohydrostatic actuators

An electrohydrostatic actuator (EHA) can be the most promising alternative compared with the traditional hydraulic servo actuators for its high power density, ease of maintenance, and reliability. As the core power unit that determines the performance and service life of the EHA, the motor-pump assembly should simultaneously possess a wide speed/pressure range and a high dynamic response.
This paper presents a method to test the performance of the motor-pump assembly through simulation and experimentation. The flow output characteristics were defined through simulation and analysis of the assembly at the beginning of the experiment, leading to the conclusion of whether the pump could meet the requirements of the EHA. A series of performance tests were conducted on the motor-pump assembly via a pump test bench in the speed range of 1,450-9,000 rpm and the pressure range of 1-30 MPa.
We tested the overall efficiency of the motor-pump assembly under various working conditions after confirming the consistency between the test results of the flow output characteristics with the simulation results. The results showed that the assembly has higher overall efficiency when working at 4,500-7,000 rpm under the pressure of 10-25 MPa and at 2,000-2,500 rpm under 5-15 MPa. Overall, this method can be utilized for determining in advance whether the motor-pump assembly meets the requirements of EHA. Moreover, this paper proposes a rapid test method of the motor-pump assembly in various working conditions, which could assist in predicting EHA performance.

The simulation result of the discharge flow (Figure 10A) indicated that the discharge flow decreased slightly with the increase in load pressure when the speed was constant. Furthermore, the output flow rate increased linearly with increasing speed when the pressure is constant, judging from the same belt width. To directly evaluate the performance of the motor-pump assembly under different working conditions, we plotted its volumetric efficiency diagram (Figure 11A</str...

Watch this Scientific Journal Video about Modeling and Experimental Analysis of the Single-Shaft Coaxial Motor-Pump Assembly in Electrohydrostatic Actuators at JoVE.com

Modeling and Experimental Analysis of the Single-Shaft Coaxial Motor-Pump Assembly in Electrohydrostatic Actuators

We built a simulation model to evaluate pump flow characteristics and performance of the single-shaft coaxial motor-pump assembly in electrohydrostatic actuators and investigate the overall efficiency in a wide set of working conditions of the motor-pump assembly experimentally.

An electrohydrostatic actuator (EHA) can be the most promising alternative compared with the traditional hydraulic servo actuators for its high power ...

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2.4K Views.  Beihang University. We built a simulation model to evaluate pump flow characteristics and performance of the single-shaft coaxial motor-pump assembly in electrohydrostatic actuators and investigate the overall efficiency in a wide set of working conditions of the motor-pump assembly experimentally.

Video: Modeling and Experimental Analysis of the Single-Shaft Coaxial Motor-Pump Assembly in Electrohydrostatic Actuators

Experimental Measurement of Settling Velocity of Spherical Particles in Unconfined and Confined Surfactant-based Shear Thinning Viscoelastic Fluids

An experimental study is performed to measure the terminal settling velocities of spherical particles in surfactant based shear thinning viscoelastic (VES) fluids. The measurements are made for particles settling in unbounded fluids&#160;and fluids between parallel walls. VES fluids over a wide range of rheological properties are prepared and rheologically characterized. The rheological characterization involves steady shear-viscosity and dynamic oscillatory-shear measurements to quantify the viscous and elastic properties respectively. The settling velocities under unbounded conditions are measured in beakers having diameters at least 25x the diameter of particles. For measuring settling velocities between parallel walls, two experimental cells with different wall spacing are constructed. Spherical particles of varying sizes are gently dropped in the fluids and allowed to settle. The process is recorded with a high resolution video camera and the trajectory of the particle is recorded using image analysis software. Terminal settling velocities are calculated from the data.
The impact of elasticity on settling velocity in unbounded fluids is quantified by comparing the experimental settling velocity to the settling velocity calculated by the inelastic drag predictions of Renaud et al.1&#160;Results show that elasticity of fluids can increase or decrease the settling velocity. The magnitude of reduction/increase is a function of the rheological properties of the fluids and properties of particles. Confining walls are observed to cause a retardation effect on settling and the retardation is measured in terms of wall factors.

This paper demonstrates the experimental procedure to measure terminal settling velocities of spherical particles in surfactant-based shear thinning viscoelastic fluids. Fluids over a wide range of rheological properties are prepared and settling velocities are measured for a range of particle sizes in unbounded fluids and fluids between parallel walls.

An experimental study is performed to measure the terminal settling velocities of spherical particles in surfactant based shear thinning viscoelastic ...

Real-Time DC-dynamic Biasing Method for Switching Time Improvement in Severely Underdamped Fringing-field Electrostatic MEMS Actuators

Mechanically underdamped electrostatic fringing-field MEMS actuators are well known for their fast switching operation in response to a unit step input bias voltage. However, the tradeoff for the improved switching performance is a relatively long settling time to reach each gap height in response to various applied voltages. Transient applied bias waveforms are employed to facilitate reduced switching times for electrostatic fringing-field MEMS actuators with high mechanical quality factors. Removing the underlying substrate of the fringing-field actuator creates the low mechanical damping environment necessary to effectively test the concept. The removal of the underlying substrate also a has substantial improvement on the reliability performance of the device in regards to failure due to stiction. Although DC-dynamic biasing is useful in improving settling time, the required slew rates for typical MEMS devices may place aggressive requirements on the charge pumps for fully-integrated on-chip designs. Additionally, there may be challenges integrating the substrate removal step into the back-end-of-line commercial CMOS processing steps. Experimental validation of fabricated actuators demonstrates an improvement of 50x in switching time when compared to conventional step biasing results. Compared to theoretical calculations, the experimental results are in good agreement.

The robust device design of fringing-field electrostatic MEMS actuators results in inherently low squeeze-film damping conditions and long settling times when performing switching operations using conventional step biasing. Real-time switching time improvement with DC-dynamic waveforms reduces the settling time of fringing-field MEMS actuators when transitioning between up-to-down and down-to-up states.

Mechanically underdamped electrostatic fringing-field MEMS actuators are well known for their fast switching operation in response to a unit step input ...

Preparation and Use of Photocatalytically Active Segmented Ag|ZnO and Coaxial TiO2-Ag Nanowires Made by Templated Electrodeposition

Photocatalytically active nanostructures require a large specific surface area with the presence of many catalytically active sites for the oxidation and reduction half reactions, and fast electron (hole) diffusion and charge separation. Nanowires present suitable architectures to meet these requirements. Axially segmented Ag|ZnO and radially segmented (coaxial) TiO2-Ag nanowires with a diameter of 200 nm and a length of 6-20 &#181;m were made by templated electrodeposition within the pores of polycarbonate track-etched (PCTE) or anodized aluminum oxide (AAO) membranes, respectively. In the photocatalytic experiments, the ZnO and TiO2 phases acted as photoanodes, and Ag as cathode. No external circuit is needed to connect both electrodes, which is a key advantage over conventional photo-electrochemical cells. For making segmented Ag|ZnO nanowires, the Ag salt electrolyte was replaced after formation of the Ag segment to form a ZnO segment attached to the Ag segment. For making coaxial TiO2-Ag nanowires, a TiO2 gel was first formed by the electrochemically induced sol-gel method. Drying and thermal annealing of the as-formed TiO2 gel resulted in the formation of crystalline TiO2 nanotubes. A subsequent Ag electrodeposition step inside the TiO2 nanotubes resulted in formation of coaxial TiO2-Ag nanowires. Due to the combination of an n-type semiconductor (ZnO or TiO2) and a metal (Ag) within the same nanowire, a Schottky barrier was created at the interface between the phases. To demonstrate the photocatalytic activity of these nanowires, the Ag|ZnO nanowires were used in a photocatalytic experiment in which H2 gas was detected upon UV illumination of the nanowires dispersed in a methanol/water mixture. After 17 min&#160;of illumination, approximately 0.2 vol% H2 gas was detected from a suspension of ~0.1 g of Ag|ZnO nanowires in a 50 ml 80 vol% aqueous methanol solution.

Preparation and Use of Photocatalytically Active Segmented Ag|ZnO and Coaxial TiO2-Ag Nanowires Made by Templated Electrodeposition

Procedures are outlined to prepare segmented and coaxial nanowires via templated electrodeposition in nanopores. As examples, segmented nanowires consisting of Ag and ZnO segments, and coaxial nanowires consisting of a TiO2 shell and a Ag core were made. The nanowires were used in photocatalytic hydrogen formation experiments.

Photocatalytically active nanostructures require a large specific surface area with the presence of many catalytically active sites for the oxidation and ...

Fabrication Process of Silicone-based Dielectric Elastomer Actuators

This contribution demonstrates the fabrication process of dielectric elastomer transducers (DETs). DETs are stretchable capacitors consisting of an elastomeric dielectric membrane sandwiched between two compliant electrodes. The large actuation strains of these transducers when used as actuators (over 300% area strain) and their soft and compliant nature has been exploited for a wide range of applications, including electrically tunable optics, haptic feedback devices, wave-energy harvesting, deformable cell-culture devices, compliant grippers, and propulsion of a bio-inspired fish-like airship. In most cases, DETs are made with a commercial proprietary acrylic elastomer and with hand-applied electrodes of carbon powder or carbon grease. This combination leads to non-reproducible and slow actuators exhibiting viscoelastic creep and a short lifetime. We present here a complete process flow for the reproducible fabrication of DETs based on thin elastomeric silicone films, including casting of thin silicone membranes, membrane release and prestretching, patterning of robust compliant electrodes, assembly and testing. The membranes are cast on flexible polyethylene terephthalate (PET) substrates coated with a water-soluble sacrificial layer for ease of release. The electrodes consist of carbon black particles dispersed into a silicone matrix and patterned using a stamping technique, which leads to precisely-defined compliant electrodes that present a high adhesion to the dielectric membrane on which they are applied.

This manuscript shows the fabrication process for the manufacture of dielectric elastomer soft actuators based on silicone membranes. The three key stages of production are presented in detail: blade casting of thin silicone membranes; pad printing of compliant electrodes; and the assembly of all the components.

This contribution demonstrates the fabrication process of dielectric elastomer transducers (DETs). DETs are stretchable capacitors consisting of an ...

Quantification of Hydrogen Concentrations in Surface and Interface Layers and Bulk Materials through Depth Profiling with Nuclear Reaction Analysis

Nuclear reaction analysis (NRA) via the resonant 1H(15N,&#945;&#947;)12C reaction is a highly effective method of depth profiling that quantitatively and non-destructively reveals the hydrogen density distribution at surfaces, at interfaces, and in the volume of solid materials with high depth resolution. The technique applies a 15N ion beam of 6.385 MeV provided by an electrostatic accelerator and specifically detects the 1H isotope in depths up to about 2 &#956;m from the target surface. Surface H coverages are measured with a sensitivity in the order of ~1013 cm-2 (~1% of a typical atomic monolayer density) and H volume concentrations with a detection limit of ~1018 cm-3 (~100 at. ppm). The near-surface depth resolution is 2-5 nm for surface-normal 15N ion incidence onto the target and can be enhanced to values below 1 nm for very flat targets by adopting a surface-grazing incidence geometry. The method is versatile and readily applied to any high vacuum compatible homogeneous material with a smooth surface (no pores). Electrically conductive targets usually tolerate the ion beam irradiation with negligible degradation. Hydrogen quantitation and correct depth analysis require knowledge of the elementary composition (besides hydrogen) and mass density of the target material. Especially in combination with ultra-high vacuum methods for in-situ target preparation and characterization, 1H(15N,&#945;&#947;)12C NRA is ideally suited for hydrogen analysis at atomically controlled surfaces and nanostructured interfaces. We exemplarily demonstrate here the application of 15N NRA at the MALT Tandem accelerator facility of the University of Tokyo to (1) quantitatively measure the surface coverage and the bulk concentration of hydrogen in the near-surface region of a H2 exposed Pd(110) single crystal, and (2) to determine the depth location and layer density of hydrogen near the interfaces of thin SiO2 films on Si(100).

We illustrate the application of 1H(15N,&#945;&#947;)12C resonant nuclear reaction analysis (NRA) to quantitatively evaluate the density of hydrogen atoms on the surface, in the volume, and at an interfacial layer of solid materials. The near-surface hydrogen depth profiling of a Pd(110) single crystal and of SiO2/Si(100) stacks is described.

Nuclear reaction analysis (NRA) via the resonant 1H(15N,&#945;&#947;)12C reaction is a highly effective method of depth profiling that quantitatively and ...

Using Synchrotron Radiation Microtomography to Investigate Multi-scale Three-dimensional Microelectronic Packages

Synchrotron radiation micro-tomography (SR&#181;T) is a non-destructive three-dimensional (3D) imaging technique that offers high flux for fast data acquisition times with high spatial resolution. In the electronics industry there is serious interest in performing failure analysis on 3D microelectronic packages, many which contain multiple levels of high-density interconnections. Often in tomography there is a trade-off between image resolution and the volume of a sample that can be imaged. This inverse relationship limits the usefulness of conventional computed tomography (CT) systems since a microelectronic package is often large in cross sectional area 100-3,600 mm2, but has important features on the micron scale. The micro-tomography beamline at the Advanced Light Source (ALS), in Berkeley, CA USA, has a setup which is adaptable and can be tailored to a sample&#39;s properties, i.e., density, thickness, etc., with a maximum allowable cross-section of 36 x 36 mm. This setup also has the option of being either monochromatic in the energy range ~7-43 keV or operating with maximum flux in white light mode using a polychromatic beam. Presented here are details of the experimental steps taken to image an entire 16 x 16 mm system within a package, in order to obtain 3D images of the system with a spatial resolution of 8.7 &#181;m all within a scan time of less than 3 min. Also shown are results from packages scanned in different orientations and a sectioned package for higher resolution imaging. In contrast a conventional CT system would take hours to record data with potentially poorer resolution. Indeed, the ratio of field-of-view to throughput time is much higher when using the synchrotron radiation tomography setup. The description below of the experimental setup can be implemented and adapted for use with many other multi-materials.

For this study synchrotron radiation micro-tomography, a non-destructive three-dimensional imaging technique, is employed to investigate an entire microelectronic package with a cross-sectional area of 16 x 16 mm. Due to the synchrotron&#39;s high flux and brightness the sample was imaged in just 3 min&#160;with an 8.7 &#181;m spatial resolution.

Synchrotron radiation micro-tomography (SR&#181;T) is a non-destructive three-dimensional (3D) imaging technique that offers high flux for fast data ...

Free-form Light Actuators &#8212; Fabrication and Control of Actuation in Microscopic Scale

Liquid crystalline elastomers (LCEs) are smart materials capable of reversible shape-change in response to external stimuli, and have attracted researchers&#39; attention in many fields. Most of the studies focused on macroscopic LCE structures (films, fibers) and their miniaturization is still in its infancy. Recently developed lithography techniques, e.g., mask exposure and replica molding, only allow for creating 2D structures on LCE thin films. Direct laser writing (DLW) opens access to truly 3D fabrication in the microscopic scale. However, controlling the actuation topology and dynamics at the same length scale remains a challenge.
In this paper we report on a method to control the liquid crystal (LC) molecular alignment in the LCE microstructures of arbitrary three-dimensional shape. This was made possible by a combination of direct laser writing for both the LCE structures as well as for micrograting patterns inducing local LC alignment. Several types of grating patterns were used to introduce different LC alignments, which can be subsequently patterned into the LCE structures. This protocol allows one to obtain LCE microstructures with engineered alignments able to perform multiple opto-mechanical actuation, thus being capable of multiple functionalities. Applications can be foreseen in the fields of tunable photonics, micro-robotics, lab-on-chip technology and others.

Free-form Light Actuators &amp;#8212; Fabrication and Control of Actuation in Microscopic Scale

Here, we fabricate 3D polymeric micro/nano structures in which both the shape and the molecular alignment can be engineered with nanometer scale accuracy by the use of direct laser writing. Light induced deformation of several types of liquid crystalline elastomer microstructures can be controlled in the microscopic scale.

Liquid crystalline elastomers (LCEs) are smart materials capable of reversible shape-change in response to external stimuli, and have attracted ...

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

We demonstrate the use of two nuclear-based analytical methods that can follow the modifications of microstructural arrangement of iron-based metallic glasses (MGs). Despite their amorphous nature, the identification of hyperfine interactions unveils faint structural modifications. For this purpose, we have employed two techniques that utilize nuclear resonance among nuclear levels of a stable 57Fe isotope, namely M&#246;ssbauer spectrometry and nuclear forward scattering (NFS) of synchrotron radiation. The effects of heat treatment upon (Fe2.85Co1)77Mo8Cu1B14 MG are discussed using the results of ex situ and in situ experiments, respectively. As both methods are sensitive to hyperfine interactions, information on structural arrangement as well as on magnetic microstructure is readily available. M&#246;ssbauer spectrometry performed ex situ describes how the structural arrangement and magnetic microstructure appears at room temperature after the annealing under certain conditions (temperature, time), and thus this technique inspects steady states. On the other hand, NFS data are recorded in situ during dynamically changing temperature and NFS examines transient states. The use of both techniques provides complementary information. In general, they can be applied to any suitable system in which it is important to know its steady state but also transient states.

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

Here, we present a protocol to describe ex situ and in situ investigations of structural transformations in metallic glasses. We employed nuclear-based analytical methods which inspect hyperfine interactions. We demonstrate the applicability of M&#246;ssbauer spectrometry and nuclear forward scattering of synchrotron radiation during temperature-driven experiments.

We demonstrate the use of two nuclear-based analytical methods that can follow the modifications of microstructural arrangement of iron-based metallic ...

Fabrication of Soft Pneumatic Network Actuators with Oblique Chambers

Soft pneumatic network actuators have become one of the most promising actuation devices in soft robotics which benefits from their large bending deformation and low input. However, their monotonous bending motion form in two-dimensional (2-D) space keeps them away from wide applications. This paper presents a detailed fabrication method of soft pneumatic network actuators with oblique chambers, to explore their motions in three-dimensional (3-D) space. The design of oblique chambers enables actuators with tunable coupled bending and twisting capabilities, which gives them the possibility to move dexterously in flexible manipulators, to become biologically inspired robots and medical devices. The fabrication process is based on the molding method, including the silicone elastomer preparation, chamber and base parts fabrication, actuator assembly, tubing connections, checks for leaks, and actuator repair. The fabrication method guarantees the rapid manufacturing of a series of actuators with only a few modifications in the molds. The test results show the high quality of the actuators and their prominent bending and twisting capabilities. Experiments of the gripper demonstrate the advantages of the development in adapting to objects with different diameters and providing sufficient friction.

Here we present a fabrication method of soft pneumatic network actuators with oblique chambers. The actuators are capable of generating coupled bending and twisting motions, which broadens their application in soft robotics.

Soft pneumatic network actuators have become one of the most promising actuation devices in soft robotics which benefits from their large bending ...

Crack Monitoring in Resonance Fatigue Testing of Welded Specimens Using Digital Image Correlation

A procedure using digital image correlation (DIC) to detect cracks on welded specimens during fatigue tests on resonance testing machines is presented. It is intended as a practical and reproducible procedure to identify macroscopic cracks at an early stage and monitor crack propagation during fatigue tests. It consists of strain field measurements at the weld using DIC. Images are taken at fixed load cycle intervals. Cracks become visible in the computed strain field as elevated strains. This way, the whole width of a small-scale specimen can be monitored to detect where and when a crack initiates. Subsequently, it is possible to monitor the development of the crack length. Because the resulting images are saved, the results are verifiable and comparable. The procedure is limited to cracks initiating at the surface and is intended for fatigue tests under laboratory conditions. By visualizing the crack, the presented procedure allows direct observation of macrocracks from their formation until rupture of the specimen.

Digital image correlation is used in fatigue tests on a resonance testing machine to detect macroscopic cracks and monitor crack propagation in welded specimens. Cracks on the specimen surface become visible as increased strains.

A procedure using digital image correlation (DIC) to detect cracks on welded specimens during fatigue tests on resonance testing machines is presented. It ...