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Volume 6
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Micromachines, Volume 6, Issue 8 (August 2015) – 14 articles , Pages 969-1212

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808 KiB  
Article
Micro-Machined Flow Sensors Mimicking Lateral Line Canal Neuromasts
by Hendrik Herzog, Siegfried Steltenkamp, Adrian Klein, Simon Tätzner, Elisabeth Schulze and Horst Bleckmann
Micromachines 2015, 6(8), 1189-1212; https://doi.org/10.3390/mi6081189 - 24 Aug 2015
Cited by 35 | Viewed by 7444
Abstract
Fish sense water motions with their lateral line. The lateral line is a sensory system that contains up to several thousand mechanoreceptors, called neuromasts. Neuromasts occur freestanding on the skin and in subepidermal canals. We developed arrays of flow sensors based on lateral [...] Read more.
Fish sense water motions with their lateral line. The lateral line is a sensory system that contains up to several thousand mechanoreceptors, called neuromasts. Neuromasts occur freestanding on the skin and in subepidermal canals. We developed arrays of flow sensors based on lateral line canal neuromasts using a biomimetic approach. Each flow sensor was equipped with a PDMS (polydimethylsiloxane) lamella integrated into a canal system by means of thick- and thin-film technology. Our artificial lateral line system can estimate bulk flow velocity from the spatio-temporal propagation of flow fluctuations. Based on the modular sensor design, we were able to detect flow rates in an industrial application of tap water flow metering. Our sensory system withstood water pressures of up to six bar. We used finite element modeling to study the fluid flow inside the canal system and how this flow depends on canal dimensions. In a second set of experiments, we separated the flow sensors from the main stream by means of a flexible membrane. Nevertheless, these biomimetic neuromasts were still able to sense flow fluctuations. Fluid separation is a prerequisite for flow measurements in medical and pharmaceutical applications. Full article
(This article belongs to the Special Issue Biomimetic Systems)
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Scheme of the lateral line system. (<b>A</b>) Superficial neuromasts (SNs) are located on the skin of the animal and are sensitive to flow velocity; (<b>B</b>) canal neuromasts (CNs) are located in subepidermal canals. They are sensitive to fluid motion inside the canal caused by pressure gradients between adjacent canal pores. Solid-lined arrows indicate fluid motion; dashed-lined arrows indicate pressure acting on the pores. Modified from [<a href="#B23-micromachines-06-01189" class="html-bibr">23</a>].</p> Full article ">Figure 2
<p>Assembly of the micro-machined CN. (<b>A</b>) Assembly of the sensory device featuring the Si-chip (a), housing (b), LED (c), electronics PCB (d) with the optical detector (e); (<b>B</b>) magnified Si-chip featuring a PDMS lamella (f) and a glass plate (g). Note that the illustration is not to scale. Modified from [<a href="#B69-micromachines-06-01189" class="html-bibr">69</a>].</p> Full article ">Figure 3
<p>Optical read-out principles and sensor electronics. Various sensor read-out principles that were used to detect the deflection of the light-guiding PDMS lamella (left) and corresponding electronic circuits (right). (<b>A</b>) The photo transistor principle uses a Darlington configuration for amplification of the photo transistor current (<b>B</b>) (modified from [<a href="#B51-micromachines-06-01189" class="html-bibr">51</a>]). (<b>C</b>) The position-sensitive photo diode (PSD) in photo cell operation mode in combination with a voltage subtractor and a capacitive coupled amplifier (<b>D</b>). (<b>E</b>) The differential photo diode (DD) combined with a trans-impedance amplifier followed by a voltage subtractor and a current source used for driving the LED (<b>F</b>).</p> Full article ">Figure 4
<p>Measuring setup and original recording traces obtained in the proof of principle study. (<b>A</b>) Array of eight sensors equipped with mid-sized lamellae built in thick-film technology; (<b>B</b>) The original recording traces of the sensors while stimulated with a bulk flow rate of 672 L/h. Please note that the temporal offsets between similar waveforms from Sensors S4 to S7 (black lines) are also shown in <a href="#micromachines-06-01189-f005" class="html-fig">Figure 5</a>. Arrows in (<b>A</b>) indicate flow. Amplitudes are normalized to view the signal shape and are not to scale.</p> Full article ">Figure 5
<p>Original signals and cross-correlation functions of the proof of principle study. (<b>A</b>–<b>E</b>) Signals of the adjacent Sensors S6 (gray line) and S7 (black line). Flow rate 797 L/h (<b>A</b>), 672 L/h (<b>B</b>), 485 L/h (<b>C</b>) 308 L/h (<b>D</b>) and 0 L/h (no flow condition) (<b>E</b>). Gray bars indicate expected temporal delay between waveforms. Amplitudes are normalized and not to scale. (<b>F</b>–<b>J</b>) The cross-correlation functions of the two sensor signals shown in (<b>A</b>) to (<b>E</b>) for a time interval of 10 s.</p> Full article ">Figure 6
<p>Flow rate estimation from temporal delayed waveforms in the proof of principle study. The plot shows the mean values and standard errors for reference flow rates that ranged from 0 to 797 L/h. Sensors were spaced 5 mm apart (open circles, adjacent sensors), 10 mm apart (gray circles) and 15 mm apart (black circles). Data points of estimated flow rates exceeding the range of 0 to 2000 L/h were excluded from this figure (about 35% for adjacent sensors, 25% for 10 mm and 3% for 15 mm sensor distance). Please note that reference values along the <span class="html-italic">x</span>-axis are not equally spaced.</p> Full article ">Figure 7
<p>Setup and output signals of the micro-machined sensors in the tap water metering application. (<b>A</b>) Measuring tube featuring three MEMS sensors (S1, S2 and S3) mounted on adapter plates (see <a href="#micromachines-06-01189-f002" class="html-fig">Figure 2</a>). (<b>B</b>–<b>F</b>) The output signals of the three sensors obtained while applying flow rates of 4066 L/h (<b>B</b>), 2550 L/h (<b>C</b>), 1536 L/h (<b>D</b>), 500 L/h (<b>E</b>), and 50 L/h (<b>F</b>). Gray bars indicate expected delay of waveforms.</p> Full article ">Figure 8
<p>Cross-correlation (CC) functions of the output signals of the micro-machined sensors in the tap water application. Cross-correlations, each based on two of the micro-machined sensors and a 10 s time interval for the reference velocities of 4066 L/h (<b>A</b>), 2550 L/h (<b>B</b>), 1536 L/h (<b>C</b>), and 500 L/h (<b>D</b>). Arrows indicate temporal offset expected from the reference flow rate applied.</p> Full article ">Figure 9
<p>Estimated flow rates for reference flow rates ranging from 500 to 4066 L/h. The plot shows mean values and standard errors. Flow rates were estimated from cross-correlations of sensors 1 and 2 (black circles), sensors 2 and 3 (gray circles) and sensors 1 and 3 (open circles) according to Equation (<a href="#FD1-micromachines-06-01189" class="html-disp-formula">1</a>). Note that estimated flow rates exceeding the range of 0 to 10,000 L/h were excluded from the figure (about 12% for S1 and S2, 8% for S2 and S3, 35% for S1 and S3). Please note that reference values along the <span class="html-italic">x</span>-axis are not equally spaced.</p> Full article ">Figure 10
<p>Finite element simulation of mechanical cross-talk induced by the canal geometry. (<b>A</b>) Simple canals (top) with variable canal widths (cw) and pore dimensions (pd). Complex canals included septa or diminutions (below). Fluid flow was examined at locations S1 to S8 when stimulated with alternating pressure of 1 Pa at 10 Hz. (<b>B</b>) The velocity components in the horizontal direction at locations S1 to S8 (see the double-headed arrows in (<b>A</b>)). The colors of the curves do not correspond to the colors in (<b>D</b>)/(<b>E</b>). (<b>C</b>) The flow field inside the basic canal in logarithmic scaling (see also <a href="#micromachines-06-01189-f004" class="html-fig">Figure 4</a>A). (<b>D</b>) Peak-to-peak amplitudes at locations S1 to S8 for various canal shapes and dimensions (shown in (<b>A</b>)) (<b>E</b>) Normalized peak-to-peak amplitudes from (<b>D</b>), referenced to the velocity at location S3.</p> Full article ">Figure 11
<p>Verification of an artificial CN sealed with a PDMS membrane by flow-induced fluctuations. (<b>A</b>) Schematic drawing of the sensor setup featuring a metering tube (a), a PDMS membrane (b), an aluminum adapter with pores (c), a Si-chip with lamellae (d), mineral oil filling (e) and sealed read-out electronics (f); (<b>B</b>) Output signals of a sensor with open pores and with pores covered by different PDMS membranes (thicknesses of 14, 66, 117 and 197 µm). Bulk flow velocities varied from 0 to 1 m/s.</p> Full article ">
4955 KiB  
Article
Centrifugal Step Emulsification can Produce Water in Oil Emulsions with Extremely High Internal Volume Fractions
by Friedrich Schuler, Nils Paust, Roland Zengerle and Felix Von Stetten
Micromachines 2015, 6(8), 1180-1188; https://doi.org/10.3390/mi6081180 - 20 Aug 2015
Cited by 23 | Viewed by 8575
Abstract
The high throughput preparation of emulsions with high internal volume fractions is important for many different applications, e.g., drug delivery. However, most emulsification techniques reach only low internal volume fractions and need stable flow rates that are often difficult to control. Here, we [...] Read more.
The high throughput preparation of emulsions with high internal volume fractions is important for many different applications, e.g., drug delivery. However, most emulsification techniques reach only low internal volume fractions and need stable flow rates that are often difficult to control. Here, we present a centrifugal high throughput step emulsification disk for the fast and easy production of emulsions with high internal volume fractions above 95%. The disk produces droplets at generation rates of up to 3700 droplets/s and, for the first time, enables the generation of emulsions with internal volume fractions of >97%. The coefficient of variation between droplet sizes is very good (4%). We apply our system to show the in situ generation of gel emulsion. In the future, the recently introduced unit operation of centrifugal step emulsification may be used for the high throughput production of droplets as reaction compartments for clinical diagnostics or as starting material for micromaterial synthesis. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>(<b>a</b>) Schematic top view of the high-throughput centrifugal step emulsification structure. The inlet chamber is located close to the center of rotation. A channel emerges from the inlet chamber and is split multiple times before leading to 8 sets of nozzles. These nozzles lead to the droplet collection chamber. Supporting pillars prevent the sealing film on top of the emulsification chamber to fall down to the bottom of the chamber during sealing. (<b>b</b>) Image of the production of ink emulsion in a similar setup taken under rotation. The black ink droplets can be seen rising in the surrounding fluorinated oil.</p> Full article ">Figure 2
<p>(<b>a</b>) Microscopic image of droplets after production in the droplet collection chamber. In the lower part of the image the feed channel and nozzles can be seen. In the middle, the droplets form a monolayer since the droplet collection chamber is shallow. In the upper part of the images many layers of droplets lie on top of each other since the chamber is very deep at this point. Therefore, no individual droplets can be seen anymore. This image was taken without centrifugal forces being applied. Since the droplets are not pushed towards the center of rotation by buoyancy in the artificial gravity field the droplets fill the whole droplet chamber. Since very little oil surrounds the droplets, they are forced to form a hexagonal pattern. This is visible in the shallow area after the 1st step, where a monolayer of droplets is formed (as opposed to the deep area, where multiple layers are stacked on top of each other). (<b>b</b>) Photographic image of gel emulsion with 97.2% internal phase. The gel emulsion is stable enough to turn it upside down in a 0.5 mL vial. At the bottom of the picture, the structure of individual droplets can be identified.</p> Full article ">
14243 KiB  
Article
Comparative Analysis of Passive Micromixers at a Wide Range of Reynolds Numbers
by Vladimir Viktorov, Md Readul Mahmud and Carmen Visconte
Micromachines 2015, 6(8), 1166-1179; https://doi.org/10.3390/mi6081166 - 18 Aug 2015
Cited by 21 | Viewed by 5846
Abstract
Two novel passive micromixers, denoted as the Y-Y mixer and the H-C mixer, based on split-and-recombine (SAR) principle are studied both experimentally and numerically over Reynolds numbers ranging from 1 to 100. An image analysis technique was used to evaluate mixture homogeneity at [...] Read more.
Two novel passive micromixers, denoted as the Y-Y mixer and the H-C mixer, based on split-and-recombine (SAR) principle are studied both experimentally and numerically over Reynolds numbers ranging from 1 to 100. An image analysis technique was used to evaluate mixture homogeneity at four target areas. Numerical simulations were found to be a useful support for the design phase, since a general idea of mixing of fluids can be inferred from the segregation or the distribution of path lines. Comparison with a well-known mixer, the Tear-drop one, was also performed. Over the examined range of Reynolds numbers 1 ≤ Re ≤ 100, the Y-Y and H-C mixers showed at their exit an almost flat mixing index characteristic, with a mixing efficiency higher than 90%; conversely the Tear-drop mixer showed a relevant decrease of efficiency at mid-range. Furthermore, the Y-Y and the H-C showed significantly less pressure drop than the Tear-drop mixer. Full article
(This article belongs to the Special Issue Micromixer & Micromixing)
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Figure 1

Figure 1
<p>Geometry of the Tear-drop micromixer (dimensions in mm): (<b>a</b>) three-dimensional view; (<b>b</b>) top view of one element and cross-section.</p> Full article ">Figure 2
<p>Geometry of the Y-Y micromixer (dimensions in mm): (<b>a</b>) three-dimensional view; (<b>b</b>) top view of one element and cross-section.</p> Full article ">Figure 3
<p>Geometry of the H-C micromixer (dimensions in mm): (<b>a</b>) three-dimensional view; (<b>b</b>) top view of one element and cross-sections.</p> Full article ">Figure 4
<p>Experimental setup.</p> Full article ">Figure 5
<p>Micromixers after filling with fluids at Re = 1.</p> Full article ">Figure 6
<p>Path lines at the exit of the micromixers at different Reynolds numbers.</p> Full article ">Figure 7
<p>Comparison between the images of the Tear-drop, the Y-Y, and the H-C mixers taken from computer simulation and experiments.</p> Full article ">Figure 8
<p>Experimental and numerical mixing efficiency of the Tear-drop, the Y-Y and the H-C mixers after four elements, varying Reynolds numbers.</p> Full article ">Figure 9
<p>Experimental and numerical mixing efficiency of the Tear-drop, the Y-Y, and the H-C micromixers, varying their number of elements: (<b>a</b>) Re = 1; (<b>b</b>) Re = 50.</p> Full article ">Figure 10
<p>Numerical and experimental pressure drop of the Tear-drop, the Y-Y, and the H-C micromixers: (<b>a</b>) varying flow rate; (<b>b</b>) varying Reynolds numbers.</p> Full article ">
5491 KiB  
Article
Tunable Focus Liquid Lens with Radial-Patterned Electrode
by Miao Xu, Xiahui Wang and Hongwen Ren
Micromachines 2015, 6(8), 1157-1165; https://doi.org/10.3390/mi6081157 - 17 Aug 2015
Cited by 16 | Viewed by 7209
Abstract
A dielectric liquid lens is prepared based on our previous work. By optimizing the device structure, the liquid lens presents a converging focus with good resolution and changes its focal length over a broad range with a low driving voltage. For a liquid [...] Read more.
A dielectric liquid lens is prepared based on our previous work. By optimizing the device structure, the liquid lens presents a converging focus with good resolution and changes its focal length over a broad range with a low driving voltage. For a liquid lens with ~2.3 mm diameter in the relaxed state, it can resolve ~40 lp/mm. The resolution does not degrade during focus change. Its focal length can be varied from ~12 to ~5 mm when the applied voltage is changed from 0 to 28 Vrms. The response time of one cycle is ~2.5 s. Our liquid lens, with a low driving voltage for a large dynamic range, has potential applications in imaging, biometrics, optoelectronic, and lab-on-chip devices. Full article
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Figure 1

Figure 1
<p>A liquid droplet placed on a radial-patterned electrode in the (<b>a</b>) relaxed state and (<b>b</b>) contracted state. The right chart of (<b>b</b>) shows the fringing field between adjacent ITO stripes.</p> Full article ">Figure 2
<p>(<b>a</b>) Image of partial ITO pattern and (<b>b</b>) side-view structure of the lens cell.</p> Full article ">Figure 3
<p>Image of a toy observed through the liquid lens at various voltages. (<b>a</b>) <span class="html-italic">V</span> = 0, (<b>b</b>) <span class="html-italic">V</span> = 18 <span class="html-italic">V</span><sub>rms</sub>, (<b>c</b>) <span class="html-italic">V</span> = 30 <span class="html-italic">V</span><sub>rms</sub>, (<b>d</b>) <span class="html-italic">V</span> = 45 <span class="html-italic">V</span><sub>rms</sub>, and (<b>e</b>) refocus at <span class="html-italic">V</span> = 45 <span class="html-italic">V</span><sub>rms</sub>, (<b>f</b>) image of resolution target at <span class="html-italic">V</span> = 0.</p> Full article ">Figure 4
<p>Voltage-dependent shape change of the liquid droplet. A dynamic video showing the shape change of the droplet is given at <span class="html-italic">V</span> = 45 <span class="html-italic">V</span><sub>rms</sub>.</p> Full article ">Figure 5
<p>The contact angle and the diameter of the droplet aperture changed with voltages.</p> Full article ">Figure 6
<p>The measured focal length (triangles) and the calculated focal length (dots) of the liquid lens changed with voltages.</p> Full article ">Figure 7
<p>Dynamic response of the liquid lens impacted by voltage pulses.</p> Full article ">
1590 KiB  
Article
Insect-Inspired Micropump: Flow in a Tube with Local Contractions
by Yasser Aboelkassem
Micromachines 2015, 6(8), 1143-1156; https://doi.org/10.3390/mi6081143 - 14 Aug 2015
Cited by 17 | Viewed by 5400
Abstract
A biologically-inspired micropumping model in a three-dimensional tube subjected to localized wall constrictions is given in this article. The present study extends our previous pumping model where a 3D channel with a square cross-section is considered. The proposed pumping approach herein applies to [...] Read more.
A biologically-inspired micropumping model in a three-dimensional tube subjected to localized wall constrictions is given in this article. The present study extends our previous pumping model where a 3D channel with a square cross-section is considered. The proposed pumping approach herein applies to tubular geometries and is given to mimic an insect respiration mode, where the tracheal tube rhythmic wall contractions are used/hypothesized to enhance the internal flow transport within the entire respiration network. The method of regularized Stokeslets-mesh-free computations is used to reconstruct the flow motions induced by the wall movements and to calculate the time-averaged net flow rate. The time-averaged net flow rates from both the tube and channel models are compared. Results have shown that an inelastic tube with at least two contractions forced to move with a specific time lag protocol can work as a micropump. The system is simple and expected to be useful in many biomedical applications. Full article
(This article belongs to the Special Issue Biomimetic Systems)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Problem schematic given to mimic the insect’s main tracheal tube segment with two contractions [<a href="#B1-micromachines-06-01143" class="html-bibr">1</a>] and the Stokeslets-mesh-free numerical setup: (<b>a</b>) 3<span class="html-italic">D</span> tube with moving upper wall contraction profile <math display="inline"> <mrow> <mi>R</mi> <mo>(</mo> <mi>z</mi> <mo>,</mo> <mi>t</mi> <mo>)</mo> </mrow> </math>; (<b>b</b>) <math display="inline"> <mrow> <msub> <mi>g</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> </mrow> </math> and <math display="inline"> <mrow> <msub> <mi>g</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> </mrow> </math>, the motion protocols assigned to the first and second contractions, respectively.</p> Full article ">Figure 2
<p>Axial velocity contour lines: (<b>a</b>) 3D computations at <math display="inline"> <mrow> <mi>t</mi> <mo>=</mo> <mi>T</mi> <mo>/</mo> <mn>4</mn> </mrow> </math>, <math display="inline"> <mrow> <msub> <mi>θ</mi> <mn>12</mn> </msub> <mo>=</mo> <msup> <mn>30</mn> <mo>∘</mo> </msup> </mrow> </math>; (<b>b</b>) 3D computations at <math display="inline"> <mrow> <mi>t</mi> <mo>=</mo> <mn>3</mn> <mi>T</mi> <mo>/</mo> <mn>4</mn> </mrow> </math>, <math display="inline"> <mrow> <msub> <mi>θ</mi> <mn>12</mn> </msub> <mo>=</mo> <msup> <mn>30</mn> <mo>∘</mo> </msup> </mrow> </math>; (<b>c</b>) 2D theory at <math display="inline"> <mrow> <mi>t</mi> <mo>=</mo> <mi>T</mi> <mo>/</mo> <mn>4</mn> </mrow> </math>, <math display="inline"> <mrow> <msub> <mi>θ</mi> <mn>12</mn> </msub> <mo>=</mo> <msup> <mn>30</mn> <mo>∘</mo> </msup> </mrow> </math>; (<b>d</b>) 2D theory at <math display="inline"> <mrow> <mi>t</mi> <mo>=</mo> <mn>3</mn> <mi>T</mi> <mo>/</mo> <mn>4</mn> </mrow> </math>, <math display="inline"> <mrow> <msub> <mi>θ</mi> <mn>12</mn> </msub> <mo>=</mo> <msup> <mn>30</mn> <mo>∘</mo> </msup> </mrow> </math>.</p> Full article ">Figure 3
<p>Vertical velocity contour lines: (<b>a</b>) 3D computations at <math display="inline"> <mrow> <mi>t</mi> <mo>=</mo> <mi>T</mi> <mo>/</mo> <mn>4</mn> </mrow> </math>, <math display="inline"> <mrow> <msub> <mi>θ</mi> <mn>12</mn> </msub> <mo>=</mo> <msup> <mn>30</mn> <mo>∘</mo> </msup> </mrow> </math>; (<b>b</b>) 3D computations at <math display="inline"> <mrow> <mi>t</mi> <mo>=</mo> <mn>3</mn> <mi>T</mi> <mo>/</mo> <mn>4</mn> </mrow> </math>, <math display="inline"> <mrow> <msub> <mi>θ</mi> <mn>12</mn> </msub> <mo>=</mo> <msup> <mn>30</mn> <mo>∘</mo> </msup> </mrow> </math>; (<b>c</b>) 2D theory at <math display="inline"> <mrow> <mi>t</mi> <mo>=</mo> <mi>T</mi> <mo>/</mo> <mn>4</mn> </mrow> </math>, <math display="inline"> <mrow> <msub> <mi>θ</mi> <mn>12</mn> </msub> <mo>=</mo> <msup> <mn>30</mn> <mo>∘</mo> </msup> </mrow> </math>; (<b>d</b>) 2D theory at <math display="inline"> <mrow> <mi>t</mi> <mo>=</mo> <mn>3</mn> <mi>T</mi> <mo>/</mo> <mn>4</mn> </mrow> </math>, <math display="inline"> <mrow> <msub> <mi>θ</mi> <mn>12</mn> </msub> <mo>=</mo> <msup> <mn>0</mn> <mo>∘</mo> </msup> </mrow> </math>.</p> Full article ">Figure 4
<p>Pressure contour lines: (<b>a</b>) 3D computations at <math display="inline"> <mrow> <mi>t</mi> <mo>=</mo> <mi>T</mi> <mo>/</mo> <mn>4</mn> </mrow> </math>, <math display="inline"> <mrow> <msub> <mi>θ</mi> <mn>12</mn> </msub> <mo>=</mo> <msup> <mn>30</mn> <mo>∘</mo> </msup> </mrow> </math>; (<b>b</b>) 3D computations at <math display="inline"> <mrow> <mi>t</mi> <mo>=</mo> <mn>3</mn> <mi>T</mi> <mo>/</mo> <mn>4</mn> </mrow> </math>, <math display="inline"> <mrow> <msub> <mi>θ</mi> <mn>12</mn> </msub> <mo>=</mo> <msup> <mn>30</mn> <mo>∘</mo> </msup> </mrow> </math>; (<b>c</b>) 2D theory at <math display="inline"> <mrow> <mi>t</mi> <mo>=</mo> <mi>T</mi> <mo>/</mo> <mn>4</mn> </mrow> </math>, <math display="inline"> <mrow> <msub> <mi>θ</mi> <mn>12</mn> </msub> <mo>=</mo> <msup> <mn>30</mn> <mo>∘</mo> </msup> </mrow> </math>; (<b>d</b>) 2D theory at <math display="inline"> <mrow> <mi>t</mi> <mo>=</mo> <mn>3</mn> <mi>T</mi> <mo>/</mo> <mn>4</mn> </mrow> </math>, <math display="inline"> <mrow> <msub> <mi>θ</mi> <mn>12</mn> </msub> <mo>=</mo> <msup> <mn>30</mn> <mo>∘</mo> </msup> </mrow> </math>.</p> Full article ">Figure 5
<p>Time-averaged net flow rate comparisons between the 2<span class="html-italic">D</span> analytical solution and 3<span class="html-italic">D</span> Stokeslets-mesh-free computations.</p> Full article ">
3077 KiB  
Article
Multiple Silicon Nanowires with Enzymatic Modification for Measuring Glucose Concentration
by Cheng-Chih Hsu, Yu-Ching Liao, Yen-Ting Tsai, Hsin-I Yeh and Chyan-Chyi Wu
Micromachines 2015, 6(8), 1135-1142; https://doi.org/10.3390/mi6081135 - 14 Aug 2015
Cited by 10 | Viewed by 4536
Abstract
This study fabricated a multiple poly-Si nanowires sensor through a top-down method and immobilized glucose oxidase on the multiple nanowires for determining glucose concentration. The proposed sensor is 340 nm in width and uses five physically identical and parallel nanowires. The sensor contained [...] Read more.
This study fabricated a multiple poly-Si nanowires sensor through a top-down method and immobilized glucose oxidase on the multiple nanowires for determining glucose concentration. The proposed sensor is 340 nm in width and uses five physically identical and parallel nanowires. The sensor contained nanowires of various lengths (3, 5, and 10 μm). Experimental results showed that sensor sensitivity is inversely proportional to nanowire length. The sensor with 3 μm in nanowire length exhibited a theoretical resolution of 0.003 mg/dL and the highest sensitivity of 0.03 μA/(mg/dL). Furthermore, the proposed sensor retains this performance when reused for up to 10 applications. Full article
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Figure 1

Figure 1
<p>(<b>a</b>) Diagram of the device structure and the experimental setup; (<b>b</b>) Top-view scanning electron microscope (SEM) image of the proposed sensor containing various nanowire lengths.</p> Full article ">Figure 2
<p>(<b>a</b>) <span class="html-italic">I</span><sub>D</sub>-<span class="html-italic">V</span><sub>D</sub> measurement for different fabricated poly-Si nanowires; (<b>b</b>) <span class="html-italic">I</span><sub>D</sub>-<span class="html-italic">V</span><sub>G</sub> measurement for different fabricated poly-Si nanowires.</p> Full article ">Figure 3
<p>Current-time response curve of the proposed sensor with nanowire lengths of (<b>a</b>) 3 µm, (<b>b</b>) 5 µm and (<b>c</b>) 10 µm.</p> Full article ">Figure 4
<p>(<b>a</b>) Reusability of the proposed sensor; (<b>b</b>) Top-view SEM image of the proposed sensor used more than 10 applications.</p> Full article ">Figure 5
<p>Calibration curves of the proposed sensor with nanowire lengths of (<b>a</b>) 3 µm, (<b>b</b>) 5 µm and (<b>c</b>) 10 µm.</p> Full article ">Figure 6
<p>Current fluctuation in the proposed sensor.</p> Full article ">
25362 KiB  
Article
Activity Recognition Using Fusion of Low-Cost Sensors on a Smartphone for Mobile Navigation Application
by Sara Saeedi and Naser El-Sheimy
Micromachines 2015, 6(8), 1100-1134; https://doi.org/10.3390/mi6081100 - 14 Aug 2015
Cited by 39 | Viewed by 12079
Abstract
Low-cost inertial and motion sensors embedded on smartphones have provided a new platform for dynamic activity pattern inference. In this research, a comparison has been conducted on different sensor data, feature spaces and feature selection methods to increase the efficiency and reduce the [...] Read more.
Low-cost inertial and motion sensors embedded on smartphones have provided a new platform for dynamic activity pattern inference. In this research, a comparison has been conducted on different sensor data, feature spaces and feature selection methods to increase the efficiency and reduce the computation cost of activity recognition on the smartphones. We evaluated a variety of feature spaces and a number of classification algorithms from the area of Machine Learning, including Naive Bayes, Decision Trees, Artificial Neural Networks and Support Vector Machine classifiers. A smartphone app that performs activity recognition is being developed to collect data and send them to a server for activity recognition. Using extensive experiments, the performance of various feature spaces has been evaluated. The results showed that the Bayesian Network classifier yields recognition accuracy of 96.21% using four features while requiring fewer computations. Full article
(This article belongs to the Special Issue Next Generation MEMS-Based Navigation—Systems and Applications)
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<p>The steps involved in activity recognition using a feature-level sensor fusion.</p> Full article ">Figure 2
<p>Six different positions for calibration of the accelerometer and gyroscope (each sensitive axis pointing alternately up and down). (<b>a</b>) <span class="html-italic">Z</span>-axis is along with <span class="html-italic">g</span> but in the opposite direction; (<b>b</b>) <span class="html-italic">X</span>-axis is along with <span class="html-italic">g</span> but in the opposite direction; (<b>c</b>) <span class="html-italic">Z</span>-axis is along with <span class="html-italic">g</span> and with the same direction; (<b>d</b>) <span class="html-italic">X</span>-axis is along with <span class="html-italic">g</span> and with the same direction; (<b>e</b>) <span class="html-italic">Y</span>-axis is along with <span class="html-italic">g</span> but in the opposite direction; (<b>f</b>) <span class="html-italic">Y</span>-axis is along with <span class="html-italic">g</span> and with the same direction.</p> Full article ">Figure 3
<p>Schematic diagram of the data collection process.</p> Full article ">Figure 4
<p>Collecting training datasets for different activities and device placements.</p> Full article ">Figure 5
<p>Calibrates accelerometers and gyros outputs in different placement mode.</p> Full article ">Figure 6
<p>Different activity contexts assumed for personal navigation services.</p> Full article ">Figure 7
<p>Recognition accuracy using different sets of sensors for different activity modes (Classifier: Bayesian Network, Number of features: 46).</p> Full article ">Figure 8
<p>Time consumption of using different sensors for different activities modes (Classifier: BN, Number of features: 46).</p> Full article ">Figure 9
<p>Feature extraction GUI from activity recognition module (From left to right and up to down, this GUI includes: Data Selection, Window Size, Features, Show Feature and Save Dataset panels).</p> Full article ">Figure 10
<p>Time efficiency of feature extraction techniques on a window of 80 samples.</p> Full article ">Figure 11
<p>Recognition accuracy using different number of features for different activity modes (Classifier: Bayesian Network, Number of features: 46).</p> Full article ">Figure 12
<p>Recognition accuracy using different classifier for different activity modes using four essential features selected by the SVM method.</p> Full article ">
937 KiB  
Article
Quantitative Analysis to the Impacts of IMU Quality in GPS/INS Deep Integration
by Xiaoji Niu, Yalong Ban, Quan Zhang, Tisheng Zhang, Hongping Zhang and Jingnan Liu
Micromachines 2015, 6(8), 1082-1099; https://doi.org/10.3390/mi6081082 - 11 Aug 2015
Cited by 23 | Viewed by 5978
Abstract
In the Global Positioning System (GPS)/Inertial Navigation System (INS) deep integration system, the pure negative effect of the INS aiding is mainly the INS navigation error that is independent with the motion dynamics, which determine whether the INS aiding is worthy. This paper [...] Read more.
In the Global Positioning System (GPS)/Inertial Navigation System (INS) deep integration system, the pure negative effect of the INS aiding is mainly the INS navigation error that is independent with the motion dynamics, which determine whether the INS aiding is worthy. This paper quantitatively assesses the negative effects of the inertial aiding information from different grades of INS by modeling the phase-locked loops (PLLs) based on the scalar-based GPS/INS deep integration system under stationary conditions. Results show that the largest maneuver-independent velocity error caused by the error sources of micro-electro-mechanical System (MEMS) inertial measurement unit (IMU) is less than 0.1 m/s, and less than 0.05 m/s for the case of tactical IMU during the typical GPS update interval (i.e., 1 s). The consequent carrier phase tracking error in the typical tracking loop is below 1.2 degrees for MEMS IMU case and 0.8 degrees for the tactical IMU case, which are much less than the receiver inherent errors. Conclusions can be reached that even the low-end MEMS IMU has the ability of aiding the receiver signal tracking. The tactical grade IMU can provide higher quality aiding information and has potential for the open loop tracking of GPS. Full article
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<p>Two architectures of GPS/INS deeply coupled integration. (<b>a</b>) Scalar-based architechture; (<b>b</b>) Vector-based architechture.</p> Full article ">Figure 2
<p>The residual dynamics of the tracking loop with INS aiding.</p> Full article ">Figure 3
<p>The quantitative velocity errors caused by micro-electro-mechanical system (MEMS) INS error sources.</p> Full article ">Figure 4
<p>The quantitative velocity errors caused by tactical grade INS error sources.</p> Full article ">Figure 5
<p>The total maneuver-independent velocity errors caused by all error sources.</p> Full article ">Figure 6
<p>The maneuver-independent velocity errors of the real tests data from different grades of IMUs comparing to theoretical analysis results.</p> Full article ">Figure 7
<p>Mathematical model of GPS receiver tracking loop with INS aiding.</p> Full article ">Figure 8
<p>Carrier phase tracking errors caused by the maneuver-independent velocity error sources of MEMS IMU.</p> Full article ">Figure 9
<p>Carrier phase tracking errors caused by the maneuver-independent velocity error sources of tactical grade IMU.</p> Full article ">Figure 10
<p>Total carrier phase tracking errors caused by the maneuver-independent velocity errors of different grades of IMUs.</p> Full article ">
5045 KiB  
Article
Non-Linear Piezoelectric Actuator with a Preloaded Cantilever Beam
by Yue Wu, Jingshi Dong, Xinbo Li, Zhigang Yang and Qingping Liu
Micromachines 2015, 6(8), 1066-1081; https://doi.org/10.3390/mi6081066 - 11 Aug 2015
Cited by 5 | Viewed by 8122
Abstract
Piezoelectric actuation is widely used for the active vibration control of smart structural systems, and corresponding research has largely focused on linear electromechanical devices. This paper investigates the design and analysis of a novel piezoelectric actuator that uses a piezoelectric cantilever beam with [...] Read more.
Piezoelectric actuation is widely used for the active vibration control of smart structural systems, and corresponding research has largely focused on linear electromechanical devices. This paper investigates the design and analysis of a novel piezoelectric actuator that uses a piezoelectric cantilever beam with a loading spring to produce displacement outputs. This device has a special nonlinear property relating to converting between kinetic energy and potential energy, and it can be used to increase the output displacement at a lower voltage. The system is analytically modeled with Lagrangian functional and Euler–Lagrange equations, numerically simulated with MATLAB, and experimentally realized to demonstrate its enhanced capabilities. The model is validated using an experimental device with several pretensions of the loading spring, therein representing three interesting cases: a linear system, a low natural frequency system with a pre-buckled beam, and a system with a buckled beam. The motivating hypothesis for the current work is that nonlinear phenomena could be exploited to improve the effectiveness of the piezoelectric actuator’s displacement output. The most practical configuration seems to be the pre-buckled case, in which the proposed system has a low natural frequency, a high tip displacement, and a stable balanced position. Full article
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Schematic diagram of a preloaded piezoelectric actuator.</p> Full article ">Figure 2
<p>Detailed view of the geometry of the analytical actuator model.</p> Full article ">Figure 3
<p>Variation in total elastic energy as a function of tip displacements with preloading.</p> Full article ">Figure 4
<p>Static mechanical potential energy for a loading spring pretension of (<b>a</b>) 0.01 mm, (<b>b</b>) 1.25 mm and (<b>c</b>) 2 mm. The quadratic restoring potential of the beam (thin solid line) and the nonlinear potential of the loading spring (dotted line) are added to give the total potential energy (dark solid line) as a function of the tip displacement.</p> Full article ">Figure 5
<p>The equilibrium position of the loading piezoelectric actuator (<span class="html-italic">k<sub>b</sub></span> = 10 kN/m). The dashed line denotes unstable equilibrium positions.</p> Full article ">Figure 6
<p>The simulation results for the (<b>a</b>) amplitudes and (<b>b</b>) amplified factors for a stiffness of 10 kN/m, applied voltage of 10 V, and pretension of 0.4, 0.8, and 1.2 mm over a range of frequencies.</p> Full article ">Figure 7
<p>The simulated results for a stiffness of 10 kN/m, applied voltage of 10 V (dash-dot), 50 V (dot), 100 V (dashed), 200 V (solid), and pretension of (<b>a</b>) 0.4 mm, (<b>b</b>) 0.8 mm and (<b>c</b>) 1.2 mm over a range of frequencies.</p> Full article ">Figure 8
<p>The simulation results for the (<b>a</b>) balance positions, (<b>b</b>) amplitudes of the tip displacement and (<b>c</b>) amplified factors for pretensions of 0 mm (dash-dot), 1.2 mm (dot), 1.3 mm (dash), and 1.6 mm (solid).</p> Full article ">Figure 9
<p>The simulated results with applied voltages of (<b>a</b>) 10 V, (<b>b</b>) 100 V, and (<b>c</b>) 200 V for pretensions of 1.30 mm (dot), 1.34 mm (dashed), and 1.37 mm (solid).</p> Full article ">Figure 10
<p>(<b>a</b>) The structure of the experimental pretension actuator; (<b>b</b>) the remaining necessary experimental equipment.</p> Full article ">Figure 11
<p>The response measured via laser experiment (points) and simulation (lines) for a stiffness of 10 kN/m and pretensions of Δ<span class="html-italic">l<sub>b</sub></span> = 0 mm (asterisks and solid line), 0.4 mm (circles and dashed line), 1.29 mm (triangles and dotted line), and 1.4 mm (squares and dashed-dotted line) over a range of frequencies.</p> Full article ">
2173 KiB  
Review
Nanoelectromechanical Switches for Low-Power Digital Computing
by Alexis Peschot, Chuang Qian and Tsu-Jae King Liu
Micromachines 2015, 6(8), 1046-1065; https://doi.org/10.3390/mi6081046 - 10 Aug 2015
Cited by 66 | Viewed by 12026
Abstract
The need for more energy-efficient solid-state switches beyond complementary metal-oxide-semiconductor (CMOS) transistors has become a major concern as the power consumption of electronic integrated circuits (ICs) steadily increases with technology scaling. Nano-Electro-Mechanical (NEM) relays control current flow by nanometer-scale motion to make or [...] Read more.
The need for more energy-efficient solid-state switches beyond complementary metal-oxide-semiconductor (CMOS) transistors has become a major concern as the power consumption of electronic integrated circuits (ICs) steadily increases with technology scaling. Nano-Electro-Mechanical (NEM) relays control current flow by nanometer-scale motion to make or break physical contact between electrodes, and offer advantages over transistors for low-power digital logic applications: virtually zero leakage current for negligible static power consumption; the ability to operate with very small voltage signals for low dynamic power consumption; and robustness against harsh environments such as extreme temperatures. Therefore, NEM logic switches (relays) have been investigated by several research groups during the past decade. Circuit simulations calibrated to experimental data indicate that scaled relay technology can overcome the energy-efficiency limit of CMOS technology. This paper reviews recent progress toward this goal, providing an overview of the different relay designs and experimental results achieved by various research groups, as well as of relay-based IC design principles. Remaining challenges for realizing the promise of nano-mechanical computing, and ongoing efforts to address these, are discussed. Full article
(This article belongs to the Special Issue CMOS-MEMS Sensors and Devices)
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<p>Trends for metal-oxide-semiconductor field-effect transistor (MOSFET) threshold voltage (<span class="html-italic">V</span><sub>TH</sub>) and operating voltage (<span class="html-italic">V</span><sub>DD</sub>), and corresponding transistor OFF-state leakage (<span class="html-italic">I</span><sub>OFF</sub>), for high-performance digital logic [<a href="#B2-micromachines-06-01046" class="html-bibr">2</a>].</p> Full article ">Figure 2
<p>Schematic illustrations of the MOSFET (<b>a</b>) structure, (<b>b</b>) transfer characteristics (output current <span class="html-italic">I</span><sub>D</sub> <span class="html-italic">vs</span>. input voltage <span class="html-italic">V</span><sub>G</sub>). If the operating voltage (<span class="html-italic">V</span><sub>DD</sub>) is to be reduced, then the threshold voltage (<span class="html-italic">V</span><sub>TH</sub>) should be reduced (<span class="html-italic">i.e.</span>, the <span class="html-italic">I</span>-<span class="html-italic">V</span> curve should be shifted to the left) to maintain the same peak level of ON-state current, but this would result in an exponential increase in OFF-state leakage current (<span class="html-italic">I</span><sub>OFF</sub>).</p> Full article ">Figure 3
<p>Illustration of an electrostatic 3T relay: (<b>a</b>) as fabricated, (<b>b</b>) actuated into the ON state.</p> Full article ">Figure 4
<p>(<b>a</b>) Electrical characteristics of a nano-electro-mechanical (NEM) relay. (<b>b</b>) Spring model of a NEM relay.</p> Full article ">Figure 5
<p>Illustration of the apparent, mechanical, and electrical contact areas.</p> Full article ">Figure 6
<p>(<b>a</b>) First demonstration of NEM relay using MWCNT [<a href="#B29-micromachines-06-01046" class="html-bibr">29</a>] (Reprinted with permission from [<a href="#B29-micromachines-06-01046" class="html-bibr">29</a>], copyright 2005, AIP Publishing LLC). (<b>b</b>) Demonstration of “top-down” fabricated 3T relay developed in KAIST [<a href="#B42-micromachines-06-01046" class="html-bibr">42</a>] (© 2009 IEEE, reprinted with permission from [<a href="#B42-micromachines-06-01046" class="html-bibr">42</a>]).</p> Full article ">Figure 7
<p>Scanning electron micrographs of a logic relay fabricated by researchers at the University of California, Berkeley: (<b>a</b>) Plan view of a 6T relay [<a href="#B46-micromachines-06-01046" class="html-bibr">46</a>] (© 2012 IEEE, reprinted with permission from [<a href="#B46-micromachines-06-01046" class="html-bibr">46</a>]). (<b>b</b>) Tilted cross-sectional view of the relay along the channel, source, and drain of the relay.</p> Full article ">Figure 8
<p>(<b>a</b>) NEM relay with a curved cantilever [<a href="#B57-micromachines-06-01046" class="html-bibr">57</a>] (© 2014 IEEE, reprinted with permission from [<a href="#B57-micromachines-06-01046" class="html-bibr">57</a>]). (<b>b</b>) SiC relay [<a href="#B59-micromachines-06-01046" class="html-bibr">59</a>] (© 2013 IEEE, reprinted with permission from [<a href="#B59-micromachines-06-01046" class="html-bibr">59</a>]).</p> Full article ">Figure 9
<p>Illustration of digital signal propagation delay in optimally designed (<b>a</b>) complementary metal-oxide-semiconductor (CMOS) logic circuit, (<b>b</b>) NEM relay-based logic circuit.</p> Full article ">Figure 10
<p>(<b>a</b>) New vertical NEM relay structure using BEOL metal layers (adapted from [<a href="#B68-micromachines-06-01046" class="html-bibr">68</a>]). (<b>b</b>) The most advanced BEOL technology incorporates air-gaps between metal interconnects [<a href="#B71-micromachines-06-01046" class="html-bibr">71</a>] (© 2014 IEEE, reprinted with permission from [<a href="#B71-micromachines-06-01046" class="html-bibr">71</a>]).</p> Full article ">
5008 KiB  
Review
Tunnel Junction with Perpendicular Magnetic Anisotropy: Status and Challenges
by Mengxing Wang, Yue Zhang, Xiaoxuan Zhao and Weisheng Zhao
Micromachines 2015, 6(8), 1023-1045; https://doi.org/10.3390/mi6081023 - 10 Aug 2015
Cited by 42 | Viewed by 17939
Abstract
Magnetic tunnel junction (MTJ), which arises from emerging spintronics, has the potential to become the basic component of novel memory, logic circuits, and other applications. Particularly since the first demonstration of current induced magnetization switching in MTJ, spin transfer torque magnetic random access [...] Read more.
Magnetic tunnel junction (MTJ), which arises from emerging spintronics, has the potential to become the basic component of novel memory, logic circuits, and other applications. Particularly since the first demonstration of current induced magnetization switching in MTJ, spin transfer torque magnetic random access memory (STT-MRAM) has sparked a huge interest thanks to its non-volatility, fast access speed, and infinite endurance. However, along with the advanced nodes scaling, MTJ with in-plane magnetic anisotropy suffers from modest thermal stability, high power consumption, and manufactural challenges. To address these concerns, focus of research has converted to the preferable perpendicular magnetic anisotropy (PMA) based MTJ, whereas a number of conditions still have to be met before its practical application. This paper overviews the principles of PMA and STT, where relevant issues are preliminarily discussed. Centering on the interfacial PMA in CoFeB/MgO system, we present the fundamentals and latest progress in the engineering, material, and structural points of view. The last part illustrates potential investigations and applications with regard to MTJ with interfacial PMA. Full article
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<p>(<b>a</b>) One transistor one magnetic tunnel junction (MTJ) cell using mechanism of spin transfer switching, where the MTJ is selected by word line and transistor, and operated by bit line. (<b>b</b>) Comparison between in-plane and perpendicular anisotropy based MTJ nano-pillar [<a href="#B25-micromachines-06-01023" class="html-bibr">25</a>].</p> Full article ">Figure 2
<p>(<b>a</b>) Topology of spin transfer torque magnetic random access memory (STT-MRAM) with two cells atop the silicon based complementary metal oxide semiconductor (CMOS) front-end circuit. M1/M2 and V1 denote different level of metal layers and via, separately. (<b>b</b>) Typical flow of MTJ device fabrication corresponding to (<b>a</b>).</p> Full article ">Figure 3
<p>Annealing temperature dependence of (<b>a</b>) magnetic moment per unit volume (m/V); (<b>b</b>) <span class="html-italic">K</span><sub>eff</sub> for films Ta 1/CoFeB <span class="html-italic">t</span>/MgO 2/Ta 1 (units in nm): <span class="html-italic">t</span> is 0.6 nm for the black squares and 1.2 nm for the red circle. Reproduced with permission from Sinha <span class="html-italic">et al.</span> [<a href="#B30-micromachines-06-01023" class="html-bibr">30</a>], Journal of Applied Physics; published by AIP Publishing, 2015.</p> Full article ">Figure 4
<p>Schematic illustration of (<b>a</b>) ion beam etching (IBE) with endpoint detector (EPD), <span class="html-italic">i.e.</span>, secondary ion mass spectroscopy (SIMS), wafer tilt and rotation; (<b>b</b>) inductively coupled plasma (ICP) using an optical emission spectrometer (OES).</p> Full article ">Figure 5
<p>Cross-section image of MTJ stack, where free and synthetic antiferromagnetic (SAF) reference layers separated by ultra-thin 1.09 nm MgO tunnel barrier can be recognized respectively with high resolution.</p> Full article ">Figure 6
<p>(<b>a</b>) Perpendicular magnetic anisotropy (PMA) MTJ with double CoFeB/MgO interfaces and ultra-thin Co/Pt multilayer based synthetic ferrimagnetic (SyF) reference layer, which has demonstrated suppressed exchange bias and high thermal stability. [<a href="#B53-micromachines-06-01023" class="html-bibr">53</a>] (<b>b</b>) Average threshold current with respect to junction diameter down to 1X nm (Reproduced with permission from Ikeda <span class="html-italic">et al.</span> [<a href="#B53-micromachines-06-01023" class="html-bibr">53</a>], International Electron Devices Meeting (IEDM); published by IEEE, 2014).</p> Full article ">Figure 7
<p>Mechanism of the spin Hall effect (SHE) assisted STT switching in PMA MTJ based three-terminal device. SHE write current is injected from terminal T2 and T3 into β-W strap or other heavy metal on the bottom, while the STT write current from terminal T1 penetrates the nano-pillar. Magnetization direction of the free layer can be reversed in absence of external magnetic field.</p> Full article ">Figure 8
<p>Perpendicular magnetic field sensor with (<b>a</b>) out-of-plane and in-plane magnetization direction for sensing and reference layer; (<b>b</b>) the opposite situation. The solid arrow indicate the easy axis, while it orientates to the dash arrow direction in the presence of external magnetic field H.</p> Full article ">Figure 9
<p>(<b>a</b>) Magnetic flip-flop (MFF) built with PMA MTJ devices and MOS transistors for logic-in-memory architecture. (<b>b</b>) The three-input logic device to realize stateful logic. When top electrode D, E, and F are grounded, the device executes AND/OR functions under the control of input C. Total current from input A, B, and C should be less than the breakdown current.</p> Full article ">Figure 10
<p>All spin logic gate AND/OR built with PMA-based MTJs. Data is communicated through bottom graphene channels in the form of spin current injected from input MTJ A, B, and C, of which the sum induces the STT switching in the output MTJ.</p> Full article ">
6897 KiB  
Article
Biomimetic-Based Output Feedback for Attitude Stabilization of Rigid Bodies: Real-Time Experimentation on a Quadrotor
by José Fermi Guerrero-Castellanos, Hala Rifaï, Nicolas Marchand, Rafael Cruz-José, Samer Mohammed, W. Fermín Guerrero-Sánchez and Gerardo Mino-Aguilar
Micromachines 2015, 6(8), 993-1022; https://doi.org/10.3390/mi6080993 - 5 Aug 2015
Viewed by 5875
Abstract
The present paper deals with the development of bounded feedback control laws mimicking the strategy adopted by flapping flyers to stabilize the attitude of systems falling within the framework of rigid bodies. Flapping flyers are able to orient their trajectory without any knowledge [...] Read more.
The present paper deals with the development of bounded feedback control laws mimicking the strategy adopted by flapping flyers to stabilize the attitude of systems falling within the framework of rigid bodies. Flapping flyers are able to orient their trajectory without any knowledge of their current attitude and without any attitude computation. They rely on the measurements of some sensitive organs: halteres, leg sensilla and magnetic sense, which give information about their angular velocity and the orientation of gravity and magnetic field vectors. Therefore, the proposed feedback laws are computed using direct inertial sensors measurements, that is vector observations with/without angular velocity measurements. Hence, the attitude is not explicitly required. This biomimetic approach is very simple, requires little computational power and is suitable for embedded applications on small control units. The boundedness of the control signal is taken into consideration through the design of the control laws by saturation of the actuators’ input. The asymptotic stability of the closed loop system is proven by Lyapunov analysis. Real-time experiments are carried out on a quadrotor using MEMS inertial sensors in order to emphasize the efficiency of this biomimetic strategy by showing the convergence of the body’s states in hovering mode, as well as the robustness with respect to external disturbances. Full article
(This article belongs to the Special Issue Next Generation MEMS-Based Navigation—Systems and Applications)
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<p>Symmetry with respect to the normal vector <math display="inline"> <mover accent="true"> <mi>n</mi> <mo>→</mo> </mover> </math> to the plane Π (<b>a)</b>; the symmetry with respect to the plane (<math display="inline"> <mrow> <msubsup> <mover accent="true"> <mi>e</mi> <mo>→</mo> </mover> <mn>1</mn> <mi>f</mi> </msubsup> <mo>,</mo> <msubsup> <mover accent="true"> <mi>e</mi> <mo>→</mo> </mover> <mn>3</mn> <mi>f</mi> </msubsup> </mrow> </math>) (<b>b</b>).</p> Full article ">Figure 2
<p>Biologically-inspired attitude stabilization.</p> Full article ">Figure 3
<p>Quadrotor: fixed frame <math display="inline"> <mrow> <msup> <mi mathvariant="bold">E</mi> <mi>f</mi> </msup> <mo>=</mo> <mrow> <mo stretchy="false">[</mo> <msubsup> <mover accent="true"> <mi>e</mi> <mo>→</mo> </mover> <mn>1</mn> <mi>f</mi> </msubsup> <mo>,</mo> <msubsup> <mover accent="true"> <mi>e</mi> <mo>→</mo> </mover> <mn>2</mn> <mi>f</mi> </msubsup> <mo>,</mo> <msubsup> <mover accent="true"> <mi>e</mi> <mo>→</mo> </mover> <mn>3</mn> <mi>f</mi> </msubsup> <mo stretchy="false">]</mo> </mrow> </mrow> </math> and body-fixed frame <math display="inline"> <mrow> <msup> <mi mathvariant="bold">E</mi> <mi>b</mi> </msup> <mo>=</mo> <mspace width="3.33333pt"/> <mrow> <mo stretchy="false">[</mo> <msubsup> <mover accent="true"> <mi>e</mi> <mo>→</mo> </mover> <mn>1</mn> <mi>b</mi> </msubsup> <mo>,</mo> <msubsup> <mover accent="true"> <mi>e</mi> <mo>→</mo> </mover> <mn>2</mn> <mi>b</mi> </msubsup> <mo>,</mo> <msubsup> <mover accent="true"> <mi>e</mi> <mo>→</mo> </mover> <mn>3</mn> <mi>b</mi> </msubsup> <mo stretchy="false">]</mo> </mrow> </mrow> </math>.</p> Full article ">Figure 4
<p>The quadrotor mini-helicopter in flight.</p> Full article ">Figure 5
<p>The block diagram of the quadrotor’s attitude control system.</p> Full article ">Figure 6
<p>Control law of Corollary 1: the evolution of the roll, pitch and yaw angles.</p> Full article ">Figure 7
<p>Control law of Corollary 1: the evolution of the body’s angular velocity.</p> Full article ">Figure 8
<p>Control law of Corollary 1: the evolution of the accelerometer measurement <math display="inline"> <msubsup> <mi>s</mi> <mrow> <mn>1</mn> </mrow> <mi>b</mi> </msubsup> </math>.</p> Full article ">Figure 9
<p>Control law of Corollary 1: the evolution of the magnetometer measurement <math display="inline"> <msubsup> <mi>s</mi> <mrow> <mn>2</mn> </mrow> <mi>b</mi> </msubsup> </math>.</p> Full article ">Figure 10
<p>The bounded control torques of Corollary 1. The red dashed lines define the bounds of the control torques.</p> Full article ">Figure 11
<p>Control law of Corollary 1: the pulse width of the four motors’ control signals. The red dashed lines define the bounds of the pulse width.</p> Full article ">Figure 12
<p>Control law of Corollary 2: the evolution of the roll, pitch and yaw angles.</p> Full article ">Figure 13
<p>Control law of Corollary 2: the evolution of the body’s angular velocity.</p> Full article ">Figure 14
<p>Control law of Corollary 2: the evolution of the accelerometer measurement <math display="inline"> <msubsup> <mi>s</mi> <mrow> <mn>1</mn> </mrow> <mi>b</mi> </msubsup> </math>.</p> Full article ">Figure 15
<p>Control law of Corollary 2: the evolution of the magnetometer measurement <math display="inline"> <msubsup> <mi>s</mi> <mrow> <mn>2</mn> </mrow> <mi>b</mi> </msubsup> </math>.</p> Full article ">Figure 16
<p>The bounded control torques of Corollary 2. The red dashed lines define the bounds of the control torques.</p> Full article ">Figure 17
<p>Control law of Corollary 2: the pulse width of the four motors’ control signals. The red dashed lines define the bounds of the pulse width.</p> Full article ">
3858 KiB  
Article
An Electromagnetic MEMS Energy Harvester Array with Multiple Vibration Modes
by Huicong Liu, Tao Chen, Lining Sun and Chengkuo Lee
Micromachines 2015, 6(8), 984-992; https://doi.org/10.3390/mi6080984 - 24 Jul 2015
Cited by 42 | Viewed by 7499
Abstract
This paper reports the design, micromachining and characterization of an array of electromagnetic energy harvesters (EHs) with multiple frequency peaks. The authors present the combination of three multi-modal spring-mass structures so as to realize at least nine resonant peaks within a single microelectromechanical [...] Read more.
This paper reports the design, micromachining and characterization of an array of electromagnetic energy harvesters (EHs) with multiple frequency peaks. The authors present the combination of three multi-modal spring-mass structures so as to realize at least nine resonant peaks within a single microelectromechanical systems (MEMS) chip. It is assembled with permanent magnet to show an electromagnetic-based energy harvesting capability. This is the first demonstration of multi-frequency MEMS EH existing with more than three resonant peaks within a limited frequency range of 189 to 662 Hz. It provides a more effective approach to harvest energy from the vibration sources of multiple frequency peaks. Full article
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<p>3D drawing of (<b>a</b>) the proposed multi-frequency microelectromechanical systems (MEMS) energy harvester (EH) chip and (<b>b</b>) the assembled electromagnetic EH device.</p> Full article ">Figure 2
<p>Microfabrication process of the EH array device. (<b>a</b>) Si<sub>3</sub>N<sub>4</sub> deposition; (<b>b</b>) patterning of the 1st metal and isolation layers; (<b>c</b>) patterning of the 2nd metal and isolation layers; (<b>d</b>) frontside deep reactive ion etching (DRIE); (<b>e</b>) grounding and backside DRIE; (<b>f</b>) etch of SiO<sub>2</sub>.</p> Full article ">Figure 3
<p>(<b>a</b>) A closed-loop vibration control system with assembled EH array device; (<b>b</b>) the scanning electron microscope (SEM) image of the enlarge spring.</p> Full article ">Figure 4
<p>The output voltages of the EH array against frequencies for (<b>a</b>) up and (<b>b</b>) down coils at acceleration of 1 <span class="html-italic">g</span> along <span class="html-italic">x</span>-axis.</p> Full article ">
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Article
Experimental and Numerical Simulation Research on Micro-Gears Fabrication by Laser Shock Punching Process
by Huixia Liu, Jianwen Li, Zongbao Shen, Qing Qian, Hongfeng Zhang and Xiao Wang
Micromachines 2015, 6(8), 969-983; https://doi.org/10.3390/mi6080969 - 23 Jul 2015
Cited by 16 | Viewed by 7185
Abstract
The aim of this paper is to fabricate micro-gears via laser shock punching with Spitlight 2000 Nd-YAG Laser, and to discuss effects of process parameters namely laser energy, soft punch properties and blank-holder on the quality of micro-gears deeply. Results show that dimensional [...] Read more.
The aim of this paper is to fabricate micro-gears via laser shock punching with Spitlight 2000 Nd-YAG Laser, and to discuss effects of process parameters namely laser energy, soft punch properties and blank-holder on the quality of micro-gears deeply. Results show that dimensional accuracy is the best shocked at 1690 mJ. Tensile fracture instead of shear fracture is the main fracture mode under low laser energy. The soft punch might cause damage to punching quality when too high energy is employed. Appropriate thickness and hardness of soft punch is necessary. Silica gel with 200 µm in thickness is beneficial to not only homogenize energy but also propagate the shock wave. Polyurethane films need more energy than silica gel with the same thickness. In addition, blank-holders with different weight levels are used. A heavier blank-holder is more beneficial to improve the cutting quality. Furthermore, the simulation is conducted to reveal typical stages and the different deformation behavior under high and low pulse energy. The simulation results show that the fracture mode changes under lower energy. Full article
(This article belongs to the Special Issue Laser Micromachining and Microfabrication)
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<p>Schematic of the laser shock punching process.</p> Full article ">Figure 2
<p>(<b>a</b>) Top view and details of the punching die; (<b>b</b>) sectional view of the punching die; and (<b>c</b>) dimension of designed tooth profile.</p> Full article ">Figure 3
<p>Effect of the laser energy on quality of micro-gears: (<b>a</b>) punched by lighter blank-holder and (<b>b</b>) heavier blank-holder. Error bar: Standard deviation.</p> Full article ">Figure 4
<p>The detailed top-view picture of the gears and holes.</p> Full article ">Figure 5
<p>Top view of micro-gears punched by different thickness of silica gel: (<b>a</b>) 100 µm; (<b>b</b>) 200 µm; and (<b>c</b>) 300 µm.</p> Full article ">Figure 6
<p>Schematic propagation of elastic waves: <span class="html-italic">C</span><sub>p</sub> is the velocity of elastic wave; <span class="html-italic">C</span><sub>off</sub> is the velocity of unloading wave.</p> Full article ">Figure 7
<p>Top view of micro-gears punched by different thickness of polyurethane films: (<b>a</b>) 100 µm; (<b>b</b>) 200 µm; and (<b>c</b>) 300 µm.</p> Full article ">Figure 8
<p>Reflection and transmission of elastic waves.</p> Full article ">Figure 9
<p>Comparision of dimensional accuracy with different blank-holders: (<b>a</b>) addendum circle; (<b>b</b>) dedendum circle; and (<b>c</b>) hole. Error bar: Standard deviation.</p> Full article ">Figure 10
<p>The deformation behavior in laser shock punching process.</p> Full article ">Figure 11
<p>The curve of load <span class="html-italic">versus</span> time.</p> Full article ">Figure 12
<p>Typical stages of material deformation in laser shock punching process.</p> Full article ">Figure 13
<p>Differences in material deformation between high and low laser energy in the cross section (<b>a</b>) high energy and (<b>b</b>) low energy.</p> Full article ">
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