Hajjaj, Amal; Nanaiah, Karumbaiah Chappanda; Batra, Nitin M; Hafiz, Md Abdullah Al; Da Costa, Pedro M. F. J.; Younis, Mohammad I.(Sensors and Actuators A: Physical, Elsevier BV, 2019-04-05)[Article]
Conventional pressure sensors rely on diaphragms with large surface areas, which deform in response to pressure. Down scalability of these devices is one of the major challenges of the technology along with reducing the overall actuation voltage and achieving ultra-high sensitivity. We present a sensitive miniature pressure sensor based on the change in the physisorbed gases with the pressure of the surrounding air. The sensor consists of a suspended individual multiwall carbon nanotube (MWCNT) clamped on Au electrodes by electron-beam-induced deposition (EBID) of Pt. The variation in the surrounding pressure is shown to be tracked by monitoring the change in the resistivity, hence resistance, of the MWCNT bridge structure due to the change in percentage of oxygen and humidity in the surrounding medium with pressure. The experimental data reveal the practicability and simplicity of the proposed pressure sensor.
Jaber, Nizar; Ilyas, Saad; Shekhah, Osama; Eddaoudi, Mohamed; Younis, Mohammad I.(Sensors and Actuators A: Physical, Elsevier BV, 2018-10-04)[Article]
Smart sensing systems suffer complexity requiring interface circuits, microcontrollers, switches, and actuators to detect and sense, process the signal and take a decision, and trigger an action upon demand. This increases the device footprint and boosts significantly the power required to actuate the system. Here, we present a hybrid sensor and switch device, which is capable of accurately measuring gas concentration and perform switching when the concentration exceeds specific (safe) threshold. The device is based on a clamped-clamped microbeam coated with metal-organic frameworks (MOFs). Using the electrostatic harmonic voltage, we employ dynamic multi-modal actuation in which the microbeam is simultaneously excited at the first mode of vibration, near the pull-in band, and at the third mode. We demonstrate experimentally the effectiveness of this technique in measuring the concentration of water vapor and achieving switching when the concentration exceeds a threshold value. In contrast to the first mode operation, we show that monitoring the third mode enhances sensitivity, improves accuracy, and lowers the sensor sensitivity to noise.
We report a novel modular plug-and-play microfluidic device for versatile emulsion generation, which consists of three parts: a top module for the dispersed phase supply, a glass capillary for emulsion creation and a bottom module for the continuous phase supply. By combining different modules and tapered glass capillaries, single emulsions, Janus emulsions and double emulsions have been successfully produced. The hybrid strategy allows us to produce smaller droplets through the tapered glass nozzles compared to current fully 3D-printed devices. On the other hand, it provides a simple and plug-and-play assembly manner compared to conventional microfluidic devices. Screw-thread plus gasket strategy has been proved to successfully seal the device and separate different liquid phases. Finally, magnetically responsive microparticles are synthesized based on the droplet templates produced in our device, which can be potentially applied in sensor and actuator fields.
Alcheikh, Nouha; Tella, Sherif Adekunle; Younis, Mohammad I.(Sensors and Actuators A: Physical, Elsevier BV, 2018-07-26)[Article]
We investigate theoretically and experimentally the mechanical behavior of Micro electromechanical systems MEMS resonators with multiple input (actuation) and output (detection) methods. The devices are based on a compound resonator consisting of an in-plane clamped-guided arch beam that is mechanically coupled from its guided side to another T-shaped resonant beam. Tensile and compressive bi-directional electrostatic axial forces are induced on the T-shaped resonator, which modulate the stiffness of both the arch and the T-shaped beams resonators, thereby changing their resonance frequencies to lower or higher values. At the coupling point of the two resonators, additional two flexure beams are attached, which provide another electrothermal tuning capability. The electrothermal actuators can be configured in various ways to adjust, as desired, the mechanical stiffness of the resonators; thereby controlling their resonance frequency. Therefore, this structure offers various electrothermal and electrostatic actuation and read-out possibilities, which can lead to complex device functionalities based on multiple inputs and outputs. As an example, we experimentally demonstrate an electromechanical resonant 1:2 DEMUX logic element. The logic operation is based on the linear frequency modulation. This study demonstrates that with such compound MEMS resonators, it is possible to build more complex logic functionalities.
Alcheikh, Nouha; Tella, Sherif Adekunle; Younis, Mohammad I.(Sensors and Actuators A: Physical, Elsevier BV, 2018-02-14)[Article]
The paper presents adjustable static and dynamic actuations of in-plane clamped-guided beams. The structures, of variable stiffness, can be used as highly tunable resonators and actuators. Axial loads are applied through electrothermal U-shaped and flexure beams actuators stacked near the edges of curved (arch) beams. The electrothermal actuators can be configurred in various ways to adjust as desired the mechanical stiffness of the structures; thereby controlling their deformation stroke as actuators and their operating resonance frequency as resonators. The experimental and finite element results demonstrate the flexibility of the designs in terms of static displacements and resonance frequencies of the first and second symmetric modes of the arches. The results show considerable increase in the resonance frequency and deflection of the microbeam upon changing end actuation conditions, which can be promising for low voltage actuation and tunable resonators applications, such as filters and memory devices. As case studies of potential device configurations of the proposed design, we demonstrate eight possibilities of achieving new static and dynamic behaviors, which produce various resonance frequencies and static displacement curves. The ability to actively shift the entire frequency response curve of a device is desirable for several applications to compensate for in-use anchor degradations and deformations. As an example, we experimentally demonstrate using the device as a resonant logic gate, with active resonance tuning, showing fundamental 2-bit logic functions, such as AND,XOR, and NOR.
Ilyas, Saad; Nanaiah, Karumbaiah Chappanda; Hafiz, Md Abdullah Al; Ramini, Abdallah; Younis, Mohammad I.(Sensors and Actuators A: Physical, Elsevier BV, 2016-06-27)[Article]
We present an experimental and theoretical investigation of the static and dynamic behavior of electrostatically coupled laterally actuated silicon microbeams. The coupled beam resonators are composed of two almost identical flexible cantilever beams forming the two sides of a capacitor. The experimental and theoretical analysis of the coupled system is carried out and compared against the results of beams actuated with fixed electrodes individually. The pull-in characteristics of the electrostatically coupled beams are studied, including the pull-in time. The dynamics of the coupled dual beams are explored via frequency sweeps around the neighborhood of the natural frequencies of the system for different input voltages. Good agreement is reported among the simulation results and the experimental data. The results show considerable drop in the pull-in values as compared to single microbeam resonators. The dynamics of the coupled beam resonators are demonstrated as a way to increase the bandwidth of the resonator near primary resonance as well as a way to introduce increased frequency shift, which can be promising for resonant sensing applications. Moreover the dynamic pull-in characteristics are also studied and proposed as a way to sense the shift in resonance frequency.
Jaber, Nizar; Ramini, Abdallah; Al Hennawi, Qais M.; Younis, Mohammad I.(Sensors and Actuators A: Physical, Elsevier BV, 2016-03-09)[Article]
We demonstrate the excitation of combination resonances of additive and subtractive types and their exploitations to realize a large bandwidth micro-machined resonator of large amplitude even at higher harmonic modes of vibrations. The investigation is conducted on a Microelectromechanical systems (MEMS) clamped-clamped microbeam fabricated using polyimide as a structural layer coated with nickel from top and chromium and gold layers from bottom. The microbeam is excited by a two-source harmonic excitation, where the first frequency source is swept around the targeted resonance (first or third mode of vibration) while the second source frequency is kept fixed. We report for the first time a large bandwidth and large amplitude response near the higher order modes of vibration. Also, we show that by properly tuning the frequency and amplitude of the excitation force, the frequency bandwidth of the resonator is controlled.
Ilyas, Saad; Carreno, Armando Arpys Arevalo; Bayes, Ernesto; Foulds, Ian G.; Younis, Mohammad I.(Sensors and Actuators A: Physical, Elsevier BV, 2015-10-28)[Article]
In this work we demonstrate torsion based complementary MEMS logic device, which is capable, of performing INVERTER, AND, NAND, NOR, and OR gates using one physical structure within an operating range of 0-10 volts. It can also perform XOR and XNOR with one access inverter using the same structure with different electrical interconnects. The paper presents modeling, fabrication and experimental calculations of various performance features of the device including lifetime, power consumption and resonance frequency. The fabricated device is 535 μm by 150 μm with a gap of 1.92 μm and a resonant frequency of 6.51 kHz. The device is capable of performing the switching operation with a frequency of 1 kHz.
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