Mohamed Sultan Mohamed Ali

Wireless microfluidic control with integrated shape-memory-alloy actuators operated by field frequency modulation

This paper reports wireless microfluidic control enabled by the selective operation of multiple bulk-micromachined shape-memory-alloy actuators using external radiofrequency magnetic fields. Each shape-memory-alloy actuator is driven by a wireless resonant heater which generates heat only when the field frequency is tuned to the resonant frequency of the heater. Multiple actuators coupled with the heater circuits that are designed to have different resonant frequencies in the range of 135–295 MHz are selectively and simultaneously controlled by modulating the field frequency to the resonant frequencies of the corresponding heaters. A wireless microsyringe device that has three actuator–heater components and a flexible parylene reservoir is developed. The 5 µl reservoir is squeezed by the 5 mm long cantilever-type actuators to eject controlled amount of liquid from the reservoir. Using the device with an acidic solution loaded in the reservoir, sequential modifications of the pH level in the liquid are experimentally demonstrated through the selective control of the three actuators. The thermal characterization of the actuator using infrared imaging shows a temperature increase of 50 °C in 4 s and the full activation of the actuator in 8 s with 300 mW field output power.

Transforming carbon nanotube forest from darkest absorber to reflective mirror

Carbon nanotube (CNT) forests are known to be among the darkest materials on earth. They can absorb the entire visible range of electromagnetic wave more efficiently than any other known black material. We have attempted controlled mechanical processing of the CNTs and, surprisingly, observed mirror-like reflection from the processed area with 10%–15% reflectivity, a level higher than typical reflectivity of pure forests by over two orders of magnitude, for a wide range of the spectrum (570–1100 nm). Patterning of micro mirrors in the forest is demonstrated to show its potential application for producing monolithically integrated reflector-absorber arrays in the material.

Radio-Controlled Microactuator Based on Shape-Memory-Alloy Spiral-Coil Inductor

This paper reports a bulk-micromachined shape-memory-alloy (SMA) actuator in the form of a spiral coil that constitutes an inductor-capacitor resonant circuit. The out-of-plane actuation of the SMA spiral-coil inductor is wirelessly controlled using external radio frequency (RF) magnetic fields. The resonant circuit is used as a frequency-selective wireless heater in which the SMA inductor produces heat to activate its own actuation when resonated with the RF magnetic field. The direct integration of bulk-micromachined nitinol SMA with a threshold temperature of 65 °C into a planar microfabrication process is enabled to build the 3-D spiral-coil SMA actuator in a self-assembled manner using a SiO2 reset layer patterned on the SMA coil. The fabricated SMA structure yields an out-of-plane displacement of 466 μm in the cold state. The full actuation to the flat state is reached at 70°C upon tuning the field frequency to ~ 230 MHz with an RF output power of 0.7 W. The developed actuator is demonstrated to provide a maximum force of 30 mN. The temporal response of the actuator is revealed to be two to three times faster than that of previously reported wireless SMA actuators with separate heat sources.

Micromachined Shape-Memory-Alloy Microactuators and Their Application in Biomedical Devices

Shape memory alloys (SMAs) are a class of smart materials characterized by shape memory effect and pseudo-elastic behavior. They have the capability to retain their original form when subjected to certain stimuli, such as heat or a magnetic field. These unique properties have attracted many researchers to seek their application in various fields including transportation, aerospace, and biomedical. The ease process adaption from semiconductor manufacturing technology provides many opportunities for designing micro-scale devices using this material. This paper gives an overview of the fabrication and manufacturing technique of thin-film and bulk micromachined SMAs. Key features such as material properties, transformation temperature, material composition, and actuation method are also presented. The application and micromechanism for both thin-film and bulk SMA are described. Finally, the microactuator devices emphasized for biomedical applications such as microgrippers and micropumps are highlighted. The presented review will provide information for researchers who are actively working on the development of SMA-based microscale biomedical devices.

Inductive antenna stent: design, fabrication and characterization

This paper describes the design, fabrication, and electromechanical characteristics of inductive stents developed for intelligent stent applications. The stents, fabricated out of 316L stainless-steel tubes using laser machining, are patterned to have zigzag loops without bridge struts, and when expanded, become a helix-like structure. Highly conductive metals such as copper and gold are coated on the stents to improve their inductive/antenna function. The Q-factor of the stent is shown to increase by a factor of 7 at 150?MHz with copper coating. The expansion of the stent from 2 to 4?mm diameter results in a 3.2??increase in the inductance, obtaining ?1??H at a similar frequency. The stent passivated by Parylene-C film is used to characterize its resonance in different media including saline. The copper-coated inductive stent exhibits a 2.4??radial stiffness for 1?mm strain as well as a 16??bending compliance compared with a commercial stent, each of which is potentially beneficial in preventing/mitigating stent failures such as recoil as well as enabling easier navigation through intricate blood vessels. The mechanical stiffness may be tailored by adjusting stent-wire thickness while maintaining necessary coating thickness to achieve particular mechanical requirements and high inductive performance simultaneously.

Planar Variable Inductor Controlled by Ferrofluid Actuation

This paper reports a micropatterned variable inductor that utilizes ferrofluid as the movable magnetic core. Ferrofluid is displaced over the planar inductor using the magnetic field provided by another “actuation” coil aligned to the inductor, varying permeability distribution on the inductor to control its inductance. Superimposing a bias field on the varying magnetic field uniquely enables repelling of the fluid from the inductor, as well as switching between repelling and attracting motions simply by changing the direction of the driving current to the actuation coil. Microfabricated devices are tested to reveal that the repelling-mode operation provides 6.1 × larger inductive changes than those available with the attracting mode. The continuous modulation of inductance is demonstrated with a tuning range of 16% using input currents up to 1.2 A. Frequency tuning using a resonant tank formed with the device is also demonstrated to show a 76-ppm/mA frequency sensitivity to the input current.

Detecting inconsistencies in multi-platform mobile apps

Due to the increasing popularity and diversity of mobile devices, developers write the same mobile app for different platforms. Since each platform requires its own unique environment in terms of programming languages and tools, the teams building these multi-platform mobile apps are usually separate. This in turn can result in inconsistencies in the apps developed. In this paper, we propose an automated technique for detecting inconsistencies in the same native app implemented for iOS and Android platforms. Our technique (1) automatically instruments and traces the app on each platform for given execution scenarios, (2) infers abstract models from each platform execution trace, (3) compares the models using a set of code-based and GUI-based criteria to expose any discrepancies, and finally (4) generates a visualization of the models, highlighting any detected inconsistencies. We have implemented our approach in a tool called CheckCAMP. CheckCAMP can help mobile developers in testing their apps across multiple platforms. An evaluation of our approach with a set of 14 industrial and open-source multi-platform native mobile app-pairs indicates that CheckCAMP can correctly extract and abstract the models of mobile apps from multiple platforms, infer likely mappings between the generated models based on different comparison criteria, and detect inconsistencies at multiple levels of granularity.

Wireless displacement sensing of micromachined spiral-coil actuator using resonant frequency tracking.

This paper reports a method that enables real-time displacement monitoring and control of micromachined resonant-type actuators using wireless radiofrequency (RF). The method is applied to an out-of-plane, spiral-coil microactuator based on shape-memory-alloy (SMA). The SMA spiral coil forms an inductor-capacitor resonant circuit that is excited using external RF magnetic fields to thermally actuate the coil. The actuation causes a shift in the circuits resonance as the coil is displaced vertically, which is wirelessly monitored through an external antenna to track the displacements. Controlled actuation and displacement monitoring using the developed method is demonstrated with the microfabricated device. The device exhibits a frequency sensitivity to displacement of 10 kHz/μm or more for a full out-of-plane travel range of 466 μm and an average actuation velocity of up to 155 μm/s. The method described permits the actuator to have a self-sensing function that is passively operated, thereby eliminating the need for separate sensors and batteries on the device, thus realizing precise control while attaining a high level of miniaturization in the device.

Wirelessly addressable heater array for centrifugal microfluidics and escherichia coli sterilization

Localized temperature control and heater interface remain challenges in centrifugal microfluidics and integrated lab-on-a-chip devices. This paper presents a new wireless heating method that enables selective activation of micropatterned resonant heaters using external radiofrequency (RF) fields and its applications. The wireless heaters in an array are individually activated by modulating the frequency of the external field. Temperature of 93°C is achieved in the heater when resonated with a 0.49-W RF output power. The wireless method is demonstrated to be fully effective for heating samples under spinning at high speeds, showing its applicability to centrifugal systems. Selective sterilization of Escherichia coli through the wireless heating is also demonstrated. Healthcare applications with a focus on wound sterilization are discussed along with preliminary experiments, showing promising results.

Selective RF wireless control of integrated bulk-micromachined shape-memory-alloy actuators and its microfluidic application

This paper reports wireless microfluidic control enabled by selective operation of multiple bulk-micromachined shape-memory-alloy actuators using radiofrequency external magnetic fields. Each shape-memory-alloy actuator is driven by a wireless resonant heater, which generates heat only when the field frequency is tuned to the resonant frequency of the heater. Multiple actuators coupled with the heater circuits that are designed to have different resonant frequencies in a range of 135–295 MHz are selectively controlled by modulating the field frequency to the resonant frequencies of the corresponding heaters with a constant output power. A wireless microsyringe device that has three actuator-heater components and a flexible parylene reservoir is developed. The 5-µl reservoir is squeezed by the 5-mm-long cantilever-type SMA actuators to eject controlled amounts of liquid from the reservoir. Wireless modification of pH in liquid is demonstrated using the device loaded with acidic solution through the selective control of the three actuators based on the frequency modulation technique.