@article{wang_khan_dickey_adams_2017, title={A Compound Frequency- and Polarization-Reconfigurable Crossed Dipole Using Multidirectional Spreading of Liquid Metal}, volume={16}, ISSN={["1548-5757"]}, DOI={10.1109/lawp.2016.2556983}, abstractNote={We present a crossed dipole with frequency and polarization agility using electrochemically actuated liquid metal. For the first time, this antenna uses multidirectional displacement of liquid metal to enable frequency and polarization reconfiguration without the need for mechanical pumps or semiconductor devices. The dipole arms are composed of liquid metal that can be shortened and lengthened within the capillaries by applying DC voltages to each arm. Varying the lengths of the dipole arms generates two independently tuned, linearly polarized resonances from 0.8 to 3 GHz and polarization that can be switched from linear to circular over a portion of this band (0.89–1.63 GHz). Moreover, a circuit model predicts the circular polarization frequency from the input impedance. Simulation and experimental results validate the antenna concept and analysis techniques.}, journal={IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Wang, Meng and Khan, Mohammad Rashed and Dickey, Michael D. and Adams, Jacob J.}, year={2017}, pages={79–82} }
 @article{cooper_arutselvan_liu_armstrong_lin_khan_genzer_dickey_2017, title={Stretchable Capacitive Sensors of Torsion, Strain, and Touch Using Double Helix Liquid Metal Fibers}, volume={27}, ISSN={["1616-3028"]}, DOI={10.1002/adfm.201605630}, abstractNote={Soft and stretchable sensors have the potential to be incorporated into soft robotics and conformal electronics. Liquid metals represent a promising class of materials for creating these sensors because they can undergo large deformations while retaining electrical continuity. Incorporating liquid metal into hollow elastomeric capillaries results in fibers that can integrate with textiles, comply with complex surfaces, and be mass produced at high speeds. Liquid metal is injected into the core of hollow and extremely stretchable elastomeric fibers and the resulting fibers are intertwined into a helix to fabricate capacitive sensors of torsion, strain, and touch. Twisting or elongating the fibers changes the geometry and, thus, the capacitance between the fibers in a predictable way. These sensors offer a simple mechanism to measure torsion up to 800 rad m−1—two orders of magnitude higher than current torsion sensors. These intertwined fibers can also sense strain capacitively. In a complementary embodiment, the fibers are injected with different lengths of liquid metal to create sensors capable of distinguishing touch along the length of a small bundle of fibers via self‐capacitance. The three capacitive‐based modes of sensing described here may enable new sensing applications that employ the unique attributes of stretchable fibers.}, number={20}, journal={ADVANCED FUNCTIONAL MATERIALS}, publisher={Wiley}, author={Cooper, Christopher B. and Arutselvan, Kuralamudhan and Liu, Ying and Armstrong, Daniel and Lin, Yiliang and Khan, Mohammad Rashed and Genzer, Jan and Dickey, Michael D.}, year={2017}, month={May} }
 @article{eaker_khan_dickey_2016, title={A Method to Manipulate Surface Tension of a Liquid Metal via Surface Oxidation and Reduction}, volume={1}, ISSN={["1940-087X"]}, DOI={10.3791/53567}, abstractNote={Controlling interfacial tension is an effective method for manipulating the shape, position, and flow of fluids at sub-millimeter length scales, where interfacial tension is a dominant force. A variety of methods exist for controlling the interfacial tension of aqueous and organic liquids on this scale; however, these techniques have limited utility for liquid metals due to their large interfacial tension. Liquid metals can form soft, stretchable, and shape-reconfigurable components in electronic and electromagnetic devices. Although it is possible to manipulate these fluids via mechanical methods (e.g., pumping), electrical methods are easier to miniaturize, control, and implement. However, most electrical techniques have their own constraints: electrowetting-on-dielectric requires large (kV) potentials for modest actuation, electrocapillarity can affect relatively small changes in the interfacial tension, and continuous electrowetting is limited to plugs of the liquid metal in capillaries. Here, we present a method for actuating gallium and gallium-based liquid metal alloys via an electrochemical surface reaction. Controlling the electrochemical potential on the surface of the liquid metal in electrolyte rapidly and reversibly changes the interfacial tension by over two orders of magnitude ( ̴500 mN/m to near zero). Furthermore, this method requires only a very modest potential (< 1 V) applied relative to a counter electrode. The resulting change in tension is due primarily to the electrochemical deposition of a surface oxide layer, which acts as a surfactant; removal of the oxide increases the interfacial tension, and vice versa. This technique can be applied in a wide variety of electrolytes and is independent of the substrate on which it rests.}, number={107}, journal={JOVE-JOURNAL OF VISUALIZED EXPERIMENTS}, publisher={MyJove Corporation}, author={Eaker, Collin B. and Khan, M. Rashed and Dickey, Michael D.}, year={2016}, month={Jan} }
 @article{wang_trlica_khan_dickey_adams_2015, title={A reconfigurable liquid metal antenna driven by electrochemically controlled capillarity}, volume={117}, ISSN={["1089-7550"]}, DOI={10.1063/1.4919605}, abstractNote={We describe a new electrochemical method for reversible, pump-free control of liquid eutectic gallium and indium (EGaIn) in a capillary. Electrochemical deposition (or removal) of a surface oxide on the EGaIn significantly lowers (or increases) its interfacial tension as a means to induce the liquid metal in (or out) of the capillary. A fabricated prototype demonstrates this method in a reconfigurable antenna application in which EGaIn forms the radiating element. By inducing a change in the physical length of the EGaIn, the operating frequency of the antenna tunes over a large bandwidth. This purely electrochemical mechanism uses low, DC voltages to tune the antenna continuously and reversibly between 0.66 GHz and 3.4 GHz resulting in a 5:1 tuning range. Gain and radiation pattern measurements agree with electromagnetic simulations of the device, and its measured radiation efficiency varies from 41% to 70% over its tuning range.}, number={19}, journal={JOURNAL OF APPLIED PHYSICS}, publisher={AIP Publishing}, author={Wang, M. and Trlica, C. and Khan, M. R. and Dickey, M. D. and Adams, J. J.}, year={2015}, month={May} }
 @inproceedings{wang_khan_trlica_dickey_adams_2015, title={Pump-free feedback control of a frequency reconfigurable liquid metal monopole}, DOI={10.1109/aps.2015.7305500}, abstractNote={We demonstrate a pump-free method to control the length of liquid metal in a capillary as a means to change the operating frequency of a monopole antenna. An applied DC voltage controls the surface tension of the liquid metal filament, causing it to lengthen or contract, varying the antenna's resonant length. A closed-loop feedback system tracks the antenna's operating frequency and adjusts the applied voltage to shape the liquid metal towards the desired response. Measurements show that the process is controlled and fully reversible, dynamically adjusting to a programmed frequency.}, booktitle={2015 ieee international symposium on antennas and propagation & usnc/ursi national radio science meeting}, author={Wang, M. and Khan, M. R. and Trlica, C. and Dickey, Michael and Adams, Jacob}, year={2015}, pages={2223–2224} }
 @article{khan_trlica_dickey_2015, title={Recapillarity: Electrochemically Controlled Capillary Withdrawal of a Liquid Metal Alloy from Microchannels}, volume={25}, ISSN={["1616-3028"]}, DOI={10.1002/adfm.201403042}, abstractNote={This paper describes the mechanistic details of an electrochemical method to control the withdrawal of a liquid metal alloy, eutectic gallium indium (EGaIn), from microfluidic channels. EGaIn is one of several alloys of gallium that are liquid at room temperature and form a thin (nm scale) surface oxide that stabilizes the shape of the metal in microchannels. Applying a reductive potential to the metal removes the oxide in the presence of electrolyte and induces capillary behavior; we call this behavior “recapillarity” because of the importance of electrochemical reduction to the process. Recapillarity can repeatably toggle on and off capillary behavior by applying voltage, which is useful for controlling the withdrawal of metal from microchannels. This paper explores the mechanism of withdrawal and identifies the applied current as the key factor dictating the withdrawal velocity. Experimental observations suggest that this current may be necessary to reduce the oxide on the leading interface of the metal as well as the oxide sandwiched between the wall of the microchannel and the bulk liquid metal. The ability to control the shape and position of a metal using an applied voltage may prove useful for shape reconfigurable electronics, optics, transient circuits, and microfluidic components.}, number={5}, journal={ADVANCED FUNCTIONAL MATERIALS}, publisher={Wiley}, author={Khan, Mohammad R. and Trlica, Chris and Dickey, Michael D.}, year={2015}, month={Feb}, pages={671–678} }
 @article{khan_eaker_bowden_dickey_2014, title={Giant and switchable surface activity of liquid metal via surface oxidation}, volume={111}, ISSN={0027-8424 1091-6490}, url={http://dx.doi.org/10.1073/pnas.1412227111}, DOI={10.1073/pnas.1412227111}, abstractNote={Significance}, number={39}, journal={Proceedings of the National Academy of Sciences}, publisher={Proceedings of the National Academy of Sciences}, author={Khan, Mohammad Rashed and Eaker, Collin B. and Bowden, Edmond F. and Dickey, Michael D.}, year={2014}, month={Sep}, pages={14047–14051} }
 @article{khan_trlica_so_valeri_dickey_2014, title={Influence of Water on the Interfacial Behavior of Gallium Liquid Metal Alloys}, volume={6}, ISSN={["1944-8252"]}, DOI={10.1021/am506496u}, abstractNote={Eutectic gallium indium (EGaIn) is a promising liquid metal for a variety of electrical and optical applications that take advantage of its soft and fluid properties. The presence of a rapidly forming oxide skin on the surface of the metal causes it to stick to many surfaces, which limits the ability to easily reconfigure its shape on demand. This paper shows that water can provide an interfacial slip layer between EGaIn and other surfaces, which allows the metal to flow smoothly through capillaries and across surfaces without sticking. Rheological and surface characterization shows that the presence of water also changes the chemical composition of the oxide skin and weakens its mechanical strength, although not enough to allow the metal to flow freely in microchannels without the slip layer. The slip layer provides new opportunities to control and actuate liquid metal plugs in microchannels-including the use of continuous electrowetting-enabling new possibilities for shape reconfigurable electronics, sensors, actuators, and antennas.}, number={24}, journal={ACS APPLIED MATERIALS & INTERFACES}, publisher={American Chemical Society (ACS)}, author={Khan, Mohammad R. and Trlica, Chris and So, Ju-Hee and Valeri, Michael and Dickey, Michael D.}, year={2014}, month={Dec}, pages={22467–22473} }
 @article{khan_hayes_so_lazzi_dickey_2011, title={A frequency shifting liquid metal antenna with pressure responsiveness}, volume={99}, ISSN={["0003-6951"]}, DOI={10.1063/1.3603961}, abstractNote={This letter describes the fabrication and characterization of a shape shifting antenna that changes electrical length and therefore, frequency, in a controlled and rapid response to pressure. The antenna is composed of a liquid metal alloy (eutectic gallium indium) injected into microfluidic channels that feature rows of posts that separate adjacent segments of the metal. The initial shape of the antenna is stabilized mechanically by a thin oxide skin that forms on the liquid metal. Rupturing the skin merges distinct segments of the metal, which rapidly changes the length, and therefore frequency, of the antenna. A high speed camera elucidates the mechanism of merging and simulations model accurately the spectral properties of the antennas.}, number={1}, journal={APPLIED PHYSICS LETTERS}, publisher={AIP Publishing}, author={Khan, Mohammad Rashed and Hayes, Gerard J. and So, Ju-Hee and Lazzi, Gianluca and Dickey, Michael D.}, year={2011}, month={Jul} }