An Ultra-Shapeable, Smart Sensing Platform Based on a Multimodal Ferrofluid-Infused Surface
Abdelsalam Ahmed,* Islam Hassan, Islam M. Mosa, Esraa Elsanadidy, Mohamed Sharafeldin, James F. Rusling, and Shenqiang Ren
Dr. I. M. Mosa, E. Elsanadidy, M. Sharafeldin, Prof. J. F. RuslingDepartment of ChemistryUniversity of ConnecticutStorrs, CT 06269, USAProf. J. F. RuslingDepartment of Surgery and Neag Cancer CenterUConn HealthFarmington, CT 06032, USAProf. J. F. RuslingSchool of ChemistryNational University of IrelandGalway H91 TK33, IrelandProf. S. RenDepartment of Mechanical and Aerospace Engineeringand Research and Education in EnergyEnvironment & Water (RENEW) InstituteUniversity at BuffaloThe State University of New YorkBuffalo, NY 14260, USA
DOI: 10.1002/adma.201807201
big challenge.[1] Safety hazards include, but not limited to, high level of noise or strong magnetic field, that are consid-ered as risk factors for human health.[2–8] High adaptive, self-powered sensors can be an effective self-monitoring alert and hazard avoidance platform. As a new self-powered sensing technology, the estab-lished triboelectric nanogenerator (TENG), based on a coupled effect of triboelectrifica-tion and electrostatic induction is a prom-ising type of sensing platform because of their simple fabrication, small size, low cost, and lightweight.[9–16] Lately, based on thin-film approach, there are various types of self-powered sensors, including, motion, pressure, tactile, strain, acoustics, and magnetic sensors are reported.[7,17–26] However, these devices have constrained sensing capabilities, restricted deformable ability, and limited durability which cannot satisfy the requirements raised by the rapid advance of smart wearables.
In this work, we developed a stretchable, multimodal, ferro-fluid-based triboelectric nanogenerator (FO-TENG) that signifi-cantly enables multifunctional sensing ability with extremely confirmability. The developed smart sensing platform can be
The development of wearable, all-in-one sensors that can simultaneously monitor several hazard conditions in a real-time fashion imposes the emergent requirement for a smart and stretchable hazard avoidance sensing platform that is stretchable and skin-like. Multifunctional sensors with these features are problematic and challenging to accomplish. In this context, a multimodal ferrofluid-based triboelectric nanogenerator (FO-TENG), featuring sensing capabilities to a variety of hazard stimulus such as a strong magnetic field, noise level, and falling or drowning is reported. The FO-TENG consists of a deformable elastomer tube filled with a ferrofluid, as a triboelectric layer, surrounded by a patterned copper wire, as an electrode, endowing the FO-TENG with excellent waterproof ability, conformability, and stretchability (up to 300%). In addition, The FO-TENG is highly flexible and sustains structural integrity and detection capability under repetitive deformations, including bending and twisting. This FO-TENG represents a smart multifaceted sensing platform that has a unique capacity in diverse applications including hazard preventive wearables, and remote healthcare monitoring.
Wearable Sensors
Nowadays, noticeable attention is spotlighted on smart and deformable electronics but incorporating a stretchable and multifunctional safety hazard sensors into wearables for personal safety and healthcare monitoring applications still a
Dr. A. Ahmed[+]
School of Mechanical & Industrial EngineeringUniversity of TorontoToronto, ON M5S 3G8, CanadaE-mail: [email protected]. HassanDepartment of Mechanical EngineeringMcMaster UniversityHamilton, ON L8S 4L7, CanadaI. HassanNanoGenerators and NanoEngineering LaboratorySchool of Mechanical & Industrial EngineeringUniversity of TorontoToronto, ON M5S 3G8, Canada
The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adma.201807201.
[+]Present address: Department of Mechanical Engineering, McMaster University, Hamilton, ON L8S 4L7, Canada, and School of Biomedical Engineering, McMaster University, Hamilton, ON L8S 4L7, Canada
activated/stimulated to promote hazard signals by different types of mechanical stimuli, including endogenous forces such as compressive force, and tensile force or vibration (body motion) as well as, remotely triggered by exogenous forces such as magnetic and acoustic field. Moreover, the waterproof FO-TENG device composed of ferrofluid as a triboelectric layer, silicone rubber tube, and a patterned copper wire electrode. Taking advantage of the exceptional fluidity of the ferrofluid,[27] along with the high elasticity of the silicone, The FO-TENG is able to functional to a strain as large as ≈300% without deg-radation of the electrical properties. Furthermore, ferrofluid can act as the triboelectric layer for the FO-TENG, which sub-stantially extends the range of its sensing capabilities to many hazardous cues such as mechanical, acoustics, and magnetic forces (Scheme 1). In addition, The FO-TENG is functional as a wearable multifunctional self-powered sensor by integrating with the human body in three different arrangements, i.e., textilelike, ringlike, and bracelet-like. This effort opens up a new approach for hazard avoidance wearable electronics, and self-powered safety sensors.
The FO-TENG, shown in Figure 1, composed of a silicone shell (as an internal triboelectric layer) filled with the ferrofluid wrapped in a coiled copper wire (with turns density equal to 1 turn/mm, and wire diameter 100 µm) integrated into outer Ecoflex gel as encapsulation and external triboelectric layer. Fer-rofluid is first injected into the 5 mm diameter silicone tube (thickness, 250 µm) to the required fill ratio; then the tube is sealed up at both ends with waterproof glue. A copper wire is coiled on the outer surface of the silicone tube to form a threaded-shape wrapping covered by Ecoflex gel that is cured at 100 °C, as illustrated in Figure 1a. The Ecoflex gel layer had
a thickness of 150 µm, and its surface is roughened using a sandpaper template introducing microstructures (≈20 µm in diameter), as shown in Figure 1b.[28–30] These microstructures can increase the active surface area, subsequently, enhancing the triboelectric charge density on the triboelectrification layer.[31] Moreover, the flexibility and stretchability of the FO-TENG are examined under different deformation condi-tions including twisting, crumpling, and bending, as shown in Figure 1c. The FO-TENG achieved excellent stretchability, expanding up to 300% of its original size before breaking proving the high elasticity, as shown in Figure 1d.
Furthermore, magnetoactive ferrofluids are colloidal suspensions of magnetically soft, multi-domain NPs (Fe nanoparticles) in a carrier liquid, which can respond immediately and dramatically to an applied magnetic field and features reversible change from liquid to semisolid.[32,33] In the absence of an external magnetic field, the ferrofluid behavior is similar to metal particles in suspension, as shown in Figure 1e-i. However, ferrofluid is momentarily influenced by approaching magnetic fields; correspondingly the ferrofluids are responsive to external magnetic fields, as seen in Figure 1e-i. The mechanical adaptive response under magnetic stimulation is attributed to the particle arrangement, which gradually changed from random orien-tation to spike structures. The magnetic NPs are well sus-pended that they would not separate over time but maintain the same shape as long as a magnetic field is present. The spikes have restricted side range because of the energy cost of gathering field lines together as they prevent one another. Moreover, the ferrofluid has two main parameters that are affected by an applied magnetic field; the distance between
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Scheme 1. Hazard preventive wearable platform. Different forms of mechanical force that can be typically obtained by the human body or induced externally by magnetic or acoustic field. By sensing different hazardous sources, the introduced design can be used as a multimodal wearable magnetic, acoustics, and biomechanical sensor for hazard avoidance applications. In the landscape of personalized wearable sensors integrated into “smart” wristbands will generate vast streams of data possibly of human safety. Gathered sensor analyses can be construed with big-data methods to uncover actionable connections towards Internet of prevention.
peaks (pitch), and the peak height (H). A diagram of the topography of ferrofluid inside the silicone tube under the applied magnetic field is demonstrated in Figure 1e (ii,iii).
This smart ferrofluid enables the emergence of smart func-tionalities such as multimodal energy harvesting, and multi-functional sensing capabilities.
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Figure 1. Fabrication steps and mechanical properties of FO-TENG. a) Flow diagram of the fabrication procedures for FO-TENG. b) Photographs of the as-fabricated FO-TENG, scale bar (1 cm). The inset shows the scanning electron microscopy images of the Efcoflex gel surface with microstructures. c) Photographs show of the FO-TENG under different elastic deformation. d) Photographs of the FO-TENG elastic expansion up to 300% of its original size. Characterization of ferrofluid motion inside FO-TENG. e) Schematic illustration of dynamic topography of ferrofluid. (i) Two topographical states of a ferrofluid scattering on a free surface, depicting the change from the plane interface to macroscale peaks in response to an external magnetic field. (ii) Diagram of the microtopography shaped by the structured substrate for the ferrofluid inside the tube under magnetic field. (iii) Carriage methods involved in the creation of macro- and micro-topographical features, and the corresponding schematics of the ferrofluid–air interface inside a macro-tube with magnet movement. f) Variation of output voltage for the FO-TENG containing different molar fractions of magnetic NPs in the presence of a magnetic field. g) The influence of different ferrofluid fill ratios on FO-TENG behavior in the applied magnetic field conditions.
Carriage method is used to create a macro and micro topo-graphical feature at the liquid–air interface inside the silicone tubing by moving a permanent magnet in a parallel direction to the tube axis. Subsequently, the ferrofluid will follow the magnet movement, and its shape changes correspondingly with the position and direction of the magnetic field, as shown in Figure 1e-iii. We applied some physical equivalences and analytical formulas, derived from magnetostatics, to estimate the universal force applied to a ferrofluid when it is exposed to an external magnetic field. Previous reports used the Kelvin law (Equation (1)) to calculate the magnetic force density,[34] while others proposed another formula (Equation (2)) as Kelvin law is not able to describe the total force density.[35] In our case, it is essential to consider the surface force contribution. Local force expression can be calculated using (Equation (3)).[35]
0ff MM HHµµ ( )= ⋅∇ (1)
0 0ff MM HHµµ ( )= ⋅∇ (2)
20
0 2ff MM HH MMµµ µµ ( )( )= ⋅∇ + ∇ (3)
where f is the local magnetic force, µ0 is the vacuum perme-ability [H m−1], M is the magnetization of the material [A m−1], H0 is the external magnetic field in which the body is placed, and H is the magnetic field in the material [A m−1].
To investigate the electrical behavior of the as-designed FO-TENG, in presences of the magnetic field, several param-eters are varied to optimize the performance of the FO-TENG. The effect of varying molar fractions of magnetic NPs on the open circuit voltage (VOC) is studied (see Figure 1f). The NPs moalr fractions is correlated to the VOC growing when the concentration is increased from 5% to 15% before VOC reaching the steady state when the NPs moalr fraction reaches 20% or higher, as demonstrated in Figure 1f. In the presence of magnetic field, this electrical behavior is observed due to the effect of NPs concentration on ferrofluid liquidity (liquid, semi-solid, solid, etc.).[36] However, with higher NPs concentration (more than 20%), the ferrofluid viscosity will increase (becomes more solid or semisolid) and thus the output performance will decrease.
The effect of the fill ratio of the ferrofluid inside the silicone tube on the response of FO-TENG to the applied magnetic field is also examined. Open circuit voltage is increased with increasing fill ratio from 10–60%, and then diminished. Thus, the maximum corresponding output voltage is achieved at optimally 60%, as shown in Figures 1g. This behavior can be attributed to the increased dynamic flow friction between ferro-fluid and silicone tube surface with increasing fill ratio until it reached its maximum at 60%, after which flow inside the tube would be limited decreasing the output performance.
Here, the operating principle of the mechanical force-triggered FO-TENG is based on the induction of electrical signal as a response to different mechanical force-triggering which classified as induced forces generated by other stimuli like magnetic and acoustic field as well as direct interaction forces, including compressive and tensile forces (Figure 2). With the
aid of the magnetic-responsive ferrofluid, when the magnet approached the FO-TENG, physical deformation enables con-tact occurs between the ferrofluid and inner surface of the silicone tube (act as an internal triboelectric layer). However, In the absence of an external magnetic field, the ferrofluid is static, and the device had zero electric output indicating no charge transfer. The friction between the inner surface of silicone tube and movable ferrofluid is generating positive and nega-tive charges equivalently at the interface between them. When the magnet is removed, the ferrofluid is separated from the silicone inner layer and electrons are then transported from the ground electrode to the copper wire due to the potential differ-ence (Figure 2a). Due to double site fixation for the FO-TENG in the current experiment setup, magnet induced bending of the flexible wall of the FO-TENG toward the magnetic field. On the other hand, in case of acoustics waves applied to FO-TENG, sound pressure/force can trigger the vibrations of the ferrofluid inside the silicone tubing where frictions between ferrofluid and inner surface would generate electric potential and electrons would flow from the copper wire to the ground (Figure 2b). This process depends on the frequency and inten-sity of the acoustic wave, which will affect the ferrofluid move-ment and the output signal.
In case of impact force scenario, Figure 2c demonstrated a pressure responsive, single electrode FO-TENG platform in which the latex layer is used to represent an external stimulus activating the Ecoflex gel surface (as an external triboelectri-fication layer) however ferrofluid is used to serve an internal stimulus triggering the inner silicone tube surface (as an internal triboelectrification layer). In the absence of physical contact between the latex and Ecoflex gel layers, no charge transfer occurs leading to no electrical potential build up. When contact between the latex and Ecoflex gel takes place, charges are produced and transported from their corresponding sur-faces that generated negative and positive charges equivalently at the contacting interfaces. When the Ecoflex gel layer is sepa-rated from the latex layer, the electrons move from the ground electrode to the copper wire as the result of the potential differ-ence (Figure 2c). When the distance between the two contact surfaces increases, current flow stops as it reaches electrostatic equilibrium. Using of the ferrofluid as a smart and adaptable triggering layer enables FO-TENG-based self-powered wearable sensor with a wide sensing capability that will be investigated in the following sections.
Supported by the magnetic nature of the ferrofluid with a stretchable silicone tube, we introduced a wearable self-powered magnetic FO-TEN sensor (Figure 3, see Movie 1, Supporting Information). Real photos of FO-TENG as a wearable magnetic sensor on the finger and the hand wrist are demonstrated in Figure 3a. By moving a magnet toward the sensor, electrical output is generated, depending on the magnetic strength and the distance between the magnet and sensor. Characteriza-tion of the three different magnets (see Expermintal Section) at different distances from the FO-TENG sensor indicated that the magnet strength decreases with increasing distance (Figure 3b). Magnet no.3 showed the highest magnetic flux and is selected for further studies where Isc signals decreased as the sensor moves away from the magnet (Figure 3c). Compar-ison between the magnetic flux measured using a gaussmeter,
and Isc as a function of device distance indicated the behavior similarity (Figure 3d). Short-circuit current signals, gener-ated from FO-TENG using different magnets with different strengths at a constant distance, are measured and presented in Figure 3e. The output Isc increased with the increase in the magnetic strength. In addition, the FO-TENG output cur-rent generated from three different magnets at 1 cm distance from the sensor are compared to magnetic flux measured at the same distance (Figure 3f). Both values have slope similarity indicating a good correlation between FO-TENG responses to the applied magnetic field strength. Moreover, strong magnetic field is hazardous and has well-known effects on the visual and nervous system.[37] However, people are surrounded by different magnetic field sources, such as electrical power cables, and high voltage power lines. Consequently, the successful dem-onstration of FO-TENG as wearable, reliable magnetic sensor FO-TENG is a critical step toward personal safety and magnetic hazard avoidance.
Moreover, the FO-TENG can act as an acoustics sensor because of liquidity of the ferrofluid and its high flexibility. To establish the capability of sensing and to quantify acoustic waves, a speaker is used to generate different sound pres-sure levels at different frequencies. This setup is included in an isolated chamber containing the FO-TENG device beneath the speaker. The relationship between FO-TENG normalized output current signals and varying frequencies from 10 to 200 Hz, generated by sound levels of 70, 90, 105, and 108 dB
and detected by using the sound level meter, is used to esti-mate the resonance frequency of FO-TENG (Figure 3g). Reso-nance frequency corresponds to the maximum of normalized short-circuit currents (ΔI/I0) as a function of acoustic frequency showed that the resonance frequency is around 60 Hz. Esti-mated resonance frequencies are consistent with the calculated first mode natural frequency of 61 Hz.[38] The output current of the device induced with a 105 dB sound level showed two folds increase more than that with the pre-stress of 70 dB. The normalized short-circuit current signals at acoustic frequencies ranging from 10 to 200 Hz corresponding to acoustic pressures at 70 dB are shown in Figures 3h.
At resonant frequency of 50 Hz, the decrease in acoustic level from 105 to 70 dB is accompanied by a reduction in the maximum normalized short-circuit current from 0.28 to 0.12, which could explain the sensitivity to noise and its closeness to the resonance frequency. Therefore, this FO-TENG could work in total noise environments, where it is maintained within the accepted exposure limit (Figure 3i). A linear rela-tionship is observed when the FO-TENG is functioning as an active acoustic sensor for sound level assessment explaining that the higher sound source level, the higher output signals (Figures 3i). Consequently, FO-TENG can sense high acous-tics pressure level. The noise level up to 80 dB is in the normal range. However, over 80 dB is considered a hearing hazard range, and over 120 dB is the pain threshold level.[39] A human being can be surrounded with many noise sources such as
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Figure 2. Operating principles of the multimodal FO-TENG as magnetic, acoustic, and impact force sensor platform, respectively. a) Operating principle of the FO-TENG powered by a magnetic responsive ferrofluid. b) Triggering process of the FO-TENG under acoustic waves from a predefined sound source. c) Working principle of the FO-TENG in mechanical impact force scenario.
traffic, but those with the highest risks are the coworkers of the drilling industry, aerospace industry, and massive industrial fields. Correspondingly, using FO-TENG as an active wearable noise level monitoring and the self-alert sensor is very effective due to its sensitivity and conformability.
In addition, the stretchable FO-TENG has widespread applications in daily life. It can not only confirm on random surfaces but also attach on moving components. Thus, we utilized the self-powered FO-TENG as a biomechanical sensor, to track body movements and activities. The FO-TENG showed an increase in the open circuit output signals with increasing stretching levels that reached 300% of the device’s original size (Figure 4a). The sensor is found to perform flawlessly after
relaxation with no notable change in performance after several stretching cycles. In addition, crumpling/no crumpling and twisting/untwisting movement cycles are monitored as shown in (Figure 4b,c). The sensor signals (accelerometer) for different motions such as walking, running, jumping, and marching is monitored using FO-TENG as shown in Figure 4d with a signal strength proportional to the motion intensity. Furthermore, FO-TENG is attached to a finger for detection of the bending angle. The output current signal is dependent on the finger bending angles where ISC values increased from 0.5 to 3 nA when the bending angle increased from 15° to 90° (Figure 4e). To this end, the stability and durability tests over 1200 cycles at 3 Hz are also conducted to confirm the robustness of the
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Figure 3. Self-powered wearable magnetic and acoustic sensor, respectively. a) Photographs of FO-TENG as a wearable magnetic sensor. b) Characterization of the magnetic field strength generated from three different magnets with the same diameter but at different distances. c) The FO-TENG short-circuit current signals using magnet-3 with varying distance between the sensor and the magnet. d) The relationship between the magnet-3 strength and FO-TENG current outputs versus the device distance in cm indicating the behavior similarity. e) Short-circuit current signals of the effect of magnetic strength on the FO-TENG outputs. f) Comparison between the magnetic strength of the three magnets with the FO-TENG short-circuits current outputs indicating the slope similarity at a 1 cm distance. g) Normalized short-circuit currents as a function of acoustic frequency with different sound levels of 70, 90, and 105 dB. h) Normalized short-circuit current signals as a function of acoustic frequency at a sound level of 90 dB. i) FO-TENG performance as an active acoustic sensor for sound level measurement.
FO-TENG, as shown in Figure 4f. The results validate excep-tionally durable and reliable sensing performance endorsed by the excellent mechanical properties of the device under extreme deformation conditions.
Furthermore, the waterproof advantage of FO-TENG extents its sensing capability in many harsh environments such as an ath-lete monitoring platform for swimming or as a drowning alarm system. To validate the underwater FO-TENG’s sensing ability, a testing setup consists of a glass gallon with water and a wave gen-erator is constructed, as presented in Figure 5. The wave generator is used to generate various tunable water waves (pulsed waves, sine waves, random waves, and steady flow waves) by altering the water-beating behavior. The FO-TENG is tested at different wave types, and the dependence of the sensor electrical output voltage are investigated, as shown in Figure 5b. We observed that the open-circuit voltage profiles are different with varying types of waves. Therefore, the fabricated FO-TENG device could suc-cessfully differentiate between different wave motions (Figure 5b, see Movie 2, Supporting Information). In addition, the resulting signal from FO-TENG also depended on the distance between the wave generator and the FO-TENG (Figure 5c), where the wave energy would dissipate as the distance between the FO-TENG and the generator increased leading to a voltage decrease from 3 to 0.5 V when the distance increased from 5 to 50 mm (Figure 5c). Besides detecting wave types, the FO-TENG is also able to detect changes in the speed of water waves. When the water feed rate increased from 1 to 4 m3 h−1 in pulsed wave mode, sensor voltage rose from 1 to 2.5 V due to the progressive increase in the mechanical vibration energy (Figure 5d, see Movie 3, Supporting Information). Thus, the sensor voltage changes are dependent on the wave feed rates and the relation between the sensor output and the input feed rate as illustrated in Figure 5d.
Subsequently, FO-TENG offered a promising opportunity as a personalized healthcare monitoring system. FO-TENG is physically flexible enabling the monitoring of subjects in their natural environment. FO-TENG has the potential to provide a rich stream of information about athletes involved in swim-ming sport, taking advantage of its waterproof feature. As shown in Figure 5e, a schematic illustration shows the attached FO-TENG on the swimmer’s body. Correspondingly, FO-TENG generated electrical outputs related to the swimmer speed and swimming style. As the swimmer speed increased, the electrical voltage amplitude increased which has been proved on the wave sensor demonstration (Figure 5e). Also, the sche-matic signal shape will be changed with different swimming techniques (Figure 5e), like detecting wave types in Figure 5c. Accidental drowns, as shown in Figure 5f, are one reason of death. In the case of drowning, the FO-TENG signal should be higher than the normal because the swimmer will be struggling and moving randomly with giant amplitude. This demonstrates that our low-cost and durable FO-TENG based sensor has promising applications such as exercise monitoring and emer-gency alarm systems.
In summary, we have developed a wearable, multifunc-tional, self-powered alerting sensor enabled by the smart fer-rofluid-based FO-TENG as a powerful platform for real-time hazard monitoring. Several dangerous signals, i.e., harmful magnetic, high level of acoustic, and large mechanical force with high sensitivity, were acquired by the sensor. The sensing performance can be well maintained under repeated defor-mations (such as bending and twisting). The unique design and adaptable components made the device highly adjustable, waterproof, and stretchable reaching ≈300% of its original size. This work offers an all-purpose and promising approach
Figure 4. Self-powered multifunctional wearable biomechanical sensor. a) The signals at different stretching strains show an increase of FO-TENG output with greater stretching extents. b,c) The electrical signals from crumpling and twisting. d) Changes in the FO-TENG electrical signal output with various motion types including walking, running, jumping, and marching (FO-TENG device positioned on the knee). e) Measuring the finger-bending angle with the inset of the attached FO-TENG. f) Stability test of FO-TENG under 1200 cycles and 3 Hz.
in the fabrication of the next-generation preventive weara-bles or implantables, multifunctional safety alert sensing platforms.
Generally speaking, a mechanical-force-based stimulus-responsive system offers a convenient and robust sensing platform and has attracted increasing attention.[40] Compared to chemical or biological triggers, mechanical forces provide a relatively predictable control in direction and an adjustable magnitude management toward precise execution of sensing functionalities. In addition, the smart liquid-based FO-TENG would reconfigure and change shape according to a specific exogenous command or by means of a fully integrated adap-tive system, and provide an innovative solution for many future applications, such as space exploration in extreme or otherwise challenging environments, compliant wearable devices, and even in the medical field for in vivo applications. We anticipate this simple and effective sensing platform can further offer a
generic platform broadly applicable to a multitude of intelligent wearable electronics.
To our best knowledge, this is the first report of an inte-grated stretchable sensor that can efficiently detect a diversity of human-related hazard signals, showing a vital step toward prac-tical applications. On the other hand, future work could include more development of the sensor performance and integrability through extensively studying of the ferrofluid topography and manipulation[41] and optimizing the device structure to more skin-like.[42] Moreover, incorporation the sensor with a signal processing unit,[43] and artificial intelligence algorisms[44] wire-less technology[45] thus sensory information can be identified, organized, interpreted, thus the sensing capabilities advance through knowledge then transmitted wirelessly, which enables fully autonomous and real-time continuous hazard monitoring toward internet of prevention and wearable hazard avoidance electronics.
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Figure 5. Self-powered wearable swimming related monitoring and drowning detector. a) Schematic illustration of the setup of the FO-TENG water wave characterizing sensor. b) The open circuit voltage profiles plot with different water waves types. c) The voltage changes of FO-TENG sensor as a function of the distance between the sensor and the wave source. d) The open-circuit voltage profiles with different water feed rates. e) FO-TENG positioned at the swimmer body to monitor the swimmer speed, and style. f) The drowning detection system based on FO-TNEG sensor to imitate the alarm as a safety consideration for the swimmer.
Experimental SectionMaterials: Ferrofluid was purchased from Ferrotec (USA) Corporation; the
mixture composition consists of magnetite (5% v/v), oil soluble dispersant (30%), and carrier liquid (55%). Three different permanent magnets were purchased from Hangzhou Relian Magnet Co., Ltd; neodymium magnet disc (NdFeB) with grade varying from N40-N50. Ecoflex gel was purchased from Smooth-On, Inc. A commercial hollow silicone tubes with different diameters were purchased from McMaster-Carr. The microstructures on the Ecoflex gel surface was patterned using commercial sandpaper purchased from McMaster-Carr. Moreover, a wave generator and glass gallon were purchased from Amazon.
Measurements: The morphology of the microstructured silicone surface was characterized by a field emission scanning electron microscope (Hitachi SU8010). The FO-TENGs electrical output measurements were obtained by a programmable electrometer (KEITHLEY 6514 System Electrometer), and the data were collected and recorded by computer-controlled using LabVIEW interface. As for FO-TENG based magnetic sensor, the magnetic flux was measured using a 3-channel gaussmeter. Lastly, the acoustic sensor-based FO-TENG was tested using a commercial PC speaker (Sony, SRS) as a sound source. The sound frequency was modified by a computer and audio software, and a microphone was used to measure the sound pressure.
Supporting InformationSupporting Information is available from the Wiley Online Library or from the author.
AcknowledgementsA.A. and I.H. contributed equally to this work. The authors thank Mr. Ayman Negm, Mr. Ali Radhi, Ayman Farid, and Khaled Youssef for discussion on some sections of this work. The authors acknowledge the support from the U.S. National Science Foundation (NSF) under the CAREER Award No: NSF-DMR-1830749 (Magnetism), and the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award DE-SC0017928 (organic ferroics). J.F.R., I.M.M., E.E., and M.S. are grateful for financial support from NIH Grant No. ES03154.
Conflict of InterestThe authors declare no conflict of interest.
Received: November 7, 2018Revised: December 19, 2018
Published online:
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