silver flake composite on flexible and stretchable TPU substrate

Accepted Manuscript Title: Printed strain sensor based on silver nanowire/silver flake composite on flexible and stretchable TPU substrate Authors: Mohammed Mohammed Ali, Dinesh Maddipatla, Binu Baby Narakathu, Amer Abdulmahdi Chlaihawi, Sepehr Emamian, Farah Janabi, Bradley J. Bazuin, Massood Z. Atashbar PII: DOI: Reference:

S0924-4247(17)32122-2 https://doi.org/10.1016/j.sna.2018.03.003 SNA 10669

To appear in:

Sensors and Actuators A

Received date: Revised date: Accepted date:

22-11-2017 2-3-2018 3-3-2018

Please cite this article as: Ali MM, Maddipatla D, Narakathu BB, Chlaihawi AA, Emamian S, Janabi F, Bazuin BJ, Atashbar MZ, Printed strain sensor based on silver nanowire/silver flake composite on flexible and stretchable TPU substrate, Sensors and Actuators: A Physical (2010), https://doi.org/10.1016/j.sna.2018.03.003 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Printed Strain Sensor Based on Silver Nanowire/Silver Flake Composite on Flexible and Stretchable TPU Substrate Mohammed Mohammed Ali*, Dinesh Maddipatla, Binu Baby Narakathu, Amer Abdulmahdi Chlaihawi, Sepehr Emamian, Farah Janabi, Bradley J. Bazuin, and Massood Z. Atashbar Department of Electrical and Computer Engineering Western Michigan University

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Michigan-49008, USA

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Corresponding authors:

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*Email: [email protected] Address: 4601 Campus Drive, Western Michigan University, Department of Electrical and Computer Engineering Kalamazoo, Michigan - 49008 Tel: +1 269 276 3148

Highlights

A screen printable metal-metal composite ink was developed.

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A strain sensor was fabricated on a flexible and stretchable substrate.



Electro-mechanical response of sensor towards varying elongations was investigated.



Strain sensor with wavy line configuration performs better than the straight line.

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ABSTRACT A novel printed strain sensor, based on metal-metal composite, was developed for applications in the biomedical and civil infrastructural industries. The sensor was fabricated by

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screen printing a silver nanowire (Ag NW)/silver (Ag) flake composite on a flexible and stretchable thermoplastic polyurethane (TPU) substrate in two design configurations: straight line and wavy line. The capability of the fabricated strain sensors was investigated by studying its electro-mechanical response towards varying elongations. Average resistance changes of 104.8 %, 177.3 % and 238.9 %, over 100 cycles, and 46.8 %, 141.4 % and 243.6 %, over 200 cycles, were

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obtained for the sensors with the straight and wavy line configurations at elongations of 1 mm,

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2 mm and 3 mm, respectively. A sensitivity of 21 % and 33 %, in resistance change for every 1 %

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strain, was calculated for the printed strain sensors with the straight and wavy line configurations,

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respectively. The results obtained thus demonstrate the feasibility of employing conventional addictive screen printing process for the development of strain sensors for applications that require

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a flexible and stretchable form factor.

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Keywords: Strain Sensor; Silver Nanowires, Screen Printing; Thermoplastic Polyurethane (TPU);

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Straight Line Configuration; Wavy Line Configuration

1. Introduction Over the past decades, strain sensors have been receiving an increased interest for applications such as human body movement tracking in the biomedical industry as well as for

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monitoring deformations or structural changes in civil infrastructural assets [1]. Typically, strain sensors have been developed by depositing metal layers such as silver (Ag), gold (Au) and copper (Cu) [2-4]. However, these sensors are often fabricated on substrates that are not stretchable and are thus prone to mechanical failures due to its limited stretchable capabilities. Research has also demonstrated the development of strain sensors using metal-polymer composites such as elastomer

(Evoprene®)/carbon

black

nanoparticle

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thermoplastic

[5],

silver

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nanoparticles/elastomeric fibres [6], metal coated carbon nanofiller/epoxy [7] and silver

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nanowire/polymer [8] as well as polymer-polymer composites such as graphene composite

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films [9], polycarbonate/multiwall carbon nanotube [10] and ultra-high-molecular-weight

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polyethylene (UHMWPE) /polyaniline (PANI) [11]. The major drawback associated with these

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sensors is the reduction in conductivity due to the use of polymeric materials. The use of metalmetal composite based strain sensors on flexible and stretchable substrates, which could potentially

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overcome these disadvantages, has not yet been investigated. The fabrication of novel strain sensors that utilize a metal-metal composite is thus a promising solution for applications in the

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biomedical and civil infrastructural industries.

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Recent advancements in the field of printed electronics (PE) has demonstrated the

development of flexible and stretchable electronic devices for applications in the biomedical [1214], military [15] and tactile robotic industries [16].The advantages associated with PE include additive manufacturing techniques, minimal usage of resources and low manufacturing temperatures in comparison to silicon based technology, which often involves photolithographic

patterning techniques along with high-vacuum and high-temperature deposition processes. PE devices such as solar cells [17], displays [18], electrochemical sensors [19] and piezo resistive sensors [20] have been fabricated using traditional printing processes such as gravure [21],

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inkjet [22], flexography [23] and screen printing [24]. Moreover, the flexible and stretchable capabilities, made possible by the use of PE, can help in the implementation of wearable electronic devices for monitoring temperature [25], hydration [26], electrocardiogram (ECG) [27], electromyography (EMG) [28] and human body movement. Wearable devices require flexible and stretchable electrodes that provides high conductivity and mechanical stability for varying

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strains [29]. Therefore, the development of printed strain sensors on flexible and stretchable

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substrates is bound to have a significant impact in the field of wearable electronics.

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In this work, a metal-metal composite based strain sensor was fabricated on a flexible and

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stretchable thermoplastic polyurethane (TPU) substrate. A silver nanowire (Ag NW)/Ag flake

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composite was screen printed on the TPU substrate as the metal-metal composite. Silver nanowire

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was chosen as the stretchable filler because of its ability to maintain electrical conductivity for tensile strains ranging from 16 % - 50 % [30, 31]. Silver flake was chosen due to its viscous nature

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(12 Pa.s) and good adhesion capabilities, both of which are compatible with the screen printing process [32]. The capability of the fabricated strain sensor was demonstrated by investigating its

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electro-mechanical response for elongations of 1 mm, 2 mm and 3 mm.

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2. Experimental 2.1 Chemicals and Materials Flexible and stretchable TPU (ST604) from Bemis Associates, Inc, was used as a substrate for the fabrication of the strain sensor. The metal-metal composite was prepared using Ag NWs (Blue Nano SLV-NW-90, 1.25 % Ag NW and 98.75 % ethanol), with 25 µm

length and 90 nm diameter, and Ag flake ink (Electrodag 479SS, 74.6 % Ag and 25.4 % carbitol acetate) from Henkel. 2.2 Design of Strain Sensor

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Schematics of the strain sensors are shown in Fig. 1. Standard straight line and wavy line configurations were chosen as the designs, to investigate the effect of structural changes on the electro-mechanical response of the sensor. The straight line (Fig. 1(a)) has a width (w) of 0.8 mm with overall dimension of 28 mm × 4 mm. It has been reported that a smaller ratio of width to radius (r) for the wavy line (w/r) configuration, results in more stretchability due to reduced

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stresses on the sensor as well as reduced resistance change [25]. The parameters for the wavy line

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was thus chosen with an aim of maintaining a smaller w/r ratio and with similar overall dimensions

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as that of the straight line, for comparison purposes. The wavy line (Fig. 1(b)), which is formed

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with two half circles connected to each other [25], was designed with a width of 0.8 mm, radius of

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2 mm and overall dimension of 28 mm × 4 mm which results in a w/r ratio of 0.4.

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2.3 Fabrication of Strain Sensor

0.4 g of Ag NWs was mixed with 5 g of the Ag flake ink by magnetically stirring it on a

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hot plate (VWR Professional series 7x7), at 400 rpm speed and at 70 °C for 30 minutes. This

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results in a composite of 0.13 % Ag NW in Ag flake ink. The prepared Ag NW/Ag flake composite ink was then screen printed at room temperature using a screen printer (AMI MSP 485) from

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Affiliated Manufacturers Inc. on the flexible TPU substrate. A stainless steel screen from Microsceen® with 325 mesh count and 12.7 μm thick MS-22 emulsion was used. The printed sample was then thermally cured in a VWR 1320 oven for 30 minutes at 120 °C to obtain the strain sensor (Fig. 1(c) and Fig 1(d)). Figure 2 shows the 3D profilometry images of the printed samples measured using a Bruker CounterGT-K vertical scanning interferometer 3D optical microscope.

An average thickness of 18.19 μm (Fig. 2(a)) and 19.83 μm (Fig. 2(b)) was measured for the straight and wavy lines, respectively. 2.4 Experiment Setup

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The experiment setup is shown in Fig. 3. The strain sensor (printed straight and wavy lines) was placed in between the clamps of a force gauge (Mark-10 ESM 301 motorized test stand), with a vertically movable platform. The platform, capable of moving upwards and downwards, was used to apply varying elongations of 1 mm, 2 mm and 3 mm. Ag conductive epoxy paste (CircuitWorks® CW2400) was used to bond the connecting wires to the contact pads of the printed

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lines. The wires were then connected to an Agilent E4980A precision LCR meter using alligator

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clips. A cyclic elongation test was performed on the sensor, at 3 Hz operating frequency. The

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electro-mechanical based response of the strain sensor was acquired using a custom built

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LabVIEW™ program installed on a computer. The resistance change of the printed sensors was

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recorded during each stretch-release cycle and the dynamic range was determined for each sensor.

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3. Results and Discussion

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The performance of the printed strain sensors was demonstrated by investigating the electro-mechanical response obtained for elongations of 1 mm, 2 mm and 3 mm, at 3 Hz operating

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frequency. Tests were performed on three different sensors for each of the straight and wavy line

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configurations.

Figure 4 shows the response of the printed strain sensor during the stretch-release cyclic

elongation test, for 1 mm (Fig. 4(a)), 2 mm (Fig. 4(b)) and 3 mm (Fig. 4(c)). The average resistance, over 100 cycles, changed from 7.5 ± 0.6 Ω to 15.3 ± 0.4 Ω, 17.1 ± 3.7 Ω to 47.5 ± 8.5 Ω and 38.4 ± 5.4 Ω to 130.3 ± 22.8 Ω for the 1 mm, 2 mm and 3 mm elongations,

respectively. A drift in the base-line resistance was observed after the sensor was subject to every 100 cycles of stretch- release tests. This can be attributed to the fact that the sensor was getting fatigued, a phenomenon demonstrated in several research studies [18, 25]. The average change in

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resistance for the 1 mm, 2 mm and 3 mm elongations was calculated to be 7.8 ± 1.0 Ω, 30.4 ± 12.2 Ω and 91.9 ± 28.2 Ω, respectively (Fig. 5). The average percentage changes in resistance and strain on the sensor were mathematically calculated using Eq. (1) and Eq. (2), respectively. 𝑅1 −𝑅0

%=(

𝛥𝐿 𝐿0

=

) × 100%

(𝐿1 −𝐿0 ) 𝐿0

(1)

× 100%

(2)

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𝜀% =

𝑅0

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𝑅0

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∆𝑅

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where, R0 is the average base resistance, R1 is the average value of the resistance after

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stretching the sensor over 100 cycles, L0 is the initial length of the strain sensor and L1 is the final

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length of the strain sensor after stretching. The results thus correspond to a 104.8 %, 177.3 % and 238.9 % average change of the resistance in response to 3.5 %, 7 % and 10 % strains, respectively

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(Fig. 6). A sensitivity of 21 % resistance change for every 1 % strain, with a correlation coefficient

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of 0.9982, was thus obtained. Similarly, cyclic stretch-release tests were performed on the printed strain sensor with the

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wavy line configuration, for 1 mm, 2 mm and 3 mm elongations. It was observed that the average resistance, over 200 cycles, changed from 14.0 ± 2.6 Ω to 20.5 ± 2.1 Ω, 21.2 ± 6.8 Ω to 51.2 ± 12.5 Ω and 55.4 ± 17.7 Ω to 190.4 ± 44.1 Ω for the 1 mm, 2 mm and 3 mm elongations, respectively. A base-line drift in resistance, similar to that of the sensor with the straight line configuration, was observed for this sensor as well after every 200 cycles of stretch-release tests,

due to the effect of sensor fatigue. The increase in number of cycles is because of the capability of the wavy design to perform better, in terms of stretchability while maintaining conductivity, when compared to the sensor with a straight line configuration [25]. The average change in resistance

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for the 1 mm, 2 mm and 3 mm elongations was calculated to be 6.5 ± 4.7 Ω, 30.0 ± 19.3 Ω and 135.0 ± 61.8 Ω, respectively (Fig. 7). These results correspond to an average change of 46.8 %, 141.4 % and 243.6 %, for a strain of 3.5 %, 7 % and 10 %, respectively on the printed strain sensor (Fig. 8). For the strain sensor with the wavy line configuration, a higher sensitivity of 33 % resistance change for every 1 % strain, with a correlation coefficient of 0.995,

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was obtained. Table 1 depicts a comparison summary of some recently reported flexible strain

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sensors in which it can be seen this work has an appreciable sensitivity.

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The hysteresis curves of the printed strain sensors for increasing and decreasing

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elongations of 1 mm, 2 mm and 3 mm was measured. A maximum hysteresis of 2.94 Ω and 0.64 Ω

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was observed at 1 mm and 2 mm, respectively for the sensors with the straight line configuration

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(Fig. 9). Similarly, a maximum hysteresis of 2.07 Ω and 1.44 Ω was observed at 1 mm and 2 mm, respectively for wavy line configuration (Fig. 10). The results obtained from the electro-

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mechanical responses of the printed sensors demonstrate that the sensor with the wavy line configuration is better suitable for strain monitoring applications since the change in resistance

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was greater when compared to that of the sensor with the straight line configuration. It was also

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concluded that the sensor with the wavy line configuration can be implemented for applications that require a stretchable form factor. The temperature coefficient of resistance (TCR) for the sensor structures (straight line and wavy configurations) were measured for temperatures ranging from 10 ⁰ C to 100 ⁰ C. A temperature coefficient of resistance (TCR) of ≈0.4%/⁰ C was measured for sensor structures. The

results demonstrate that the effect of temperature change is minimal. For most applications, the change in temperature (ΔT) is typically within ±10 °C, which results in a maximum variation of ± 4% in resistance. For example, for the straight line sensor, the variation in the sensor performance

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for a 1 mm displacement and temperature variation of ±10 °C will be 104.8 ± 4%. The results obtained demonstrate that the developed metal-metal composite (Ag NW/Ag) can also be employed as a metallization layer for other flexible hybrid electronic (FHE) applications that requires conformability, flexibility and stretchability. Furthermore, other opportunities could include investigation of two dimensional (2D) printable materials including

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metal-metal composites (copper, aluminum), metal-oxides (aluminum oxide), semiconductors

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(gallium sulfide) or insulator dielectrics (hafnium oxide) [38, 39] for FHE applications.

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4. Conclusion

A novel printed strain sensor, based on metal-metal composite, was successfully fabricated

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by screen printing a Ag NW/Ag flake composite on a flexible and stretchable TPU substrate. The

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capability of the fabricated strain sensor, printed in two design configurations: straight line and

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wavy line, was investigated by studying its electro-mechanical response towards varying elongations of 1 mm, 2 mm and 3 mm. For the printed sensor with the straight line configuration,

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average resistance changes of 104.8 %, 177.3 % and 238.9 %, over 100 cycles, were observed for the 1 mm, 2 mm and 3 mm elongations, respectively. However, the printed sensor with the wavy

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line configuration demonstrated a better dynamic range over 200 cycles with average resistance changes of 46.8 %, 141.4 % and 243.6 % for elongations of 1 mm, 2 mm and 3 mm, respectively. In addition, the wavy line strain sensor showed a better performance (33 % change in resistance for every 1 % strain), in terms of sensitivity, when compared to the straight line strain sensor (21 % change in resistance for every 1 % strain). A temperature coefficient of resistance (TCR) of

≈0.4%/⁰ C was measured for sensor structure. The results obtained thus demonstrate that the wavy line strain sensor configuration was better suited for applications that require a flexible and stretchable form factor. Future work includes research to investigate the potential of increasing the

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sensitivity and dynamic range of the printed sensors for more than 100 and 200 cycles for the straight and wavy line configurations, respectively by investigating alternate materials including

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2D printable metal-metal composites, metal-oxides and semiconductors.

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Author Biographies

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Mohammed Mudher Mohammed Ali received the B.Sc. degree in Control and Systems Engineering from University of Technology, Baghdad, Iraq and the M.Sc. degree in Electrical Engineering from Western Michigan University, USA in 2016. He is currently pursuing the Ph.D. degree in Electrical and Computer Engineering at Western Michigan University, USA. His research interest includes design, fabrication, and characterization of printed, flexible and stretchable sensor structures, biochemical sensing systems, strain sensors, pressure sensors based on liquid metal, wearable sensors and lab-on-a-chip sensing systems. Dinesh Maddipatla received his B.E. degree in Electrical and Electronics Engineering from Anna University, Chennai, India in 2013 and the M.Sc. degree in Electrical Engineering from Western Michigan University, USA in 2016. He is currently working as a Research Associate in Electrical and Computer Engineering Department in Western Michigan University, USA. He is also working as Research Assistant in the Centre for Advanced Smart Sensors and Structures (CASSS), Western Michigan University, Kalamazoo, USA. His research interests includes all aspects of design, fabrication and characterization of printed electronics focusing on flexible sensor structures, microfluidics, electrochemical sensors, gas sensors and lab-on-a-chip sensing systems.

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Dr. Binu Baby Narakathu received the B.E. degree in Electronics and Communication Engineering from Visvesvaraya Technological University, Bangalore, India; the M.Sc. degree in Computer Engineering from Western Michigan University, USA in 2009 and the Ph.D. degree from the Department of Electrical and Computer Engineering at Western Michigan University, USA in 2014. From 2015 to 2017, he was a Postdoctoral Fellow with the Sensor Technology Laboratory (STL), Department of Electrical and Computer Engineering, Western Michigan University, USA. He is currently a Research Associate in the Center for Advanced Smart Sensors and Structures (CASSS), Department of Electrical and Computer Engineering, Western Michigan University, USA. His research interests include all aspects of design, fabrication, and characterization of high performance sensing systems, microfluidic devices, lab-on-a-chip for point-of-care testing (POCT), biosensors, bioelectronics, printed electronic devices and BioMEMS devices for applications in the biomedical, environmental and defense industries.

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Amer A. Chlaihawi received the B.Sc. degree in Electrical and Electronic Engineering from University of Technology, Baghdad, Iraq; the M.Sc. degree in Electrical and Electronic Engineering from University of Technology, Baghdad, Iraq. He received Ph.D. degree in Electrical and Computer Engineering at Western Michigan University, USA in 2017. His research interest includes interests include design, fabrication and characterization of printed sensor, printed electronics, biomedical sensing, magnetic sensing, lab-on-a-chip, embedded system, smart sensing, and energy harvesting systems.

Sepehr Emamian received the B.Sc. degree in Electrical Engineering from the Isfahan University of Technology, Isfahan, Iran, in 2010 and the M.Sc. degree in Electrical Engineering from the Sharif University of Technology, Tehran, Iran, in 2012. He is currently pursuing the Ph.D. degree in Electrical and Computer Engineering at Western Michigan University, Kalamazoo, USA. His research interest includes printed electronics, design, fabrication, and characterization of printed sensor structures, piezoelectric based touch sensors, and energy harvesters.

Farah Janabi received the B.Sc. degree in Control and Systems Engineering from University of Technology, Baghdad, Iraq; the M.Sc. degree in Electrical Engineering from Western Michigan University, USA in 2017. She is currently working at Eaton Power Management Company. Her research interest includes design and fabrication, of printed biochemical, optical sensor systems and lab-on-a-chip sensing systems.

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Dr. Bradley J. Bazuin received the B.S. degree in Electrical Engineering from Yale University, New Haven, CT, USA, in 1980, and the M.S. and Ph.D. degrees in Electrical Engineering from Stanford University, Stanford, CA, USA, in 1982 and 1989, respectively. He was a Research Assistant with the Center for Integrated Electronics in Medicine associated with the Integrates Circuits Laboratory, Center for Integrated Systems, Stanford University, from 1981 to 1988, a part-time MTS and System Engineer from 1981 to 1989, a Principal Engineer with ARGOSystems, Sunnyvale, CA, USA, from 1989 to 1991, and a Senior Systems Engineer with Radix Technologies, Mountain View, CA, USA, from 1991 to 2000. He has been a Term Appointed Assistant Professor and an Assistant Professor since 2000, and is currently an Associate Professor of Electrical and Computer Engineering with Western Michigan University, Kalamazoo, MI, USA. His current research interests include printed electronics, electronic and printed circuit board circuit design and fabrication, custom integrated circuit design, embedded signal processing, wireless communication, software defined radios, and advanced digital signal processing algorithms for physical layer communication systems. Dr. Bazuin is a member of the American Society for Engineering Education and the Institute of Navigation.

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Dr. Massood Z. Atashbar received the B.Sc. degree in Electrical Engineering from the Isfahan University of Technology, Isfahan, Iran, the M.Sc. degree in Electrical Engineering from the Sharif University of Technology, Tehran, Iran, and the Ph.D. degree from the Department of Communication and Electronic Engineering, Royal Melbourne Institute of Technology University, Melbourne, Australia, in 1998. From 1998 to 1999, he was a Postdoctoral Fellow with the Center for Electronic Engineering and Acoustic Materials, The Pennsylvania State University, University Park. He is currently a Professor with the Electrical and Computer Engineering Department, Western Michigan University, Kalamazoo. His research interests include physical and chemical microsensor development, wireless sensors, and applications of nanotechnology in sensors, digital electronics, and printed electronic devices. He is the author of more than 190 articles in refereed journals and refereed conference proceedings. He was a member of the editorial board and associate editor for the journal of IEEE Sensors from 2006 to 2016.

Figures Captions Fig. 1. Schematic of (a) straight line, (b) wavy line configuration for the strain sensor (Not to Scale); photographs of screen printed (c) straight and (d) wavy line configuration based

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strain sensors on flexible and stretchable TPU substrate. Fig. 2. 3D profilometry scan of the (a) straight line showing an average thickness (ΔZ) of 18.18 μm and (b) wavy line showing an average thickness (ΔZ) of 19.82 μm. Fig. 3. Experiment setup.

Fig. 4. Electro-mechanical response of printed strain sensor, with straight line configuration, when

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subject to cyclic stretch-release test, for elongations of (a) 1 mm, (b) 2 mm,

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(c) 3 mm; at 3 Hz for100 cycles.

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Fig. 5. Average change in resistance of printed strain sensor, with straight line configuration, for

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elongations of 1 mm, 2 mm, 3 mm; at 3 Hz for 100 cycles. Fig. 6. Effect of strain applied on printed strain sensor, with straight line configuration.

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Fig. 7. Average change in resistance of printed strain sensor, with wavy line configuration, for

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elongations of 1 mm, 2 mm, 3 mm; at 3 Hz for 200 cycles.

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Fig. 8. Effect of strain applied on printed strain sensor, with wavy line configuration. Fig. 9. Hysteresis curve for the printed strain sensor with straight configuration for elongations of

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1 mm, 2 mm and 3 mm.

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Fig. 10. Hysteresis curve for the printed strain sensor with wavy line configuration for elongations of 1 mm, 2 mm and 3 mm.

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28 mm

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(a)

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(c)

4 mm

28 mm

2 mm (r)

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Figure 1

(d)

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(b)

Figure 2

Strain Sensor

Mark-10 Test Stand Placed in

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between clamps

Connected via alligator clips Connected via

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USB port

LCR Meter

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Figure 3

Electro-Mechanical Response of Printed Strain Sensor Towards 1 mm Stretch-Release Cyclic Elongations 100 90 Sensor#1 Sensor#2 Sensor#3

70 60 50 40 30 20 10 0 0

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Number of Cycles

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Electro-Mechanical Response of Printed Strain Sensor Towards 2 mm Stretch-Release Cyclic Elongations

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Electro-Mechanical Response of Printed Strain Sensor Towards 3 mm Stretch-Release Cyclic Elongations

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Figure 4

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Change in Resistance Vs. Elongation 150

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ΔR (Ω)

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Figure 5

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Effect of Strain on Electro-Mechanical Response of Printed Strain Sensor 400 350 y = 21.018x + 33.747 R² = 0.9982

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Figure 6

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Change in Resistance Vs. Elongation 150

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ΔR (Ω)

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Figure 7

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Effect of Strain on Electro-Mechanical Response of Printed Strain Sensor (Wavy Line Configuration) 600 500

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ΔR/R(%)

400 y = 33.269x - 72.67 R² = 0.995

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Figure 8

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Hysteresis Curve for the Printed Strain Sensor (Straight Line Configuration) 35

Hysteresis = 0.64 Ω

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Hysteresis = 2.94 Ω

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Figure 9

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Hysteresis Curve for the Printed Strain Sensor (Wavy Line Configuration) 35

Hysteresis = 2.07 Ω

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Hysteresis = 1.44 Ω

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Figure 10

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Table 1: Comparison summary of some recently reported flexible strain sensors. Material

Sensitivity

References

Shu Gong et al. (2015)

Gold nanowires

9.9 (0-5%)

[33]

Park et al. (2015)

Graphene nanoplatelets/PVA/NCYR

1.4 (100%)

[34]

Song Chen et al. (2016)

Graphene/Silver nanoparticle composite

7 (50%)

[35]

Mingchao Zhang et al. (2016)

Graphite oxide-PVDF composite

14.5 (0-15%)

[36]

Xin Wang et al. (2017)

Carbon nanotubes

6.42 (0-0.8%)

[37]

Mohammed Ali et al. (2018)

Silver nanowire /silver flake composite

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Author

22 (straight line) 33 (wavy line) (0-10%)

Present work