A Flexible Magnetic Field Sensor Based on AgNWs & MNs-PDMS
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This paper presents a new flexible magnetic field sensor based on Ag nanowires and magnetic nanoparticles doped in polydimethylsiloxane (AgNWs & MNs-PDMS) with sandwich structure. The MNs act as the sensitive unit for magnetic field sensing in this work. Besides, the conductive networks are made by AgNWs during deformation. Magnetostriction leads to the resistance change of the AgNWs & MNs-PDMS sensors. Furthermore, the MNs increase the conductive paths for electrons, leading to lower initial resistance and higher sensitivity of the resulting sensor during deformation. A point worth emphasizing is that the interaction of the AgNWs and MNs plays irreplaceable role in magnetic field sensing, so the resistance change during stretching and shrinking was investigated. The flexible magnetic field sensor based on the mass ratio of MNs and AgNWs is 1:5 showed the highest sensitivity of 24.14 Ω/T in magnetic field sensing experiment. Finally, the magnetostrictive and piezoresistive sensing model were established to explore the mechanism of the sensor.
KeywordsNanomaterials Flexible sensor Magnetic field detection
Scanning electron microscope
Flexible electronic devices have recently attracted tremendous attention due to their facile interaction long-term monitoring capabilities [1, 2, 3, 4, 5]. They become one of the most prospective electrical sensors due to the advantages such as light weight, portable, excellent electrical properties, and high integration [6, 7, 8, 9, 10, 11]. Indubitably, nanomaterials play irreplaceable role in flexible sensors due to their outstanding properties, for instance small sizes, surface effect, and quantum tunneling effect [12, 13, 14]. Based on resonant tunneling effect of nanomaterials, many researches focus on piezoresistive strain sensors whose resistances change with deformation [15, 16, 17]. One of the key applications of the soft strain sensors is flexible electronic skin, so multi-fictionalizations are the development trend of the sensors. Some reports declared adding temperature [18, 19] and humidity [20, 21] sensing modules in the strain sensing arrays.
Besides strain, temperature, and humidity sensing abilities, the electronic skin sensing arrays are badly in need of some new functions. In another word, more functions make the electronic skin more intelligent. Among the new functions, magnetic field sensing is a novel application. It has to mention that only the soft magnetic field sensor can be used as a module for electronic skin in the future. Owning to soft magnetic field sensors can be used in more complex areas based on its flexibility and elasticity, some researchers are working on this field [22, 23, 24, 25, 26]. Chlaihawi et al. prepared ME flexible thin film sensor for Hac sensing applications . Jogschies et al. investigated thin NiFe 81/19 polyimide layers for magnetic field sensing . Tekgül et al. applied the CoFe/Cu magnetic multilayers on GMR sensors . Melzer et al. reported flexible magnetic field sensors relying on the Hall effect . A number of flexible optical magnetic field sensor have been studied as well [31, 32, 33, 34]. Comparing with traditional magnetic field detectors, flexible magnetic field sensors are more convenient to apply and they are smaller and more suitable for detection in complex environments. However, the studies about soft magnetic field sensor facing muti-functional electronic skin have been rarely reported as far as we know.
Due to the excellent electronic and magnetic properties of the Ag NWs [35, 36, 37] and MNs (Ni-Fe) [38, 39] respectively, this paper proposes the design and measurement of flexible AgNWs & MNs-PDMS magnetic field sensors with sandwich structure based on magnetostrictive and piezoresistive effects. MNs were introduced as magnetic field-sensitive units in AgNWs-based piezoresistive strain sensor. The different magnetostrictive deformation of the AgNWs & MNs-PDMS-based sensor causes the different resistance variations. After characterization of the nanomaterials, three different mass ratios of MNs and AgNWs (AgNWs & MNs; 1:1, 1:2, 1:5) were used to prepare flexible magnetic field sensors. Before the magnetic field sensing properties of the sensors were investigated, the relationships between resistance changes and stretching or retraction were studied to conclude the interaction of MNs and AgNWs. Based on the characterization results, the magnetic field sensor obtained in this work can be applied on muti-functional electronic in the future.
Preparation of Flexible Sensors
AgNWs & MNs with different mixing ratios were characterized via scanning electron microscope (SEM, S4700 SEM Hitachi Corporation, Tokyo, Japan). The components of AgNWs & MNs in different mass ratios were characterized by XRD measurements (Buker D8 Advance) using Cu K radiation of wavelength 1.5406 Å.
The current-voltage curves were measured by the Keithley 2400 Source Meter at room temperature (the room temperature was 25 °C). Stretching experiments were carried out on the stretching platform (Zolix TSM25-1A and Zolix TSMV60-1 s, Zolix Corporation, Beijing, China), and the resistance of the sensors was measured by Keithley 2400 Source Meterat. Magnetic field sensing experiments were taken when the flexible sensor was fixed in different magnetic field. The magnetic field intensity started from 0 T and increases by 0.1 T.
Results and Discussion
It can be calculated from Fig. 4a that the resistance of the sensor is 41.58 Ω when the sensitive unit is pure AgNWs. The resistances of the sensors based on AgNWs & MNs in mass ratio of 1:0, 5:1, 2:1, and 1:1 are 30.2 Ω, 5.04 Ω, and 2.87 Ω as shown in Fig. 4b–d. It shows a decreasing resistance trend when MNs were introduced into sensitive cells. Comparing the resistances of the four sensors, it can be concluded that the resistances of flexible magnetic field sensors decrease with the increasing proportion of MNs, and the minimal resistance occurs at the sensor with AgNWs & MNs in mass ratio of 1:1. It can also prove that the mixing of AgNWs & MNs in a certain proportion helps to reduce the resistance, because the conductive components of the MNs led more conductive paths in the networks.
Parameters of the strain sensors based on different ratios of MNs and AgNWs
Mass ratio of MNs: AgNWs value
Stretching range (%)
Shrinking range (%)
(magnetic field intensity = 0.4 T)
It can be calculated that the sensitivity of the magnetic field sensor is 24.14 Ω/T. In conclusion, when the mass ratio of MNs and AgNWs is 1:5, the sensor’s response of the changing magnetic field is most sensitive with a sensitivity of 24.14 Ω/T. The flexible magnetic field sensor obtained in this work can be further applied on detection of the intensity of magnetic field. The test results of this application are corresponding to the shrink process of the sensor when comparing the results in Figs. 7 and 8. This means that the nanomaterials in the sensors move together when they were put in magnetic field. The mechanism analysis declares in detail as following.
The device designed in this paper conforms with the development trend of flexible electronics. A flexible magnetic field sensor based on AgNWs & MNs-PDMS with sandwich structure was studied in this work. Based on SEM and XRD characterizations, the components and morphologies of the different ratios of nanomaterials were determined. Then, the current-voltage curves and resistance changes of the sensors based on AgNWs & MNs in mass ratio of 1:0, 5:1, 2:1, and 1:1 with stretch and shrink were measured respectively. The interaction between the AgNWs and MNs during deformation was concluded through the characterization results. Then, sensors based on different mass ratio of MNs and AgNWs were investigated for magnetic field sensing properties. When the mass ratio of AgNWs and MNs is 5:1, the as-prepared sensor shows highest sensitivity of 24.14 Ω/T. The experimental results show that the sensor shrink with the magnetic field intensity increasing. Moreover, the magnetostrictive and piezoresistive sensing model were established to explore the mechanism of this sensor.
This study was financially supported by National Natural Science Foundation of China (NO. 61703298; NO. 51705354; NO.51622507; NO.61474079) Basic Research Program of Shanxi for Youths (No. 201701D221110, 201701D221111).
This research was supported by the National Natural Science Foundation of China (Project No. 61471255).
Availability of Data and Materials
The datasets supporting the conclusions of this article are included within the article (and its additional file(s)).
QZ, YD, KZ, JJ, ZY, WZ, and SS designed the experiments. YS provided the magnetic nanomaterials. YD and YS performed the experiments. QZ, SS, and WZ analyzed the data. QZ and YD wrote the paper. All authors discussed the results and commented on the manuscript. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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