Soft actuators are required to deform, fold, or unfold in order to interact with their surroundings.[1] One strategy to achieve the movement of mechanically soft systems is
the use of magnetic fields for untethered actuation. Flexible magnetic composites have been demonstrated as functional grippers, rollers, and walkers upon applied external magnetic fields.
[2] Being controlled with electromagnetic coils, magnetic actuators can profit from high-speed actuation to quickly respond to their environment.[3]
The development of an appropriate sensory tracking system for soft actuators is a research topic with open challenges. Light, conformal, and mechanically imperceptible sensing systems
are to be developed to be compatible with soft actuators. In this work, we present flexible magnetosensitive electronic skin which relies on thin-film magnetic field sensors to enable
onboard folding control of origami-like soft actuators. The flexible electronic skin consists of thin film giant magnetoresistive GMR and Hall effect sensors that are used to measure the
magnetization state of the actuator, the applied magnetic fields, and the completeness of the bending process. The resulting intelligent material is mechanically designed to fold even when
the flexible magnetic skin is attached to the soft actuator.[4]
The magnetic origami actuators are made of thin DiAPLEX foils, a shape memory polymer, with embedded NdFeB particles. Such composite can be used to achieve magnetically induced
motion using magnetic fields and a directed light source to increase locally the temperature. We experimentally found the best thickness (60 μm) and concentration (40 NdFeB wt%)
parameters to achieve magnetic folds.[4]
The integration of magnetic soft actuators with e-skins allowed the self-guided assembly of the origami foils. We showed two case studies showing that this approach is useful for
assembling boxes and boat-like origami shapes. This integration process was monitored, followed, and controlled by the output of the laminated sensors. [4] 

**References:** 

[1] A. Miriyev, K. Stack, H. Lipson, et al. Nat. Commun., Vol. 8, p.596 (2017) 
[2] S. Wu, W. Hu, Q. Ze, et al. Multifunct. Mater. Vol. 3, p.042003 (2020) 
[3] X. Wang, G. Mao, G. Jin, et al. Commun. Matter. Vol. 1, p.67 (2020) 
[4] M. Ha, G.S. Cañón Bermúdez, J.A.-C- Liu, et al. Adv. Mater. Vol. 33, p.2008751 (2021)

Magnetically Sensitive Electronic Skins for Supervised Folding of Origami Actuators

The development of functional printable materials enables the production of electronic components in unconventional materials and different form factors[1]. Here, we
show magnetically sensitive inks/pastes based on magnetoresistive powder that can be printed via stencil, dispenser, or screen printing. We employ bismuth microparticles[2] as well as
[Co/Cu], [Py/Cu],[3] and permalloy [4] flakes showing giant, anisotropic, or non-saturating large magnetoresistance, respectively.
We demonstrate that magnetic field sensors based on various types of magnetoresistive flakes can be printed onto rigid, flexible, and deformable substrates. We employed blockcopolymers
and elastic binders to enable mechanical resilience of these sensors: they can withstand bending down to 16 μm, 100% of stretching, and bending for hundreds of cycles
without losing functionality.[3]
Additionally, by automatizing the dispenser printing process of bismuth-based pastes, we demonstrate the production of fully printed magnetic field sensors. The use of a micro-optically
optimized high-power diode laser array provided a versatile approach for selective sintering of sensors over flexible foils in areas exceeding several square centimeters. In this work we
experimentally confirm that such sensors retain their non-saturating magnetoresistive performance (MR = 146%) in high field conditions, allowing operation above 5 T. [2]
Our printed magnetic field sensors can be used to create interfaces that are responsive to magnetic fields through remote human input. Being flexible, they can be laminated on the skin, or
stuck onto any object, from a desk to a house wall. We demonstrate the capabilities of printed magnetic field sensors to work as an interface to navigate through digital maps, as input
panels for smart home applications, and as interactive wallpapers. 

**References:** 

[1] A. Kamyshny, S. Magdassi. Chem. Soc. Rev. Vol. 48, p.1712 (2019) 
[2] E.S. Oliveros-Mata, G.S. Cañón Bermúdez, M. Ha, et al. Appl. Phys. A Vol. 127, p.280 (2021) 
[3] M. Ha, G.S. Cañón Bermúdez, T. Kosub, et al. Adv. Mater. Vol. 33, p.2005521 (2021) 
[4] E.S. Oliveros-Mata, C. Voigt, G.S. Cañón Bermúdez, et al. Adv. Mater. Technol. p.2200227 (2022)

Detecting Magnetic Fields with Printed Magnetoresistive Sensors on Rigid and Flexible Substrates

Magnetic field sensors in a rigid format have been typically associated with recording heads, hard disk drives and the automotive industry. Unlocking new application scenarios requires changing the intrinsic properties of these sensors to make them adaptable to new challenges. One way to accomplish this goal, is to allow these sensors to change shape and be flexible, stretchable or solution-processable, what we call shapeable magnetoelectronics [1]. This technology relies on the smart combination of inorganic thin films prepared directly on flexible or elastomeric substrates. Shapeable magnetoelectronics resulted from the cooperative effort of fundamental and application-oriented communities in the field of curvilinear magnetism [2], and the involvement of fabrication methods for flexible electronics [3], [4]. The combination of these research fields has resulted in a variety of flexible [5], [6], printable [7]–[9], stretchable [10]–[12] and imperceptible17,35–37 magnetic field sensing elements. Stemming from these developments, various applications like automotive [19], consumer electronics and point of care [6], [13], [14], and virtual reality [15]–[17], have emerged. For automotive purposes, shapeable magnetic sensors can be useful to monitor the magnetic field profile the nonplanar and narrow gaps inside electrical motors, to minimize losses and improve the overall efficiency [5]. In point-of-care applications, they can enable fast biosensing methods for wearable health monitoring based on magnetofluidics [6], [13]. For virtual reality they allow a whole new set of touchless interaction possibilities using the ambient magnetic fields as input stimuli [15]–[17]. One example of this application is an on-skin sensor, which can dim the intensity of a virtual lightbulb based on the relative angle between the sensor and the magnetic field of a permanent magnet [16]. This idea was further improved to remove the need for permanent magnets and instead use the earth’s magnetic field as input stimulus. Reaching this level of sensitivity required the use of barber pole [18] modified anisotropic magnetoresistive (AMR) sensors, which allowed detecting magnetic fields of µT with a flexible on-skin patch. Aside from enable artificial magnetoception, the patch can be used as an interactive device for virtual reality which only uses the geomagnetic field [15] (Fig. 1). Further works have improved the sensitivity to about 200 nT, which could have applications for highly sensitive point-of-care devices [14]. In recent works, we have demonstrated shapeable magnetoelectronics which are multimodal, so that they transduce and discriminate both tactile (via mechanical pressure) and touchless (via magnetic field) stimuli in real time [17]. Such a feat is attained by fabricating a magnetic microelectromechanical platform (m-MEMS), which combines flexible magnets based on polymer composites and mechanically compliant magnetic sensors. These m-MEMS e-skins enable complex interactions with magnetically functionalized objects in the real world, which supplement the content data appearing in virtual reality. For example, an augmented reality menu with multiple layers of interaction can be operated with one single sensor using its embedded multidimensional touch (Fig. 2, top). A challenging aspect for shapeable magnetoelectronics is the fact that output signals are usually amplified by rigid components outside the flexible supports. This readout scheme can introduce substantial noise through the cabling which is then amplified together with the signals. Eliminating this noise requires including amplifying elements directly on the flexible support, which implies using intrinsically flexible, thin-film transistor technologies. We have demonstrated such an approach, by combining highly sensitive magnetic field sensorics with high performance InGaZnO based readout electronics, on the same flexible support [19] (Fig. 2, bottom). Although entirely flexible, this platform outperforms commercial rigid magnetic sensor systems in responsivity by at least one order of magnitude. This noteworthy performance is achieved by designing a giant magnetoresistive sensor bridge connected to a cascade of differential and power amplifiers acting as readout circuity. Combining all these features in robust on-skin devices will propel this field beyond exploratory research and towards full-fledged applications, where shapeable magnetic sensors can be crucial for maximizing device performance.

**References:**

[1] D. Makarov, M. Melzer, D. Karnaushenko, and O. G. Schmidt, “Shapeable magnetoelectronics,” Applied Physics Reviews, vol. 3, no. 1, p. 011101, Mar. 2016, doi: 10.1063/1.4938497. [2] R. Streubel et al., “Magnetism in curved geometries,” J. Phys. D: Appl. Phys., vol. 49, no. 36, p. 363001, Aug. 2016, doi: 10.1088/1751-8113/48/12/125202. [3] S. Huang, Y. Liu, Y. Zhao, Z. Ren, and C. F. Guo, “Flexible Electronics: Stretchable Electrodes and Their Future,” Advanced Functional Materials, vol. 29, no. 6, p. 1805924, 2019, doi: https://doi.org/10.1002/adfm.201805924. [4] Y. Liu, M. Pharr, and G. A. Salvatore, “Lab-on-Skin: A Review of Flexible and Stretchable Electronics for Wearable Health Monitoring,” ACS Nano, vol. 11, no. 10, pp. 9614–9635, Oct. 2017, doi: 10.1021/acsnano.7b04898. [5] M. Melzer et al., “Wearable Magnetic Field Sensors for Flexible Electronics,” Advanced Materials, vol. 27, no. 7, pp. 1274–1280, Feb. 2015, doi: 10.1002/adma.201405027. [6] G. Lin, D. Makarov, M. Melzer, W. Si, C. Yan, and O. G. Schmidt, “A highly flexible and compact magnetoresistive analytic device,” Lab Chip, vol. 14, no. 20, pp. 4050–4058, 2014, doi: 10.1039/C4LC00751D. [7] D. Karnaushenko, D. Makarov, C. Yan, R. Streubel, and O. G. Schmidt, “Printable Giant Magnetoresistive Devices,” Advanced Materials, vol. 24, no. 33, pp. 4518–4522, Aug. 2012, doi: 10.1002/adma.201201190. [8] D. Karnaushenko, D. Makarov, M. Stöber, D. D. Karnaushenko, S. Baunack, and O. G. Schmidt, “High-Performance Magnetic Sensorics for Printable and Flexible Electronics,” Adv. Mater., vol. 27, no. 5, pp. 880–885, Feb. 2015, doi: 10.1002/adma.201403907. [9] D. Makarov, D. Karnaushenko, and O. G. Schmidt, “Printable Magnetoelectronics,” ChemPhysChem, vol. 14, no. 9, pp. 1771–1776, 2013, doi: 10.1002/cphc.201300162. [10] M. Melzer et al., “Stretchable Magnetoelectronics,” Nano Letters, vol. 11, no. 6, pp. 2522–2526, Jun. 2011, doi: 10.1021/nl201108b. [11] M. Melzer, D. Karnaushenko, G. Lin, S. Baunack, D. Makarov, and O. G. Schmidt, “Direct Transfer of Magnetic Sensor Devices to Elastomeric Supports for Stretchable Electronics,” Advanced Materials, vol. 27, no. 8, pp. 1333–1338, Feb. 2015, doi: 10.1002/adma.201403998. [12] M. Melzer, D. Makarov, and O. G. Schmidt, “A review on stretchable magnetic field sensorics,” J. Phys. D: Appl. Phys., vol. 53, no. 8, p. 083002, Feb. 2020, doi: 10.1088/1361-6463/ab52cf. [13] G. Lin, D. Makarov, and O. G. Schmidt, “Magnetic sensing platform technologies for biomedical applications,” Lab Chip, vol. 17, no. 11, pp. 1884–1912, May 2017, doi: 10.1039/C7LC00026J. [14] P. N. Granell et al., “Highly compliant planar Hall effect sensor with sub 200 nT sensitivity,” npj Flexible Electronics, vol. 3, no. 1, p. 3, Feb. 2019, doi: 10.1038/s41528-018-0046-9. [15] G. S. Cañón Bermúdez, H. Fuchs, L. Bischoff, J. Fassbender, and D. Makarov, “Electronic-skin compasses for geomagnetic field-driven artificial magnetoreception and interactive electronics,” Nature Electronics, vol. 1, no. 11, p. 589, Nov. 2018, doi: 10.1038/s41928-018-0161-6. [16] G. S. Cañón Bermúdez et al., “Magnetosensitive e-skins with directional perception for augmented reality,” Science Advances, vol. 4, no. 1, p. eaao2623, Jan. 2018, doi: 10.1126/sciadv.aao2623. [17] J. Ge et al., “A bimodal soft electronic skin for tactile and touchless interaction in real time,” Nat Commun, vol. 10, no. 1, p. 4405, Dec. 2019, doi: 10.1038/s41467-019-12303-5. [18] K. Kuijk, W. van Gestel, and F. Gorter, “The barber pole, a linear magnetoresistive head,” IEEE Transactions on Magnetics, vol. 11, no. 5, pp. 1215–1217, Sep. 1975, doi: 10.1109/TMAG.1975.1058886. [19] N. Münzenrieder et al., “Entirely Flexible On-Site Conditioned Magnetic Sensorics,” Advanced Electronic Materials, vol. 2, no. 8, p. 1600188, Aug. 2016, doi: 10.1002/aelm.201600188.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/3ba71cee33031382721e1689312e1f2a.jpg)
Fig. 1 Shapeable magnetic sensors as touchless interactive devices for virtual reality. (left) Human hand wearing the on-skin magnetic sensor and approaching a permanent magnet. (center) As the user turns it hands over the magnet, the intensity of virtual lightbulb is dimmed. This two panels are adapted from reference [18]. (right) Applying the same concept but changing the sensing principle allows controlling a virtual character on screen using only the earth's magnetic field. This panel is adapted from reference [17]

![](https://assets.underline.io/uploads/markdown_image/1/image/c1fa368c68af4887c7567f763724f9c8.jpg)
Fig. 2 Multimodal shapeable magnetoelectronics and fully flexible conditioning electronics. (top left) Schematic of a m-MEMS. (top center) Approaching an object using the touchless mode of the m-MEMS activates the first layer of interaction. (top right) Touching the object activates a second layer of interaction and opening a new menu. (center) Entirely flexible and on-site conditioned magnetic field sensing platform containing a power amplifying cascade (bottom left) and a giant magnetoresistive sensor Wheatstone bridge (bottom right).

 Mechanically shapeable magnetic field sensor technologies INVITED

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Magnetically Sensitive Electronic Skins for Supervised Folding of Origami Actuators

Detecting Magnetic Fields with Printed Magnetoresistive Sensors on Rigid and Flexible Substrates

Mechanically shapeable magnetic field sensor technologies INVITED

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