Research ArticleAPPLIED SCIENCES AND ENGINEERING

Magnetosensitive e-skins with directional perception for augmented reality

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Science Advances  19 Jan 2018:
Vol. 4, no. 1, eaao2623
DOI: 10.1126/sciadv.aao2623
  • Fig. 1 Touchless manipulation of objects based on the interaction with magnetic fields.

    (A) Concept of touchless manipulation of an object on a (wearable or virtual) screen by moving a hand. (B and C) An on-skin magnetic field sensor is applied to a palm of the hand. Its angular position with respect to the direction of the external magnetic field is monitored and is used to reconstruct the spatial position of the hand. This information can be used to display the position of the hand in a virtual reality scene or/and to enable interaction with objects in virtual or augmented reality.

  • Fig. 2 Fabrication and compliancy characterization of a 2D magnetic field sensor on ultrathin polyimide foils.

    (A) Schematic summary of the key fabrication steps to prepare a 2D magnetic field sensor on ultrathin polyimide foils. An SEM image of the sample cross section reveals the complete layer stack consisting of a novel polyimide foil covered with a firmly attached 27-nm-thick sensing layer, which follows the surface morphology (A, VIII). The total thickness of the polymer is about 3.5 μm, including two bonded 1.7-μm-thick foils. The resulting polymeric layer is perfectly homogeneous and the bonding plane cannot be resolved. (B) Optical microscopy image of a 2D sensor containing two Wheatstone bridges accommodating in total eight spin valves properly arranged with respect to their EB direction. An individual spin valve element can compliantly cover a hair (diameter, 50 μm) or a doctor blade (diameter, 10 μm) as shown in (C) and (D), respectively. (E and F) Photographs of the entire 2D sensor conveniently placed on skin.

  • Fig. 3 Mechanical characterization of spin valves and angle reconstruction.

    (A) GMR performance of an individual spin valve sensor. The magnetic field is applied along the EB direction. The sensor response (properties of the sensing layer, orange shaded region) does not change when the sensor is bent down to a radius of curvature of 1 mm. An array of spin valve sensors prepared on thermally stable polyimide-based ultrathin foils is shown as inset in (A). The EB direction is set in the same direction for all the sensors in the array. (B) Individual spin valve sensors are arranged with respect to their EB direction in two Wheatstone bridges each containing four spin valve sensors to realize a 2D magnetic field sensor. The response of the inner/outer Wheatstone bridge (indicated in white/red) is proportional to the cosine/sine of the angle θ between the bridge magnetization axis and the orientation of the external magnetic field, H. (C) Reconstruction of the magnetic field angle. The measurement is carried out using a 2D magnetic field sensor transferred to a rigid flat support (after being peeled off). (D) Geometry of the experiment: The signal of the Wheatstone bridges depends on the orientation of a permanent magnet. (E) Characterization of the 2D sensor. Voltage output signals of the inner (Vcos) and outer (Vsin) Wheatstone bridges of the 2D sensor. The period of the signals closely corresponds to the rotational speed set by the software (1.6 revolutions/s). There is a phase shift of 90° between the inner and outer bridge signals, which allows the reconstruction of the angle of the magnetic field (F).

  • Fig. 4 Virtual keypad addressed in a touchless manner.

    (A) The characters “+,” “9,” “4,” and “1” are encoded in angular segments around 270°, 180°, 90°, and 0°, respectively. (B) Photograph showing a 2D sensor mounted on an elastic wristband resembling a virtual keypad. The encoded symbols are displayed when a corresponding angular segment of a sensor is exposed to a magnetic field of a small permanent magnet at the fingertip (movie S3).

  • Fig. 5 Light dimming of a virtual bulb.

    (A) Skin-applied 2D sensor as on-skin electronics with directional perception. (B and C) Movie snapshots demonstrating touchless manipulation of a virtual object using our on-skin 2D magnetic field sensor. The hand is turned with respect to the direction of the magnetic field lines of a permanent magnet. This motion of the hand is monitored and the angular position is transformed into the setting of a virtual dial, in turn controlling the light intensity of a virtual bulb (movie S4).

  • Table 1 Comparison of commercial polymers with the novel ultrathin polyimide foils.

    The table summarizes the most important parameters involved in our study, such as thickness (t), glass transition temperature (Tg), melting temperature (Tm), breaking temperature (Tbr), and cross-sectional area (A).

    Polymert (μm)Tg (°C)Tm (°C)Tbr (°C)A (m2)
    PET10073.3 (38)250 (38)752 × 10−6
    PEEK100145 (39)340 (39)1502 × 10−6
    Mylar2.573.3 (38)250 (38)1405 × 10−8
    This work1.73003253444 × 10−8

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/1/eaao2623/DC1

    fig. S1. Fabrication flow.

    fig. S2. Mechanical characterization of spin valves.

    fig. S3. Compliancy of a flexible spin valve to a hair.

    fig. S4. Angle characterization setup.

    fig. S5. Encapsulation experiments for a spin valve sensor.

    fig. S6. Mechanical stability of the sensor layer stack upon bending.

    fig. S7. Development of cracks in strongly curved devices.

    fig. S8. Schematics of the setup used to measure the angle response of the sensor in a rotating magnetic field of a permanent magnet.

    fig. S9. Surface quality characterization.

    fig. S10. Thermal stability of the foils.

    fig. S11. Elongation of polymeric foil versus temperature.

    fig. S12. Temperature compensation of the sensor bridge.

    movie S1. Response of a spin valve upon bending.

    movie S2. Reconstruction of the magnetic field angle using 2D sensor.

    movie S3. Reconstruction of the magnetic field angle under irregular field excitation.

    movie S4. Demonstrator 1: Virtual keypad applications.

    movie S5. Demonstrator 2: Interactive light dimming by touchless manipulation.

    movie S6. Stability of the sensor response submerged in aqueous and saline solution.

    movie S7. Temperature stability of the novel ultrathin polyimide foils and a commercial foil.

    movie S8. Temperature compensation of the bridge.

  • Supplementary Materials



    This PDF file includes:

          
    • fig. S1. Fabrication flow.    
    • fig. S2. Mechanical characterization of spin valves.    
    • fig. S3. Compliancy of a flexible spin valve to a hair.

    • fig. S4. Angle characterization setup.

    • fig. S5. Encapsulation experiments for a spin valve sensor.

    • fig. S6. Mechanical stability of the sensor layer stack upon bending.

    • fig. S7. Development of cracks in strongly curved devices.

    • fig. S8. Schematics of the setup used to measure the angle response of the sensor in a rotating magnetic field of a permanent magnet.

    • fig. S9. Surface quality characterization.

    • fig. S10. Thermal stability of the foils.  

    • fig. S11. Elongation of polymeric foil versus temperature.  
    • fig. S12. Temperature compensation of the sensor bridge.  
    • Legends for movies S1 to S8










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      • Movie S1 -

        Response of a spin valve upon bending.

      • Movie S2 -

        Reconstruction of the magnetic field angle using 2D sensor.

      • Movie S3 -

        Reconstruction of the magnetic field angle under irregular field excitation.

      • Movie S4 -

        Demonstrator 1: Virtual keypad applications.

      • Movie S5 -

        Demonstrator 2: Interactive light dimming by touchless manipulation.

      • Movie S6 -

        Stability of the sensor response submerged in aqueous and saline solution.

      • Movie S7 -

        Temperature stability of the novel ultrathin polyimide foils and a commercial foil.

      • Movie S8 -

        Temperature compensation of the bridge.

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