Coils are small types of electromagnets consisting of copper wire wound about in a circu-lar shape. In some cases, due to short lengths of wire usage, the magnetic field produced by the electrons flow is reduced and commonly leads to a magnetic core addition in the center of the coil. Usually, the core contains soft ferromagnetic materials like iron to en-hance the field of the system since the even small magnetic induction produced by the coil is enough to align extra magnetic moments. With the current increment, more moments change their direction to the magnetic field’s direction leading to an exponential incre-ment of the overall magnetic attraction until the saturation of the core. Following that, a similar phenomenon was performed using the second coil tested in the section previous to the magnets. For the magnetic core choice, magnet 4 was the option due to its dimen-sions since all the presented magnets had a ferromagnetic behavior, which did not allow substantial improvements with the current increment for any. Nonetheless, the upfront increase in the magnetic field measured should be enough for the desired objective.
The experiment was performed using the signal generator to power the coil using a sinusoidal function with an amplitude of 10Vppand, initially, a frequency of 1 Hz, being
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PROGRAMMABLE MAGNETIC ATTRACTIVE MATERIALS: AN APPROACH FOR SHAPE-CHANGING CARS’INTERIORS
(A) Permanent magnet lower state (B) Permanent magnet upper state
FIGURE4.6: Variation of the magnet position with an applied sinusoidal wave function with a frequency of 10Hzand an amplitude of 15Vpp
the magnet placed inside at a 2 mmdistance of coil’s top. When turned on the power, a different phenomenon to the one predicted was observed. Instead of merely increasing the overall magnetic field, the magnet oscillated vertically inside the coil at the power sig-nal frequency. The amplitude of its variation was slight, as seen in figure4.6*, but enough to spark the possibility of application. As explained previously, the coil magnetic field lines have a higher concentration inside the cavity, leading to a more intense field in that region. The magnet, being a ferromagnetic material, was presumed that its magnetization would only be affected by enormous fields, yet it showed sensibility to small ones. Thus, when placed inside the coil, the small cylinder was repelled from the coil’s center at the signal maximum and attracted back at the minimum.
Since the magnet possesses a high magnetization, those variations caused by the coil would probably be sufficient to observe considerable deformations on the samples with-out any mechanical or pneumatic system. Moreover, it could also be programmable with various degrees of freedom, such as amplitude, frequency, and, in a more complex imple-mentation, phase. Amplitudes from 5 to 20Vpp and frequencies from 0.1 to 10 Hzwere tested successfully, showing a wide range of customization, placing the method as the primary option to generate the variable magnetic field.
*A video of the magnet position variation experiment can be seen herehttps://drive.google.com/
file/d/1YyEBI6i6bqYT4mFikrIaYGDx1 Z8uWFI/view?usp=sharingor through the QR code in fig-ureA.2on appendixA
Chapter 5
Interior cars’ materials embedded with magnetic elements
Turning traditional materials used in cars’ interiors into magnetic ones was a crucial part of the project since, without that property, the magnetic generators would not affect them, which would mean not obtaining the final purpose. The road taken was to incorporate magnetic nanoparticles into different components during the production steps usually taken in TMG Automotive.
Commonly, materials used in car interiors have a base structure similar to each appli-cation which consists of multiple liquids, pastes, and solid layers stacked over each other, allowing an identical production process for different goals. In the bottom, a PVC paste is used, giving rigidity and support to the system, followed by a filling layer responsible for the cushioning and height. On the top is laid down a PVC layer coated with two lacquers, which are the components that will be seen and interacted with by occupants.
However, given the initial state of the idea, the samples produced consisted only of one PVC paste layer and lacquers in which were embedded different weight percent-ages of MNPs to study the best manner to obtain the optimal magnetic material. In this section, a characterization of the produced NPs is initially performed, followed by the presentation and analysis of the fabricated samples in a wide range of properties. Tests on fundamental characteristics of this type of material, in addition to magnetic ones, al-lowed the determination of the optimum sample used in the initial experimental proof of concept.
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PROGRAMMABLE MAGNETIC ATTRACTIVE MATERIALS: AN APPROACH FOR SHAPE-CHANGING CARS’INTERIORS
5.1 Magnetic nanoparticles characterization
MNPs were produced using a co-precipitation method in IFIMUP and then taken to TMG Automotive facilities to be incorporated into the production. Fabrication of controlled NPs, with prior knowledge of their properties, such as magnetization, stability, and size, assured a reliable final result with stable and high-intensity nanoparticles. Stability was a key factor since the next step consisted of mixing them with other materials with whom there was no previous understanding by the company of what type of interactions and reactions there would be. Yet, due to the nanoparticles possessing high surface tension related to their size [63], there was also a probability of cluster formation that could neg-atively influence the NPs’ magnetic properties. Moreover, being a lab-scale production process meant that each batch would only result in about 2 gof NPs. Additionally, the fabrication had a two-hour step that prevented multiple iterations during a day. All the restrictions summed up resulted in a limit of 6 g of MnFe2O4 nanoparticles produced for a day, equivalent to the amount presented in figure5.1, which highly restrained the capability of future sample fabrication.
FIGURE5.1: Container of 15mLwith approximately 6gofMnFe2O4nanoparticles pow-der
5.1.1 X-Ray diffraction
X-ray diffraction (XRD) experiments were performed on the produced magnetic nanopar-ticles powder to study their crystalographic structure and obtain an estimated particle size. The obtained pattern, presented in figure5.2, indexes the peak angles 29.70◦, 35.07◦,
5. INTERIOR CARS’MATERIALS EMBEDDED WITH MAGNETIC ELEMENTS 39
42.73◦, 53.08◦, 56.42◦, and 61.98◦to the respective lattice planes (220), (311), (400), (422), (333), and (440), following the information on the database present in Rigaku’s system.
As per JCPDS card no. 74-2403 [58,64] and Pearsons’ crystal database, the NPs produced possess a face-centered cubic spinel manganese ferrite structure, therefore, positioned on space groupFd¯3m[65]. From the graph, it can be inferred that no other peak than the ones expected for the NPs appeared, showing the quality of the nanoparticle production.
Moreover, the sharpness observed in the diffraction peaks indicates that the nanoparticles are highly crystalline.
FIGURE5.2: X ray spectrum ofMnFe2O4nanoparticles
In addition, with the application of the Debye-Scherrer’s relation, XRD also allows the determination of the average diameter of the analyzed sample. Equation5.1represents the mentioned correlation, whereKis an equation constant (≈0.9 for spherical particles), λ the X-ray beam wavelength used, and β and θ are the full width at half-maximum (FWHM) in radians and half of an angle 2θposition of the peak respectively.
d= Kλ
βcos(θ) (5.1)
By using the highest intensity peak (plane (311)), an average particle diameter of 10.19 nmwas obtained, a result very close to the attained on the reference article of the NPs pro-cedure [47]. Thus, the results present a first proof of the quality of the produced nanopar-ticles.
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PROGRAMMABLE MAGNETIC ATTRACTIVE MATERIALS: AN APPROACH FOR SHAPE-CHANGING CARS’INTERIORS
5.1.2 SQUID
MNPs magnetization, due to the particles’ size, cannot remain stable without an exter-nal magnetic induction, possessing characteristic behavior proportioexter-nal to the Langevin function when only magnetic and thermal energy terms are used [66]. That way, magne-tization is zero when the external field is also zero and swiftly attains saturation with the field increase. In Magnetism, this type of relation between the magnetic field and mag-netization is called superparamagnetism. Figure 5.3presents the loop obtained through a SQUID analysis on nanoparticles produced, which corroborates the theoretical expecta-tions. It can be observed an exponential growth and decrease of the magnetization when the field increases to positive or negative values, reaching a semi-stabilization for values greater, in modulus, than 0.5 or -0.5T. Afterward, saturation is attained, and the magne-tization remains near the value of 60emu/gin modulus.
FIGURE5.3: Magnetization dependency on the external magnetic field for theMnFe2O4
nanoparticles
Nonetheless, to perform a rigorous and complete analysis, three characteristic points of the hysteresis loops were obtained from the graph. Saturation magnetization, Msat, represents the value of the maximum obtained magnetization for the applied fields, while the remanence magnetization, MR, and coercive field, HC, indicate material magnetiza-tion when no field is present, and the field needed to go from no magnetizamagnetiza-tion to the saturation one, respectively.
5. INTERIOR CARS’MATERIALS EMBEDDED WITH MAGNETIC ELEMENTS 41
The test performed on isolatedMnFe2O4nanoparticles revealed a saturation magneti-zation of(62±3)emu/gat a 300Ktemperature and 5Tof an applied field. The presented high values were in the expected range for the NPs, confirming one of the most important reasons for their choice, the notable magnetization that the particles could reach. Liter-ature [67,68] corroborates that in those conditions, the magnetization value obtained is similar to their experiments, certifying the quality of the lab-made MNPs. Yet, the mag-netization does not thoroughly saturate but, instead, has a slow increase with the field.
This phenomenon is not observed in a nanoparticle system since the magnetic moment in-stantly aligns with the applied field. However, as previously referred, among the powder, there are substantial clusters that behave as more complex magnetic materials, possess-ing multiple domains with magnetic moments that can be semi-dependent on each other, contrary to the isolated NPs. In those cases, the magnetic alignment can be difficulted, which retards the complete saturation [69].
Both remanence magnetization and coercive field have associated uncertainties that are greater than the value itself, meaning that, for the used resolution (with only seventy points taken), the quantities can be considered negligible*. The values obtained differ slightly for zero due to NPs’ size distribution since, without the cluster formation, the magnetic moment of each particle would constantly oscillate independent from the rest, preventing multiple equally aligned magnetic moments. This fact would lead to the non-existence of the remanence field, but with the agglomerates’ presence, that independence of moments slightly falls through, allowing few remanence. However, when a minimal external field is applied, the magnetic moments still tend to align with it, reaching close to the saturation magnetization within a small field. Thus, the magnetic properties of the NPs powder indicate encouraging expectations for the following step of NPs embedment into the interior cars’ material to create a magnetic attractive system.