6. MULTI-FUNCTIONAL CARS’INTERIOR MATERIALS PROTOTYPES 63
Hence, the first functional prototype was created using a single coil, with a permanent magnet inside, connected to a waveform generator capable of producing a sinusoidal wave with 15Vppamplitude and frequencies from 0.1 to 10Hz. However, for further ad-vances, the system would need a generator with three primary upgrades: reduced size, multiple outputs, and the capability of signal programming. Size reduction would be cru-cial for the embedment procedures in a small and compact space such as a dashboard or a door panel. Additionally, possessing multiple outputs ports is essential for the applica-tion in large areas, which would need various coils. Finally, the capability of varying the output signal in its amplitude, frequency, and even phase for systems with multiple coils would bring the potentiality of personalization for the user and the producer, which could adapt the material’s deformation depending on the interaction or external feedback such as music. Thus, based on the presented prototype, more development was performed to obtain a system with all the mentioned improvements to be tested in larger samples.
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PROGRAMMABLE MAGNETIC ATTRACTIVE MATERIALS: AN APPROACH FOR SHAPE-CHANGING CARS’INTERIORS
is possible to obtain with the feed shown, possibly already present inside a car. The code used during the prototype experiment can be found in the appendixB.
FIGURE6.2: Schematic of the hardware used from the Arduino-based prototype, where an Arduino, programmed by a computer, emits an analog signal through port 4 that is
amplified by an OpAmp by a factor of 1+RR2
1, powering the coil with the magnet inside
6.2.1 OP07 OpAmp
Initially, the OpAmp used to amplify the Arduino signal was an OP07 that checked all the specifications intended. After assembly, the system tests denoted a lack of sample deformation contrary to the expected for an amplitude signal of 10V. Therefore, to verify the circuit amplification, an oscilloscope was connected to both the output of the Arduino and the amplifier. That way, a comparison between the initial and final signals could be performed to determine possible irregularities. Figure 6.3 presents in yellow the wave after Arduino and in blue after the OpAmp in two distinct moments*. In subfigure (A) are the signals without the coil connected to the circuit, and in (B) are the analogous waves when the coil enters the circuit. With its insertion, the amplified signal seems to return the original amplitude outputted by the Arduino, justifying the lack of deformation observed when testing the system. The phenomenon observed has its origin in the incapability of the OpAmp to constantly feed the current that the coil demands for that power input, returning to the initial state as malfunction contingency.
In addition to the current supply failure, the oscilloscope observation also shows that the signal outputted by the Arduino does not follow a sinusoidal shape but instead a
*Videos of the complete waves variation with an OP07 OpAmp in the oscilloscope can be seen here https://drive.google.com/drive/folders/1o3xciWkYqWqjsDgmF4BV3hlUNFU4TC-S?usp=sharingor through the QR code present in figureA.6(A) on appendixA
6. MULTI-FUNCTIONAL CARS’INTERIOR MATERIALS PROTOTYPES 65
(A) Oscilloscope detected signals without the coil on the circuit
(B) Oscilloscope detected signals with the coil on the circuit
FIGURE6.3: Signals detected by the oscilloscope after the Arduino output (yellow) and after the OP07 OpAmp application (blue) for without (A) and with (B) the coil present in
the circuit
square one. This shape discrepancy goes as predicted since common Arduinos, as the Arduino UNO used, do not possess a Digital to Analog converter (DAC), leading to the output behaving as a digital signal with the chosen frequency. Yet, an RC filter application could counter that phenomenon at the cost of considerable attenuation and make the system frequency dependent. Another option would be the addition of a DAC module for Arduino, but it would restrain the entire microcontroller output to one signal.
6.2.2 Low-noise Amplifier
A low-noise amplifier fromStandford research systemswas used as a replacement for the OP07 to counter the presented flaws of the system. TheModel SR650, in addition to the multiple amplification options, possessed the possibility of filter application with a varied range of cutoff frequencies. This time, before any test performance, the oscilloscope was placed immediately in the circuit with the same configuration as previously. Figure6.4 shows a small attenuation with the coil insertion of the system, maintaining a consider-able coil input amplitude*. Nonetheless, with or without the magnetic generator on the circuit, the maximum after the amplifier does not remain fixed for half a period, decreas-ing linearly in that region. The reason for the decrease is unknown and was not expected, but has as the most probable responsible the amplifier configuration.
Thus, after understanding that the final signal possessed a considerable approxima-tion to the amplificaapproxima-tion wanted, the magnet was inserted in the coil interior with a piece of S9 sample on its top to test the entire system. Arduino program remained the same to observe the frequencies change with different intervals. The observed variation of the
*Videos of the complete waves variation with a low-noise amplifier in the oscilloscope can be seen here https://drive.google.com/drive/folders/1zVjNw-aXVWba1iog7t82xG-BV6tRXWap?usp= sharingor through the QR code present in figureA.6(B) on appendixA
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PROGRAMMABLE MAGNETIC ATTRACTIVE MATERIALS: AN APPROACH FOR SHAPE-CHANGING CARS’INTERIORS
(A) Oscilloscope detected signals without the coil on the circuit
(B) Oscilloscope detected signals with the coil on the circuit
FIGURE6.4: Signals detected by the oscilloscope after the Arduino output (yellow) and after the low-noise amplifier application (blue) for without (A) and with (B) the coil
present in the circuit
magnet did not correspond to 10Vppbut more closely to the viewed with 7Vpp, which was expected with the attenuation presented in the oscilloscope*. Nevertheless, the wanted material deformation with the frequency variation was successfully obtained, demon-strating the potentiality of the concept for controllable shape change. However, it was not obtained amplitude variation during the test, with the output wave out of the Arduino always possessing the same amplitude, the maximum of 5 V, since the microcontroller did not have that capacity due to the lack of the DAC module.
(A) Permanent magnet lower state (B) Permanent magnet upper state FIGURE6.5: Magnetic sample deformation obtained in the Arduino-based prototype
After all, the Arduino-based prototype was capable of producing a controllable system for sample material deformation, at least in terms of frequency. Even so, some problems are still present related to the capacity of the microprocessor to output the correct wave signal, which becomes less problematic if the amplitude can be varied. Also, the low-noise amplifier use is not ideal due to its size, which would not be a problem if the Arduino could oscillate the magnet with the 5 V amplitude. To obtain that, the magnet would
*Video of functioning of the Arduino-based prototype can be seen herehttps://drive.google.com/
file/d/1wcWIZBd2dGDqhoLi dZcMlbuZjVxkVV6/view?usp=sharing or through the QR code present in figureA.4(B) on appendixA
6. MULTI-FUNCTIONAL CARS’INTERIOR MATERIALS PROTOTYPES 67
need to be smaller or the coil optimized to produce a higher field. Both solutions could be used with benefits for the final application but would demand further development.
A new coil could possess a smaller size that would help the embedment, while a tinnier magnet usage meant the creation of more pixelized deformation that could be interesting for complex applications. Despite the promising solutions presented, at the moment of the development, neither was able to be implemented, leading to the course of prototype creation diverging from the primary idea to the proven one of permanent magnets with a controllable mechanical system.