## 4 Discussion  
This work reports a new low-cost fabrication technique for developing low electrical percolation threshold sensors based on magnetically oriented MWCNT/PDMS nanocomposites. Compared with randomly distributed MWCNT composites, these sensors originate electrodes with low electrical resistance, suitable for developing flexible piezoresistive and triboelectric sensors.  
The MWCNTs were observed to present a magnetic response due to impurities remaining from their fabrication process. SEM/EDS analysis detected the presence of aluminium and iron. SQUID analysis confirmed the ferroelectric properties of the MWCNT powder. The magnetic response of the MWCNTs was used to control their localisation inside a polymer matrix, PDMS, using magnetic fields. The use of magnetic fields to localise the MWCNTs decreased the electrical percolation threshold compared to the nanocomposites prepared with a random distribution of the MWCNTs, thus reducing the concentration of conductive nanomaterial necessary while creating patterned electrodes that can be used for the fabrication of flexible sensors.  
The different interactions between permanent magnets were simulated and tested in the lab, showing that the use of an alternating polarity configuration allowed the fabrication  
Figure 16: Piezoresistive and triboelectric effects under a deformation force for the nanocomposite prepared with the parallel lines magnetic pattern. (**a**) 0.5 wt%. of MWCNT/PDMS under a peak force of 6.6 N (**b**) 1 wt%. Of MWCNT/PDMS sample under a force of 8.1 N for 10 s.  
of continuous conductive lines of MWCNTs. Finally, nanocomposites with three different electrode designs were simulated and fabricated. Although all designs produced electrodes with an adequate response, the pattern obtained with parallel lines was produced and tested for piezoelectric and triboelectric properties. The nanocomposites were tested under bending forces between 6 and 9 N, showing a stable response under fast and slow deformation. The developed sensors proved to be stable for touch detection and deformation under the range of forces.  
Future work can include the scale-up of this fabrication technique and its extension using different polymer matrices. A detailed analysis of the stability of the sensors and their application as multi-sensors will be carried out. The fabrication process presented may be used in the near future to develop sensors for soft robotics applications. It may be applied to monitor large and unconventional areas; it can be adapted to different moulds and polymer matrices since it is an adaptable, low-cost solution that does not require expensive equipment or materials.  
Conceptualization, D.S.E. and N.D.; methodology, D.S.E., E.W.S., R.P. and A.M.; software, D.S.E.; validation, D.S.E., E.W.S. and N.D.; formal analysis, D.S.E.; investigation, D.S.E. and E.W.S.; resources, N.D. and E.W.S.; writing--original draft preparation, D.S.E.; writing--review and editing, D.S.E., E.W.S., M.C.P. and N.D.; supervision, E.W.S., M.C.P. and N.D.; project administration, E.W.S. and N.D. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
This research is part of the PhD project at the Doctoral Program in Advanced Materials and Processing--FEUP. We would like to thank CeNTI for providing resources (labs, equipment and consumables) to perform the fabrication and characterisation of the samples. The authors thank CEMUP for expert assistance ([PERSON]) with SEM-EDS. IPC acknowledges the support of FCT through National Funds References UIDB/05256/2020 and UIDP/05256/2020.  
The authors declare no conflict of interest.