Method for assembling conductive particles into conductive pathways and sensors thus formed
A sensor is achieved by applying a layer of a mixture that contains polymer and conductive particles over a substrate or first surface, when the mixture has a first viscosity that allows the conductive particles to rearrange within the material. An electric field is applied over the layer, so that a number of the conductive particles are assembled into one or more chain-like conductive pathways with the field and thereafter the viscosity of the layer is changed to a second, higher viscosity, in order to mechanically stabilise the material. The conductivity of the pathway is highly sensitive to the deformations and it can therefore act as deformation sensor. The pathways can be transparent and is thus suited for conductive and resistive touch screens. Other sensors such as strain gauge and vapour sensor can also be achieved.
1. A capacitive sensor comprising one or more conductive pathways formed from conductive particles in a matrix, wherein the conductive particles comprise carbon particles or silver particles,
wherein the number of particles in the pathways is below the number of particles that constitutes a percolation threshold if the particles were homogenously distributed in the matrix.
2. The capacitive sensor of claim 1 , wherein the capacitive sensor comprises a substrate, and the conductivity of the aligned particles is influenced by the substrate deformations or bending.
3. A hybrid sensor, comprising:
the capacitive sensor of claim 1 and
a resistive sensor,
wherein the capacitance of the pathways is influenced by the presence of an object or a human.
4. The capacitive sensor of claim 1 , wherein the conductive particles have an aspect ratio range of 1-20.
5. The capacitive sensor of claim 1 , wherein the conductive particles comprise carbon particles selected from the group consisting of irregular graphitic particles, spherical carbon black (CB) particles, disc-like particles, and conical carbon particles (carbon nanocones CNCs).
6. The capacitive sensor of claim 1 , wherein the matrix is a thermoset polymer, a thermoplastic polymer system, a lyotropic system or a mixture thereof.
7. The capacitive sensor of claim 1 , wherein the matrix comprises a UV-curable polymer.
8. The capacitive sensor of claim 1 , wherein the matrix comprises an elastomer.
9. The capacitive sensor of claim 1 , wherein the conductive particles comprise CB particles.
10. The capacitive sensor of claim 1 , wherein the matrix comprises a polymer material.
11. The capacitive sensor of claim 1 , wherein said capacitive sensor is a micro-mechanical strain sensor.
12. A cantilever sensor, comprising the capacitive sensor in accordance with claim 1 .
13. A nanomechanical cantilever sensor, comprising the capacitive sensor in accordance with claim 1 .
14. A vapour sensor comprising the capacitive sensor in accordance with claim 1 .
15. The capacitive sensor of claim 1 , where the capacitive sensor also functions as at least one of an anti-static coating, a thermal conductor, an antenna and an electro-magnetic shielding.
16. A robot skin application, comprising the capacitive sensor in accordance with claim 1 .
17. A moisture sensor comprising the capacitive sensor in accordance with claim 1 .
18. A method for nonintrusive bio monitoring, the method comprising:
measuring a pulse of a patient in need thereof as strain on the patient's skin with the capacitive sensor of claim 1 .
19. The method of claim 18 , wherein the capacitive sensor measures a change in capacitance due to the patient's heartbeat.
20. A method for nonintrusive bio monitoring, the method comprising:
measuring moisture or vapour from a patient in need thereof as changes in conductance or capacitance with the capacitive sensor of claim 1 .