Low hysteresis and flexible pressure sensitive composite
A sensing structure and a method of fabricating a sensing structure for a compressive-type pressure sensor. The method comprises the steps of providing an elastic micropatterned substrate defining a plurality of 3-dimensional microstructures, each microstructure comprising a tip portion pointing away from the substrate in a first direction; forming a conductive film on the elastic micropatterned substrate such that the 3-dimensional microstructures are substantially covered by the conductive film; and forming cracks in the conductive film in areas on 3-dimensional microstructures.
1. A sensing structure for a compressive-type pressure sensor, the sensing structure comprising:
an elastic micropatterned substrate defining a plurality of 3-dimensional microstructures, each microstructure comprising a tip portion pointing away from the substrate in a first direction; and
a conductive film on the elastic micropatterned substrate such that the 3-dimensional microstructures are substantially covered by the conductive film, wherein the conductive film comprises cracks in areas on 3-dimensional microstructures;
wherein the conductive film is free from cracks at the tip portions of the 3-dimensional microstructures.
2. The sensing structure of claim 1 , wherein the cracks comprise substantially annular cracks in areas around the 3-dimensional microstructures that are displaced from the tip portions.
3. The sensing structure of claim 2 , wherein the 3-dimensional microstructures are in the form of micropyramids.
4. The sensing structure of claim 1 , further comprising: electrodes configured to be disposed on the conductive film covered tip portions of the 3-dimensional microstructures for measuring a resistance of a conductive path comprising portions of the conductive film in the areas on the 3-dimensional microstructures when a load is applied to the sensor for deforming the 3-dimensional microstructures in a second direction substantially opposite to the first direction.
5. The sensing structure of claim 4 , exhibiting a ratio of a highest sensitivity of the sensing structure, the sensitivity being a change rate of resistance in Ω with increasing pressure in kPa applied on the sensor structure, to electrical hysteresis, expressed as:
H
=
❘
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∑
A
F
-
∑
A
B
∑
A
F
❘
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×
100
%
where
A
FIB
=
∑
k
=
1
n
-
1
1
2
(
P
k
+
1
-
P
k
)
[
R
FIB
(
P
k
+
1
)
+
R
FIB
(
P
k
)
]
and where:
H is an indicator of electric hysteresis, in %, A F ,
A B are integration areas of a resistance-pressure curve of the sensing structure for forward and backward path, respectively, and
P is pressure on kPa.
6. The sensing structure of claim 4 , wherein the electrodes are formed on an electrode substrate.
7. The sensing structure of claim 4 , wherein the electrodes comprise flexible electrodes.
8. The sensing structure of claim 7 , wherein the flexible electrodes are formed on a flexible electrode substrate.
9. A method of fabricating the sensing structure for the compressive-type pressure sensor of claim 1 , the method comprising the steps of:
providing the elastic micropatterned substrate defining the plurality of 3-dimensional microstructures, each microstructure comprising the tip portion pointing away from the substrate in a first direction;
forming the conductive film on the elastic micropatterned substrate such that the 3-dimensional microstructures are substantially covered by the conductive film; and
forming the cracks in the conductive film in areas on 3-dimensional microstructures;
wherein forming the cracks comprises leaving the conductive film free from cracks at the tip portions of the 3-dimensional microstructures.
10. The method of claim 9 , wherein forming the cracks comprises providing a rigid substrate on the conductive film covered 3-dimensional microstructures and applying a load to the 3-dimensional microstructures via the rigid substrate.
11. The method of claim 9 , comprising providing a soft cushioning material between the rigid substrate and the conductive film covered 3-dimensional microstructures during the applying of the load.
12. The method of claim 9 , wherein forming the cracks comprises forming substantially annular cracks in areas on the 3-dimensional microstructures.
13. The method of claim 9 , further comprising:
disposing electrodes on the conductive film covered tip portions of the 3-dimensional microstructures for measuring a resistance of a conductive path comprising portions of the conductive film in the areas on the 3-dimensional microstructures when a load is applied to the sensor for deforming the 3-dimensional microstructures in a second direction substantially opposite to the first direction.
14. The method of claim 13 , comprising forming the electrodes on an electrode substrate.
15. The method of claim 13 , wherein the electrodes comprise flexible electrodes.
16. The method of claim 15 , comprising forming the flexible electrodes on a flexible electrode substrate.
17. The sensing structure of claim 1 , wherein the 3-dimensional microstructures are in the form of micropyramids.