Do different patterns and materials affect the capacity of knitted capacitors and if so in which way?
Experimentation Setup
Various tests of knitted capacitors within the following frame conditions: The capacitors were knitted with an electronic knitting machine (Brother KH-930), the capacitor samples have a fixed size of 48 rows and 48 stitches.
The materials used in the tests are the following: copper wire, silver thread (7×1 Karl Grimm) and normal/nonconductive (polyester/acrylic) thread.
X … two isolated copper wires and one white thread
0 … two nonconductive, grey threads
1. Test
Sample #14: 1,13nF
Sample pattern:
X0X0X0X0X
X0X0X0X0X
Sample #15: 1,31nF
Sample pattern:
X0X0X0X0
0X0X0X0X
Measuring these two samples, it becomes clear that the pattern affects the capacity value. Assuming that the reason for the different capacity values is the difference in how tight the two copper wires are knitted together, the following two tests are conducted to test that assumption.
2. Test
The patterns are similar to the one used in the previous tests, but every stitch/color is repeated. These patterns show no significant difference in the capacity values. Also, the capacity of #15 is stil higher.
- The tighter the wires are knitted together, the smaller the isolation between them and the higher the capacity.
- The longer the wires are lying on the back/left side of the fabric, the higher the capacity.
Sample #21: 1,21nF
Sample pattern:
00XX00XX
00XX00XX
00XX00XX
00XX00XX
Sample #16: 1,19nF
Sample pattern:
00XX00XX
00XX00XX
XX00XX00
XX00XX00
3. Test
In the next test, we tried out a pattern in which more stitches with wires are left out, so that the lines in the back get longer.
The capacity is clearly smaller (about 820 pF).
Assumed reason for the difference: less stitches with the copper wires, less conductive material.
Sample #22: 820pF
Sample pattern:
X000X000
00X000X0
X000X000
00X000X0
4. Test
Based on the same amount of conductive material (4m of copper wire), we measured the capacity of twisted copper wires and two different patterns.
X … two isolated copper wires and one grey thread
0 … two nonconductive, white threads
non-knitted twisted copper wire, capacity: 300 pF
Sample capacity: 270pF
Sample pattern:
XX00XX00
00XX00XX
Sample pattern:
XXXX0000
0000XXXX
The capacitor with two twisted copper wires has the higher capacity. Also, longer/flat lying wires cause a better capacity, but on the other hand, it uses less less conductive material in the pattern.
5th test
Trying to knit the wires tighter together and using as much conductive material as possible within the 48 rows and 48 stitches.
Sample #20: 2,1 nF
Sample pattern (X … two isolated copper wires and one grey thread):
XXXXXXXX
XXXXXXXX
Sample #19: 1,8 nF
Sample pattern (X … two isolated copper wires):
XXXXXXXX
XXXXXXXX
The capacity of #20 is higher, probably because through the extra thread the wires are knitted closer together.
6. Test
Trying using other material and various tensions to minimize the isolation between the wires.
Sample #17: 2,1 nF, tension 8
Sample pattern (X … one copper wire (isolated), one silver thread (unisolated), one grey nonconductive thread):
XXXXXX
XXXXXX
Sample #18: 2nF, tension 6 (tighter than tension 8)
Sample pattern (X … one copper wire (isolated), one silver thread (unisolated), one grey nonconductive thread):
XXXXXX
XXXXXX
There is no significant difference in the capacity between the variable tensions. Furthermore, comparing the silver thread and the copper wire, there is neither a significant difference in the capacity. So knitting the wires tighter together has positive effects on the capacity values, but just to a certain extent. Higher tension causes more curves in the wires. As you can see in test 4, curves have a negative impact on capacity values.
Summary
- The more conductive material (like copper wire), the higher the capacity.
- The tighter the wires are knitted together, the less the isolation, the higher the capacity.
- The longer the lines of the wires in the pattern/ the less curves in the wire, the higher the capacity.