Spongillator: A sponge based audio oscillator
Oscillator sweeps from 20kHz to 20Hz controlled by sponge capacitor. Sponge material shows an extremely large dielectric constant (>1k), enabling a wide range variable capacitor when clamped between two metal plates and compressed. Variable capacitors up to to 100nF can be made with only a few cm^2 of sponge material. Note that this concept differs completely from the common resistive based pressure sensors. To demonstrate applications, a sponge-based oscillator and a sponge-based lowpass filter were build
Documents:
In the file: "Spongetronics.pdf" you can find circuits, scope measurements and other info.
Movie: https://youtu.be/BFPNdyaWR40
Hear sounds, see the related waveforms on a scopescreen and the circuits.
Sponge types that I could identify:
1-cellulose based
2-organic
3-synthetic, plastic based
This project uses the common (human-made) cellulose based household sponge, sometimes confusingly called "natural sponge".
The material works fine and should be really dry for this purpose.
The second type is made of the remains of real organic sponges that lived in the sea, I did not try this type.
A third type is synthetic (plastic based) household sponge, that one fails, it does not show a high capacitance.
Limitations and capacitance/dielectric constant values:
Limitations I found is that these "sponge capacitors" have a relative large ESR and dc-leakage but for the applications described it worked out well. The document Spongetronics.pdf" gives some numbers.
For these reasons most simple capacitance meters are not able to measure well here. My numbers are based on measured RC-curves were R is known and on swapping with a normal capacitor trying to get the same frequency in my spongillator. From the plate capacitor formula I then have to conclude that the compressed sponge material must have a dielectric constant >1000.
Follow-up suggestion:
Having a sponge controlled audio oscillator (SCO) and a sponge controlled filter (SCF) then building a "Spongesizer" could be the next step in Spongetronics...
Further reading:
Althoug this project was curiousity driven and mostly for fun, I later found also serious applications reported.
some links:
https://phys.org/news/2015-02-kitchen-sponge-supercapacitor-porous-benefits.html
High-performance supercapacitors using graphene/polyaniline composites deposited onkitchen sponge:
https://iopscience.iop.org/article/10.1088/0957-4484/26/7/075702
https://www.researchgate.net/publication/231014778_Giant_Dielectric_Response_of_the_Sponge_Phase
In the file: "Spongetronics.pdf" you can find circuits, scope measurements and other info.
Movie: https://youtu.be/BFPNdyaWR40
Hear sounds, see the related waveforms on a scopescreen and the circuits.
Sponge types that I could identify:
1-cellulose based
2-organic
3-synthetic, plastic based
This project uses the common (human-made) cellulose based household sponge, sometimes confusingly called "natural sponge".
The material works fine and should be really dry for this purpose.
The second type is made of the remains of real organic sponges that lived in the sea, I did not try this type.
A third type is synthetic (plastic based) household sponge, that one fails, it does not show a high capacitance.
Limitations and capacitance/dielectric constant values:
Limitations I found is that these "sponge capacitors" have a relative large ESR and dc-leakage but for the applications described it worked out well. The document Spongetronics.pdf" gives some numbers.
For these reasons most simple capacitance meters are not able to measure well here. My numbers are based on measured RC-curves were R is known and on swapping with a normal capacitor trying to get the same frequency in my spongillator. From the plate capacitor formula I then have to conclude that the compressed sponge material must have a dielectric constant >1000.
Follow-up suggestion:
Having a sponge controlled audio oscillator (SCO) and a sponge controlled filter (SCF) then building a "Spongesizer" could be the next step in Spongetronics...
Further reading:
Althoug this project was curiousity driven and mostly for fun, I later found also serious applications reported.
some links:
https://phys.org/news/2015-02-kitchen-sponge-supercapacitor-porous-benefits.html
High-performance supercapacitors using graphene/polyaniline composites deposited onkitchen sponge:
https://iopscience.iop.org/article/10.1088/0957-4484/26/7/075702
https://www.researchgate.net/publication/231014778_Giant_Dielectric_Response_of_the_Sponge_Phase
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