Subpage:Spongetronics, sponge based electronics
design 2025
Introduction:
Sponge material shows an extremely large dielectric constant that changes with the amount of compression.
It can be made into a wide range variable capacitor when clamped between two metal plates.
Variable capacitors changing from less than 1nF to 100nF can be made with only a few cm^2 of sponge material,
indicating a dielectric constant of >1000 when compressed.
Note that this concept differs completely from the common resistive based pressure sensors.
To demonstrate applications, both a sponge-based oscillator and a sponge-based lowpass filter were build
where the sponge-capacitor is setting the frequency.
Document "Spongetronics" with overview of circuits, measurements etc.
YouTube movie, demonstrating oscillator and filter
The sponge based variable capacitor, as used in the oscillator and filter:
The sponge based tunable audio oscillator (the Spongillator) and the sponge based tunablelow-pass filter:
The sponge based tunable audio oscillator circuit and the sponge based tunable low-pass filter circuit:
Sponge types that I could identify:
1-cellulose based household sponge
2-organic
3-synthetic, plastic based household sponge
This project uses the common (human-made) cellulose based 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) sponge, that one fails, it does not show a high capacitance.
Follow-up:
Having a sponge controlled oscillator (SCO) and a sponge controlled filter (SCF)
then building a "Spongesizer" could be the next step in Spongetronics...
Limitations I found is that these "sponge capacitors" have a relative large ESR and dc-leakage,
more details in the document "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
https://iopscience.iop.org/article/10.1088/0957-4484/26/7/075702
https://www.researchgate.net/publication/271536256_Highperformance_supercapacitors_
using_graphenepolyaniline_composites_deposited_on_kitchen_sponge
https://www.researchgate.net/publication/231014778_Giant_Dielectric_Response_of_the_Sponge_Phase