Piezoelectric sensors - Energy harvasting

[Nikos A.]

Hi everyone, I am designing a smast insole and I want to include energy harvasting from piezoelectric sensors (probably PZTs) as an auxiliary charging system. I want to ask if anyone has experience with piezo energy harvesting and how should I connect the sensors (I am not sure for the quantity) with the ic ( I am looking for the BQ25505 of Texas Instrumenrs)

Thanks in advance
Nick

[moffy]

Where are you getting your PZT material from? I looked a while back and found it hard to source at a reasonable price.

[Nikos A.]

There are available PZT disks on Amazon

https://www.amazon.com/Prewired-Elements-Buzzer-Sounder-Trigger/dp/B01N5HN94S/ref=mp_s_a_1_8?keywords=piezoelectric+sensor&qid=1579282176&sprefix=piezoe&sr=8-8

[Conrad Hoffman]

PZTs are great at generating impressive voltages into high impedance loads, but absolutely terrible at energy conversion. IOW, they don't produce much actual power. Expect charging anything useful to take a very long time.

[Twoflower]

In a newspaper I found a link to some commercial products: https://piezo.com/collections/piezoelectric-energy-harvesters?_=pf&pf_t_quantity=Quantity__1

Not really cheap as it looks like. Especially if you check the output power: 26mW for $60.

[moffy]

The amazon PZT's appear quite reasonable. Pity they are only round.

[Nikos A.]

I am trying to figure out how to connect/combine the piezoelectric sensors since the output voltage of each one would not be the same ( it is proportional to the applied pressure and since they are intented for insole application the output of each one will differ according to the pressure applied by the foot)

Any help?

[Marco]

Wouldn't dielectric elastomers be much better for energy harvesting in a sole? (ie. a charged capacitor with a compressible dielectric.)

[Nikos A.]

Maybe.. I do not know how this technology works but at the moment I want to proceed with piezoelectric..

[Conrad Hoffman]

If you distribute them it's almost certain they will be working at cross purposes. No doubt one could use diodes to steer the charge, with the associated losses of course. I'd find one location that moves in a predictable fashion and put the device(s) there. Not sure if it's best to go parallel or series.

[Marco]

You should probably prestress the piezo discs, they are meant to bend like this along the entire edge of the disc, not compress or bend along just one axis.

So put a tiny bit of rubber in between two discs and then clamp/glue the edges together. That way when you compress the rubber they bend like they are supposed to.

[soubitos]

Might be aware of this, might not, i found it very interesting read though.
https://www.researchgate.net/publication/326905148_Experimental_Evaluation_of_Piezoelectric_Buzzers_as_Devices_for_Energy_Harvesting

[Nikos A.]

Thank you, I am going to conduct some experiments and will come back with a feedback!!