Impedance of LTC3588 Energy Harvestor

Hello!

I’m looking to create an impedance matching circuit for this Energy Harvester unit. I was unable to find impedance for the harvester in the spec sheet, so I was wondering if there was info on this somewhere. If there is a way to test for it, I’m also willing to set up a circuit and see if I can’t find an impedance value. Thank you so much for your time!