Without seeing the OTHER side of the PC board, I'm not convinced you have a microphone there.
If it is an electret microphone capsule (with the impedance converting transistor circuit inside) then you must apply power to the microphone to make it work. It is not a passive device that generates voltage.
I did power it. I used a variable PSU and a biasing resistor. I have used electret mic capsules in the past so I have an idea on how they work and how they should behave.
If you're talking about the tiny round PCB with a transistor and two caps on it, the back side is this one.
If you're talking about the flex PCB the device is mounted to, it is just a ground plane.
The part is not much of use for me, just a curiosity on what it really is. What I really want is to ID the LED