Here it is. it's from an AE101 GTZ Levin, running a MAP 4AGZE.

You can see the piezo element in the first picture with the two connections between the piezo element and the prong to the plug for the sensor wire to the ECU (redundancy I guess, in case one breaks) the other side of the piezo earths to the case of the sensor which in turn earths to the engine block.

In the second picture, you can see the cavity inside the sensor. I assume this cavity is tuned in size to respond to the knock frequency of the engine. I'm not sure though.......