Micro Acoustic Cartridges

Does anyone remember the operation principle of these cartridges?

Here’s an excellent summary on the company history and the cartridge(s) construction/design principles: http://www.roger-russell.com/sonopg/micropg.htm

Back in the day I used the following models: QDC-1E, 2002E and 530MP. All were fitted to a very low mass tonearm with knife-edge bearings (Infinity Black Widow). All shared similar basic characteristics: low physical mass, lightning fast transient response and excellent tacking at 1 gram tracking force. (The later very much counter to what we’ve learned since.)

Correction: tracking, not tacking.
I owned one of the 2002 series (when my ears were younger) and I remember fantastic amounts of "micro" detail.
Yep.  Loved the 2002e back in 1978.  It was pretty good in my basic system powering Large Advents.  Piezoelectric, if I recall.
Tubegb, thanks for the link. I have never heard the shimmering symbols on Paul Simmon's " Slip Slide'n Away" reproduced better than a Mico Acoustic cartridge did it. Also, the rain in "Fresh Air One" was extraordinarily palpable.