Hi all.

Bought several tiny nebulizers to humidify a germinating room.  Testing one for two weeks, ceased to produce the fog.  Do not know how to revive.  By cleaning sort of worked at half production for an hour.  Read about and found :

---> https://www.electroschematics.com/mist-maker/

But the surprising specification says "5um"  "740 holes"

 

So I projected a laser to the stainless piezodisc and yes, shined trough the supposed-to-be holes in metal (5 micrometres per above) invisible to eyes or magnifying lens.  Confirming it is a microperforated disc.  Never saw a piezoelement perforated.  How is the principle of operation of such nebulizer ?  I have other piezo nebulizers with solid discs.

Is the perforated material part of the PZT, or above it? I could envision water going into a gap and being forced through the holed by an oscillating piezo, producing a mist.

I think stainless steel is a substrate or housing, and not a piezo itself.

The PZT is of annular shape about 5mm id and 12mm od;, its center void has attached the stainless disc which found to have microperforations and emits/sprays  the mist on its top; contacts the water at its bottom.

The misting image shows the PZM on top of a wet sponge instead of floating on water.

 

Overview of the little white buoy ---> https://www.youtube.com/watch?v=PlRgi6Mn6CQ

 

So, as I said, I think the piezo draws water in and forces it through the perforated piece as it oscillates 

Looks to be exactly the same as a piezo buzzer, except, instead of contacting a solid plate to make noise, it pushes droplets of water through a perforated plate ( as suggested by Swansont ).
A simple circuit, where an oscillator switches a transistor to provide a voltage/current to the piezo element, can be adjusted with higher/lower drive voltage, and different oscillator frequency.

Thanks.   

Appears now like the different density restrictions are a clue... The top outlet side is free to air; the other side below has a wet spongy presenting a much denser on-water restriction.  While vibrating, suction works by the partial vacuum on a denser media (water) and no vacuum on the expulsion side into air, forming a flow valve.  Am I guessing near right ?

When the diaphragm pushes down, has difficulty 'pumping' whatever is in its pores into dense water.  When the diaphragm bows up, encounters no resistance in expelling.  That differential creates the flow ? Yes, poor wording as always. 

What am unsure in reasoning if expulsion of droplets happens when diaphragm bows down or when bows up, or during the transit upwards or downwards...

1 hour ago, Externet said:

What am unsure in reasoning if expulsion of droplets happens when diaphragm bows down or when bows up, or during the transit upwards or downwards...

Upwards, I would think. Exerting pressure on the water, forcing it through the holes, which presents less resistance than forcing water elsewhere.