Do you know this S curve's name? I'm making a ad-sales predictor and try to make it fit by using the S curve's below.

$ ()= \frac{}{1+} (1−^{−}) $


$f(x)$ is an ad-sales
$x$ is an advertise cost
both $a$ and $b$ are fitting parameters.


It looks like logistic function curve. I actually don't know a name of it though I have to use it for our client order. Do you know a name of the function or any text referring it?
From a quick search, the function you provided doesn't seem to have a particular name.

Are you sure the function belongs to Sigmoidal curves? The function does not remind too much of an S-shape.