How do airport x-ray scanners accurately detect through multiple layers of luggage


If I’m travelling with a backpack for example, and lay it flat , there will be around 15 layers at certain parts considering clothing, the separated compartments etc.
How can the display accurately display every overlapping item to the point where the people checking can be certain there is nothing prohibited within the backpack?

This may just be a stupid question but one which I’ve always wondered about so any answers would be appreciated 👍

In: 2

Different substances reflect radiation at different levels. As the signals are sent through the items, a detector measures the different levels of signals being absorbed, and creates an image based on that.

The purpose of the scanner isn’t to take an accurate inventory of the contents of your bag. It’s to look for materials that may be a weapon or a bomb or something prohibited. The machine is basically designed to ignore materials that aren’t a threat. If you have 15 layers of fabric, the scanner doesn’t sort them out; it doesn’t need to know what’s a shirt and what’s a sweater and what’s a pair of dirty underwear. The rays just pass through fabric like it isn’t there. If you’ve been to the airport, there’s often a display of stuff you aren’t allowed to have in your bag. In addition to guns and knives, there are also things like peanut butter. That’s because a jar of peanut butter can look like something else on the scanner — plastic explosive or whatever.