How does Apple achieve the all aluminium enclosure with RF on the MacBook Pro? Since 2016, Apple has been able to make these laptops with no visible “window” of plastic or glass for RF signals to travel through. As an electrical engineer, I’m intrigued. 

If you look at older MacBook pros, they have a black plastic hinge. For the Pixel chrome book, it’s got a whole glass half of the lid for that. 

My guess was the hinge or the glass screen, but neither would work when the lid is closed, and you can very much use your MBP while the lid is fully closed with WiFi and Bluetooth (think when you have external displays). 

How does Bluetooth and WiFi work on the 2018 MacBook Pro models?
Apple cleverly places the WiFi antenna assembly adjacent to the cooling vent to seemingly "circumvent the laws of physics" and get around the Faraday cage problem.

Looking at the underside of the MacBook Pro (15" 2017), you can see a cooling vent that goes for about 80% of the width of the machine.





The WiFi antenna assemblies are put on either side of the MacBook directly adjacent to the cooling vent.  So, while it appears that the WiFi antenna is hidden behind an all aluminum case, it's actually out in the open which is how it receives WiFi signals in closed-clamshell mode.