I think the 'x-ray' table in the article works with IR cameras and illuminators under the table, and tablecloth that is slightly IR transparent.

You could still compare the internal structure of the package and bonding, but the die itself is mostly destroyed.

If you can choose, it's best to take a TDD license, as the duplexer required for FDD base station operation is a relatively expensive device when operating on an uncommon band.

1) Private 4G wasn't really a big thing in EU, but in most countries the license you get is technology neutral and can be used with a 4G base station as well.

PS: Connecting the private LTE to the public telephone network with a publicly reachable number requires a public telecom operator permit in some countries. You will also need to pay for the block of phone numbers. Roaming to the public cellular network requires many extra things which are not cheap or easy to obtain. And of course you need to have a roaming agreement with the other operator.

Not really a vulnerability, and many types of bluetooth dongle firmwares can be updated by the host...

https://shop.sysmocom.de/sysmoEUICC1-eUICC-for-consumer-eSIM...

https://esim.me/

To improve the quality you can pre-distort the output signal. Taking the square root works quite well, but expands the bandwidth significantly (infinitely, in theory). There is a lot of literature on pre-distortion with bandwidth constraints for telecom power amplifier linearisation. You will also need a linear amplifier to power the array.

The ultrasonic transducers used in this post are very narrowband, having a resonance peak of merely a few 100Hz. You can reduce the Q factor with resistive loading but the output power significantly drops. It seemed these transducers quickly start making an audible whining noise when used for continuous transmission at higher powers. I don't know what caused that, apart from this effect they seemed to hold up for essentially infinite duration.

Using a larger wideband ultrasonic transducer instead of an array of small narrowband transducers again increases the sound quality a lot. We did not find a commercial supplier of such transducer for a reasonable cost, but made some improvised custom electrostatic ones with conductive foil. There is a lot of literature on how to construct ultrasonic transducers but this is not my field.

You will not be able to play bass notes due to physics, the power required would be insane.

Espressif apparently has their own WiFi implementation, which makes sense as they are a major vendor of very cheap tablet and cell phone WiFi radios. This is likely why they can offer that feature so cheaply.

Bluetooth Low Energy is way simpler BTW.

Making a single core with two instruction decoders but a shared register file, caches, prediction logic and ALU would make sense for a very high-end application processor type core, but not for these small devices. You would also need an instruction set license from ARM for that, vs just licensing the M33 netlist.