I'm still working on material for the imaging option and have started the HL part. There's actually not much content in the HL extension, it's all from the old medical physics option. In my text book I used a very simple model to explain the way ultrasound is produced and detected, here I decided to try something a bit more realistic. This is a quartz molecule being squashed to show how a PD is created across it, I made it in Algodoo of course. There are a lot of hidden springs and rigid bars connecting the atoms..