Ultherapy uses focused ultrasound targeting the 4.5 mm layer beneath the skin...

https://www.alphabookmarks.win/ultherapy-targets-the-deep-4-5-mm-smas-layer-using-ultrasound-to-lift-and

Ultherapy uses focused ultrasound targeting the 4.5 mm layer beneath the skin called SMAS, which few treatments reach. It triggers collagen buildup over 3 to 6 months for natural lift