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

https://cristiansinterestingthoughtss.opalvector.com/posts/how-long-do-ultherapy-results-last-is-the-12-to-18-months-claim-real

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