Ultherapy uses focused ultrasound to target the SMAS layer at about 4.5 mm...

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

Ultherapy uses focused ultrasound to target the SMAS layer at about 4.5 mm deep, stimulating natural collagen over 3 to 6 months. Unlike RF, which heats skin to 40 to 45°C mainly in the dermis, Ultherapy reaches deeper for lifting