Zenbud (https://zenbud.health/) is a low intensity focused ultrasound (LIFU) wearable that targets the auricular branch of the vagus nerve at the cymba concha (just above the ear canal opening). It uses a 5.3 MHz ultrasound frequency that pulses at 41 Hz. Sessions last for 5-30 minutes.
They did a preliminary clinical trial (no control group) with 28 patients who have anxiety (https://pmc.ncbi.nlm.nih.gov/articles/PMC12671299/). Each day for 4 weeks they stimulated the ear for 5 minutes. 93% of the patients had decreased anxiety, 89% were less depressed, 82% had reduced PTSD symptoms and 65% had improved sleep quality.
Interesting to note that a pulse rate of 40 Hz is one of the target pulse frequencies that