The goal of this study is to explore the efficacy and safety of 4Hz transcranial alternating current stimulation (tACS) in patients with mild Alzheimer's disease (AD). The study will recruit 40 individuals with mild AD, and the participants will be randomized to either a 4 Hz tACS group or a sham stimulation group. Both groups will undergo 30 one-hour sessions across 3 weeks (21 days). At the end of the intervention and 3-month follow-up, all subjects will repeat the baseline assessments.