Apply tACS to Alleviate Anxiety Symptoms

Inclusion Criteria: * Meet SCID-5/MINI KID criteria for one of the above-mentioned anxiety disorders. * Subject, or legally acceptable representative (LAR), is able to read, understand, and provide written informed consent and assent, as applicable. * Subjects requiring an LAR will have an identified caregiver who meets the following criteria: Able to reliably report and communicate on the subject's level of functioning and either lives with the subject or sees the subject on average for ≥ 3 hours/day ≥ 4 days/week, or receives reports from a caregiver, such as an aide, who meets this criteria, and in the investigator's opinion - the extent of contact is sufficient to provide meaningful assessment of changes in subject behavior and function over time * Able to be compliant with all study procedures * Age range: 5 years of age or older * Stable medications for non-excluded concurrent medical conditions for eight weeks prior to randomization * If receiving psychotherapy, participants must have started psychotherapy at least 2 months prior to randomization * Health: Physically acceptable for the study with no expected medical conditions likely to occur during or immediately after the study, as confirmed by medical history * Clinical laboratory values of TSH and T4, within 90 days from randomization must be within normal limits or judged not clinically related by the physician sub-investigator or PI to the subject's cognitive impairment if abnormalities are present. Exclusion Criteria: 1. Neurodegenerative disease 2. Epilepsy 3. Intellectual Disability 4. Pregnancy or lactation 5. Convexity skull defects 6. Raised intracranial pressure 7. Intracranial electrodes 8. Vascular clips or shunts in the brain 9. Cardiac pacemakers or other implanted biomedical devices 10. An active medical disorder that could explain, in the opinion of the PI or by medical history, the anxiety disorder. 11. Had an abrupt and significant change in functioning within 3 months of randomization. 12. Meets criteria for any substance use addiction as defined by DSM-5/SCID-5 CV. 13. Active alcoholism as defined by 3 or more bottles of beer or glasses of wine or 2 hard liquor drinks per day/night 3 or \> times per week at any time within the past 12 weeks of screening or any other addiction to non-prescription substances. 14. Schizophrenia spectrum disorders and bipolar spectrum disorders. 15. Active suicidal tendency (evaluated by Columbia-Suicide Severity Rating Scale \[C-SSRS\], traditional version). Note: If the BDI or CDS of the participants significantly increase, the CSSRS will be repeated. 16. Unstable medical condition (including expected medication change/titration). 17. Premenstrual dysphoric disorder. 18. Factious/malingering disorder and any patients applying for disability warranty. 19. Somatoform disorders subtypes: conversion and hypochondriasis.