Search notes:

System.Security.Principal.NTAccount (class)

System.Security.Principal.NTAccount represents a user or group account.
The class derives from System.Security.Principal.IdentityReference.
PowerShell exampe 
$ntAccount =  new-object System.Security.Principal.NTAccount $env:USERDOMAIN, $env:USERNAME
$sid = $ntAccount.Translate([type]'System.Security.Principal.SecurityIdentifier')
$sid.value

Index