# Set number of days, in the past, to create log files for
$days = 14
# Set directory to create logs in
$directory = "C:\Test\Logs"

$i=1
While($i -lt $days){
    # Get Date and create log file
    $date = (Get-Date).AddDays(-$i)
    $logFile = "u_ex" + ($date.Year).ToString().Substring(2,2) + (($date.Month).ToString().PadLeft(2)).Replace(" ","0") + (($date.Day).ToString().PadLeft(2)).Replace(" ","0") + ".log"
    $logPath = join-path $directory $logFile
    $date | out-file $logPath

    # Set the Creation, Write, and Access time of log file to match date
    Get-Item $logPath | % { $_.CreationTime = $date; $_.LastWriteTime = $date; $_.LastAccessTime = $date }

    $i++
}
Details
These commands will create a log file for each day, go back as many days as specified. The file attributes will be set to the past as well. This is great for testing cleanup scripts.