Check string whether is UTF-8 or UCS-2

Question

If I have a list of data:

$a = "hello";

$b= "4f60";

$c = "hi";

$d = "00480065006C006C006F";

$b and $d are UCS-2 string. I wish to display all these data in a table,so how can I know whether which data is UCS-2 so that I can convert it before being displayed ? Is it possible ? I tried mb_detect_encoding and preg_match for unicode found at php.net , but even it is an unknown symbol it still considered as unicode.

Thank you.