php- floating point number shown in exponential form

use number_format() function

echo number_format($a,6,'.',',');

the result would be 0.000022

Try this:

function f2s(float $f) {
    $s = (string)$f;
    if (!strpos($s,"E")) return $s;
    list($be,$ae)= explode("E",$s);
    $fs = "%.".(string)(strlen(explode(".",$be)[1])+(abs($ae)-1))."f";
    return sprintf($fs,$f); 
}

The exponential form is the internal one use by every (?) programming language (at least CPUs "sees" floats this way). Use sprintf() to format the output

echo sprintf('%f', $a);
// or (if you want to limit the number of fractional digits to lets say 6
echo sprintf('%.6f', $a);

See Manual: sprintf() about more information about the format parameter.