<?php

$array = array(
    'machine' => array(
        array(
            'cycle' => 12.34,
            'percent' => 0.56,
        ),
        array(
            'cycle' => 12.34,
            'percent' => 0.56,
        ),
    )
);

print json_encode($array);

/////

{"machine":[{"cycle":12.34,"percent":0.56},{"cycle":12.34,"percent":0.56}]}