Capture & Send Multiple Array Values into Ajax

HTML

<form method="post" id="unitDataForm">
    <label for="unit_id">unitID</label>
    <input type="text" name="unit_id" value="1" />
    <br />
    <button type="button" title="disabled for this demo" value="Add">Add New</button><span style="color:red">**disabled for this demo**</span>

    <br />
    <p>-------------------------</p>
    <br />
    <label for="seqImg">seqID[1]</label>
    <input type="text" name="seqImg[]" value="20" />
    <br>
    <label for="seqDesc">seqDesc[1]</label>
    <textarea name="seqDesc[]" /></textarea>
    <br />
    <p>-------------------------</p>
    <label for="seqImg">seqID[2]</label>
    <input type="text" name="seqImg[]" value="30" />
    <br>
    <label for="seqDesc">seqDesc[2]</label>
    <textarea name="seqDesc[]" /></textarea>
    <br />
    <p>-------------------------</p>
    <label for="seqImg">seqID[3]</label>
    <input type="text" name="seqImg[]" value="40" />
    <br>
    <label for="seqDesc">seqDesc[3]</label>
    <textarea name="seqDesc[]" /></textarea>
    <br />
    <p>-------------------------</p>
    <button type="submit" title="Submit" value="Submit">Submit</button>
</form>

JavaScript

$(function () {
    $('#unitDataForm').submit(function (e) {
        e.preventDefault();

        var formData = {
            'ajax_unit_id': $('input[name = unit_id]').val()
        };

        var seqCount = $('input[name="seqImg[]"]').length;
        
        //alert(seqCount);
        
            var si_array = $('input[name^="seqImg"]');
            var sd_array = $('textarea[name^="seqDesc"]');
        
        
        for (var i = 0; i < seqCount; i++) {
            //alert(i);
            
            var seq_image = 'ajax_seq_image['+i+']';
            var seq_desc = 'ajax_seq_desc['+i+']';
            var si=  si_array[i].value;
            var sd=  sd_array[i].value;
            
            //alert(seq_image+'<br>'+si);
            //alert(seq_desc+'<br>'+sd);
            
            //var seq_array = seq_image+':'+si+','+seq_desc+':'+sd+',';
            
            //alert(seq_array);
            
            formData.append(seq_image, si);
            formData.append(seq_desc, sd);
        }

        alert(formData);

        // ajax here
    });

});