如何从xsi：type string中删除“xsd”？

I have created a SoapVar object:

new SoapVar($this->caseContainer(), SOAP_ENC_OBJECT, "CaseAmb", "http://www.w3.org/2001/XMLSchema")

This is the result:

<ns1:caseDto xsi:type="xsd:n3:CaseAmb">
    ...
</ns1:caseDto>

I would like to remove the xsd from xsi:type. For example:

<ns1:caseDto xsi:type="n3:CaseAmb">
    ...
</ns1:caseDto>

Can anyone suggest a way to do this?