An ultrasonic test apparatus includes a container containing de-ionized water, a pressing member, a supporting member, and a fixing member. The air delivery system includes a PAP device having a flow generator, a patient interface, a processor and a connector, and at least a removable sensing device having at least a sensor, a front-end analog circuit and a connector. The voltage applied to the inner and outer electrodes 11, 25 can be varied independently an allows tissue underlying the device to be treated. The axial locking feature may comprise an integral annular ridge provided on one sleeve that cooperates with an annular groove provided on the other sleeve. This abstract is intended as a scanning tool for purposes of searching in the particular art and is not intended to be limiting of the present invention.