The relationship of a low acoustic impedance material such as rubber, bonded to steel (high acoustic impedance) produces a radio frequency (RF) signal with a positive-going signal as seen in Image 1 below. When a dis-bond occurs, now rubber has a higher acoustic impedance than air, a 180 degree shift in the RF signal occurs as seen in image 2 and commonly referred to as phase reversal. This technique is well-known in the NDT ultrasonic testing community however, the operator must always be watching the display to find these disbonds.   With the latest ECHO software, the operator can now turn on "auto phase detect" on ECHO 7 gages and assign which polarity to arlarm on and the ECHO will change color and vibrate on alarm to alert the user.