A sensor for detecting poor interlaminar bonding between a topmost ply and composite substrate was developed and validated. The sensor was designed for the specific application of real time process control for in situ consolidation processes, such as thermoplastic tow placement. The sensor design consists of two piezoelectric transducers oriented in a pitch catch arrangement. The transmitting transducer is angled so as to produce surface waves in the composite panel. These waves interact with defects at the top ply/substrate interface. The received signal was analyzed for wave speed, attenuation and energy dissipation (power spectral density). Experimental validation of the sensor is presented. Several composite panels were made under various manufacturing conditions so as to create poor interlaminar bonding at the topmost ply. Interlaminar bonding was then evaluated by destructive and nondestructive measures. There was good agreement between the destructive and nondestructive measures of top ply bond strength.