A new ultrasonic scanning system has been developed which is capable of accurate velocity measurements with high spatial resolution. This performance is achieved while using relatively low frequencies to minimize the cost of the instrument. A waveguide detector is used in place of the normal focused ultrasonic transducer. The waveguide receiver makes it possible to provide the needed spatial resolution without limitations imposed by the finite aperture of the transducer. An increase in the complexity of the signal processing required and reduced throughput of the instrument results from this approach. However, these disadvantages are amply compensated by the ability to investigate materials with high attenuation and low wave velocities. These measurements are not possible with traditional acoustic microscopes.