A focal point reflector is used in conjunction with a dual heterodyne circuit to reduce reception nulls that can occur when performing ultrasonic measurements. The focal plane reflector is a flat non-porous or reflective material, such as printed circuit board (PCB) that is placed behind and in parallel with an ultrasonic array of piezoelectric transducers. In accordance with the invention, the addition of the focal point reflector to the array of piezoelectric array permits the reflection of ultrasonic energy that may "fall" between the crystals in the array and then back into the crystal elements.