An ultrasonic blood flow sensor includes a plurality of adjacent triangular shaped transducer elements which transmit ultrasound waves into a blood vessel and receive reflected ultrasound waves from the blood flow in the vessel. Preferably the transducer elements are paired in pairs of transmit and receive elements. The elements are fixed in a matrix which may be attached in acoustic coupling contact with the skin The matrix retains adjacent transducer elements slightly spaced apart so that the matrix of transducer elements may bend and conform to the shape of the skin surface. The spacing between the triangular elements is neither parallel nor orthogonal to the length dimension of the matrix so that a blood vessel will not be aligned with a space between transducer elements when the matrix is affixed across the location of a blood vessel. In addition the geometry of the elements creates a beam pattern that provide more overlap between transmit and receive beam profiles, thereby increasing the area of sensor coverage.