A Method for Measuring the Directional Response of Ultrasound Receivers in the Range 0.3–80 MHz Using a Laser-Generated Ultrasound Source

A simple method for measuring the directivity of an ultrasound receiver is described. The method makes use of a custom-designed laser ultrasound source which generates a large diameter (>1 cm) broadband monopolar plane wave with a continuous frequency content extending from ≤330 kHz to ≈80 MHz. The plane wave is highly uniform in amplitude (±5% over >8 mm) and phase (equivalent to <;λ/7 at 80 MHz over ≥11 mm). To measure directivity, the source is rotated around the receiver under test in a compact centimeter-scale setup. To demonstrate the method, it was used to measure the directivity of two broadband small aperture Fabry-Perot ultrasound sensors over an angular range of ±50° at frequencies up to 80 MHz. Measurements were found to be highly repeatable with an estimated typical repeatability <;4% in the range of 0.5-25 MHz. Due to the broad bandwidth, large size, and adjustable nature of the source, the method is widely applicable and could aid the characterization of receivers used in medical ultrasound, ultrasonic nondestructive testing. and ultrasound metrology.