A non-linear response may be measured by transmitting a first pulse at an amplitude and transmit frequency, using an aperture having N elements. A first response is measured at a sub-harmonic frequency based on the transmit frequency. At least second and third pulses are transmitted at the amplitude and transmit frequency. At least second and third responses are measured at the sub-harmonic frequency. The second and third pulses have the same phase with respect to each other and use first and second sub-apertures that have different ones of the N elements. A sum of the elements within the first and second sub-apertures is equal to N. Alternatively, at least two pulses having the same aperture and different amplitudes may be transmitted, and the responses measured at the sub-harmonic frequency. The responses are combined to suppress linear echoes and determine a non-linear response.
