Improvements to a method for imaging a target, which method including the
steps of (a) transmitting ultrasonic energy at a fundamental frequency,
(b) receiving reflected ultrasonic energy at a harmonic of the fundamental
frequency and (c) generating an image responsive to reflected energy at
the harmonic, are provided. The transmitting step includes transmitting a
waveform with a positive pulse spatially defined by first and second zero
values. A positive peak amplitude of the positive pulse is a first
distance from the first zero value that is less than half a second
distance between said first and second zero values. Thus, the waveform
includes a fundamental spectral component and a harmonic spectral
component at the transducer. An attenuation normalized peak of the
harmonic spectral component is reduced at a region spaced from the
transducer as compared to the peak at a region adjacent to the transducer.
A negative peak is also shifted or pre-distorted. Various pre-distortions
of the waveform may compensate for propagation, scattering, or system
non-linearities.