A fractional harmonic excitation (FHE) method for high frequency array imaging

Described is a fractional harmonic excitation (FHE) technique suitable for imaging using ultrasound bipolar square-wave excitations. The technique differs from conventional imaging techniques as the transducer is excited using a harmonic within the excitation signal, as opposed to using the fundamental signal. As a consequence, the fundamental frequency of the FHE signal is designed at a fraction (1/3) of the intended output frequency. The advantages of the technique include a reduction in required output switching frequency and artificial extension of transmitter bandwidth. The technique is also capable of generating frequency modulated ‘chirp’ signals. Disadvantages of the technique include reduced output pressure due to excitation by a signal harmonic and potential for transducer heating. The work demonstrates that exciting the transducer in this fashion can produce coded and non-coded images. This is verified by imaging two non-destructive test phantoms using a custom imaging system (UARP, University of Leeds, UK).