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 squarewave 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).