  In this paper, a modified Maxwell's fish-eye lens is proposed in order to
achieve super-resolution imaging. This lens possesses elevated refractive index
profile compared with the traditional Maxwell's fish-eye lens. The refractive
index profile is achieved with variable thickness configuration defined in a
sheet plate structure, to realise desired changes in refractive indices. The
wave propagation behaviours and the full width at half maximum (FWHM) are
obtained from numerical simulations and experimental studies at the focal
region of the lens. Super-resolution imaging is observed in a broadband
frequency scope, with the FWHM around 0.2{\lambda} from 5 to 10 kHz. This work
provides a straightforward and flexible approach to the engineering of the MFEL
imaging characteristics and energy distributions for related applications.
