Design and phantom testing of a bi-frequency co-linear array

Ultrasound imaging with high resolution and large penetration depth has been increasingly adopted in medical diagnosis, surgery guidance and treatment assessment. Conventional ultrasound works at a particular frequency, with -6 dB fractional bandwidth of ~ 70 %, limiting the resolution or penetration depth in many ultrasound imaging cases. In this paper, a bi-frequency co-linear array with a frequency range of 5 MHz - 20 MHz was investigated to meet the requirements of resolution and penetration depth for a broad range of ultrasound imaging applications. Specifically, a 32-element bi-frequency co-linear array was designed and fabricated, followed by element characterization and real time sectorial scan (S-scan) phantom imaging using a Verasonics system. The axial resolution and lateral resolution of low frequency mode was characterized to be better than 1 mm and 2 mm, respectively. For the high frequency mode, the axial resolution was found to be better than 0.5 mm and the lateral resolution was better than 1 mm.