Design, Construction, and Characterization of the Ultra-Wideband (UWB) Directional Antennae for Biological Tissue Penetration
E Oh1*, S Han-Oh2, (1) U.S. Naval Research Lab, Washington, D.C., (2) Johns Hopkins University, Baltimore, MDSU-E-J-61 Sunday 3:00PM - 6:00PM Room: Exhibit Hall
Purpose: The need for non-invasive, non-ionizing, non-contact, and real-time technique to detect lung-tumor position during radiotherapy is an elusive feat. CT and MRI scans during radiotherapy are technically difficult and ultrasound cannot penetrate through the lung tissues. Recently, the development of the UWB radar promises a glimpse of hope in such an endeavor. Historically, the UWB was used to penetrate through walls and concrete for behind-the-wall imaging. Applying this technology to medical applications, as a first step, we investigate whether UWB can penetrate through biological tissues. For this purpose, we build and characterize uni-directional antennae to focus beam power and detect objects in free-space.
Methods:Our UWB system generating short pulses has omni-directional antenna elements. We changed to uni-directional beam by placing the element inside in-house built horn-antennae. A horn-antenna is an antenna that consists of a flaring-metal waveguide shaped like a horn to direct radio waves in a beam. We use waveguide theory to design the horn-antenna. After successful construction, we measure angular energy distribution in both the H-plane and the E-plane. The spatial resolution is measured from the time-of-arrival of the returned pulse reflected from an aluminum plate which is moved in 1-cm increment. Also, a small gold fiducial (0.1 cm by 1cm) is targeted for position detection.
Results:The in-house built uni-directional horn-antennae have beam widths containing >50% energy within for H-plane, and for E-plane at 3.5 GHz. The spatial resolution of the current system is 0.915 cm. However, with future electronics modification, the spatial resolution can improve to 0.03 cm. The gold fiducial is detected with SNR=8.
Conclusion:We built uni-directional horn-antenna and characterized angular beam width and spatial resolution. The system can detect a small size object such as gold fiducials with a high SNR. We will need further investigation to test penetration through biological tissues.