Time Reversal Imaging

Object detection with electromagnetic (EM) waves has become a fast growing topic due to the nondestructive property of the EM method. A number of EM inversion methods, for example, the Born-type iterative methods and contrast-source inversion have been developed for microwave imaging technology. Applications, such as breast cancer diagnosis and screening, subsurface sensing and through-wall imaging shows very interesting abilities of EM waves. Wavenology EM can simulate such type of problems.
The time reversal method utilizes the reciprocity of wave propagation in a time-invariant medium to find the shape and the location of an object. The focusing quality in the time-reversal method is decided by the size of the effective aperture of transmitter-receiver array. This effective aperture includes the physical size of the transmitter-receiver array and the effect of the environment. A complicated background will create so-called multipath effect and can significantly increase the aperture of transmitter-receiver array. Take the following as an example.
A 3D microwave imaging chamber with an antenna array shown in Fig. 1 is set up. The antenna array is built on a rectangular chamber with 5 PCB panels and only open at the +Z direction. There are 8 Planar Inverted F Antennas (PIFA) fabricated on each panel, hence totally 32 antennas in the chamber. Fig. 2(a) shows the structure of the PIFA antenna. Fig. 2(b) shows the layout of the antennas on one panel. All antennas share the same ground to isolate the noise from the environment. Each antenna is fed by a wave port on the coax. The wave ports are indexed from 1 to 32. The object under test is a center hollowed cube, placed at the center of the chamber, the 2D and 3D imaging results generate through Wavenology EM simulation are shown in Fig. 3 and Fig. 4. For more details about how to setup this simulation in Wavenology EM, check Wavenology EM Tutorial (Time Reversal Imaging)


Fig. 1. Structure of the chamber.

(a) (b)

Fig. 2. (a) Structure of the PIFA. (b) Antenna array at one side of the chamber.

Fig. 3. A center hollowed box was put into the chamber.

Fig. 4. Image obtained after the processing.

Through this example, it is concluded that Wavenology EM can accurately simulate the near scattered field and setup complicated configured RF devices to get scattering data which is normally obtained from expensive experiments. Using the software tool can significantly reduce the cost and enhance the efficiency when researching about advanced EM imaging algorithms or related principles.