*Corresponding author’s e-mail: hpkismet@unimas.my ASM Sc. J., 14, 2021 https://doi.org/10.32802/asmscj.2020.648 Breast Tumour Identification based on Chimera Overset Grid with Spline Interpolation in Forward-Backward Time-Stepping B.S.Wee 1, 2 , K.A.H.Ping 1∗ and S.Sahrani 1 1 Applied Electromagnetic Research Group, Department of Electrical & Electronic Engineering, Faculty of Engineering, Universiti Malaysia Sarawak, 94300 Kota Samarahan, Sarawak, Malaysia 2 Department of Electrical Engineering, Politeknik Mukah, 96400 Mukah, Sarawak, Malaysia Active microwave imaging (MI) technique has been recently recommended as a new technology for early detection of malignant breast tumours. Finite-difference Time-domain (FDTD) method is an effective numerical tool for computational electrodynamics modelling. However, the main drawback of the FDTD method is difficult to model the curved boundaries and small features of arbitrary shaped fibroglandular region due to its restriction to inherent orthogonal grids. To address this issue, Chimera Overset Grid (COG) method with spline interpolation in Forward-Backward Time- Stepping (FBTS) inverse scattering technique was proposed to overcome the limitation of FDTD method. In order to analyse the accuracy of this new method to detect a malignancy tumour embedded in different classes of breast parenchymal density, the homogeneous mostly fatty breast and extremely dense breast were chosen as Case A, and Case B, respectively. The Mean Squared Error (MSE) and normalised cost error functional for reconstructed dielectric profiles utilising the proposed method achieved significantly lower values than the FDTD method in FBTS inverse scattering. The results indicated that the proposed method could accurately identify malignancy tumour location and reconstruct the breast composition in dielectric profiles. Keywords: Chimera overset grid; biquadratic spline interpolation; breast tumour; inverse scattering I. INTRODUCTION Breast cancer is the most common cancer amongst women that causes death (Siegel et al., 2019). In 2019, the American Cancer Society reported that the new breast cancer cases are approximately 1,762,450 and 606,880 women will die from this disease (American Cancer Society, 2019). Early detection and diagnosis of breast cancer with the appropriate treatment is the key to recovery. Therefore, annual breast examination is important for early detection of malignant tumours. There are several types of breast screening techniques, such as X- ray mammography, breast ultrasound, Magnetic Resonance Imaging (MRI) and Scintimammography. X-ray mammography is currently an important and efficient technique tool by which to detect, diagnose and evaluate breast cancer (Radiological Society of North America Inc., 2019). However, this technique has several limitations due to difficulties in detecting breast tumours in their earlier stages especially for the dense breast tissue of young patients (Brennan & Houssami, 2016). It also suffers from a relatively high number of misses and false-detection rates (Tartar et al., 2008). It is an uncomfortable and perhaps painful process for patients due to the breast compression involved. Ionising radiations are released during the screening process (Hang et al., 2017). Therefore, microwave imaging (MI) technology has dreamed of using non-invasive, cost-effective, convenient, and non-ionizing electromagnetic waves to expose the human body for cancers detection (Wang, 2019). The last decade has