A compact and wideband MIMO antenna for high-data-rate biomedical ingestible capsules

Abstract

Abstract Due to recent advancements in complementary metal-oxide-semiconductor (CMOS) cameras, transferring high resolution images and videos are possible in wireless capsule endoscopy. High-data-rates communication is required for such data, which is possible using multiple-input-multiple-output (MIMO) antennas. In this paper, a low-sized, compact, high-data-rate, highly isolated two-element MIMO antenna with a large bandwidth has been proposed at 2.45 GHz for wireless capsule endoscopy. The geometry of the antenna ( $$5\times 4.2 \times 0.12\,\hbox {mm}^{3}$$ 5 × 4.2 × 0.12 mm 3 ) is kept small using meandered geometry, defected ground structure, and high permittivity of the substrate. A wider bandwidth of 620 MHz (2.15–2.77 GHz) is achieved by exciting dual-modes of the antenna using defected ground structure. Furthermore, a lower mutual coupling between the antennas (30.1 dB at 2.45 GHz) is realized, despite the small edge-to-edge gap of 0.5 mm, using combination of defected ground structure and I-shaped stub. Keeping in mind of system level configuration, this antenna is simulated and measured inside a capsule device by considering effects of the other components and the device itself. The practical measurements are performed by inserting the capsule device (containing the MIMO antenna) inside minced meat. To check the safety and effectiveness of the proposed MIMO antenna, it’s specific absorption rate (SAR) and link budget are calculated and validated. In addition, the $$2\times 2$$ 2 × 2 channel specifications are verified which shows satisfactory performance. This antenna has high channel capacity ( $$\approx 8.2 \,\hbox {bps/Hz}$$ ≈ 8.2 bps/Hz at $$\hbox {SNR} = 20 \,\hbox {dB}$$ SNR = 20 dB ) than single-input-single-output (SISO) antennas, thus, is a suitable choice for high-data-rate capsule endoscopic devices. To the best of the authors’ knowledge, this is the first implantable MIMO antenna reported so far with such lower dimension and wider bandwidth.