A Tissue-Independent Flexible Antenna With Miniaturized Size for Injectable Implants

This letter introduces a new implantable antenna operating at the Industrial, Scientific, and Medical (ISM) 2.4–2.4835 GHz band for use in muscle and fat. The antenna design comprises an unsymmetric dipole with a rectangular ground plane and a side-fed radiator. The radiator consists of a step-shaped feedline and two wound arms of different lengths. The longer arm excites a first resonance at 2.46 GHz in fat and a second resonance at 2.85 GHz in muscle. The shorter arm is added to tune the second resonance to 2.48 GHz. The measured bandwidths in muscle and fat are 2.12–2.68 GHz and 2.23–2.62 GHz, respectively. The transmission performance between the inner and external bodies is examined using a receiving antenna placed outside the body, achieving a maximum transmission coefficient of −29.1 dB at 2.45 GHz. The proposed implantable antenna is printed on a 70 μm thick polyimide substrate with a small 2 × 7 mm² footprint. Its narrow width, ultrathin thickness, and flexibility make it suitable for use in injectable minimally invasive implantations.