Advances in Miniaturized Implantable Antennas for Biomedical Telemetry: A Review and Comparative Analysis

The diversity of implantable medical devices (IMDs) has led to a variety of antenna topologies. The miniaturization of these antennas has consequences primarily affecting parameters such as the gain, penetration depth, and specific absorption rate (SAR), power handling and link margin. Given the increasing number and diversity of currently existing miniaturized implantable antenna topologies, it is time to synthesize the literature. In response to this need, this work groups recent designs into three topology classes: form-based, spatial-based, and function-based. This classification is necessary and useful as it allows for the evaluation of important design considerations. With the application of this classification, we identify the representative designs in each class and then compare them to identify future research directions. The representative form-based design achieves the smallest footprint (1.59 mm3) and offers circular polarization (CP), but it suffers from low realized gain (−30.1 to −31.9 dBi) and high SAR (439–534 W/kg), with experimental validation reported at an implantation depth of 4 mm in a tissue-equivalent head phantom. The representative spatial-based multiple-input multiple-output (MIMO) design improves isolation (31.78 dB) and supports higher data rates (120 Mbps) with moderate SAR (52.3 W/kg) at a reported depth of 50 mm in minced meat, but requires a larger footprint (5.6 mm3). In comparison, the representative functional-based duplexing design achieves a relatively high realized gain (−20.2 to −20.3 dBi), a validated implantation depth of 65 mm in minced meat, and high isolation (29.5 dB). Despite recent advances, implantable antenna performance remains constrained by tissue loss, SAR, miniaturization, isolation, flexible integration, and communication range. Yet link-budget analysis shows all topologies achieve a 5–20 m range at a 10 dB margin, confirming tissue loss and SAR as the overriding bottlenecks. To address these issues, it will be necessary to utilize the most advanced decoupling techniques, low-loss biocompatible materials, and performance-driven system optimization to develop safe, compact, high-performance implantable wireless systems for advanced biomedical telemetry applications.