fig2

Figure 2. Representative designs and working principles of microwave biosensors for non-invasive and wearable monitoring. (A) Conceptual illustration and fabricated prototype of a portable radar-driven sensor employing a four-cell CSRR configuration for non-invasive blood glucose measurement from the fingertip. Reproduced with permission^[55]. Copyright 2020, Springer; (B) Fabrication process and structural schematic of a gated graphene microwave CPW sensor. Reproduced with permission^[63]. Copyright 2024, Wiley; (C) Design of a tunable, non-invasive, wearable electromagnetic multi-sensing system inspired by vascular anatomy, showing slot antenna and band-reject filter prototypes adapted for hand and arm glucose monitoring. Reproduced with permission^[76]. Copyright 2020, AAAS; (D) Schematic of a wearable, flexible, body-matched electromagnetic sensing system employing multi-sensing and multi-location detection to correlate reflected EM waves with blood glucose variations. Reproduced with permission^[77]. Copyright 2022, Springer. SMA: SubMiniature version A; PCB: printed circuit board; Rx: Receiver; Tx: Transmitter; CSRR: complementary split-ring resonator; PDMS: polydimethylsiloxane; CPW: coplanar waveguide; FR4: flame retardant 4; EM: electromagnetic; VNA: vector network analyzer.