This communication proposes miniaturized implantable antenna systems for biomedical applications, specifically for scalp implantation. The proposed designs exhibit dual-band characteristics on the Industrial, Scientific, and Medical (ISM) bands (i.e. 915 MHz and 2450 MHz) with small volumes: 344 mm3 (System A) and 406 mm3 (System B). Each system is integrated with the microelectronic components and a battery. The key feature of the proposed implantable antenna is its small volume (8 ×6 ×0.5 = 24 mm3) with a slotless and a vialess ground plane, thereby reducing design complexity. Moreover, the structure exhibits satisfactory peak gain values of -28.5 dBi and -22.8 dBi at a lower and higher resonant band, respectively. Simulations using the finite element method (FEM) and finite-difference time-domain (FDTD) are performed to evaluate the implantable systems. For validation, measurements are carried out in a saline solution. The antenna offers a good agreement between the measured and simulated results. In addition, a link budget is calculated to analyze the data transmission range.

Wireless power transfer (WPT) is a promising technology for enabling the long-term operation of advanced implantable medical devices (IMDs). This article presents a highly efficient near-field WPT system for wirelessly driven or rechargeable miniaturized IMDs, comprising an off-body transmitter (Tx), a flexible on-body mu-negative (MNG) metasurface slab, and an in-body receiver (Rx). The Rx element with dimensions 7.5 $\times$ 7.15 $\times$ 0.75 mm $^3$ exhibits dual-band characteristics (i.e., 433 and 915 MHz) for simultaneous wireless power reception and data telemetry. The flexible MNG slab serves as a wearable device, focusing the magnetic field toward the Rx, thereby increasing the efficiency of the proposed WPT system. Simulation and measurements are conducted to analyze the systems performance. Interestingly, the MNG-coupled WPT system offered significant improvement in the power transmission efficiency (PTE) in various realistic scenarios, including misalignments and varying Tx–Rx separations. Remarkably, an increment of approximately 17% is achieved in the PTE from 3.37% to 20.36% at a 10 mm distance. In addition, a wireless communication link analysis is conducted to specify the range for biotelemetry. Moreover, a compact rectenna system is developed incorporating a rectifier with a power conversion efficiency (PCE) of 73.7% at 6 dBm input power. Simulation and real-time experimental results demonstrate the effectiveness of the proposed flexible metasurface-coupled WPT system for compact implantable biotelemetric devices.

This study proposes a miniaturized dual-band antenna with a circular-polarization (CP) characteristic for a wireless capsule endoscopic system operating in the industrial, scientific, and medical bands: 915 and 2450 MHz. The proposed capsule device is intended for deep-tissue implantation with the standard dimensions of 26 × 11 mm2. The key features of the proposed antenna are its CP characteristic at both bands, satisfactory gain values, and a smallest volume (6.5 × 6.5 × 0.05 = 2.11 mm3) with a via-less ground plane compared with the state-of-the-art device. The CP wave performance and the miniaturization of the antenna are achieved via the introduction of slots accompanied by meandered line segments in a radiating patch and open-end slots in a ground plane. Furthermore, the proposed antenna offers a reasonable axial ratio (AR) of < 3 dB at the desired frequency bands. The circularly polarized radiator attains AR bandwidths (BW) of 33.0% and 8.67% and measured 10 dB impedance BWs of 13.63% and 6.28% at 915 and 2450 MHz, respectively. The measurements of the reflection coefficient and radiation pattern are performed using a fabricated prototype of the proposed antenna system in a saline solution and minced pork. Finally, the safety considerations and link budget calculations are evaluated to analyze the performance of the proposed capsule device. Owing to the AR BW, impedance BW, and ease of fabrication, the proposed antenna system is suitable candidate for use in endoscopic applications.

Monitoring of elevated intracranial pressure (ICP) is a lifesaving procedure. This article presents an ultrasmall batteryless implantable system for ICP monitoring comprising an off-body power transmitter (Tx) and in-body biotelemetric receiver (Rx). Due to the small implantable antenna (5.6 mm x 6 mm x 0.2 mm = 6.72 mm³), the device exhibits dual-band characteristics (i.e., 915 and 1900 MHz) for simultaneous power transmission and data telemetry. The implant is powered wirelessly in the radiative near field (1900 MHz) for enhanced power transfer efficiency (PTE). Moreover, the structure demonstrates the measured peak gain values of -26.8 and -18.8 dBi with the impedance-matched bandwidths of 9.83% and 27.9% at 915 and 1900 MHz, respectively. The wireless PTE of the device was also analyzed in terms of distance variations, and a maximum PTE up to -25.9 dB at 20 mm (0.1267λ) Tx-Rx separation was achieved. The rectifier attained a maximum power conversion efficiency of 82% at 2-dBm input power. Simulations using the finite-element method and finite difference time domain were performed to evaluate the biotelemetric implantable system. For validation, measurements were conducted in a saline-filled human head phantom, as well as in minced pork. The biotelemetric system yields good agreement between the measured and simulation results.

Compact implantable medical devices (IMDs) require miniaturized and multiband antennas to efficiently navigate space limitations and diverse frequency demands in biomedical applications. This paper proposes an ultra-miniaturized implantable antenna featuring the smallest footprint with a volume of 0.7 mm ³ and exhibits quad-band characteristics: telemetry at 915 MHz, wireless power transfer at midfield bands of 1450 and 1900 MHz, and control signaling at 2450 MHz. Extensive simulation analyses were conducted for the antenna alone and integrated antenna systems to realize the versatility of the proposed antenna. For validation, measurements were performed in saline-filled realistic head and American Society for Testing and Materials phantoms. Good agreement between the simulation and measured results was observed. The antenna showed stable performance in all scenarios with a measured -10 dB bandwidth of 136, 122, 108, and 134 MHz at 915, 1450, 1900, and 2450 MHz, respectively. Moreover, the antenna exhibited satisfactory measured gain values of -27.45, -23.25, -23.14, and -22.48 dBi at the respective frequency bands. Finally, the implementation of the wireless biotelemetry feature of the proposed antenna system was achieved and demonstrated through the utilization of a pair of software-defined radios. Sustainable and stable wireless data transmission characteristics were shown at transmission distances of up to 2.5 m. With its remarkable features, the proposed antenna addresses the critical need for efficient communication in the Industrial Internet of Medical Things (IIoMT) devices, enabling telemetry, wireless power transfer, and control signaling in biomedical applications with limited space and diverse frequency demands.

This article for the “Bioelectromagnetics” column takes a deep dive into the field of wireless implants and ingestibles, with a focus on antenna design. The review discusses recent advances in implantable/ingestible antenna design, provides a protocol for the successful design of such antennas, and concludes with an overview of the wide range of real-world applications that may benefit from this research area.