Neural implants have emerged over the last decade as highly effective solutions for the treatment of dysfunctions and disorders of the nervous system. These implants establish a direct, often bidirectional, interface to the nervous system, both sensing neural signals and providing therapeutic treatments. As a result of the technological progress and successful clinical demonstrations, completely implantable solutions have become a reality and are now commercially available for the treatment of various functional disorders. Central to this development is the wireless power transfer (WPT) that has enabled implantable medical devices (IMDs) to function for extended durations in mobile subjects. In this review, we present the theory, link design, and challenges, along with their probable solutions for the traditional near-field resonant inductively coupled WPT, capacitively coupled short-ranged WPT, and more recently developed ultrasonic, mid-field, and far-field coupled WPT technologies for implantable applications. A comparison of various power transfer methods based on their power budgets and WPT range follows. Power requirements of specific implants like cochlear, retinal, cortical, and peripheral are also considered and currently available IMD solutions are discussed. Patient's safety concerns with respect to electrical, biological, physical, electromagnetic interference, and cyber security from an implanted neurotech device are also explored in this review. Finally, we discuss and anticipate future developments that will enhance the capabilities of current-day wirelessly powered implants and make them more efficient and integrable with other electronic components in IMDs.

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In this study, a compact, triple‐band, circularly polarised stacked microstrip antenna is proposed over the artificial eta‐surface called reactive impedance surface (RIS) for enhancing antenna radiation efficiency for GPS applications. The proposed design utilises the concept of combining multi‐stacked patches with RIS as imaginary‐impedance metamaterial‐ground‐plane for selective frequency reduction of lower bands with improvement in antenna radiation properties for multi‐band applications. The circularly polarised (CP) radiation with compact antenna size is achieved for triple‐band GPS frequencies of L1 (1.575 GHz), L2 (1.227 GHz) and L5 (1.176 GHz) by placing three stacked patches with two different pairs of symmetric slits, four different sized symmetric cross‐shaped slots and truncated corners over RIS. As RIS meta‐surface reduces the wave penetration through the lossy substrate beneath it, the proposed stacked patch antenna over RIS demonstrates enhanced forward gain with suppressed back radiation. The measured results for antenna prototype are (1.168–1.185 GHz): L5 band, (1.2–1.245 GHz): L2 band and (1.51–1.59 GHz): L1 band for 10 dB return loss bandwidth with good CP radiation. Forward (boresight) right‐handed CP gain of 2.88 dBic (L5 band), 3.25 dBic (L2 band) and 5.53 dBic (L1 band) is observed for compact antenna overall volume of 0.32λo × 0.32λo × 0.024λo at 1.2 GHz.

Neuromodulation of peripheral nerves with bioelectronic devices is a promising approach for treating a wide range of disorders. Wireless powering could enable long-term operation of these devices, but achieving high performance for miniaturized and deeply placed devices remains a technological challenge. We report the miniaturized integration of a wireless powering system in soft neuromodulation device (15 mm length, 2.7 mm diameter) and demonstrate high performance (about 10%) during in vivo wireless stimulation of the vagus nerve in a porcine animal model. The increased performance is enabled by the generation of a focused and circularly polarized field that enhances efficiency and provides immunity to polarization misalignment. These performance characteristics establish the clinical potential of wireless powering for emerging therapies based on neuromodulation.

The reflection coefficient phase is studied for four different artificial magnetic conductors (AMCs) having canonical frequency selective surface (FSS)‐type two‐dimensional periodic structures to be used as back reflectors for an aperture antenna. The bidirectional circularly polarised (CP) radiation of the octagonal‐shaped aperture (OSA) antenna is made unidirectional using these AMC surfaces as ground planes. The antenna height measured from the upper surface of AMC reflector to the OSA radiator is chosen to be small to realise low‐profile antenna: 0.0825λo at the lowest analysis frequency of 4.5 GHz. Different antenna parameters like voltage standing wave ratio (VSWR) of 2, 3‐dB axial ratio (AR) bandwidth, gain, and front‐to‐back ratio are studied and compared for these four AMCs and the conventionally used perfect electric conductor (PEC) ground plane as back reflectors. Four different aperture shapes with fixed aperture perimeter are designed to integrate with the square‐loop AMC as back reflector to realise a low‐profile unidirectional wideband CP aperture antenna. Hexagonal‐shaped aperture antenna over the square‐loop AMC shows the largest measured 3‐dB AR bandwidth of 23.33% (5.65–7.05 GHz), VSWR of 2 bandwidth of 36.67% (5.16–7.36 GHz), and the gain of around 7 dBic over the band for overall antenna volume of 0.72λo × 0.60λo × 0.19λo at 6.0 GHz.