Implantable antennas for biomedical applications: a systematic review

This review presents an in-depth examination of implantable antennas for various biomedical purposes. The development of implantable antennas, including their designs, materials, and operating principles, are introduced at the beginning of the discussion. An overview of the many kinds of implantable antennas utilized in implantable medical devices (IMDs) are presented in this study. The article then discusses the important factors to consider when developing implantable antennas for biomedical purposes, including implant placement, frequency range, and power needs. This investigation additionally examines the challenges and limitations encountered with implantable antennas, including the limited space available within the human body, the requirement for biocompatible materials, the impact of surrounding tissue on antenna performance, tissue attenuation, and signal interference. This review also emphasizes the most recent advances in implanted antenna technology, such as wireless power transmission, multiband operation, and miniaturization. Furthermore, it offers illustrations of several biomedical uses for implantable antennas, including pacemaker, capsule endoscopy, intracranial pressure monitoring, retinal prostheses, and bone implants. This paper concludes with a discussion of the future of implantable antennas and their possible use in bioelectronic medicine and novel medical implants. Overall, this survey offers a thorough analysis of implantable antennas in biomedical applications, emphasizing their importance in the development of implantable medical technology.

Design of a miniaturized dual circularly polarized implantable antenna by using characteristic mode method

The characteristic mode method is used to design a miniaturized dual-band dual circularly polarized (CP) implantable antenna operating in ISM bands. The miniaturization and dual-band characteristics are gained by using the slotting method and by inserting a short-circuit probe between the radiation patch and the ground plane. We use the characteristic mode method to study the current distribution of circular radiation patches with T-shaped slots in different modes. After opening a cross-shaped slot at the center of the radiation patch and the ground plane, we obtained two orthogonal modes with equal amplitude and phase difference of 90° in two operating frequency bands, ultimately achieving CP characteristics of the antenna. Its overall size is only π ×(0.014 λ 0)2 × 0.0027 λ 0, smaller than other CP implantable antennas with similar performances, and it has satisfactory radiation efficiency and gain characteristics. Measurements show that it can operate in the ISM bands of 0.9 and 2.4 GHz with an effective 3 dB axial ratio bandwidth greater than 220 MHz (0.87 to 1.09 GHz, 22.45%) and 230 MHz (2.31 to 2.54 GHz, 9.48%), and its peak gain is - 29.5 dBi and - 19.2 dBi, respectively. And, this design complies with IEEE safety guidelines.

A Robust BLE-compatible Wake-up Receiver for Ingestible Device with In-vivo Evaluation

In the evolving field of biomedical engineering, ingestible devices have emerged as pivotal tools for healthcare monitoring within the human gastrointestinal (GI) tract. This paper addresses challenges in communication, emphasizing the selection of the 2.4 GHz band and proposing a Bluetooth Low Energy (BLE)-compatible wake-up receiver (WuRx) operating at 2.48 GHz that validates with the in-vivo test. An LNA-first receiver is used to counter signal loss within the GI tract and achieves -81 dBm of sensitivity. The proposed design incorporates a low-power single clock chain with a Film Bulk Acoustic Resonator (FBAR) and a duty cycling scheme for reducing power consumption. The average power with 1% duty cycling ratio is 0.11 µW. This work introduces the first BLE-compatible WuRx for low power ingestible devices, demonstrating the potential for diverse medical applications.

Realistic 3D Phantoms for Validation of Microwave Sensing in Health Monitoring Applications

The development of new medical-monitoring applications requires precise modeling of effects on the human body as well as the simulation and the emulation of realistic scenarios and conditions. The first aim of this paper is to develop realistic and adjustable 3D human-body emulation platforms that could be used for evaluating emerging microwave-based medical monitoring/sensing applications such as the detection of brain tumors, strokes, and breast cancers, as well as for capsule endoscopy studies. New phantom recipes are developed for microwave ranges for phantom molds with realistic shapes. The second aim is to validate the feasibility and reliability of using the phantoms for practical scenarios with electromagnetic simulations using tissue-layer models and biomedical antennas. The third aim is to investigate the impact of the water temperature in the phantom-cooking phase on the dielectric properties of the stabilized phantom. The evaluations show that the dielectric properties of the developed phantoms correspond closely to those of real human tissue. The error in dielectric properties varies between 0.5-8%. In the practical-scenario simulations, the differences obtained with phantoms-based simulations in S21 parameters are 0.1-13 dB. However, the differences are smaller in the frequency ranges used for medical applications.

Radiation Patterns of RF Wireless Devices Implanted in Small Animals: Unexpected Deformations Due to Body Resonance

One challenge in designing RF wireless bioelectronic devices is the impact of the interaction between electromagnetic waves and host body tissues on far-field wireless performance. In this article, we investigate a peculiar phenomenon of implantable RF wireless devices within a small-scale host body related to the deformation of the directivity pattern. Radiation measurements of subcutaneously implanted antennas within rodent cadavers show that the direction of maximum radiation is not always identical with the direction to the closest body-air interface, as one would expect in larger-scale host bodies. For an implanted antenna in the back of a mouse, we observed the maximum directivity in the ventral direction with 4.6 dB greater gain compared to the nearest body-air interface direction. Analytic analysis within small-scale spherical body phantoms identifies two main factors for these results: the limited absorption losses due to the small body size relative to the operating wavelength and the high permittivity of the biological tissues of the host body. Due to these effects, the entire body acts as a dielectric resonator antenna, leading to deformations of the directivity pattern. These results are confirmed with the practical example of a wirelessly powered 2.4-GHz optogenetic implant, demonstrating the significance of the judicious placement of external antennas to take advantage of the deformation of the implanted antenna pattern. These findings emphasize the importance of carefully designing implantable RF wireless devices based on their placements and relative electrical dimensions in small-scale animal models.

The Secret Lives of Miniature Batteries

This article describes the design, implementation, and use of a new system to investigate the behavior of small batteries that power sensor and wireless systems that consume relatively high power during infrequent short activity periods. The system enables simple, low-cost, long-term (days to weeks) monitoring of batteries under such loads. Data collected by this system revealed a major cause of failures in wildlife tracking tags, an effect called concentration polarization, which causes a transient increase in the internal resistance of the battery. The article describes the goals and the design of the system, failures that it revealed, mechanisms to mitigate the limitations of miniature batteries, as well as a methodology to optimize and validate the design of tags powered by miniature batteries.

A Comprehensive Review of In-Body Biomedical Antennas: Design, Challenges and Applications

In-body biomedical devices (IBBDs) are receiving significant attention in the discovery of solutions to complex medical conditions. Biomedical devices, which can be ingested, injected or implanted in the human body, have made it viable to screen the physiological signs of a patient wirelessly, without regular hospital appointments and routine check-ups, where the antenna is a mandatory element for transferring bio-data from the IBBDs to the external world. However, the design of an in-body antenna is challenging due to the dispersion of the dielectric constant of the tissues and unpredictability of the organ structures of the human body, which can absorb most of the antenna radiation. Therefore, various factors must be considered for an in-body antenna, such as miniaturization, link budget, patient safety, biocompatibility, low power consumption and the ability to work effectively within acceptable medical frequency bands. This paper presents a comprehensive overview of the major facets associated with the design and challenges of in-body antennas. The review comprises surveying the design specifications and implementation methodology, simulation software and testing of in-body biomedical antennas. This work aims to summarize the recent in-body antenna innovations for biomedical applications and indicates the key research challenges.

Fiber-Optic Intracranial Pressure Monitoring System Using Wi-Fi-An In Vivo Study

BACKGROUND

Continuous invasive monitoring of intracranial pressure (ICP) is essential in neurocritical care for surveillance and management of raised ICP. Fluid-based systems and strain gauge microsensors remain the current standard. In the past few decades, several studies with wireless monitoring were developed aiming to reduce invasiveness and complications.

OBJECTIVE

To describe a novel Wi-Fi fiber-optic device for continuous ICP monitoring using smartphone in a swine model.

METHODS

Two ICP sensors (wireless prototype and wire-based reference) were implanted in the cerebral parenchyma of a swine model for a total of 120 minutes of continuous monitoring. Every 5 minutes, jugular veins compression was performed to evaluate ICP changes. The experimentation was divided in 3 phases for comparison and analysis.

RESULTS

Phase 1 showed agreement in ICP changes for both sensors during jugular compression and releasing, with a positive and strong Spearman correlation (r = 0.829, P < .001). Phase 2 started after inversion of the sensors in the burr holes; there was a positive and moderately weak Spearman correlation (r = 0.262, P < .001). For phase 3, the sensors were returned to the first burr holes; the prototype behaved similarly to the reference sensor, presenting a positive and moderately strong Spearman correlation (r = 0.669, P < .001).

CONCLUSION

A Wi-Fi ICP monitoring system was demonstrated in a comprehensive and feasible way. It was possible to observe, using smartphone, an adequate correlation regarding ICP variations. Further adaptations are already being developed.

Future regenerative medicine developments and their therapeutic applications

Although the currently available pharmacological assays can cure most pathological disorders, they have limited therapeutic value in relieving certain disorders like myocardial infarct, peripheral vascular disease, amputated limbs, or organ failure (e.g. renal failure). Pilot studies to overcome such problems using regenerative medicine (RM) delivered promising data. Comprehensive investigations of RM in zebrafish or reptilians are necessary for better understanding. However, the precise mechanisms remain poorly understood despite the tremendous amount of data obtained using the zebrafish model investigating the exact mechanisms behind their regenerative capability. Indeed, understanding such mechanisms and their application to humans can save millions of lives from dying due to potentially life-threatening events. Recent studies have launched a revolution in replacing damaged human organs via different approaches in the last few decades. The newly established branch of medicine (known as Regenerative Medicine aims to enhance natural repair mechanisms. This can be done through the application of several advanced broad-spectrum technologies such as organ transplantation, tissue engineering, and application of Scaffolds technology (support vascularization using an extracellular matrix), stem cell therapy, miRNA treatment, development of 3D mini-organs (organoids), and the construction of artificial tissues using nanomedicine and 3D bio-printers. Moreover, in the next few decades, revolutionary approaches in regenerative medicine will be applied based on artificial intelligence and wireless data exchange, soft intelligence biomaterials, nanorobotics, and even living robotics capable of self-repair. The present work presents a comprehensive overview that summarizes the new and future advances in the field of RM.

Complete Breast Cancer Detection and Monitoring System by Using Microwave Textile Based Antenna Sensors

This paper presents the development of a new complete wearable system for detecting breast tumors based on fully textile antenna-based sensors. The proposed sensor is compact and fully made of textiles so that it fits conformably and comfortably on the breasts with dimensions of 24 × 45 × 0.17 mm³ on a cotton substrate. The proposed antenna sensor is fed with a coplanar waveguide feed for easy integration with other systems. It realizes impedance bandwidth from 1.6 GHz up to 10 GHz at |S₁₁| ≤ -6 dB (VSWR ≤ 3) and from 1.8 to 2.4 GHz and from 4 up to 10 GHz at |S₁₁| ≤ -10 dB (VSWR ≤ 2). The proposed sensor acquires a low specific absorption rate (SAR) of 0.55 W/kg and 0.25 W/kg at 1g and 10 g, respectively, at 25 dBm power level over the operating band. Furthermore, the proposed system utilizes machine-learning algorithms (MLA) to differentiate between malignant tumor and benign breast tissues. Simulation examples have been recorded to verify and validate machine-learning algorithms in detecting tumors at different sizes of 10 mm and 20 mm, respectively. The classification accuracy reached 100% on the tested dataset when considering |S21| parameter features. The proposed system is vision as a "Smart Bra" that is capable of providing an easy interface for women who require continuous breast monitoring in the comfort of their homes.

A Multilevel Synchronized Optical Pulsed Modulation for High Efficiency Biotelemetry

The paper describes the design, implementation, and characterization of a novel multilevel synchronized pulse position modulation paradigm for high efficiency optical biotelemetry links. The entire optoelectronic architecture has been designed with the aim to improve the efficiency of the data transmission and decrease the overall power consumption that are key factors for the fabrication of implantable and wearable medical devices. By employing specially designed digital architectures, the proposed modulation technique automatically transmits more than one bit per symbol together with the reference clock signal enabling the decoding process of the received coded data. In the present case, the paper demonstrates the capability of the modulation technique to transmit symbols composed by 3 and 4 bits. This has been achieved by developing a prototype of an optical biotelemetry system implemented on an FPGA board that, making use of 500 ps laser pulses, operates under the following two working conditions: (i) 40 MHz clock signal corresponding to a baud rate of 40 Mega symbol per second for symbols composed by 3 bits; (ii) 30 MHz clock signal corresponding to a baud rate of 30 Mega symbol per second for symbols composed by 4 bits. Thus, for both these two configurations the transmission data rate is 120 Mbps and the measured BER was lower than 10^-10. Finally, the power consumption was found to be 1.95 and 1.8 mW and the resulting energy efficiencies were 16.25 and 15 pJ/bit for transmitted symbols composed by 3 and 4 bits/symbol, respectively.

A Survey on Wireless Wearable Body Area Networks: A Perspective of Technology and Economy

The deployment of wearable or body-worn devices is increasing rapidly, and thus researchers' interests mainly include technical and economical issues, such as networking, interoperability, security, power optimization, business growth and regulation. To address these issues properly, previous survey papers usually focused on describing the wireless body area network architecture and network protocols. This implies that deployment issues and awareness issues of wearable and BAN devices are not emphasized in previous work. To defeat this problem, in this study, we have focused on feasibility, limitations, and security concerns in wireless body area networks. In the aspect of the economy, we have focused on the compound annual growth rate of these devices in the global market, different regulations of wearable/wireless body area network devices in different regions and countries of the world and feasible research projects for wireless body area networks. In addition, this study focuses on the domain of devices that are equally important to physicians, sportsmen, trainers and coaches, computer scientists, engineers, and investors. The outcomes of this study relating to physicians, fitness trainers and coaches indicate that the use of these devices means they would be able to treat their clients in a more effective way. The study also converges the focus of businessmen on the Annual Growth Rate (CAGR) and provides manufacturers and vendors with information about different regulatory bodies that are monitoring and regulating WBAN devices. Therefore, by providing deployment issues in the aspects of technology and economy at the same time, we believe that this survey can serve as a preliminary material that will lead to more advancements and improvements in deployment in the area of wearable wireless body area networks. Finally, we present open issues and further research direction in the area of wireless body area networks.

A Review of Digital Health and Biotelemetry: Modern Approaches towards Personalized Medicine and Remote Health Assessment

With the prevalence of digitalization in all aspects of modern society, health assessment is becoming digital too. Taking advantage of the most recent technological advances and approaching medicine from an interdisciplinary perspective has allowed for important progress in healthcare services. Digital health technologies and biotelemetry devices have been more extensively employed for preventing, detecting, diagnosing, monitoring, and predicting the evolution of various diseases, without requiring wires, invasive procedures, or face-to-face interaction with medical personnel. This paper aims to review the concepts correlated to digital health, classify and describe biotelemetry devices, and present the potential of digitalization for remote health assessment, the transition to personalized medicine, and the streamlining of clinical trials.

Lithium Niobate Piezoelectric Micromachined Ultrasonic Transducers for high data-rate intrabody communication

In recent years, there has been an increased interest in continuous monitoring of patients and their Implanted Medical Devices (IMDs) with different wireless technologies such as ultrasounds. This paper demonstrates a high data-rate intrabody communication link based on Lithium Niobate (LN) Piezoelectric Micromachined Ultrasonic Transducers (pMUTs). The properties of the LN allow to activate multiple flexural mode of vibration with only top electrodes. When operating in materials like the human tissue, these modes are merging and forming a large communication bandwidth. Such large bandwidth, up to 400 kHz, allows for a high-data rate communication link for IMDs. Here we demonstrate a full communication link in a tissue phantom with a fabricated LN pMUT array of 225 elements with an area of just 3 by 3 mm square, showing data-rates up to 800 kbits/s, starting from 3.5 cm and going up to 13.5 cm, which covers the vast majority of IMDs.

This paper demonstrates Lithium Niobate based Piezoelectric Micromachined Ultrasonic Transducers. The devices allow activation of multiple vibration modes, achieve a high communication link, and monitor an implanted medical device up to 13.5 cm inside the body.

Thermoresponsive Gelatin/Chitosan Hydrogel Films for a Degradable Capacitor

Ingestible electronic devices are tools for exploring the condition of the gastrointestinal tract and adjacent organs without a burden on the patients. Making them safe requires that they be fabricated with harmless materials. In this study, we developed a capacitor using food materials for a wireless sensing component. As a safer approach, gelatin, an ingredient responsive to external stimuli, was selected as a substrate for deforming the device at the desired time. Gelatin experiences sol-gel changes near body temperature; however, it is instantly dissolved and is not suitable for long-term use in the body. Thus, to maintain its thermal responsiveness, we used a tangle of gel networks created by mixing gelatin and chitosan without cross-linking agents. Our search for the appropriate gel mixing ratio provided insights into the criteria for achieving slow sol-gel changes and how to improve the thermal durability. We transferred a sputtered gold film onto the gel films to produce electrodes and then made a capacitor by sandwiching a naturally dried sodium polyacrylate film between the electrodes. The resonance frequency measurement of RLC circuits in combination with commercial plane coils showed that the capacitor worked in the megahertz band and that it collapsed when immersed in hot water. Gastric acid detection was also achieved with this capacitor. This electronic part will contribute to the development of implanted or ingestible medical devices and a wide range of environmental sensors composed of natural ingredients.

Recent Advances in Wearable Sensing Technologies

Wearable sensing technologies are having a worldwide impact on the creation of novel business opportunities and application services that are benefiting the common citizen. By using these technologies, people have transformed the way they live, interact with each other and their surroundings, their daily routines, and how they monitor their health conditions. We review recent advances in the area of wearable sensing technologies, focusing on aspects such as sensor technologies, communication infrastructures, service infrastructures, security, and privacy. We also review the use of consumer wearables during the coronavirus disease 19 (COVID-19) pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and we discuss open challenges that must be addressed to further improve the efficacy of wearable sensing systems in the future.

Ultrasound-Powered Implants: A Critical Review of Piezoelectric Material Selection and Applications

Ultrasound-powered implants (UPIs) represent cutting edge power sources for implantable medical devices (IMDs), as their powering strategy allows for extended functional lifetime, decreased size, increased implant depth, and improved biocompatibility. IMDs are limited by their reliance on batteries. While batteries proved a stable power supply, batteries feature relatively large sizes, limited life spans, and toxic material compositions. Accordingly, energy harvesting and wireless power transfer (WPT) strategies are attracting increasing attention by researchers as alternative reliable power sources. Piezoelectric energy scavenging has shown promise for low power applications. However, energy scavenging devices need be located near sources of movement, and the power stream may suffer from occasional interruptions. WPT overcomes such challenges by more stable, on-demand power to IMDs. Among the various forms of WPT, ultrasound powering offers distinct advantages such as low tissue-mediated attenuation, a higher approved safe dose (720 mW cm^-2 ), and improved efficiency at smaller device sizes. This study presents and discusses the state-of-the-art in UPIs by reviewing piezoelectric materials and harvesting devices including lead-based inorganic, lead-free inorganic, and organic polymers. A comparative discussion is also presented of the functional material properties, architecture, and performance metrics, together with an overview of the applications where UPIs are being deployed.

Investigation of Artifacts and Optimization in Proton Resonance Frequency Thermometry Towards Heating Risk Monitoring of Implantable Medical Devices in Magnetic Resonance Imaging

OBJECTIVE

Artifacts limit the application of proton resonance frequency (PRF) thermometry for on-site, individualized heating evaluations of implantable medical devices such as deep brain stimulation (DBS) for use in magnetic resonance imaging (MRI). Its properties are unclear and the research on how to choose an unaffected measurement region is insufficient.

METHODS

The properties of PRF signals around the metallic DBS electrode were investigated through simulations and phantom experiments considering electromagnetic interferences from material susceptibility and the radio frequency (RF) interactions. A threshold method on phase difference Δϕ was used to define a measurement area to estimate heating at the electrode surface. Its performance was compared to that of the Bayesian magnitude method and probe measurements.

RESULTS

The B₀ magnetic field inhomogeneity due to the electrode susceptibility was the main influencing factor on PRF compared to the RF artifact. Δϕ around the electrode followed normal distribution but was distorted. Underestimation occurred at places with high temperature rises. The noise was increased and could be well estimated from magnitude images using a modified NEMA method. The Δϕ-threshold method based on this knowledge outperformed the Bayesian magnitude method by more than 42% in estimation error of the electrode heating.

CONCLUSION

The findings favor the use of PRF with the proposed approach as a reliable method for electrode heating estimation.

SIGNIFICANCE

This study clarified the influence of device artifacts and could improve the performance of PRF thermometry for individualized heating assessments of patients with implants under MRI.

XYZ Micropositioning System Based on Compliance Mechanisms Fabricated by Additive Manufacturing

This article presents the design and implementation of a micropositioning system actuated by three piezoelectric stacks to control its displacements on XYZ axes. The use of conventional piezoelectric buzzers allows us to reduce fabrication costs. The working or mobile platform is the base for objects that will be manipulated, for example, in automated assembling. The micropositioner can be integrated into a microgripper to generate a complete manipulation system. For micropositioner fabrication, at first, Polylactic Acid (PLA) was chosen as the structural material, but after simulation and some experimental tests performed with a micropositioner made of Acrylonitrile Butadiene Styrene (ABS), it showed larger displacement (approx. 20%) due to its lower stiffness. A third test was performed with a positioner made with Polyethylene Terephthalate Glycol (PETG), obtaining an intermediate performance. The originality of this work resides in the geometrical arrangement based on thermoplastic polymer compliance mechanisms, as well as in the use of additive manufacturing to fabricate it. An experimental setup was developed to carry out experimental tests. ANSYS™ was used for simulation.

The Effect of Human Tissue on Field Strength Measurements In Vivo Using a Resonant UHF Cavity-Backed Slot Antenna

An inward-looking wearable antenna can be used for radio communications with internal transceivers in vivo. The radio transmissions are recorded using an array of electric field sensors on the skin. This paper reports the effect of living tissue on a small cavity-backed slot antenna pressed onto soft tissue of the human torso at 2.09 GHz. In-vivo measurements were made on the skin surface at 13 torso locations using eight participants (age range, 22-68 years old), with body mass index ranging between 20.3 and 31.6 kg/m² . Ultrasound imaging was used to determine the skin and fat thickness at every measurement location. The variation in the antenna input impedance measurements demonstrated that the human tissues (fat and muscle) affect the antenna impedance but the mismatch creates field strength measurement errors of less than 2 dB. Fat thickness in the range of 3-30 mm can slightly degrade the performance of these wearable antennas. These effects can be partly mitigated by selective location and antenna retuning to improve transceiver communications. Bioelectromagnetics. 2021. © 2021 Bioelectromagnetics Society.

Video Capsule Endoscopy and Ingestible Electronics: Emerging Trends in Sensors, Circuits, Materials, Telemetry, Optics, and Rapid Reading Software

Real-time monitoring of the gastrointestinal tract in a safe and comfortable manner is valuable for the diagnosis and therapy of many diseases. Within this realm, our review captures the trends in ingestible capsule systems with a focus on hardware and software technologies used for capsule endoscopy and remote patient monitoring. We introduce the structure and functions of the gastrointestinal tract, and the FDA guidelines for ingestible wireless telemetric medical devices. We survey the advanced features incorporated in ingestible capsule systems, such as microrobotics, closed-loop feedback, physiological sensing, nerve stimulation, sampling and delivery, panoramic imaging with adaptive frame rates, and rapid reading software. Examples of experimental and commercialized capsule systems are presented with descriptions of their sensors, devices, and circuits for gastrointestinal health monitoring. We also show the recent research in biocompatible materials and batteries, edible electronics, and alternative energy sources for ingestible capsule systems. The results from clinical studies are discussed for the assessment of key performance indicators related to the safety and effectiveness of ingestible capsule procedures. Lastly, the present challenges and outlook are summarized with respect to the risks to health, clinical testing and approval process, and technology adoption by patients and clinicians.

A state-of-art review on antenna designs for ingestible application

Research interest in ingestible Wireless Capsule Endoscopy (WCE) studies in humans showed better results than conventional invasive probe endoscopy methods. Because of the structure and the position of the small intestine, proper scanning cannot be done in the area using traditional endoscopic methods. For patient comfort, continuous developments have been suggested in capsule endoscopy designs in terms of the quality of images transmitted, capsule orientation, positioning of the capsule from outside the body, link budget analysis, impedance matching and capsule miniaturization. To improve the image quality, transmission efficiency of the antenna has to be improved. This has led to the development of many antenna structures in an ingestible capsule system. Literatures have identified Med Radio and ISM (Industrial, Scientific and Medical) band as operation bands for the WCE systems. This review aims to highlight: (1) design considerations for various antenna types, (2) miniaturization techniques, (3) operating bands, specifications and various design challenges and (4) research gap, advanced design technologies and targets of ingestible antenna system. The main aim of this paper is to tutorial the up-to-date information on the recent antenna designing techniques and challenges for ingestible system.

Injectable Sensors Based on Passive Rectification of Volume-Conducted Currents

Sensing implants that can be deployed by catheterization or by injection are preferable over implants requiring invasive surgery. However, present powering methods for active implants and present interrogation methods for passive implants require bulky parts within the implants that hinder the development of such minimally invasive devices. In this article, we propose a novel approach that potentially enables the development of passive sensing systems overcoming the limitations of previous implantable sensing systems in terms of miniaturization. In this approach implants are shaped as thread-like devices suitable for implantation by injection. Their basic structure consists of a thin elongated body with two electrodes at opposite ends and a simple and small circuit made up of a diode, a capacitor and a resistor. The interrogation method to obtain measurements from the implants consists in applying innocuous bursts of high frequency (≥1 MHz) alternating current that reach the implants by volume conduction and in capturing and processing the voltage signals that the implants produce after the bursts. As proof-of-concept, and for illustrating how to put in practice this novel approach, here we describe the development and characterization of a system for measuring the conductivity of tissues surrounding the implant. We also describe the implementation and the in vitro validation of a 0.95 mm-thick, flexible injectable implant made of off-the-shelf components. For conductivities ranging from about 0.2 to 0.8 S/m, when compared to a commercial conductivity meter, the accuracy of the implemented system was about ±10%.

Wireless Body Sensor Communication Systems Based on UWB and IBC Technologies: State-of-the-Art and Open Challenges

In recent years there has been an increasing need for miniature, low-cost, commercially accessible, and user-friendly sensor solutions for wireless body area networks (WBAN), which has led to the adoption of new physical communication interfaces providing distinctive advantages over traditional wireless technologies. Ultra-wideband (UWB) and intrabody communication (IBC) have been the subject of intensive research in recent years due to their promising characteristics as means for short-range, low-power, and low-data-rate wireless interfaces for interconnection of various sensors and devices placed on, inside, or in the close vicinity of the human body. The need for safe and standardized solutions has resulted in the development of two relevant standards, IEEE 802.15.4 (for UWB) and IEEE 802.15.6 (for UWB and IBC), respectively. This paper presents an in-depth overview of recent studies and advances in the field of application of UWB and IBC technologies for wireless body sensor communication systems.

A 300 Mbps 37 pJ/bit Pulsed Optical Biotelemetry

This article reports an implantable transcutaneous telemetry for a brain machine interface that uses a novel optical communication system to achieve a highly energy-efficient link. Based on an pulse-based coding scheme, the system uses sub-nanosecond laser pulses to achieve data rates up to 300 Mbps with relatively low power levels when compared to other methods of wireless communication. This has been implemented using a combination of discrete components (semiconductor laser and driver, fast-response Si photodiode and interface) integrated at board level together with reconfigurable logic (encoder, decoder and processing circuits implemented using Xilinx KCU105 board with Kintex UltraScale FPGA). Experimental validation has been performed using a tissue sample that achieves representative level of attenuation/scattering (porcine skin) in the optical path. Results reveal that the system can operate at data rates up to 300 Mbps with a bit error rate (BER) of less than 10 ^-10, and an energy efficiency of 37 pJ/bit. This can communicate, for example, 1,024 channels of broadband neural data sampled at 18 kHz, 16-bit with only 11 mW power consumption.

Orally ingestible medical devices for gut engineering

Orally ingestible medical devices provide significant advancement for diagnosis and treatment of gastrointestinal (GI) tract-related conditions. From micro- to macroscale devices, with designs ranging from very simple to complex, these medical devices can be used for site-directed drug delivery in the GI tract, real-time imaging and sensing of gut biomarkers. Equipped with uni-direction release, or self-propulsion, or origami design, these microdevices are breaking the barriers associated with drug delivery, including biologics, across the GI tract. Further, on-board microelectronics allow imaging and sensing of gut tissue and biomarkers, providing a more comprehensive understanding of underlying pathophysiological conditions. We provide an overview of recent advances in orally ingestible medical devices towards drug delivery, imaging and sensing. Challenges associated with gut microenvironment, together with various activation/actuation modalities of medical devices for micromanipulation of the gut are discussed. We have critically examined the relationship between materials–device design–pharmacological responses with respect to existing regulatory guidelines and provided a clear roadmap for the future.

Wireless Wearables and Implants: A Dosimetry Review

Wireless wearable and implantable devices are continuing to grow in popularity, and as this growth occurs, so too does the need to consider the safety of such devices. Wearable and implantable devices require the transmitting and receiving of electromagnetic waves near and through the body, which at high enough exposure levels may damage proximate tissues. The specific absorption rate (SAR) is the quantity commonly used to enumerate exposure levels, and various national and international organizations have defined regulations limiting exposure to ensure safe operation. In this paper, we comprehensively review dosimetric studies reported in the literature up to the year 2019 for wearables and implants. We discuss antenna designs for wearables and implants as they relate to SAR values and field and thermal distributions in tissue, present designs that have made steps to reduce SAR, and then review SAR considerations as they relate to applied devices. As compared with previous review papers, this paper is the first review to focus on dosimetry aspects relative to wearable and implantable devices. Bioelectromagnetics. 2020;41:3–20 © 2019 The Authors. Bioelectromagnetics published by Wiley Periodicals, Inc.

Wirelessly Powered Signal Regeneration to Improve the Remote Detectability of an Inductive Pressure Sensor

Chronic pressure monitoring by wireless and batteryless sensors are desirable for maintaining proper function of biomedical implants. Compared to capacitive, piezoelectric, and piezoresistive sensors, inductive sensors are less susceptible to capacitance fluctuation in the environment, and they can convert loading pressure into inductance changes for wireless detection as resonance frequency shifts. However, inductive sensors normally require the use of ferromagnetic materials for frequency tuning; their frequency responses are harder to detect over larger distance separations. Without using ferromagnetic materials, we will utilize two coaxially coupled resonators whose mutual inductance (and thus resonance frequency) is modulated by the thickness of an elastic substrate that can deform under pressure loading. By modifying one of the coupled resonators into a parametric resonator that contains nonlinear capacitors and an extra conductor across its virtual grounds, the sensor can utilize wireless pumping power to enlarge backscattered signals whose peak response frequency is linearly correlated with the loading pressure. This linear relation is observable beyond the near-field region, even though the distance separation between the sensor and the measurement loop is ten-fold the sensor's circuit dimension. This novel concept of wirelessly powered signal regeneration will improve the remote detectability and operation flexibility of various physiological sensors.

Inertial wearables as pragmatic tools in dementia

Dementia is a critically important issue due to its wide impact on health services as well as its personal and societal costs. Limitations exist for current dementia protocols, and there are calls to introduce modern technology that facilitates the addition of digital biomarkers to routine clinical practice. Wearable technology (wearables) are nearly ubiquitous in everyday life, gathering discrete and continuous digital data on habitual activities, but their utility in modern medicine remains low. Due to advances in data analytics, wearables are now commonly discussed as pragmatic tools to aid the diagnosis and treatment of a range of neurological disorders. Inertial sensor-based wearables are one such technology; they offer a low-cost approach to quantify routine movements that are fundamental to normal activities of daily living, most notably postural control and gait. Here, we provide a narrative review of how wearables are providing useful postural control and gait data to facilitate the capture of digital markers to aid dementia research. We outline the history of wearables, from their humble beginnings to their current use beyond the clinic, and explore their integration into modern systems, as well as the ongoing standardisation and regulatory efforts to integrate their use in clinical trials.

A Modified Wireless Power Transfer System for Medical Implants

Wireless Power Transfer (WPT) is a promising technique, yet still an experimental solution, to replace batteries in existing implants and overcome the related health complications. However, not all techniques are adequate to meet the safety requirements of medical implants for patients. Ensuring a compromise between a small form factor and a high Power Transfer Efficiency (PTE) for transcutaneous applications still remains a challenge. In this work, we have used a resonant inductive coupling for WPT and a coil geometry optimization approach to address constraints related to maintaining a small form factor and the efficiency of power transfer. Thus, we propose a WPT system for medical implants operating at 13.56 MHz using high-efficiency Complementary Metal Oxide-Semiconductor (CMOS) components and an optimized Printed Circuit Coil (PCC). It is divided into two main circuits, a transmitter circuit located outside the human body and a receiver circuit implanted inside the body. The transmitter circuit was designed with an oscillator, driver and a Class-E power amplifier. Experimental results acquired in the air medium show that the proposed system reaches a power transfer efficiency of 75.1% for 0.5 cm and reaches 5 cm as a maximum transfer distance for 10.67% of the efficiency, all of which holds promise for implementing WPT for medical implants that don’t require further medical intervention, and without taking up a lot of space.

Immune-to-Detuning Wireless In-Body Platform for Versatile Biotelemetry Applications

BACKGROUND AND OBJECTIVE

In-body biotelemetry devices enable wireless monitoring of a wide range of physiological parameters. These devices rely on antennas to interface with external receivers, yet existing systems suffer from impedance detuning caused by the substantial differences in electromagnetic properties among various tissues. In this paper, we propose an immune-to-detuning in-body biotelemetry platform featuring a novel tissue-independent antenna design.

METHODS

Our approach uses a novel slot-patch conformal antenna integrated into a flexible polyimide printed circuit board containing the device circuitry and encapsulated within a 17.7 mm [Formula: see text]8.9 mm biocompatible shell. The antenna is synthesized and optimized using a hybrid analytical-numerical approach and, then, characterized numerically and experimentally in terms of impedance stability.

RESULTS

The proposed platform shows stable impedance, whereas operating in any mammalian tissue as well as in air. The system is optimized for the 434-MHz industrial, scientific, and medical band and can easily be returned for any MedRadio band in the 401-457-MHz spectrum.

CONCLUSION

Ultrarobust impedance characteristics were achieved. Without any modifications, the proposed biotelemetry platform can be used, for instance, as an ingestible for humans or as an implantable for a wide range of animals: from rodents to cattle.

The Promise of Mobile Technologies for the Health Care System in the Developing World: A Systematic Review

Evolution of mobile technologies and their rapid penetration into people's daily lives, especially in the developing countries, have highlighted mobile health, or m-health, as a promising solution to improve health outcomes. Several studies have been conducted that characterize the impact of m-health solutions in resource-limited settings and assess their potential to improve health care. The aim of this review is twofold: 1) to present an overview of the background and significance of m-health and 2) to summarize and discuss the existing evidence for the effectiveness of m-health in the developing world. A systematic search in the literature was performed in Pubmed, Scopus, as well as reference lists, and a broad sample of 98 relevant articles was identified, which were then categorized into five wider m-health categories. Although statistically significant conclusions cannot be drawn since the majority of studies relied on small-scale trials and limited assessment of long-term effects, this review provides a systematic and extensive analysis of the advantages, disadvantages, and challenges of m-health in developing countries in an attempt to determine future research directions of m-health interventions.

A Future with Ubiquitous Sensing and Intelligent Systems

In this paper, we discuss the relevance of sensing and biosensing for the ongoing revolution in science and technology as a product of the merging of machine learning and Big Data into affordable technologies and accessible everyday products. Possible scenarios for the next decades are described with examples of intelligent systems for various areas, most of which will rely on ubiquitous sensing. The technological and societal challenges for developing the full potential of such intelligent systems are also addressed.

Impact of type of intracranial EEG sensors on link strengths of evolving functional brain networks

Objective and Approach: Investigating properties of evolving functional brain networks has become a valuable tool to characterize the complex dynamics of the epileptic brain. Such networks are usually derived from electroencephalograms (EEG) recorded with sensors implanted chronically into deeper structures of the brain and/or placed onto the cortex. It is still unclear, however, whether the use of different sensors for an identification of network nodes affects properties of functional brain networks. We address this question by investigating properties of links of such networks that we characterize by assessing interactions in multi-sensor, multi-day EEG data recorded from 49 epilepsy patients during presurgical evaluation. These data allow us to study the impact of different types of sensors together with the impact of various physiologic and pathophysiologic activities on the properties of links.

MAIN RESULTS

We observe that different types of sensors differently impact on spatial means and temporal fluctuations of link strengths. Moreover, the impact depends on the relative anatomical location of sensors with respect to location and extent of sources of the prevailing activities.

SIGNIFICANCE

Type and location of sensors should be considered when constructing networks.

A Review of Implant Communication Technology in WBAN: Progress and Challenges

Over the past six decades, there has been tremendous progress made in the field of medical implant communications. A comprehensive review of the progress, current state of the art, and future direction is presented in this paper. Implanted medical devices (IMDs) are designed mainly for the purpose of diagnostic, therapeutic, and assistive applications in heathcare, active living, and sports technology. The primary target of IMDs' design revolves around reliable communications, sustainable power sources, and a high degree of miniaturization while maintaining biocompatibility to surrounding tissues adhering to the human safety limits set by appropriate guidelines. The role of the Internet of Things and intelligent data analysis in implant device networks as future research is presented in this paper. Finally, in addition to reviewing the state of the art, a novel intuitive lower bound on implant size is presented.

In Vivo Characterization of a Wireless Telemetry Module for a Capsule Endoscopy System Utilizing a Conformal Antenna

This paper describes the design, fabrication, packaging, and performance characterization of a conformal helix antenna created on the outside of a capsule endoscope designed to operate at a carrier frequency of 433 MHz within human tissue. Wireless data transfer was established between the integrated capsule system and an external receiver. The telemetry system was tested within a tissue phantom and in vivo porcine models. Two different types of transmission modes were tested. The first mode, replicating normal operating conditions, used data packets at a steady power level of 0 dBm, while the capsule was being withdrawn at a steady rate from the small intestine. The second mode, replicating the worst-case clinical scenario of capsule retention within the small bowel, sent data with stepwise increasing power levels of -10, 0, 6, and 10 dBm, with the capsule fixed in position. The temperature of the tissue surrounding the external antenna was monitored at all times using thermistors embedded within the capsule shell to observe potential safety issues. The recorded data showed, for both modes of operation, a low error transmission of 10^-3 packet error rate and 10^-5 bit error rate and no temperature increase of the tissue according to IEEE standards.