Implantable Antenna Research Articles

A Compact Wideband Flexible Implantable Slot Antenna Design With Enhanced Gain

In this communication, a coplanar waveguide-fed, compact, wideband dual-ring slot antenna for biomedical applications in the Industrial, Scientific and Medical frequency band is presented. This implantable antenna is designed using thin and biocompatible substrate–superstrate layers to achieve human body insulation as well as flexibility. Despite showing good antenna performances, only the realized gain value is observed to be reduced (−12 dB). To improve the antenna gain, a metamaterial (MTM) array with epsilon very large behavior has been introduced on the superstrate of the implantable antenna. Using the MTM, about 3 dB gain enhancement has been observed. Even after the introduction of the MTM superstrate, wideband characteristic and flexibility are maintained. Also, the specific absorption rate (SAR) analysis of the antenna configuration with and without MTM has been studied. A low SAR is obtained in both the cases. The fabricated antenna parameters have been measured with the in vitro test by immersing the antenna inside a single-layer tissue emulating gel, as well as, inside a chicken breast slab.

Deterministic Equation of Self-Resonant Structures for Normal-Mode Helical Antennas Implanted in a Human Body

Recently, helical antennas had been used as a very small implantable antenna in a capsule endoscopy system. For a helical antenna, a normal-mode helical antenna (NMHA) is promising because of its small size and the completeness of an antenna design method, which has already been established. However, in the human body, the effects of human tissues on the electrical characteristics of an NMHA were not clarified. The most important aspect is to determine the self-resonant structures. In this letter, a deterministic equation is derived for the self-resonant structures of an NMHA in the human body. By utilizing simulation results of an electromagnetic simulator, a capacitive reactance equation is deduced based on the electric field distributions around an antenna. An inductive reactance equation is obtained by modifying the equation of free space to the condition of inside a dielectric material. Finally, by equating the capacitive and inductive reactance equations, the self-resonant equation is determined. The accuracy of the equation is ensured through the agreements of the antenna structures given by equations and electromagnetic simulations. Moreover, by fabricating an NMHA and a human body phantom, the measured results are obtained. The self-resonant structure is ensured through the measured results.

A Wideband Circularly Polarized Implantable Antenna for 915 MHz ISM-Band Biotelemetry Devices

A wideband miniaturized circularly polarized implantable antenna operating at 915 MHz Industrial, Scientific, and Medical (ISM) band is presented and experimentally verified in this letter. Compared with previous work, the patch antenna with the dimensions of $\pi \times ({\text{4.7}})^{2}\times {\text{1.27}} {\text{mm}}^{3}$ features a better size reduction. The miniaturization of the proposed antenna is well implemented by cutting several kinds of slots to extend the current path. Moreover, a shorting pin is introduced to lower the resonant frequency and prompt circular polarization (CP) purity. Specific absorption rate is also calculated to consider whether it can meet the safety standards. The simulated results in one-layer cubic skin phantom demonstrates that the impedance bandwidth (BW) of 12.2% and the 3 dB axial-ratio BW of 19.7% can be obtained. Finally, the antenna is measured in the skin-mimicking solution, and the measured BW achieves about 17.5%, which generally agrees with the simulated.

An Implantable and Conformal Antenna for Wireless Capsule Endoscopy

This letter proposes an implantable antenna with ultrawide bandwidth operating in the medical device radio communications service band (401–406 MHz) for the wireless capsule endoscopy (WCE). The simulation and experimental results show the proposed antenna has a good performance in terms of the return loss and hence the bandwidth from 284 to 825 MHz. The maximum realized gain of this antenna is –31.5 dBi at 403 MHz. The maximum simulated input power is <1.7 mW in order to satisfy the specific absorption rate (SAR) regulations in the IEEE standard. The tolerance of the antenna owing to bendability and different WCE shell thicknesses is investigated. These indicate that the proposed antenna is a good candidate for the WCE.

High-Frequency 3-D Model for the Study of Antennas in Cochlear Implants

This paper is devoted to the modeling and analysis of the antennas in the cochlear implants. In order to accurately characterize the antenna, a 3-D model working at high frequencies has been developed, where precise dimensions of the loop antenna are given. In order to have a complete overview, the tissues (skin and mastoid bone) surrounding the implanted antenna have been defined and included in the model. The most important performance indicators have been numerically assessed. The 3-D polar representations, as well as rectangular plot and rectangular contour plot of the total radiated electric field, in far-field region, are included. The radiation pattern, Smith charts, and Smith contour plots are also obtained.

Circularly polarized implantable antenna characterization for retinal prosthesis systems

We describe a miniaturized antenna design for retinal prosthesis applications that enhances data transfer between the implant and external camera. The circularly polarized and conformal 2.4–2.48 GHz microstrip patch antenna was simulated inside the vitreous humor and is intended for biomedical applications. Modified Hilbert and serpentine geometries were used for the proposed implant antenna design. Capacitive radiator loading offered miniaturized dimensions of 5.8 × 6.5 × 2 mm³ (width × height × thickness mm³). A truncated design enhanced the intrinsic circular polarization characteristics to >3 dB axial ratio. Polydimethylsiloxane substrate and superstrate materials were used to achieve an S11 value below –15 dB across the frequency range with biocompatible characteristics. The simulated peak gains for left-hand circular polarization and right-hand circular polarization at 2.45 GHz were –50 dBi and –60 dBi, respectively. These relatively small values were due to the high conductivity of the vitreous humor (s = 1.53 S/m), which imposed significant losses. Overall, the proposed antenna had an omnidirectional radiation pattern and +8.45 dBm input to meet the specific absorption rate regulation limit.

Antennas for Intraoral Tongue Drive System at 2.4 GHz: Design, Characterization, and Comparison

The intraoral Tongue Drive System (iTDS), is a tongue-controlled wireless assistive technology, operated by a number of user-defined voluntary tongue gestures to issue control commands. In this paper, we present a new arch-shaped iTDS, occupying the buccal shelf space in the mouth, without limiting the available space for tongue motions. We describe the design, characterization, and comparison between three types of 2.4-GHz antennas for this system: patch, dipole, and planar inverted-F in terms of gain, directivity, bandwidth, and data communication performance to achieve a robust RF link despite mouth motions. The antennas are designed and simulated in a simple human mouth model and measured in the mouth. Based on simulation and measurement results, using an iTDS prototype made of commercial-off-the-shelf components, the patch antenna has the highest gain in both closed- and open-mouth states, at −10.6 and −9 dBi, respectively. We also measured the propagation loss between the iTDS intraoral antenna and out-of-mouth receiver (Rx) in a real user-case scenario and evaluated the link quality by measuring the packet error rate between the transmitter and RX. The presented antennas have larger bandwidth, smaller area, and higher gain compared to prior work on implantable antennas in the literature, resulting in a robust wireless link for the iTDS application.

Design of E and U shaped slot for ISM band application

Objectives: For implantable devices, a miniaturized antenna structure is proposed to operate in ISM band. At 2.5 GHz frequency the antenna is expected to operate. Methods/Statistical Analysis: A combination of E and U shaped slots on a rectangular patch design is proposed for biomedical applications especially operating in ISM band. The slots created here in order to changing the current path so that the radiation pattern acquired in excepted frequency. Findings: The E and U slots on a rectangular patch operates at 2.5 GHz and it provides good radiation pattern and gain. Applications/Improvements: Antennas dipped inside a human body are highly required for biotelemetry applications. Careful design of antenna is needed since the antennas are operated inside human body. The proposed structure gives good commitment towards the requirements. Keywords: Biotelemetry, E Shape, Implantable Antenna, ISM Band, U Shape

Scalp-Implantable Antenna Systems for Intracranial Pressure Monitoring

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 bands (i.e., 915 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 ( $8 \times 6 \times 0.5$ = 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 and −22.8 dBi at a lower and higher resonant band, respectively. Simulations using the finite-element method and finite-difference time domain 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 simulation results. In addition, a link budget is calculated to analyze the data transmission range.

Circularly Polarized Implantable Antenna for 915 MHz ISM-Band Far-Field Wireless Power Transmission

A wireless power link with circular polarization is studied in this letter for far-field wireless power transmission. First, a miniaturized circularly polarized (CP) implantable antenna is designed at 915 ISM band. The proposed antenna features a good miniaturization with the dimensions of 11 × 11 × 1.27 mm3 by employing the stub loading and capacitive coupling among the stubs. It has the smallest size and maintains good radiation performance, compared with previous CP implantable antennas. The simulated impedance bandwidth covers from 889 to 924 MHz for | S 11| less than −10 dB, and the axial-ratio (AR) bandwidth (AR < 3 dB) is from 901 to 912 MHz. The results show that the antenna is suitable for far-field wireless power transmission. The proposed wireless power link achieves higher converted dc power compared to previous similar letter.

Numerical Investigation of a Chip Printed Antenna Performances for Wireless Implantable Body Area Network Applications

Recently, wireless implantable body area network (WiBAN) system become an active area of research due to their various applications such as healthcare, support systems for specialized occupations and personal communications. Biomedical sensors networks mounted in the human body have drawn greater attention for health care monitoring systems. The implantable chip printed antenna for WiBAN applications is designed and the antenna performances is investigated in term of gain, efficiency, return loss, operating bandwidth and radiation pattern at different environments. This paper is presents the performances of implantable chip printed antenna in selected part of human body (hand, chest, leg, heart and skull). The numerical investigation is done by using human voxel model in built in the CST Microwave Studio Software. Results proved that the chip printed antenna is suitable to implant in the human hand model. The human hand model has less complex structure as it consists of skin, fat, muscle, blood and bone. Moreover, the antenna is implanted under the skin. Therefore the signal propagation path length to the base station at free space environment is considerably short. The antenna’s gain, efficiency and Specific Absorption Rate (SAR) are - 13.62dBi, 1.50 % and 0.12 W/kg respectively; which confirms the safety of the antenna usage. The results of the investigations can be used as guidance while designing chip implantable antenna in future.

Wireless Power Link Based on Inductive Coupling for Brain Implantable Medical Devices

An inductively powered brain implantable medical device (BIMD) in lieu of a battery-assisted BIMD has the ability to provide a reliable power supply and avoid surgical replacement of a discharged battery. In this letter, we propose a three-dimensional (3-D) bowtie implantable antenna embedded in the cerebral spinal fluid (CSF) coupled with an exterior loop antenna. The power transfer efficiency is maximized by designing a matching circuit for the exterior and implantable antennas to reduce the high intrinsic reactive part of the input impedance. To ensure safety for long-term implantation, a rigorous specific absorption rate simulation was conducted to abide with the safety standard. A liquid CSF phantom was developed to experimentally test the power transfer efficiency between the exterior and implantable antenna. Measurement of the fabricated 0.9 $\text{mm}^{3}$ implantable antenna prototype in the CSF phantom resulted in $-\text{30.12 dB}$ wireless power link, which outperforms the current work in the literature in terms of the size and link efficiency for 3-D implantable antennas.

Near-Field Inductive-Coupling Link to Power a Three-Dimensional Millimeter-Size Antenna for Brain Implantable Medical Devices.

Near-field inductive-coupling link can establish a reliable power source to a batteryless implantable medical device based on Faraday's law of induction. In this paper, the design, modeling, and experimental verification of an inductive-coupling link between an off-body loop antenna and a 0.9 three-dimensional (3-D) bowtie brain implantable antenna is presented. To ensure reliability of the design, the implantable antenna is embedded in the cerebral spinal fluid of a realistic human head model. Exposure, temperature, and propagation simulations of the near electromagnetic fields in a frequency-dispersive head model were carried out to comply with the IEEE safety standards. Concertedly, a fabrication process for the implantable antenna is proposed, which can be extended to devise and miniaturize different 3-D geometric shapes. The performance of the proposed inductive link was tested in a biological environment; in vitro measurements of the fabricated prototypes were carried in a pig's head and piglet. The measurements of the link gain demonstrated in the pig's head and in piglet. The in vitro measurement results showed that the proposed 3-D implantable antenna is suitable for integration with a miniaturized batteryless brain implantable medical device (BIMD).

Design and miniaturization of dual band implantable antennas

Two types of miniaturized dual band implantable antennas are designed and presented, one of a meander type and the other is the so called comb antenna. In medical applications the electromagnetic characteristic changes of tissue in different situations and the corresponding resonant frequency shifts, should not disturb the data transmission. The objective is to design dual band antennas in 400 MHz and 2.4 GHz with suitable bandwidths and small sizes. The meander type antenna was fabricated and its S parameters were measured using an equivalent liquid phantom of skin, fat and muscle which included propanol, butanol, purified water and salt. The experimental results are shown and compared.

MINIATURIZATION OF A PIFA ANTENNA FOR BIOMEDICAL APPLICATIONS USING ARTIFICIAL NEURAL NETWORKS

This work deals with the optimization of an inverted F dual-band implantable antenna operating in Medical Device Radiocommunications Service (MedRadio, 401-406 MHz) and Industrial Scientific Medical (ISM, 902-928 MHz) applications bands. Artificial neural networks (ANNs) are implemented to minimize the size of the initial design. The ANN's output with the physical and dielectric parameters of antenna as inputs is tested using COMSOL Multiphysics®. The obtained results regarding the return loss S11, resonant frequency and bandwidth of the antenna are presented and discussed. Indeed, the size of the antenna is reduced by 21.48% with respect to the initial size while preserving its initial good performance in both frequency bands.

Design and simulation‐based performance evaluation of a miniaturised implantable antenna for biomedical applications

Biomedical telemetry is an emerging field of research which enables the formation of a transmission link from inside a living body to an external device. Implantable medical devices are now one of such valuable advancement in the field of biomedical telemetry. Implantable patch antennas are gaining attention and are becoming more of a choice for implantable medical devices that uses mostly RF telemetry. In this work, a state-of-the-art design for a rectangular implantable flexible patch antenna is proposed. The operation band for the antenna is chosen in the Industrial, Scientific and Medical (ISM) band (2.4-2.4835 GHz). The tiny dimension of the antenna, including the 9.45 μm thickness of the patch itself allows the antenna to be highly flexible and provides excellent results even at extreme bent conditions. For simulation environment, a three-layer human tissue model was used, where the antenna was encapsulated between the fat and skin layer. CST Microwave Studio was chosen to design and simulate the antenna. Several performance parameters were simulated, such as the operating resonant frequency, the return loss, radiation pattern, specific absorption rate and also sensitivity of the antenna when introduced to bending.

A Multiband Antenna Associating Wireless Monitoring and Nonleaky Wireless Power Transfer System for Biomedical Implants

This paper presents a multiband conformal antenna for implantable as well as ingestible devices. The proposed antenna has the following three bands: medical implanted communication service (MICS: 402–405 MHz), the midfield band (1.45–1.6 GHz), and the industrial, scientific, and medical band (ISM: 2.4–2.45 GHz) for telemetry or wireless monitoring, wireless power transfer (WPT), and power conservation, respectively. A T-shaped ground slot is used to tune the antenna, and this antenna is wrapped inside a printed 3-D capsule prototype to demonstrate its applicability in different biomedical devices. Initially, the performance of the proposed antenna was measured in an American Society for Testing and Materials phantom containing a porcine heart in the MICS band for an implantable case. Furthermore, to stretch the scope of the suggested antenna to ingestible devices, the antenna performance was simulated and measured using a minced pork muscle in the ISM band. A modified version of the midfield power transfer method was incorporated to replicate the idea of WPT within the implantable 3-D printed capsule. Moreover, a near-field plate (NFP) was employed to control the leakage of power from the WPT transmitter. From the simulation and measurements, we found that use of a ground slot in the implantable antenna can improve antenna performance and can also reduce the specific absorption rate. Furthermore, by including the NFP with the midfield WPT transmitter system, unidirectional wireless power can be obtained and WPT efficiency can be increased.

An End-to-End Implanted Brain–Machine Interface Antenna System Performance Characterizations and Development

Brain-machine interface (BMI) is a multidisciplinary field that has been recently developed in an attempt to help restore functionalities for paralyzed individuals. One of the key components for the implementation of a wireless BMI necessitates unique designs for both the internal brain and external head antennas. In this paper, we initially revisited the design of an optimized 1-mm3 implantable antenna transferring power and data with a reduced size low profile external reader antenna by utilizing radio-frequency identification (RFID)-inspired backscattering. Detailed computational assessments and specific absorption rate evaluations are performed. Prototypes were characterized in terms of link efficiency through a realized RFID link with up to −25 dB link efficiency. The noise analysis for antennas in biological systems was performed using two novel absorption-noise models. And finally a channel capacity estimation was performed, proving that the BMI antenna link could support up to 100 recording channels. An end-to-end BMI antenna system characterization is detailed in this paper for multichannel implanted neural recording applications.

Tissue-Independent Implantable Antenna for In-Body Communications at 2.36–2.5 GHz

In this paper, a compact printed meandered folded dipole antenna with a volume of 114 mm3 suitable for implantation in a range of different body tissue types with diverse electrical properties is presented for operation in the 2.36–2.4 GHz MBAN and 2.4-GHz ISM bands. Its performance was verified and compared against that of a wire dipole and slot loaded monopole antenna in an implant phantom testbed containing tissue equivalent liquids representing body tissues with high and low water content. The antenna was shown to maintain its return loss performance in the 2360–2400, 2400–2483.5, and 2483.5–2500 MHz frequency bands with equivalent or better performance than a fundamental wire dipole despite having approximately half the physical length.

Multi-Polarization Reconfigurable Antenna for Wireless Biomedical System.

This paper presents a multi-polarization reconfigurable antenna with four dipole radiators for biomedical applications in body-centric wireless communication system (BWCS). The proposed multi-dipole antenna with switchable 0°, +45°, 90° and -45° linear polarizations is able to overcome the polarization mismatching and multi-path distortion in complex wireless channels as in BWCS. To realize this reconfigurable feature for the first time among all the reported antenna designs, we assembled four dipoles together with 45° rotated sequential arrangements. These dipoles are excited by the same feeding source provided by a ground tapered Balun. A metallic reflector is placed below the dipoles to generate a broadside radiation. By introducing eight PIN diodes as RF switches between the excitation source and the four dipoles, we can control a specific dipole to operate. As the results, 0°, +45°, 90° and -45° linear polarizations can be switched correspondingly to different operating dipoles. Experimental results agree with the simulation and show that the proposed antenna well works in all polarization modes with desirable electrical characteristics. The antenna has a wide impedance bandwidth of 34% from 2.2 to 3.1GHz (for the reflection coefficient ≤ -10dB) and exhibits a stable cardioid-shaped radiation pattern across the operating bandwidth with a peak gain of 5.2dBi. To validate the effectiveness of the multi-dipole antenna for biomedical applications, we also designed a meandered PIFA as the implantable antenna. Finally, the communication link measurement shows that our proposed antenna is able to minimize the polarization mismatching and maintains the optimal communication link thanks to its polarization reconfigurability.