Biomedical telemetry permits the transmission (telemetering) of physiological signals at a distance. One of its latest developments is in the field of implantable medical devices (IMDs). Patch antennas currently are receiving significant scientific interest for integration into the implantable medical devices and radio-frequency (RF)-enabled biotelemetry, because of their high flexibility in design, conformability, and shape. The design of implantable patch antennas has gained considerable attention for dealing with issues related to biocompatibility, miniaturization, patient safety, improved quality of communication with exterior monitoring/control equipment, and insensitivity to detuning. Numerical and experimental investigations for implantable patch antennas are also highly intriguing. The objective of this paper is to provide an overview of these challenges, and discuss the ways in which they have been dealt with so far in the literature.

A Review of Implantable Patch Antennas for Biomedical Telemetry: Challenges and Solutions [Wireless Corner]

소형 안테나 ( Small Antennas )

Chip-scale atomic devices combine elements of precision atomic spectroscopy, silicon micromachining, and advanced diode laser technology to create compact, low-power, and manufacturable instruments with high precision and stability. Microfabricated alkali vapor cells are at the heart of most of these technologies, and the fabrication of these cells is discussed in detail. We review the design, fabrication, and performance of chip-scale atomic clocks, magnetometers, and gyroscopes and discuss many applications in which these novel instruments are being used. Finally, we present prospects for future generations of miniaturized devices, such as photonically integrated systems and manufacturable devices, which may enable embedded absolute measurement of a broad range of physical quantities.

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Chip-scale atomic devices

A single-fed miniaturized circularly polarized microstrip patch antenna is designed and experimentally demonstrated for industrial-scientific-medical (2.4-2.48 GHz) biomedical applications. The proposed antenna is designed by utilizing the capacitive loading on the radiator. Compared with the initial topology of the proposed antenna, the so-called square patch antenna with a center-square slot, the proposed method has the advantage of good size reduction and good polarization purity. The footprint of the proposed antenna is 10×10×1.27 mm3. The simulated impedance, axial ratio, and radiation pattern are studied and compared in two simulation models: cubic skin phantom and Gustav voxel human body. The effect of different body phantoms is discussed to evaluate the sensitivity of the proposed antenna. The effect of coaxial cable is also discussed. Two typical approaches to address the biocompatibility issue for practical applications are reported as well. The simulated and measured impedance bandwidths in cubic skin phantom are 7.7% and 10.2%, respectively. The performance of the communication link between the implanted CP antenna and the external antenna is also presented.

Capacitively Loaded Circularly Polarized Implantable Patch Antenna for ISM Band Biomedical Applications

The design procedure, realization and measurements of an implantable radiator for telemetry applications are presented. First, free space analysis allows the choice of the antenna typology with reduced computation time. Subsequently the antenna, inserted in a body phantom, is designed to take into account all the necessary electronic components, power supply and bio-compatible insulation so as to realize a complete implantable device. The conformal design has suitable dimensions for subcutaneous implantation (10 × 32.1 mm). The effect of different body phantoms is discussed. The radiator works in both the Medical Device Radiocommunication Service (MedRadio, 401-406 MHz) and the Industrial, Scientific and Medical (ISM, 2.4-2.5 GHz) bands. Simulated maximum gains attain -28.8 and - 18.5 dBi in the two desired frequency ranges, respectively, when the radiator is implanted subcutaneously in a homogenous cylindrical body phantom (80 × 110 mm) with muscle equivalent dielectric properties. Three antennas are realized and characterized in order to improve simulation calibration, electromagnetic performance, and to validate the repeatability of the manufacturing process. Measurements are also presented and a good correspondence with theoretical predictions is registered.

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Design, Realization and Measurements of a Miniature Antenna for Implantable Wireless Communication Systems

This work presents the analysis of the influence of insulation on implanted antennas for biotelemetry applications in the Medical Device Radiocommunications Service band. Our goal is finding the insulation properties that facilitate power transmission, thus enhancing the communication between the implanted antenna and an external receiver. For this purpose, it has been found that a simplified model of human tissues based on spherical geometries excited by ideal sources (electric dipole, magnetic dipole and Huygens source) provides reasonable accuracy while remaining very tractable due to its analytical formulation. Our results show that a proper choice of the biocompatible internal insulation material can improve the radiation efficiency of the implanted antenna (up to six times for the investigated cases). External insulation facilitates the electromagnetic transition from the biological tissue to the outer free space, reducing the power absorbed by the human body. Summarizing, this work gives insights on the enhancement of power transmission, obtained with the use of both internal, biocompatible and external, flexible insulations. Therefore, it provides useful information for the design of implanted antennas.

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The Effect of Insulating Layers on the Performance of Implanted Antennas

This work presents the design and realization procedure of small implantable antenna for biotelemetry applications. The radiator occupies a volume smaller than 3 cm(3) (without its biocompatible insulation), is well matched within the Medical Implanted Communications System band and shows an adequate gain (-28.5 dB) while introduced in the appropriate equivalent body medium. The latter is a homogeneous phantom with muscle dielectric properties. A prototype has been manufactured and measurements agree with theoretical predictions. Particular attention is paid to the building requirements such as the presence of glue. Specific Absorption Rate (SAR) distribution has been computed evaluating the maximum power deliverable to the antenna in order to respect the regulated SAR limitation.

3D-Spiral Small Antenna Design and Realization for Biomedical Telemetry in the MICS band

The design, realization, and characterization of a compact magnetron-type microwave cavity operating with a TE011-like mode are presented. The resonator works at the rubidium hyperfine ground-state frequency (i.e., 6.835 GHz) by accommodating a glass cell of 25 mm diameter containing rubidium vapor. Its design analysis demonstrates the limitation of the loop-gap resonator lumped model when targeting such a large cell, thus numerical optimization was done to obtain the required performances. Microwave characterization of the realized prototype confirmed the expected working behavior. Double-resonance and Zeeman spectroscopy performed with this cavity indicated an excellent microwave magnetic field homogeneity: the performance validation of the cavity was done by achieving an excellent short-term clock stability as low as 2.4 × 10 −13 τ −1/2 . The achieved experimental results and the compact design make this resonator suitable for applications in portable atomic high-performance frequency standards for both terrestrial and space applications. © 2012 American Institute of Physics .[ http://dx.doi.org/10.1063/1.4759023]

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Compact microwave cavity for high performance rubidium frequency standards

Since the introduction of implantable pacemakers in the early 1960s, implantable medical devices have become more and more interesting for healthcare services. Nowadays, the devices designed to monitor physiological data from inside the human body have great promises to provide major contributions to disease prevention, diagnosis and therapy. Furthermore, minimally invasive devices allow reducing hospitalization terms, thus improving the patients' quality of life. Planning how transmitting information from inside the body to the external world requires a multidisciplinary approach. Such a challenging task combines concepts, models and applied solutions drawing from several fields, including electromagnetism, electronics, biology, and package engineering. More specifically, this work focuses on antennas to be integrated in implantable devices with far field data telemetry capabilities. Thus, in collaboration with the Laboratory of Microengineering for Manufacturing 2 and the Laboratory of Stem Cell Dynamics at the Ecole Polytechnique Federale de Lausanne, we have designed, assembled and successfully tested in vivo a Body Sensor Node for telemedicine use. Among its components, the antenna plays a key role. The presence of the human body, which is "hostile" to radio frequency propagation, the need of miniaturization and the necessity of biocompatibility participate all in determining the final characteristics of implantable antennas. Taking into account a wide range of technical and medical concerns, this thesis addresses the analysis, design, realization, in vitro characterization and in vivo testing of such radiators. The analysis is built upon the fundamental theory of antennas in lossy matter, the features of electrically small radiators and the modeling of the human body. This approach allows a clear identification of the main challenges related to implantable antennas, thus setting a solid base for the work presented further on. For instance, biocompatible insulation was found of paramount importance. Accordingly, we have elaborated and implemented physical and mathematical models showing that the proper choice of insulating layers substantially improves the radiation efficiency. The design of implantable antennas takes into account theoretical inputs, packaging considerations and technological constraints. Thus, we propose an effective design strategy that combines these three aspects, and that has been applied to design the Multilayered Spiral Antenna. This radiator integrates with the necessary electronics, power supply and bio-sensor so as to form a Body Sensor Node. In vitro characterization is discussed and carried out for the implantable antenna itself, as well as for the entire implantable device. More specifically, the former characterization is detailed so as to give the possibility of prototyping antennas at the component level. Finally, in vivo testing of the proposed Body Sensor Node was performed in a porcine animal. We believe that our results pave the way for future research oriented to the making of complete telemedicine systems.

F. Merli

Papers

Design, Realization and Measurements of a Miniature Antenna for Implantable Wireless Communication Systems

The Effect of Insulating Layers on the Performance of Implanted Antennas

3D-Spiral Small Antenna Design and Realization for Biomedical Telemetry in the MICS band

Compact microwave cavity for high performance rubidium frequency standards

Implantable Antennas for Biomedical Applications