Francesco Merli

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

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.

The Effect of Insulating Layers on the Performance of Implanted Antennas

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.

Implanted antenna for biomedical applications

In this paper we present the design, realization and measurements of a first prototype of a complete implantable device. The RF system, working over the medical implanted communication systems (MICS) bandwidth and composed of the antenna, the battery, the transceiver for the data communication and the insulation material, has been designed and realized in order to be integrated with an implanted glucose sensor.

Design strategies for implantable antennas

Considerations on the efficient design and the characterization of antennas for bio-implantable communication devices are presented. These devices are used in conjunction with health monitoring and/or health care systems. First, the main challenges to be met in designing such antennas are presented, subsequently followed by the proposition of a design procedure. Finally, the specific difficulties in characterizing implantable antennas are emphasized.

Compact microwave cavity for high performance rubidium frequency standards

The design, realization, and characterization of a compact magnetron-type microwave cavity operating with a TE(011)-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.

Analysis, Design and Realization of a Novel Directive Ultrawideband Antenna

In this paper, we present a simple log-periodic-dipole-array (LPDA) solution that allows us to achieve good ultrawideband (UWB) performances. The antenna has been manufactured and the measurements agree well with the theoretical predictions. The antenna presents an average gain of 8 dB and a return loss better than -10 dB over the band from 4.2 to 10.6 GHz. Both the measured antenna transfer function and the computed effect on pulse transmission show good performances in comparison with already known UWB antennas.

Compact high-performance continuous-wave double-resonance rubidium standard with 1.4 × 10 −13 τ −1/2 stability

We present our studies on a compact high-performance continuous wave (CW) double-resonance (DR) rubidium frequency standard in view of future portable applications. Our clock exhibits a short-term stability of 1.4 × 10-13 τ-1/2, consistent with the short-term noise budget for an optimized DR signal. The metrological studies on the medium- to longterm stability of our Rb standard with measured stabilities are presented. The dependence of microwave power shift on light intensity, and the possibility to suppress the microwave power shift is demonstrated. The instabilities arising from the vapor cell geometric effect are evaluated, and are found to act on two different time scales (fast and slow stem effects). The resulting medium- to long-term stability limit is around 5.5 × 10-14. Further required improvements, particularly focusing on medium- to long-term clock performance, are discussed.

Example of Data Telemetry for Biomedical Applications: An In Vivo Experiment

This letter describes a data telemetry biomedical experiment. An implant, consisting of a biometric data sensor, electronics, an antenna, and a biocompatible capsule, is described. All the elements were co-designed in order to maximize the transmission distance. The device was implanted in a pig for an in vivo experiment of temperature monitoring.

Dual band antenna for subcutaneous telemetry applications

The use of telemetry with implantable medical devices improves the quality of the health-care system facilitating home therapy. For this purpose, small biocompatible antennas are necessary to establish reliable communication systems [1–5]. In this work we present a dual band antenna conceived to operate in vivo in a subcutaneous environment. The selected working frequencies are: the Medical Device Radiocommunication Service band (MedRadio, 401–406 MHz) [6] and the Industrial, Scientific and Medical band (ISM, 2.4–2.5 GHz). This radiator matches the requirements of a MedRadio transceiver produced by Zarlink Semiconductors [7]. The antenna together with its electronics and power supply [8] forms a versatile im-plantable telecommunication system that can be integrated with the desired medical device.

Double-resonance in alkali vapor cells for high performance and miniature atomic clocks

We present two lines of investigations on vapor cell based laser-microwave double-resonance (DR) rubidium atomic frequency standards: a compact high-performance clock exhibiting σ_y(τ) <; 1.4×10^-13 τ^-1/2 and a miniaturized clock with σ_y(τ) <; 1×10^-11 τ^-1/2. The applications of these standards are emphasized towards portable applications such as next generation GNSS, deep space missions and telecommunications. Other techniques for DR clocks are discussed in brief.