Increase of Input Resistance of a Normal-Mode Helical Antenna (NMHA) in Human Body Application

RF communication between dual band implantable and on body antennas for biotelemetry application

This paper investigates two antennas for implantable communication, which are a wide-band, low-profile transmitting antenna with a circular polarization (CP) merit immersed in a lossy medium and a corresponding wide-band, low-profile receiving antenna with a linear polarization (LP) merit placed on human tissue. The first antenna is implantable inside a human body for sensing, monitoring, and transmitting various vital signs, while the second antenna acts as a nearby receiving end. These antennas work in the 2.4-2.4835 GHz and 5.725-5.875 GHz industrial, scientific, and medical (ISM) bands. The main features of the designed transmitting antenna are its simplicity, the wide-band characteristics, which preserve the detuning effect caused by environmental heterogeneity, and the CP property at both operational ISM bands. Moreover, for introducing an electrically small antenna footprint with proper performance, the implantable antenna is designed with an entire size of 25.4 (5× 5 × 1.016) [Formula: see text]. This antenna is designed and dissected in a homogeneous skin model (HSM) as well as a three-layer phantom. On the other hand, the wide-band receiving antenna is designed on flexible material for patients' comfort with a compact size of 134.6 ([Formula: see text]) [Formula: see text]. In addition, the implantable antenna performance is evaluated in a chicken slab as well as a saline solution, while the on-body antenna is placed on the chicken slab to measure its reflection coefficient. The measured impedance BWs of the implantable antenna are 13.04 % and 33.2 % in the chicken slab while 19.5% and 25.2 % in the saline solution at the two ISM bands, respectively. While, the measured impedance BWs of the on-body antenna are 24% and 50.4 % at two operating ISM frequencies. Finally, the measured transmission coefficient between the two antennas is evaluated.

Implantable small ultra-wideband circularly polarized antenna design for continuous blood pressure monitoring

This paper presents a miniaturized circularly polarized (CP) implantable antenna Ultra-wide bandwidth for continuous blood pressure monitoring. The miniature and CP of the antenna are gained by using a new slot method. The symmetry slots in the radiation patch, two T-shape slots in the GND, coupled with the use of a short pin make the designed antenna with good physical and radiation properties. In simulation, the fractional effective axial ratio bandwidth is 23.6% (2.36-2.94 GHz), and the peak gain is - 28.9 dBi. Its total size is only 17.78 mm3 (0.056 × 0.04 × 0.004 λ03), which size is smaller compared to other antennas with similar performance. A prototype is fabricated and measured. The experimental results are in good agreement with the simulation results. And, the radiation patterns have good symmetry both in the simulation and measurement. In addition, the maximum SAR value is in accordance with the IEEE standard safety guidelines (IEEE C95.1-2019).

Low-Cost Automated Design of Compact Branch-Line Couplers

Branch-line couplers (BLCs) are important components of wireless communication systems. Conventional BLCs are often characterized by large footprints which make miniaturization an important pre-requisite for their application in modern devices. State-of-the-art approaches to design compact BLCs are largely based on the use of high-permittivity substrates and multi-layer topologies. Alternative methods involve replacement of transmission-line sections of the circuit, with their composite counterparts, referred to as compact cells (CCs). Due to the efficient use of available space, CC-based couplers are often characterized by small footprints. The design of compact BLCs is normally conducted based on engineering experience. The process is laborious and requires many adjustments of topology followed by manual or, semi-automatic tuning of design parameters. In this work, a framework for low-cost automated design of compact BLCs using pre-defined CCs is proposed. The low cost of the presented design technique is ensured using equivalent-circuit models, space mapping correction methods, and trust-region-based local optimization algorithms. The performance of the framework is demonstrated based on three examples, concerning the design of unequal-power split coupler, comparison of automatically generated compact BLCs, as well as rapid re-design of the coupler for different substrates. Furthermore, the approach has been benchmarked against the state-of-the-art methods for low-cost design of circuits.