Maria Lucia Scarpello

Design of an Implantable Slot Dipole Conformal Flexible Antenna for Biomedical Applications

We present a flexible folded slot dipole implantable antenna operating in the Industrial, Scientific, and Medical (ISM) band (2.4-2.4835 GHz) for biomedical applications. To make the designed antenna suitable for implantation, it is embedded in biocompatible Polydimethylsiloxane (PDMS). The antenna was tested by immersing it in a phantom liquid, imitating the electrical properties of the human muscle tissue. A study of the sensitivity of the antenna performance as a function of the dielectric parameters of the environment in which it is immersed was performed. Simulations and measurements in planar and bent state demonstrate that the antenna covers the complete ISM band. In addition, Specific Absorption Rate (SAR) measurements indicate that the antenna meets the required safety regulations.

Stability and Efficiency of Screen-Printed Wearable and Washable Antennas

Wearable antennas, integrated into garments, are prone to get dirty. Therefore, for the first time in literature, washable antennas are proposed by covering textile antennas by a breathable thermoplastic polyurethane coating, protecting the antennas against water absorption and corrosion. The washability of coated wearable antennas produced by screen printing conductive ink onto a textile substrate is compared to coated wearable antennas based on an electrotextile, analyzing performance in terms of their reflection coefficient and radiation efficiency before and after washing. The combination of screen printing and coating provides stable antenna performance with sufficiently high radiation efficiency after several washing cycles.

Performance study of screen-printed textile antennas after repeated washing

Abstract The stability of wearable textile antennas after 20 reference washing cycles was evaluated by measuring the reflection coefficient of different antenna prototypes. The prototypes’ conductive parts were screen-printed on several textile substrates using two different silver-based conductive inks. The necessity of coating the antennas with a thermoplastic polyurethane (TPU) coating was investigated by comparing coated with uncoated antennas. It is shown that covering the antennas with the TPU layer not only protects the screen-printed conductive area but also prevents delamination of the multilayered textile fabric substrates, making the antennas washable for up to 20 cycles. Furthermore, it is proven that coating is not necessary for maintaining antenna operation and this up to 20 washing cycles. However, connector detachment caused by friction during the washing process was the main problem of antenna performance degradation. Hence, other flexible, durable methods should be developed for establishing a stable electrical connection.

Indoor Off-Body Wireless Communication: Static Beamforming versus Space-Time Coding

The performance of beamforming versus space-time coding using a body-worn textile antenna array is experimentally evaluated for an indoor environment, where a walking rescue worker transmits data in the 2.45 GHz ISM band, relying on a vertical textile four-antenna array integrated into his garment. The two transmission scenarios considered are static beamforming at low-elevation angles and space-time code based transmit diversity. Signals are received by a base station equipped with a horizontal array of four dipole antennas providing spatial receive diversity through maximum-ratio combining. Signal-to-noise ratios, bit error rate characteristics, and signal correlation properties are assessed for both off-body transmission scenarios. Without receiver diversity, the performance of space-time coding is generally better. In case of fourth-order receiver diversity, beamforming is superior in line-of-sight conditions. For non-line-of-sight propagation, the space-time codes perform better as soon as bit error rates are low enough for a reliable data link.

High-Gain Textile Antenna Array System for Off-Body Communication

A novel high-gain textile antenna array system, fully integrated into a rescue-worker’s vest and operating in the Industrial, Scientific, and Medical wireless band (2.4–2.4835 GHz), is presented. The system comprises an array consisting of four tip-truncated equilateral triangular microstrip patch antennas (ETMPAs), a power divider, line stretchers, and coaxial cables. The array is vertically positioned on the human torso to produce a narrow beam in elevation, as such reducing fading and allowing to steer the maximum gain in a small angular sector centered around the broadside direction. To allow simple low-cost beam steering, we specifically minimize mutual coupling by using a relative large distance between the patches and by selecting the ETMPA element as the most suited topology from three potential patch geometries. Moreover, we investigate the stability of return loss and mutual coupling characteristics under different relative humidity conditions, when bending the array, when placing the system on-body, and when covering it by different textile layers. Reflection coefficient and gain patterns are simulated and measured for the antenna system in free space and placed on the human body.

Washable Screen Printed Textile Antennas

The wireless communication systems are applied in different applications such as computers, mobile phones, satellites and antennas for off-body communication. A lot of efforts were made to have the antennas in a smaller size, flat and with better performance. In the last decade the rigid antennas are replaced with textile in order to be flexible and to be integrated into garments in order to have wearable textile systems. The textile antennas can find use in medical, military and first responders monitoring. The conductivity of the antennas can be achieved by using coated textile materials which are available in the market, conductive threads for embroidery or conductive inks. When using the conductive coated textile it is necessary to cut the patch in the desired pattern but using a simple cutting tool sometimes is not very precise and accurate. Thus in our study we decide to screen print with silver conductive inks on Polyester and Cotton/Polyester substrates. The screen printed antennas are than washed in order to conform that antennas for off-body communication integrated in garments can be easily washed five times.

In-body path loss models for implants in heterogeneous human tissues using implantable slot dipole conformal flexible antennas

A wireless body area network (WBAN) consists of a wireless network with devices placed close to, attached on, or implanted into the human body. Wireless communication within a human body experiences loss in the form of attenuation and absorption. A path loss model is necessary to account for these losses. In this article, path loss is studied in the heterogeneous anatomical model of a 6-year male child from the Virtual Family using an implantable slot dipole conformal flexible antenna and an in-body path loss model is proposed at 2.45 GHz with application to implants in a human body. The model is based on 3D electromagnetic simulations and is compared to models in a homogeneous muscle tissue medium.

Simulation of path loss between biocompatible antennas embedded in homogeneous human tissues and comparison of their specific absorption rate

A Wireless Body Area Network (WBAN) is a network, consisting of nodes that communicate wirelessly and are located on or in the body of a person. In this paper, we study the wave propagation using biocompatible folded slot dipole antennas within various lossy human tissues such as the muscle tissue, skin and the fat layer and obtain their path loss (PL) and specific absorption rate (SAR) by means of simulations, and fit a suitable path loss model to the propagation scenario at hand.