Elham Moradi

Miniature implantable and wearable on-body antennas: towards the new era of wireless body-centric systems [antenna applications corner]

Wireless body-centric sensing systems have an important role in the fields of biomedicine, personal healthcare, safety, and security. Body-centric radio-frequency identification (RFID) technology provides a wireless and maintenance-free communication link between the human body and the surroundings through wearable and implanted antennas. This enables real-time monitoring of human vital signs everywhere. Seamlessly integrated wearable and implanted miniaturized antennas thus have the potential to revolutionize the everyday life of people, and to contribute to independent living. Low-cost and low-power system solutions will make widespread use of such technology become reality. The primary target applications for this research are body-centric sensing systems and the relatively new interdisciplinary field of wireless brain-machine interface (BMI) systems. Providing a direct wireless pathway between the brain and an external device, a wireless brain-machine interface holds an enormous potential for helping people suffering from severely disabling neurological conditions to communicate and manage their everyday life more independently. In this paper, we discuss RFID-inspired wireless brain-machine interface systems. We demonstrate that mm-size loop implanted antennas are capable of efficiently coupling to an external transmitting loop antenna through an inductive link. In addition, we focus on wearable antennas based on electrically conductive textiles and threads, and present design guidelines for their use as wearable-antenna conductive elements. Overall, our results constitute an important milestone in the development of wireless brain-machine interface systems, and a new era of wireless body-centric systems.

Effects of Sewing Pattern on the Performance of Embroidered Dipole-Type RFID Tag Antennas

Embroidered tag antennas can be used in on-body applications, such as access control, human monitoring, and sensor tag antennas. The objective of this letter is to investigate the performance of dipole-type tag antennas sewed with different thread densities and with two different sewing patterns. This letter shows that the performance of sewed dipole-type tag antennas improves if the sewing pattern consists of sewed lines along the direction of current flow in the antenna. The sewed simple dipole, which consists of sewed lines along the length of the dipole, achieved up to 7.5 m read range in free space, which is comparable to the performance of the corresponding copper dipole.

Characterization of embroidered dipole-type RFID tag antennas

Wearable RFID tags and wireless sensors can be used for on-body and human monitoring applications. Embroidery with conductive thread provides compelling means for the fabrication of seamlessly garment-integrable antennas for wearable tags and wireless sensors. In this paper, we present the fabrication of fully assembled tags based on embroidered dipole-type antennas. The prototype tags achieve 5.5-to-7 meters read range. Moreover, we present a method for estimating the effective conductivity of the embroidery pattern, which depends on the sewing pattern and the stitch density. This will enable the judicious optimization of embroidered tag antennas using electromagnetic simulation tools.

Backscattering Neural Tags for Wireless Brain-Machine Interface Systems

Brain-machine interface (BMI) technology has tremendous potential to revolutionize healthcare by greatly improving the quality of life of millions of people suffering from a wide variety of neurological conditions. Radio-frequency identification (RFID)-inspired backscattering is a promising approach for wireless powering of miniature neural sensors required in BMI interfaces. We analyze the functionality of millimeter-size loop antennas in the wireless powering of miniature cortical implants through measurements in a human head equivalent liquid phantom and in the head of a postmortem pig. For the first time, we present the design and measurement of a miniature 1×1×1 mm3 backscattering device based on a cubic loop connected with an RFID integrated circuit (IC). Our measurement results show that this very small loop receives sufficient electromagnetic power to activate the IC when the device is implanted in a pigs head. This demonstrates the feasibility of extremely small implant antennas in challenging wireless biomedical systems.

Analysis of wireless powering of mm-size neural recording tags in RFID-inspired wireless brain-machine interface systems

This paper provides a full analysis of powering mm-size cortical implants wirelessly. An effective approach for wireless power and data transfer in neurorecording microsystems is the backscattering-based RFID-inspired communication. In this mechanism, an external interrogator powers the implant unit by microwave radiation power, and the implant IC superimposes the neurosignal on top of the signal backscattered to the interrogator. This paper characterizes wireless RF link between an external transmit antenna and an implantable antenna using the two-port model. It presents the design of a novel 1-mm3 implantable loop antenna and four different external loop antennas with various features to analyze aspects and factors limiting the wireless power transfer.

Design and realization of stretchable sewn chipless RFID tags and sensors for wearable applications

This paper presents the design of a sewed chipless RFID tag and sensor, on a fabric for wearable applications. The proposed design is based on three sewn scatterers on cotton textile. The tag is realized using a computer-aided sewing machine and electro-thread plated with silver. The simulation and frequency-domain measurement results validate the design from 3 to 6 GHz. The tags static backscattered response can be identified in free space and on the human body. Some preliminary results from a sewn stretchable sensor are also given to demonstrate the potential for biomedical applications. Finally, we discuss the main challenges concerning the practical implementation of this technology.

Embroidered RFID tags in body-centric communication

Wearable Radio Frequency Identification (RFID) tags for body-centric communication can be used in security, healthcare and biomedical applications. Embroidered tags using conductive threads are strong candidates for the implementation of wearable antennas. They provide several important features, such as flexibility, integrability, and light-weight structures. In this paper, the on-body performance of embroidered dipole-type ultra-high frequency (UHF) RFID tags is studied. First, modeling techniques for the embroidered tag antennas and for the human body are presented. The simulation models are then used to design and optimize an embroidered dipole tag to provide a read range of 2.5 m when separated from the human arm with a 1-mm thick layer of cotton fabric.

Measurement of Wireless Link for Brain–Machine Interface Systems Using Human-Head Equivalent Liquid

In this letter, we analyze the wireless power transfer from an on-body transmit antenna to a millimeter-size antenna in a cortical implant. The studied wireless link provides power and data telemetry for a battery-free wireless brain-machine interface microelectronic system. We present a cubic 2 × 2 × 2 mm3 implant loop and analyze the effect of a magneto-dielectric core material on the performance of the antenna. We compare the wireless link performances to two different transmit antennas: solid and 2-segmented loops. Our simulation results show that the 2-segmented loop provides reduced near electric field, but maintains the link power efficiency. Finally, we validate the simulated link power efficiencies through measurements in air and in human-head equivalent liquid at 300 MHz.

Biotelemetric Wireless Intracranial Pressure Monitoring: An In Vitro Study

Assessment of intracranial pressure (ICP) is of great importance in management of traumatic brain injuries (TBIs). The existing clinically established ICP measurement methods require catheter insertion in the cranial cavity. This increases the risk of infection and hemorrhage. Thus, noninvasive but accurate techniques are attractive. In this paper, we present two wireless, batteryless, and minimally invasive implantable sensors for continuous ICP monitoring. The implants comprise ultrathin (50 μm) flexible spiral coils connected in parallel to a capacitive microelectromechanical systems (MEMS) pressure sensor. The implantable sensors are inductively coupled to an external on-body reader antenna. The ICP variation can be detected wirelessly through measuring the reader antenna’s input impedance. This paper also proposes novel implant placement to improve the efficiency of the inductive link. In this study, the performance of the proposed telemetry system was evaluated in a hydrostatic pressure measurement setup. The impact of the human tissues on the inductive link was simulated using a 5 mm layer of pig skin. The results from the in vitro measurement proved the capability of our developed sensors to detect ICP variations ranging from 0 to 70 mmHg at 2.5 mmHg intervals.

Antenna design for implanted tags in wireless brain machine interface system

Backscattering-based RFID-inspired communication provides an effective approach for wireless power and data transfer for implantable battery-free brain machine interface microsystems. We compare conventional and segmented transmit loop configurations to reduce the specific absorption rate (SAR) into human body. Moreover, we present novel cubic-millimeter implant antennas and link performance comparisons in terms of both power and voltage delivery to the implant.