Polydimethylsiloxane-Embedded Conductive Fabric: Characterization and Application for Realization of Robust Passive and Active Flexible Wearable Antennas

© 2013 IEEE. We present our study on polydimethylsiloxane (PDMS)-embedded conductive fabric, which we propose as a simple yet effective solution to the challenging issue of poor PDMS-metal adhesion, allowing for a relatively easy realization of robust flexible antennas for wearable applications. The method combines the use of conductive fabric as a radiator with PDMS, which acts as the substrate and a protective encapsulation simultaneously. For the first time, a holistic study on the mechanical and electrical properties of the proposed combination of materials is presented thoroughly using a number of fabricated samples. As concept demonstrations, a microstrip patch and a reconfigurable patch antenna are fabricated using the proposed technique to validate the idea. The inclusion of a PDMS-ceramic composite as part of the antenna's substrate, which leads to over 50% reduction in the size compared with a pure PDMS, is also demonstrated to showcase further the versatility of the proposed technique. The fabricated antennas are tested in several wearable scenarios and consistent performance including reconfigurability is obtained even after the antennas are exposed to harsh environments, i.e., extreme bending and machine-washing

Studies in RF power communication, SAR, and temperature elevation in wireless implantable neural interfaces

Implantable neural interfaces are designed to provide a high spatial and temporal precision control signal implementing high degree of freedom real-time prosthetic systems. The development of a Radio Frequency (RF) wireless neural interface has the potential to expand the number of applications as well as extend the robustness and longevity compared to wired neural interfaces. However, it is well known that RF signal is absorbed by the body and can result in tissue heating. In this work, numerical studies with analytical validations are performed to provide an assessment of power, heating and specific absorption rate (SAR) associated with the wireless RF transmitting within the human head. The receiving antenna on the neural interface is designed with different geometries and modeled at a range of implanted depths within the brain in order to estimate the maximum receiving power without violating SAR and tissue temperature elevation safety regulations. Based on the size of the designed antenna, sets of frequencies between 1 GHz to 4 GHz have been investigated. As expected the simulations demonstrate that longer receiving antennas (dipole) and lower working frequencies result in greater power availability prior to violating SAR regulations. For a 15 mm dipole antenna operating at 1.24 GHz on the surface of the brain, 730 uW of power could be harvested at the Federal Communications Commission (FCC) SAR violation limit. At approximately 5 cm inside the head, this same antenna would receive 190 uW of power prior to violating SAR regulations. Finally, the 3-D bio-heat simulation results show that for all evaluated antennas and frequency combinations we reach FCC SAR limits well before 1 °C. It is clear that powering neural interfaces via RF is possible, but ultra-low power circuit designs combined with advanced simulation will be required to develop a functional antenna that meets all system requirements. © 2013 Zhao et al

Washing Durability of PDMS-Conductive Fabric Composite: Realizing Washable UHF RFID Tags

In this letter, we present experimental investigations on washing durability of a polydimethylsiloxane (PDMS)-conductive fabric composite to validate its applicability for the realization of flexible wearable antennas that can withstand multiple washing cycles. For this purpose, we designed an ultrahigh-frequency (UHF) radio frequency identification (RFID) passive tag antenna and fabricated several prototypes using such materials combination. Understanding the challenge of having a robust integration of a lumped electronic component (e.g., RFID IC) on a flexible antenna, a new way to improve the interconnection has also been investigated. The tag prototypes were subjected to recurrent machine-washing tests, and after each washing cycle, their performance was analyzed mainly in terms of the read range. The results reveal that, with a proper treatment on the antenna-IC fixture interconnection, the tag antennas developed with the PDMS-conductive fabric composite can maintain their performance very well, showing a minimum degradation in the read range after 15 cycles of washing

Washing Durability of PDMS-Conductive Fabric Composite Realizing Washable UHF RFID Tags

International audienceIn this letter, we present experimental investigations on washing durability of a polydimethylsiloxane (PDMS)-conductive fabric composite to validate its applicability for the realization of flexible wearable antennas that can withstand multiple washing cycles. For this purpose, we designed an ultrahigh-frequency (UHF) radio frequency identification (RFID) passive tag antenna and fabricated several prototypes using such materials combination. Understanding the challenge of having a robust integration of a lumped electronic component (e.g., RFID IC) on a flexible antenna, a new way to improve the interconnection has also been investigated. The tag prototypes were subjected to recurrent machine-washing tests, and after each washing cycle, their performance was analyzed mainly in terms of the read range. The results reveal that, with a proper treatment on the antenna-IC fixture interconnection, the tag antennas developed with the PDMS-conductive fabric composite can maintain their performance very well, showing a minimum degradation in the read range after 15 cycles of washing. © 2002-2011 IEEE

Optically Transparent Flexible Robust Circularly Polarized Antenna for UHF RFID Tags

© 2002-2011 IEEE. Optically transparent flexible tag antennas are highly desired for some applications, where unobtrusiveness and capability of mounting on curved surfaces are required. On the other hand, circular polarization minimizes signal degradation due to polarization mismatch between the reader and tag antennas, thus ensuring good communication quality and accuracy. In this letter, we present an optically transparent and flexible radio frequency identification passive tag antenna operating in the ultrahigh frequency band and exhibits circular polarization. It is thin, lightweight, and completely encapsulated inside transparent polymer, which protects it against dust, water, heat, and mechanical stress. The tag antenna is made by utilizing highly flexible and transparent conductive-mesh-polymer composite through a simple and low-cost manufacturing process. The antenna design is based on a planar square ring. It achieves a measured maximum read range of about 8.3 m and approximately 47 MHz (885-932 MHz) 3 dB axial-ratio bandwidth (ARBW)

A Minimally Invasive 64-Channel Wireless μeCoG Implant

Emerging applications in brain-machine interface systems require high-resolution, chronic multisite cortical recordings, which cannot be obtained with existing technologies due to high power consumption, high invasiveness, or inability to transmit data wirelessly. In this paper, we describe a microsystem based on electrocorticography (ECoG) that overcomes these difficulties, enabling chronic recording and wireless transmission of neural signals from the surface of the cerebral cortex. The device is comprised of a highly flexible, high-density, polymer-based 64-channel electrode array and a flexible antenna, bonded to 2.4 mm × 2.4 mm CMOS integrated circuit (IC) that performs 64-channel acquisition, wireless power and data transmission. The IC digitizes the signal from each electrode at 1 kS/s with 1.2 μV input referred noise, and transmits the serialized data using a 1 Mb/s backscattering modulator. A dual-mode power-receiving rectifier reduces data-dependent supply ripple, enabling the integration of small decoupling capacitors on chip and eliminating the need for external components. Design techniques in the wireless and baseband circuits result in over 16× reduction in die area with a simultaneous 3× improvement in power efficiency over the state of the art. The IC consumes 225 μW and can be powered by an external reader transmitting 12 mW at 300 MHz, which is over 3× lower than IEEE and FCC regulations