Showing papers by "Toni Bjorninen published in 2015"

A Minimally Invasive 64-Channel Wireless μECoG Implant

Abstract: 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.

The effects of recurrent stretching on the performance of electro-textile and screen-printed ultra-high-frequency radio-frequency identification tags

Abstract: Future welfare and healthcare applications require wearable radio-frequency identification (RFID) tags where the tag antenna is an integral part of clothing and endures repeated stretching. In this study, wearable passive ultra-high-frequency (UHF) RFID tag antennas were fabricated from silver-plated stretchable fabric and by screen printing them on non-conductive, stretchable fabric. The reliability of the tags was studied by stretching them repeatedly from the initial length of 10 cm to 13.5 cm, up to 200 stretching cycles. According to our results, the electro-textile tags achieved read ranges of 6.5 meters, also after the 200 harsh stretches. The screen-printed tags initially achieved read ranges of 9.5 meters and after the 200 stretches the read ranges were only 2.5 meters shorter, that is, still about 7 meters. These measurement results and the strengths and weaknesses of both types of wearable tags are discussed in this paper.

Backscattering Neural Tags for Wireless Brain-Machine Interface Systems

Abstract: 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 $1\times 1\times 1\ {\rm mm}^{3}$ 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 pig's head. This demonstrates the feasibility of extremely small implant antennas in challenging wireless biomedical systems.

Inkjet-Printed Wideband Planar Monopole Antenna on Cardboard for RF Energy-Harvesting Applications

Abstract: We present a fully inkjet-printed novel wideband planar monopole antenna on thin packaging cardboard available in bulk for low-cost and environmentally-friendly mass manufacturing. We outline the characterization and the dielectric properties of the cardboard that are imperative for the successful design of an antenna on a paper-based substrate. To achieve highly conductive inkjet-printed pattern on the fibrous and porous cardboard, we deposit thin dielectric coating on the cardboard in the same inkjet process. The operation of the antenna is attested through simulations and measurements in the frequency range of 600–1500 MHz, where there are several strong radio signals present for ambient RF energy harvesting.

Experimental Study on the Washing Durability of Electro-Textile UHF RFID Tags

Abstract: In this letter, we investigate the impact of washing on the performance of passive ultra-high frequency (UHF) radio frequency identification (RFID) tags based on dipole antennas fabricated from silver and copper fabrics. Initially, the tags achieved read ranges of 6 and 10.8 m, respectively, under the European RFID emission regulation. To assess the impact of washing on the performance of the tags, they were washed repeatedly in a washing machine and measured after every washing cycle. The silver fabric tag was found to be more durable without any coating and maintained a read range of over 2 m after 10 washing cycles. We also tested two conformal coatings to protect the tags from wear and tear during washing and found regular textile glue to be a promising conformal coating for both types of textile tags. Finally, we present simulation results to confirm the relationship between reduction in the antenna conductivity and the measured read ranges of the tags during the washing test.

Implementation and wireless readout of passive UHF RFID strain sensor tags based on electro-textile antennas

Abstract: Sensing capabilities embedded in a passive UHF RFID tag provide a battery-free wireless sensor equipped with a digital identifier. We present an RFID strain sensor tag based on a stretchable antenna made of conductive fabrics. To create an efficient antenna for the sensor tag, we use non-stretchable and highly conductive copper-coated fabric to form the main antenna body and join a section of stretchable conductive fabric by means of sewing with conductive thread. We test wirelessly two different sensors with 1 cm and 3 cm stretchable sections and characterize them in terms of the maximal sensor readout distance and the response of its backscatter strength to the antenna elongation. Our results show that the percentage change in the backscatter strength is in approximately linear relation with the antenna elongation.

Towards Washable Electrotextile UHF RFID Tags: Reliability Study of Epoxy-Coated Copper Fabric Antennas

Abstract: We investigate the impact of washing on the performance of passive UHF RFID tags based on dipole antennas fabricated from copper fabric and coated with protective epoxy coating. Initially, the tags achieved read ranges of about 8 meters, under the European RFID emission regulation. To assess the impact of washing on the performance of the tags, they were washed repeatedly in a washing machine and measured after every washing cycle. Despite the reliability challenges related to mechanical stress, the used epoxy coating was found to be a promising coating for electrotextile tags in moist conditions.

Biotelemetric Wireless Intracranial Pressure Monitoring: An In Vitro Study

Abstract: 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.

Manufacturing of antennas for passive UHF RFID tags by direct write dispensing of copper and silver inks on textiles

Abstract: We report for the first time the deposition antennas on textiles using the direct write dispensing of a copper ink. We outline the steps of the dispensing process and share our insight on how to control it on the rough and porous textile surface. The well-known heat sintering is not applicable on copper inks. Below we outline the process of intense pulsed light sintering to form copper based electro-textile. Using the manufactured electro-textile antenna we have assembled a fully functional radio-frequency identification tag. We compare its performance with other tags based on electro-textile antennas manufactured with several other methods and materials.

Possibilities of 3D direct write dispensing for textile UHF RFID tag manufacturing

Abstract: We outline the possibilities of 3D direct write dispensing in the manufacturing of UHF RFID tags on textile materials and present considerations regarding the process parameters to achieve high-performance tags when the antenna is deposited directly on the rough and porous textile material. We also show that it is possible to use the dispensing to form the antenna-microchip connection using conductive ink only in order to simplify the manufacturing process. Our measurement results confirm that the manufactured textile-based RFID tags achieve high performance with the attainable read ranges of 8.5-to-11 meters in air.

2.4 GHz inkjet-printed RF energy harvester on bulk cardboard substrate

Abstract: An experimental investigation on the inkjetprinted power harvester for 2.4GHz and review of RF characterization of substrate and printed conductors are presented in this paper. A one stage discrete rectifier based on a voltage doubler structure and a planar monopole antenna are fabricated on cardboard using inkjet printing. The performance of the whole system is examined by measuring the output voltage of the RF power harvester. By the utilization of the proposed idea, the fabrication of low-cost environmentally-friendly battery-less wireless modules is conceivable.

Signal strength readout and miniaturised antenna for metal-mountable UHF RFID threshold temperature sensor tag

Abstract: A new method for the wireless monitoring of a battery-free threshold temperature sensor based on a passive ultra-high-frequency radio-frequency identification (RFID) tag integrated with a bimetal thermostat switch is presented. The strategic placement of the switch brings about a strong modification in the tag antenna impedance as the temperature crosses over a threshold value. Optimisation of the narrow-band tag antenna to operate at the edges of the 902–928 MHz frequency-hopping spread spectrum RFID in the different switch states provides separate sub-bands for the readout above and below a threshold temperature. The results show that this enables an unambiguous sensor readout by monitoring the backscattered signal strength.

Two-turns antenna and magnetic materials for effective powering of mm-size implant in wireless brain-machine interface system

Abstract: We analyze a two-turns antenna to provide power wirelessly to 2×2×2 mm3 cubic cortical implant. We present simulation of available power and voltage to the implant and assess the impact of a inserting a magnetic core in the antennas for further performance enhancement. We have fabricated the studied antennas and verified the simulated link power efficiency through measurement in a liquid phantom.

Inkjet-printed monopole antenna and voltage doubler on cardboard for RF energy harvesting

Abstract: We outline the development of an RF energy harvester manufactured on regular packaging cardboard using the inkjet-printing technology. The harvester is composed of a planar monopole antenna, impedance matching network and a voltage doubler circuit. The paper summarizes the procedure of achieving highly conductive traces on rough and porous cardboard, describes the circuit and antenna design, and presents simulated and measured results.

Design and Technical Evaluation of an Implantable Passive Sensor for Minimally Invasive Wireless Intracranial Pressure Monitoring

Abstract: Elevated Intracranial pressure (ICP) is characterized as neurological problem mainly caused as a consequence of traumatic brain injuries (TBI). Early detection of increasing ICP is of great importance in management of TBI. In this paper, we present a fully implantable passive sensor for continuous wireless subdural ICP monitoring. The implantable sensor consists of a 30-turn spiral loop in parallel with a mmsize (1.4×1.4×0.8 mm3 ) microelectromechanical systems (MEMS) capacitive pressure sensor forming an LC tank. The sensor at normal air pressure resonates at 14 MHz. Wireless operation is based on near field inductive coupling between the implantable sensor and an on-body reader coil. The sensor is made on an ultra-thin (50 μm) flexible polyimide substrate making it minimally invasive for implantation. Evaluation of the designed sensor showed the capability of the highly linear pressure measurement ranging from 0 to 70 mmHg at 5-mmHg intervals.

Effect of magnetic core and higher operational frequency on sensitivity in frequency shift detection in wireless passive minimally invasive Intracranial Pressure Monitoring

Abstract: In this paper we study the effect of magnetic core in both the implant and the external reader antenna and higher operational frequency of the implant for wireless passive Intracranial Pressure Monitoring (ICP). Implant and external reader antenna are inductively coupled. ICP can be monitored through the change of implant resonance frequency or external reader antenna input impedance phase dip. We demonstrate that improvement in the sensitivity of ICP monitoring through change of implant resonance frequency can be done by resonating implant at higher frequency. Moreover we perform measurement in biological environment by placing pig skin of 5 mm ± 1 mm between implant and external reader antenna.

Electro-textiles — The enabling technology for wearable antennas in wireless body-centric systems

Abstract: Wireless body-centric sensing systems require light-weight and wearable sensor nodes for remote health monitoring of people. This imposes the need for wearable antennas which are comfortable to the users. In this article we demonstrate the capability of conductive fabrics and embroidered structures in the fabrication of such antennas and sensors. We also outline their measured performance in several prominent applications.

Evaluation of an implantable passive sensor for wireless intracranial pressure monitoring

Abstract: This paper proposes and evaluates a fully implantable passive sensor for minimally invasive intracranial pressure monitoring. The sensor is inductively linked with an on-body reader coil to detect pressure variations. Evaluation of the sensor proved the capability of highly linear pressure measurement ranging from 0 to 70 mmHg at 5-mmHg intervals.