M. Waqas A. Khan

Fabrication and Characterization of Graphene Antenna for Low-Cost and Environmentally Friendly RFID Tags

We present the fabrication and testing of graphene-based dipole antennas on cardboard, which is a promising low-cost, recyclable, and flexible substrate for future wireless electronics. The letter presents the details of the manufacturing, as well as results from the measurements and simulations. The measured sheet resistance of graphene antenna is 1.9 Ω/sq. Overall, a graphene-based planar dipole antenna with the length of 143 mm achieved the measured total efficiency of 40% and the realized gain of - 2.18 dBi at 889 MHz. Moreover, a passive ultra-high-frequency radio-frequency tag based on a graphene dipole antenna on cardboard achieved the attainable read range of more than 5 m at 950 MHz.

Remotely Powered Piezoresistive Pressure Sensor: Toward Wireless Monitoring of Intracranial Pressure

This paper presents the results of pressure measurements taken after the successful activation of an implantable piezoresistive pressure sensor. The sensor was activated using inductive power transmission for an Intracranial Pressure (ICP) monitoring application. This generated sufficient power (4.47 mW) and voltage (1.894 V) at the sensor input to monitor the pressure changes. Although the changes in voltage were monitored through wires, the required electronics for wireless voltage transfer and measurement in a biological environment are planned in the future. The simulated and measured results of the wireless link, along with the measured changes in pressure are presented. The results are the first step towards a wirelessly powered implant for ICP monitoring.

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

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.

Miniature Coplanar Implantable Antenna on Thin and Flexible Platform for Fully Wireless Intracranial Pressure Monitoring System

Minimally invasive approach to intracranial pressure monitoring is desired for long-term diagnostics. The monitored pressure is transmitted outside the skull through an implant antenna. We present a new miniature (6 mm × 5 mm) coplanar implant antenna and its integration on a sensor platform to establish a far-field data link for the sensor readout at distances of 0.5 to 1 meter. The implant antenna was developed using full-wave electromagnetic simulator and measured in a liquid phantom mimicking the dielectric properties of the human head. It achieved impedance reflection coefficient better than −10 dB from 2.38 GHz to 2.54 GHz which covers the targeted industrial, scientific, and medical band. Experiments resulted in an acceptable peak gain of approximately −23 dBi. The implant antenna was submerged in the liquid phantom and interfaced to a 0.5 mW voltage controlled oscillator. To verify the implant antenna performance as a part of the ICP monitoring system, we recorded the radiated signal strength using a spectrum analyzer. Using a half-wavelength dipole as the receiving antenna, we captured approximately −58.7 dBm signal at a distance of 1 m from the implant antenna which is well above for the reader with sensitivity of −80 dBm.

Inductively Powered Pressure Sensing System Integrating a Far-Field Data Transmitter for Monitoring of Intracranial Pressure

Monitoring of intracranial pressure (ICP) provides a life-saving diagnostic tool. We present a battery-free pressure sensing system for minimally invasive ICP monitoring. It comprises a cranially concealed wireless pressure sensor and on- and off-body external units. The sensor is based on a piezoresistive element and is inductively powered through an on-body unit. It is also equipped with a far-field antenna, which conveys the pressure data to the off-body unit. We present the electromagnetic modeling of the system and report results from experiments carried out in a setting, which mimics the biological operation environment. The simulation and measurement results demonstrate the wireless pressure monitoring at a distance up to one meter over the pressure range from −3 to 33 mmHg and assess the impact of an imperfectly aligned inductive link on the operation of the system.

Piezoresistive pressure sensor for ICP monitoring: Remote powering through wearable textile antenna and sensor readout experiment

We attest the feasibility of a textile antenna in remote powering of a piezoresistive pressure sensor through inductive coupling for monitoring of intracranial pressure. The textile antenna made of metallized fabric on light-weight cell foam rubber substrate. Simulated and measured results of the wireless link performance along with measured output voltage versus pressure are presented.

Statistical sensor fusion of ultra wide band ranging and real time kinematic satellite navigation

Real Time Kinematic (RTK) Global Positioning System (GPS) uses carrier phase measurement from GPS signal and it has a high accuracy but has integer ambiguity resolution problem which causes cycle slips and requires good satellite visibility as well. RTK was originally developed for applications such as surveying; in our case the target application is the tracking and the control of a robot hexacopter. The main issue in RTK is the determination of the number of cycles, called integer ambiguity, between the receiver and each satellite. Once the ambiguity is solved, it remains constant as long as the receiver maintains a phase lock on the satellite signals. However, the hexacopter maneuvers or the satellite visibility obstructions can cause the loss of phase lock, and the integer ambiguity needs to be solved again which result in degradation of RTK GPS positioning. This paper presents fusion of Ultra-Wide Band (UWB) and RTK GPS positions through loosely coupled approach in Kalman filter to overcome this issue. Measurement results show that the fusion of UWB and RTK GPS positioning solutions have better performance compared to stand-alone RTK GPS solution.

Effect of temperature variation on remote pressure readout in wirelessly powered intracranial pressure monitoring system

An implantable pressure monitoring system is a compelling approach to home monitoring of intracranial pressure in the long term. In our approach, an on-body unit powers a cranially concealed system where a piezoresistive element senses the pressure. A data transmission unit built in the same platform emits a signal at a pressure dependent frequency through a miniature far field antenna. In this work, we focus on assessing the impact of variable temperature on the pressure readout at an off-body unit through in-vitro experiments.

Performance evaluation of circularly polarized patch antenna on flexible EPDM substrate near human body

This paper presents the performance evaluation of a circularly polarized wearable antenna on flexible Ethylene Propylene Diene Monomer (EPDM) foam substrate. EPDM is a rubber based material with high flexibility, good shock resistance and easy attachment to any curved surface. The designed antenna operates for Industrial, Scientific and Medical (ISM) band and Wireless Body Area Network (WBAN) applications at 2.45 GHz. Copper tape is used as the conductive material for the patch and the ground plane on 3 mm thick EPDM foam substrate having dielectric constant 1.23 and loss tangent 0.02. A rectangular slot along diagonal axis at the center of the circular patch is used for achieving circular polarization at 2.45 GHz. The measured operating frequency range of the antenna spans from 2.36 GHz to 2.48 GHz with the gain of 6.03 dB at 2.45 GHz. A set of comparative results of the antenna in free space and different body parts like arm and leg are compared to validate the operability of the antenna in real environment. This study provides new understanding about rubber material as substrate for flexible wearable antennas.

Wirelessly powered implantable system for wireless long-term monitoring of intracranial pressure

This paper presents the pressure readout results from a piezoresistive pressure sensor in a biological environment mimicking the human head properties for intracranial pressure (ICP) monitoring application. The piezoresistive pressure sensor is powered wirelessly through inductively coupled antennas. After successful activation of the sensor, the pressure readout is demonstrated from 0 mmHg to 30 mmHg with a resolution of one mmHg.