A. Yousaf

High-Resolution, Far-Field, and Passive Temperature Sensing up to 700 °C Using an Isolated ZST Microwave Dielectric Resonator

This paper presents a high-resolution, wireless and passive temperature measurement system up to 700 °C. The sensor is based on a metallization-free monolithic microwave dielectric resonator composed of zirconium tin titanate (Zr0.8Sn0.2TiO4) operating at 2.37 GHz. The external electromagnetic fields of the tracked single mode are adequate for the far-field coupling without the need to use any conducting part on the sensor surface. The measurements are conducted in a light weight refractory bricks oven at a distance of 1.20 m between the sensor and a reader planar antenna connected to a time-domain RADAR-based interrogation unit. This method allows to retain a quality factor (Q) higher than 670 at 700 °C, while the Q-factor from other electromagnetic cavity or microwave dielectric resonators degrades below 100, hence limiting the sensing resolution and increasing the sensitivity to the environmental echoes. The effect of temperature on the tracked sensor resonance frequency, signal-to-noise ratio, Q-factor, thermal expansion, and sensing resolution is presented. The concept is suitable for applications working in extreme environments, such as aerospace applications.

Efficient Wireless Powering of Biomedical Sensor Systems for Multichannel Brain Implants

This paper describes the complete mathematical optimization process of an inductive powering system suitable for the application within implanted biomedical systems. The optimization objectives are thereby size, energy efficiency, and tissue absorption. Within the first step, the influence of the operational frequency on the given quantities is computed by means of finite element simulations, yielding a compromise of power transfer efficiency of the wireless link and acceptable tissue heating in terms of the specific absorption rate. All simulations account for the layered structure of the human head, modeling the dielectric properties with Cole-Cole dispersion effects. In the second step, the relevant coupling and loss effects of the transmission coils are modeled as a function of the geometrical design parameters, enabling a noniterative and comprehensible mathematical derivation of the optimum coil geometry given an external size constraint. Further investigations of the optimum link design also consider high-permeability structures being applied to the primary coil, enhancing the efficiency by means of an increased mutual inductance. Thereby, a final link efficiency of 80% at a coil separation distance of 5 mm and 20% at 20 mm using a 10-mm planar receiving coil can be achieved, contributing to a higher integration density of multichannel brain implanted sensors. Moreover, the given procedure does not only give insight into the optimization of the coil design, but also provides a minimized set of mathematical expressions for designing a highly efficient primary side coil driver and for selecting the components of the secondary side impedance matching. All mathematical models and descriptions have been verified by simulation and concluding measurements.

Wireless measurement system for extracting open loop micro coils paramters

Abstract We report here the wireless extraction of an open ended micro coil inductance L, parasitic capacitance C and resistance R using an inductively coupled passive system which consists of an electrically small magnetic loop antenna as a sensor coil and an open ended test micro coil. Wireless analytical model is developed which includes the gimmick effects generated due to parasitic coupling capacitances. The micro coil parameters i.e. inductance, inter winding capacitance and resistance are extracted from the wirelessly measured impedance signal and then compared with the analytical model. Further the inductively coupled system is simulated using COMSOL multiphyscics in ACDC module.

Open parallel-plate dielectric resonator for passive torque sensing

This paper presents a novel torque sensing concept, based on resonant perturbation of an open parallel plate dielectric resonator. When torque is applied to the shaft, the air gap between the parallel plates fixed on a clamp system is changed, which in turn shifts the frequency of the dielectric resonator. Finite Element Method (FEM) simulations using HFSS (ANSYS®) and experimental results regarding the effects of air gap variation on the TE01δ mode in the 2-3 GHz range are presented to prove the sensing concept.

A parallel plate dielectric resonator as a wireless passive strain sensor

This paper presents a wireless passive strain sensing concept that functions by detuning a dielectric resonator. It is shown how a high Q resonator functions as a wireless passive sensor when correctly matched with an antenna. Finite element and analytical models are compared with experimental data and the sensor cross sensitivity with respect to temperature and humidity are also explored. The sensitivity of the resonance frequency to the strain, temperature and humidity is measured to be 51.6 ppm/μm, 10.09 ppm/K and -0.65 ppm/% respectively.

Efficient inductive powering of brain implanted sensors

This paper describes a size and tissue absorption based comprehensive approach to optimize a pair of coils for the purpose of wireless powering of brain implanted sensors. In the first step, the optimum transmission frequency is determined by considering tolerable coil size, power transmission efficiency and tissue absorption effects. After modeling the important quantities at the frequency of interest, a numerical analysis is performed, revealing a set of coils suitable for efficient inductive powering. This numerical analysis was verified by both FEM simulation and concluding measurements. All simulations account for the layered structure of the human head, modeling the dielectric properties with Cole-Cole dispersion effects. Furthermore, a strategy of boosting power transmission efficiency is covered in simulation and measurement, particularly the application of a ferrite shielding to the transmission coil. In consequence, a link efficiency of 80% at a coil separation distance of 5mm and 20% at 20 mm using a 10mm planar receiving coil can be achieved, contributing to a higher integration density of multi-channel brain implanted sensors.

Wireless power distribution system for brain implants

Implants like brain pacemakers or brain computer interfaces (BCI) fundamentally requires an improved and efficient wireless power distribution system. This work therefore presents a novel concept based on an intermediate resonator, which provides the opportunity to power multiple implants and to minimize furthermore the dimensions of the external power transmitter. Numerical computations specify requirements to the antenna configuration and a model show the electrical behavior. Finally, a prototype system presents an initial implementation, allowing the evaluation of the concept.

Wireless measurement of open loop micro coils

This paper reports for the first time wireless measurement of open loop micro coils inductance, inter winding capacitance and parasitic resistance. Wireless read out is performed using an inductively coupled passive system which consists of an electrically small magnetic loop antenna as a sensing coil and an open loop test micro coil. Further an equivalent circuit model is established which includes the parasitic capacitive coupling effects of the measurement setup. The actual parameters i.e. inductance, inter winding capacitance and resistance of open micro coils are extracted from the wirelessly measured signal and compared with the modeled results.

Motion capture sensor to monitor movement patterns in animal models of disease

In this paper we present two new motion capture sensors to monitor motoric dysfunction in laboratory animals. The parameters that are recorded by our system correspond to neurological deficits that are typical for multiple sclerosis (MS)-like symptoms in animals. Normally, quantification of motor impairment requires neurological examination and complex behavioral testing. However, to perform these tests is an error-prone and time consuming process. Therefore, a strong interest exists in the automation and objective analysis of motoric behavior. Our presented small, accurate, and lightweight motion sensors provides an optimal solution for this problem. The developed motion sensors have the smallest volume and weight requirements available at the moment to monitor motoric dysfunction of animals. The collected data from the sensor is more representative since the subjective human factor is minimized and the animal can stay in its usual environment rather than being placed in a separate observation cage. We present two wireless motion sensors. An active sensor is powered with battery and saving the data on a SD-Card. The second sensor works completely passive and is powered via electromagnetic field. The sensors provide full control over the data of a three-axis accelerometer, a three-axis gyroscope, and a three-axis magnetometer. The two principles were successfully tested in an initial animal experiment.

Novel concept for a wireless and batteryless brain implant array

In case of a neuro-degenerative disorder, closed-loop brain stimulation is able to reduce tremor, rigidity, bradykinesia, as well as postural instability and consequently to improve the patients quality of life. Therefore, we investigate a human machine interface based on a multi-implant approach, which avoids drawbacks of conventional systems. The following paper presents concept, theory, as well as an initial prototype of a novel wireless power distribution / communication system together with the used signal processing. Finally, the publication shows a prospect to the future implant.