Numerical Optimization of a Fully Cross-Coupled Rectifier Circuit for Wireless Passive Ultra Low Power Sensor Nodes.

In the context of the Internet of Things, billions of devices-especially sensors-will be linked together in the next few years. A core component of wireless passive sensor nodes is the rectifier, which has to provide the circuit with sufficient operating voltage. In these devices, the rectifier has to be as energy efficient as possible in order to guarantee an optimal operation. Therefore, a numerical optimization scheme is proposed in this paper, which is able to find a unique optimal solution for an integrated Complementary Metal-Oxide-Semiconductor (CMOS) rectifier circuit with Self-Vth-Cancellation (SVC). An exploration of the parameter space is carried out in order to generate a meaningful target function for enhancing the rectified power for a fixed communication distance. In this paper, a mean conversion efficiency is introduced, which is a more valid target function for optimization than the Voltage Conversion Efficiency (VCE) and the commonly used Power Conversion Efficiency (PCE) and is defined as the arithmetic mean between PCE and VCE. Various trade-offs between output voltage, PCE, VCE and MCE are shown, which provide valuable information for low power rectifier designs. With the proposed method, a rectifier in a low power 55 nm process from Globalfoundries (GF55LPe) is optimized and simulated at -30 dBm input power. A mean PCE of 63.33% and a mean VCE of 63.40% is achieved.

Investigations into the use of handheld near-infrared spectrometer and novel semi-automated data analysis for the determination of protein content in different cultivars of Panicum miliaceumL.

A set of 42 millet (panicum miliaceum L.) samples was investigated for its protein content using standard Kjeldahl analysis and near-infrared spectroscopy. The performance of three handheld spectrometers was compared to a benchtop instrument. The used spectrometers operate in different regions of the NIR, which gives interesting insights into the applicability of each region. Additionally, semi-automated, consumer-oriented multivariate data analysis was compared to sophisticated data evaluation. The performance of the near-infrared instruments was compared using important statistical parameters of the established cross- and test set validated partial least squares regression (PLS-R) models. Milled and intact samples were analysed, in order to further evaluate the importance of homogeneity. The results showed that the benchtop spectrometer is capable of accurately analysing protein content of millet grains, with root mean square error (RMSEP) values for milled and intact grains of approximately 0.5%. Two PLS-R models of handheld instruments also yielded good results for milled grains with RMSEP values of about 0.6%. The semi-automated multivariate data analysis showed some drawbacks compared to standard data processing software. For intact grains, however, similar results could be achieved.

A novel measurement strategy to evaluate the human head as a transition medium for inductive ear-to-ear communication.

This manuscript introduces a novel concept for measuring coil coupling for extremely loose-coupled coils (coupling factors k<10-6; mutual inductance values M<10-10 H). Such a coupling is found everywhere where the ratio of solenoid diameter to coil spacing is >50. Measuring these quantities with a low-power technology requires a sophisticated setup that goes beyond the sensitivity of state-of-the art approaches. The methodology is validated using laboratory measurements with three sets of solenoids (two ferrite-cored, one air-cored) and numerical simulations with COMSOL Multiphysics 5.2a, Stockholm, Sweden. The concept is then employed to investigate the channel characteristics for inductive through-the-head communication within the 3.155-3.195 MHz band. This selected part of the spectrum is in accordance with International Telecommunication Union Radio Regulation 5.116 for low-power wireless hearing aids. By applying a phantom solution, we demonstrate that human tissue layers are transparent for magnetic fields within these frequencies. However, the influence from the relative coil arrangement is evaluated in detail as it restricts the communication range significantly. The coupling results for off-the-shelf Sonion, Roskilde, Denmark, RF 02 AA 10 solenoids considering both lateral and axial displacements might be of special interest for a number of near-field applications.

An ECG simulator with a novel ECG profile for physiological signals.

This work introduces a low-cost open-source electrocardiography (ECG) simulator comprising both MATLAB software for signal generation and a dedicated circuit board for signal output via a commercial sound card. Synthetic, rate-dependent ECG simulation is based on third-order polynomials that are calculated in sections for the main waves and spikes, respectively. Besides the heart rate, the output profile is fully adjustable with respect to Einthoven lead signals I-III, the amplitudes of the individual ECG waves and spikes, as well as the constitution and intensity of common distortions. The underlying coefficients for the synthetic ECG profile are obtained experimentally by analysing recordings of 22 healthy individuals with heart rates in the range of 40-180 bpm. Eight of these recordings are selected to determine the coefficients for the polynomials (training set) while the remaining 14 serve as test set to evaluate their applicability and accuracy. Thereby, a mean correlation of 98.57% is found which is superior in comparison with a widely accepted rate-dependent ECG profile that is generated from square root and linear terms (correlation score: 91.46%). Although other use-cases are feasible, the focus of this work is the development of an ECG simulator for academic research and university education. Both the MATLAB source code and the circuit layout files are available in the online supplement stimulating further work on this topic.