268 research outputs found
On the feasibility of noncontact ECG measurements
Get PDF“© © 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.”The article by Kranjec et al. [1], “Novel methods of
noncontact heart rate measurement: A feasibility study” is
interesting and informative as it compares different contactless
methods for heart rate detection. Nevertheless, the use of the
term “capacitively coupled ECG” (CCECG) in the article is
confusing and may mislead readers.
That article studies the feasibility of four noncontact methods
for heart rate measurement, which are classified in
two groups: “the methods measuring electromagnetic energy
generated by the bioelectrical activity within the cardiac
muscle (referred to as direct methods), and the methods
measuring displacement of a part of the subject’s body
caused by the periodic physical contractions of the heart
(referred to as indirect methods). The first group is represented
by a measuring device which detects changes in
surrounding electric field...” [sic]. Later on, this device is
described in [1] as being based on “capacitively coupled electrodes”
and hence termed “CCECG Measuring Device.” The
electrodes are two 48-cm2 metal plates placed side by side
(see [1, Fig. 3]) placed at distances from 5 to 60 cm from the
chest.Peer ReviewedPostprint (author's final draft
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Solar energy radiation measurement with a low–power solar energy harvester
Get PDFSolar energy radiation measurements are essential in precision agriculture and forest monitoring and can be readily performed by attaching commercial pyranometers to autonomous sensor nodes. However this solution significantly increases power consumption up to tens of milliwatts and can cost hundreds of euros. Since many autonomous sensor nodes are supplied from photovoltaic (PV) panels which currents depend on solar irradiance, we propose to double PV panels as solar energy sensors. In this paper, the inherent operation of the low-power solar energy harvester of a sensor node is also used to measure the open circuit voltage and the current at the maximum power point (IMPP), which allows us to determine solar irradiance and compensate for its temperature drift. The power consumption and cost added to the original solar energy harvester are minimal. Experimental results show that the relation between the measured IMPP and solar irradiance is linear for radiation above 50¿W/m2, and the relative uncertainty limit achieved for the slope is ±2.4% due the light spectra variation. The relative uncertainty limit of daily solar insolation is below ±3.6% and is hardly affected by the so called cosine error, i.e. the error caused by reflection and absorption of light in PV panel surface.Peer ReviewedPostprint (author's final draft
Noniterative algorithms for electrical resistivity imaging applied to subsurface local anomalies
Get PDFIn this paper, we compare five noniterative (one-step) algorithms for two-dimensional electrical resistivity imaging applied to the location of subsurface local anomalies. Here, we analyze the performance of two backprojection algorithms and three algorithms based on a least-squares criterion. These five algorithms can also be adapted for process and medical tomography. Algorithm performance is first assessed from synthetic data derived from an analytical solution. We show that least-squares-based algorithms outperform backprojection algorithms in all situations considered. One of the least-squares algorithms was further validated with experimental measurements involving spherical objects immersed into a water tank. Data were obtained using a 16-electrode linear array and a computer-controlled data-acquisition system. A reference measurement before immersing the objects into the water tank reduced errors in the reconstructed image attributable to the uncertain electrode position and the finite dimensions of the tank. Images deteriorated for deeper objects, but neglecting measurements with the smallest signal-to-noise ratio improved the results.Peer Reviewe
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