Electromagnetic device design and flexible electronics fabrication are combined to demonstrate mechanically tunable metamaterials operating at terahertz frequencies. Each metamaterial comprises a planar array of resonators on a highly elastic polydimethylsiloxane substrate. The resonance of the metamaterials is controllable through substrate deformation. Applying a stretching force to the substrate changes the inter-cell capacitance and hence the resonance frequency of the resonators. In the experiment, greater than 8% of the tuning range is achieved with good repeatability over several stretching-relaxing cycles. This study promises applications in remote strain sensing and other controllable metamaterial-based devices.

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BackgroundAtrial fibrillation (AF) is the most common and debilitating abnormalities of the arrhythmias worldwide, with a major impact on morbidity and mortality. The detection of AF becomes crucial in preventing both acute and chronic cardiac rhythm disorders.ObjectiveOur objective is to devise a method for real-time, automated detection of AF episodes in electrocardiograms (ECGs). This method utilizes RR intervals, and it involves several basic operations of nonlinear/linear integer filters, symbolic dynamics and the calculation of Shannon entropy. Using novel recursive algorithms, online analytical processing of this method can be achieved.ResultsFour publicly-accessible sets of clinical data (Long-Term AF, MIT-BIH AF, MIT-BIH Arrhythmia, and MIT-BIH Normal Sinus Rhythm Databases) were selected for investigation. The first database is used as a training set; in accordance with the receiver operating characteristic (ROC) curve, the best performance using this method was achieved at the discrimination threshold of 0.353: the sensitivity (Se), specificity (Sp), positive predictive value (PPV) and overall accuracy (ACC) were 96.72%, 95.07%, 96.61% and 96.05%, respectively. The other three databases are used as testing sets. Using the obtained threshold value (i.e., 0.353), for the second set, the obtained parameters were 96.89%, 98.25%, 97.62% and 97.67%, respectively; for the third database, these parameters were 97.33%, 90.78%, 55.29% and 91.46%, respectively; finally, for the fourth set, the Sp was 98.28%. The existing methods were also employed for comparison.ConclusionsOverall, in contrast to the other available techniques, the test results indicate that the newly developed approach outperforms traditional methods using these databases under assessed various experimental situations, and suggest our technique could be of practical use for clinicians in the future.

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Poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS) is a conducting polymer and is a promising material for use in optoelectronic devices. Adding dopants to PEDOT/PSS significantly affects its optoelectronic properties: in this article we use terahertz time domain spectroscopy (THz-TDS) to probe the effects of dopants dimethyl sulfoxide (DMSO) and ethylene glycol. The carrier density, mobility, and conductivity are calculated from the THz measurements by fitting the dielectric permittivity to the Drude−Smith model. This gives us an insight into the conductivity enhancement mechanisms, and we find evidence to suggest that both carrier delocalization and charge screening play a role, although the relative importance of these two mechanisms depends upon both dopant polarity and concentration. To demonstrate an application of this finding, we design and fabricate broadband terahertz neutral density filters based upon 6% DMSO doped PEDOT/PSS thin films of varying thickness and demonstrate optical densities between 0.14 and 0.53 from 0.5 to 2.2 THz with a comparable frequency variation to commercially available optical frequency ND filters.