Rene Martinus Maria Derkx

Theoretical Analysis of a First-Order Azimuth-Steerable Superdirective Microphone Array

A first-order azimuth-steerable superdirectional microphone response can be constructed by means of a linear combination of three eigenbeams (monopole and two orthogonal dipoles). Via this method, we can construct any first-order directivity pattern (monopole, cardioid, hypercardioid, etc.) that can be electronically steered to a certain angle on the 2-D plane to capture the desired signal. In this paper, the superdirectional responses are generated via a planar microphone array with a square geometry. We analyze the influence of spatial aliasing on the captured desired signal and the directivity index. Furthermore, we investigate the sensitivity for uncorrelated sensor noise and the sensitivity for phase- and magnitude-errors on the individual sensors. Finally, two rules of thumb are derived to choose the size of the microphone array.

New constraining method for partitioned block frequency-domain adaptive filters

For adaptive filters with many taps, a short processing delay, and relative low computational complexity, the partitioned block frequency-domain adaptive filter (PBFDAF) is a good choice. The computational complexity of this algorithm is significantly reduced by using the alternated constrained PBFDAF. This particular algorithm applies gradient constraints in an alternating manner. In this paper, a serious problem in performance of the alternated constrained PBFDAF is described. Furthermore, a modification is proposed that effectively alleviates this problem. By using this modification together with a gradient constraint approximation, a new efficient alternated constrained PBFDAF is developed. Compared with the fully constrained PBFDAF, this new constraining method does not show any significant performance loss and still has a much smaller computational complexity.

Towards an algorithm for automatic accelerometer-based pulse presence detection during cardiopulmonary resuscitation

Manual palpation is still the gold standard for assessment of pulse presence during cardiopulmonary resuscitation (CPR) for professional rescuers. However, this method is unreliable, time-consuming and subjective. Therefore, reliable, quick and objectified assessment of pulse presence in cardiac arrest situations to assist professional rescuers is still an unmet need. Accelerometers may present a promising sensor modality as pulse palpation technology for which pulse detection at the carotid artery has been demonstrated to be feasible. This study extends previous work by presenting an algorithm for automatic, accelerometer-based pulse presence detection at the carotid site during CPR. We show that accelerometers might be helpful in automated detection of pulse presence during CPR.

Pulse detection with a single accelerometer placed at the carotid artery: Performance in a real-life diagnostic test during acute hypotension

Pulse detection via palpation is a basic and essential procedure in daily medical practice. We have been investigating the performance of a single accelerometer placed above the carotid artery, which is one of the recommended locations for manual palpation. A low-cost sensor attached by an adhesive measures accelerations due to carotid dilatations and whole body vibrations. A real-time demonstrator has been developed to classify 10 second- windows in “Pulse”, “Motion” and “No Pulse” and to infer pulse rate. Data were obtained during a scheduled head-up tilt table test (HUTT). Our results show for a subgroup of 10 patients with acute hypotension a wide spread of “good” signal coverage ranging from as low as 37% up to 100%. Key factors compromising the performance in HUTT are motion artifacts, arrhythmias, sensor placement and sensor-skin coupling. In conclusion, pulse detection with a single accelerometer is sufficiently accurate, if good signal coverage can be achieved.

Performance of an accelerometer-based pulse presence detection approach compared to a reference sensor

Accelerometer sensors are ubiquitously available in consumer electronics such as smart phones and wearables. So far, mainly biomedical applications using accelerometers focus on providing contextual information like step counting, activity monitoring or motion artifact detection and suppression. Still, these sensors offer interesting opportunities for vital sign monitoring, even potentially for the demanding case around cardiac arrest. In this paper we show a basic feasibility study to compare the performance of an accelerometer (ACC) based pulse detection approach versus a commercially available device. For healthy subjects we found an excellent sensitivity of ACC-based pulse detection. The ACC performance was not influenced by changes in position, and ACC sensor placement was easy. The decision time for the commercial pulse detection device ranged from 10.0 – 25 s, while for our ACC-based approach it was 3.5 – 5.0 s using a trained classifier. From this preliminary study we conclude that ACC sensors might offer interesting opportunities for applications in emergency care for vital sign detection.