Direction-sensitive visitor counting sensors can be used in demand-controlled ventilation (DCV). The counting performance of two light beam sensors and three camera sensors, all direction sensitive, was simultaneously evaluated at an indoor location. Direction insensitive sensors (two mat sensors and one light beam sensor) were additionally tested as a reference. Bidirectional counting data of free people flow was collected for 36 days in one-hour resolution, including five hours of manual counting. Compared to the manual results, one of the light beam sensors had the most equally balanced directional overall counting errors (4.6% and 5.2%). The collected data of this sensor was used to model the air transportation energy consumption of visitor counting sensor-based DCV and constant air volume ventilation (CAV). The results suggest that potential savings in air transportation energy consumption could be gained with the modeled DCV as its total daily airflow during the test period was 54% of the total daily airflow of the modeled CAV on average. A virtually real-time control of ventilation could be realized with minute-level counting resolution. Site-specific calibration of the visitor counting sensors is advisable and they could be complemented with presence detectors to avoid unnecessary ventilation during unoccupied periods of the room. A combination of CO 2 and visitor counting sensors could be exploited in DCV to always guarantee sufficient ventilation with a short response time.

No abstract

A single-ended second-order active low-pass filter can simultaneously provide high gain factor and dc voltage subtraction. This makes it possible to reduce the number of components and signal processing stages needed in an application where small voltage changes are measured on the top of large dc voltage masked by a large amplitude oscillating carrier. The filter described in this paper is constructed from a conventional 3-op-amp instrumentation amplifier and five passive circuit elements.

Objective: Photoplethysmography (PPG) has become the standard technology used in wearable health and fitness monitoring devices. Although, PPG works well at rest, trying to incorporate it for continuous monitoring is challenging, since the signal is inevitably corrupted by motion artifacts. This paper explores the feasibility of a reflective PPG sensor aiming at reducing the changes caused by motion in the non-pulsatile component of the signal, e.g., changes in venous filling. Approach: The tested sensor consisted of two back-to-back connected photodiodes and a light source with a peak wavelength around 575 nm. Additionally, the second photodiode was covered by a 575±5 nm optical notch filter. Main results: When compared to standard PPG (single detector) on one test subject, the tested sensor provided 4.38 dB of attenuation for a change in venous blood during a gentle lift of upper extremity. Moreover, over 40 dB rejection was measured in the baseline resulting in a very small 'direct current' (DC) component. Furthermore, the baseline wander due to respiratory modulation tended to be smaller for the tested sensor. The sensor was not either susceptible for the changes in ambient light or the drift caused by the light source heating up. Significance: We believe that this is the first work that proposes the back-to-back connected photodiodes and a notch filter to reduce in-band noise in PPG. The positive results encourage to further optimize and integrate the sensor. The novelty of the method also brings new perspective to the PPG measurements.

BackgroundTomographic imaging has revealed that the body mass index does not give a reliable state of overall fitness. However, high measurement costs make the tomographic imaging unsuitable for large scale studies or repeated individual use. This paper reports an experimental investigation of a new electromagnetic method and its feasibility for assessing body composition. The method is called body electrical loss analysis (BELA).MethodsThe BELA method uses a high-Q parallel resonant circuit to produce a time-varying magnetic field. The Q of the resonator changes when the sample is placed in its coil. This is caused by induced eddy currents in the sample. The new idea in the BELA method is the altered spatial distribution of the electrical losses generated by these currents. The distribution of losses is varied using different excitation frequencies. The feasibility of the method was tested using simplified phantoms. Two of these phantoms were rough estimations of human torso. One had fat in the middle of its volume and saline solution in the outer shell volume. The other had reversed conductivity distributions. The phantoms were placed in the resonator and the change in the losses was measured. Five different excitation frequencies from 100 kHz to 200 kHz were used.ResultsThe rate of loss as a function of frequency was observed to be approximately three times larger for a phantom with fat in the middle of its volume than for one with fat in its outer shell volume.ConclusionsAt higher frequencies the major signal contribution can be shifted toward outer shell volume. This enables probing the conductivity distribution of the subject by weighting outer structural components. The authors expect that the loss changing rate over frequency can be a potential index for body composition analysis.