Microwave doppler radar offers significant improvements for unobtrusive heart and respiration measurement. Radar monitoring enables non-contact measurement, through clothing, of heart and respiration rate, which is desired in several applications ranging from medical sleep laboratory measurements to home health care measurements and stress monitoring. The use of high frequency radar ( 10 GHz) instead of lower frequencies ( 2.4 GHz) increases the signal-to-noise-ratio of the signal and enables the utilization of commercial radar modules. However, if high frequency radar is used, linear combining of quadrature radar channels is inadequate. Instead, a nonlinear channel combining algorithm is needed. The combining can be performed with an arctangent function if center, amplitude error, and phase error are estimated accurately and corrected. In this paper, we show that the Levenberg-Marquardt (LM) center estimation algorithm outperforms the state-of-the-art center estimation algorithm precision-wise and is computationally less complex. The simulated results show that the root mean squared error with the LM method is always less than 1%, while it is around 5%-13% with the compared method, depending on the breathing signal model used. In addition, the computational complexity of the LM method stays almost constant as the size of the data set increases, whereas with the reference method, it increases exponentially. In this paper, the LM method is validated both with simulations and with real data.Index Terms-Biomedical signal processing, Doppler radar measurement, non-contact heart and respiration measurement, physiological monitoring, remote sensing.

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The modest low-frequency attenuation of the conventional passive hearing protector can be improved electronically by active noise cancellation techniques. This paper presents the theory and some of the actual limitations of an active noise cancellation hearing protector. Three prototypes with similar types of controller, but with different mechanical construction were made and their performance was measured. The electronics of the system were implemented using analog electronics and feedback construction. The measurement results were compared with the results of an equivalent passive hearing protector with no internal electronics and with an intact earcup. The results show that the integration of the controller inside the earcups degrades the passive attenuation of the hearing protector at frequencies below 200 Hz. With proper design, an active noise cancellation hearing protector can still have 15 dB more noise attenuation at 100 - 200 Hz range than an equivalent passive hearing protector.

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When designing an active noise cancellation hearing protector, it is relatively easy to implement a laboratory prototype with high performance. However, when the device is taken out of the laboratory into real extremely noisy situations, it must be capable of producing very high sound pressure levels. In this paper, the factors, which limit the low frequency performance and dynamic range are analysed. The results show that the voltage swing of the loudspeaker amplifier and the force factor of the loudspeaker are two important limiting factors in extremely loud situations. A prototype of an active noise cancellation hearing protector was implemented and its performance was measured in an authentic noisy situation. The developed device attenuated 125 Hz tonal noise by 18 dB. The active noise cancellation system attenuated noise even at a sound pressure level of 118 dB SPL. This can be considered sufficient for most situations.