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Loudspeakers are often modelled as a rigid piston in an infinite baffle. This model is for real loudspeakers somewhat limited in two ways. One issue is that a loudspeaker is not rigid and a second issue is that a loudspeaker is mostly used in a cabinet. Both issues are addressed here by developing the velocity of the radiator in terms oforthogonal polynomials known from optical diffraction theory as Zernike circle polynomials. Using these polynomials we develop semi-analytic expressions for the sound pressure from the radiator in two different cases: as a flexible flat radiator mounted in an infinite baffle, and as the cap of a rigid sphere. In the latter case the comparison is done not only for the pressure but also for other quantitiesviz. the baffle-step response, sound power and directivity, and theacoustic center of the radiator. These quantities are compared withthose from a real loudspeaker.

The theory of orthogonal polynomial (Zernike) expansions of functions on a disk, as used in the diffraction theory of optical aberrations, is applied to obtain (semi-) analytical expressions for the spatial impulse responses arising from a non-uniformly moving, baffled, circular piston. These expressions are in terms of the expansion coefficients of the non-uniformity and the responses of the orthogonal expansion functions. The latter impulse responses have a closed formas finite series involving Legendre functions and the sinc function.The method is compared with a similar method, proposed in P.R. Stepanishen, J. Acoust. Soc. Am. 70, 1176-1181, 1981 where zero-th orderorthogonal Bessel functions, rather than Zernike polynomials, are used as expansion functions. The method is also considered for retrieval of a non-uniform velocity profile from measured spatial impulseresponses on the level of expansion coefficients, which can be applied to acoustic holography for loudspeakers.

Snoring is a prevalent disorder affecting 20-40% of the general population. The mechanism of snoring is vibration of anatomical structures in the pharyngeal airway. Flutter of the soft palate accounts forthe harsh aspect of the snoring sound. Natural or drug-induced sleep is required for its appearance. Snoring is subject to many influences such as body position, sleep stage, route of breathing and the presence or absence of sleep-disordered breathing. Its presentation may be variable within or between nights. While snoring is generallyperceived as a social nuisance, rating of its noisiness is highly subjective and, therefore, inconsistent. Objective assessment of snoring is important to evaluate the effect of treatment interventions. Moreover, snoring carries information on the site and degree of obstruction of the upper airway. If evidence for monolevel snoring at thelevel of the soft palate is provided, the patient may benefit frompalatal surgery. These considerations have inspired researchers to scrutinize the acoustic characteristics of snoring events. Similarlyto speech, snoring is produced in the vocal tract. Because of this analogy, existing techniques for speech analysis have been applied toevaluate snoring sounds. It appears that the pitch of the snoring sound is in the low frequency range (< 500 Hz) and corresponds to a fundamental frequency with associated harmonics. The pitch of snoringis determined by vibration of the soft palate, while nonpalatal snoring is more noise-like, and has scattered energy content in the higher spectral sub-bands (> 500 Hz). To evaluate acoustic propertiesof snoring, sleep nasendoscopy is often performed. Recent evidencesuggests that the quality of snoring is markedly different in drug-induced sleep as compared with natural sleep. Most often, palatal surgery alters sound characteristics of snoring, but is no cure for this disorder. It is uncertain whether the perceived improvement afterpalatal surgery, as judged by the bed partner, is due to an alteredsound spectrum. Whether some acoustic aspects of snoring, such as changes in pitch, have predictive value for the presence of obstructive sleep apnea is at present not sufficiently substantiated.

Brain computer interfaces (BCI) that use the steady-state-visual-evoked-potential (SSVEP) as neural source, offer two main advantages over other types of BCIs: shorter calibration times and higher information transfer rates. SSVEPs elicited by high frequency (larger than30 Hz) repetitive visual stimulation are less prone to cause visualfatigue, safer, and more comfortable for the user. However in the high frequency range there is a practical limitation because only fewfrequencies can elicit sufficiently strong SSVEPs for BCI purposes.We bypass this limitation by using only one stimulation frequency and different phases. To detect the phase from the recorded SSVEP, weuse spatial filtering combined to phase synchrony analysis. We developed an online BCI implementation which was tested on six subjects and resulted on an average accuracy of 95.5% and an average bit rateof 34 bits-per-minute. Our approach has the advantage of entailing only minimal visual annoyance for the user.

It has been suggested by Morse and Ingard that the sound radiation of a loudspeaker in a box is comparable to that of a spherical cap ona rigid sphere. This has been established recently by the present authors, who developed a computation scheme for the forward and inverse calculation of the pressure due to a harmonically excited, flexible cap on a rigid sphere with an axially symmetric velocity distribution. In this paper the comparison is made for other quantities relevant to audio engineers, namely, the baffle-step response, sound power and directivity, and the acoustic center of a radiator.

This paper describes a method to adapt the spectral features extracted from heart rate variability (HRV) for sleep and wake classification. HRV series can be derived from electrocardiogram (ECG) signals obtained from single-night polysomnography (PSG) recordings. Traditionally, the HRV spectral features are extracted from the spectrum ofan HRV series with fixed boundaries specifying bands of very low frequency (VLF), low frequency (LF), and high frequency (HF). However,because they are fixed, they may fail to accurately reflect certainaspects of autonomic nervous activity, which in turn may limit theirdiscriminative power when using HRV spectral features, e.g., in sleep and wake classification. This is in part related to the fact thatthe sympathetic tone (partially reflected in the LF band) and the respiratory activity (modulated in the HF band) will vary over time.In order to minimize the impact of these differences, we adapt the HRV spectral boundaries using time-frequency analysis. Experiments conducted on a dataset acquired from 15 healthy subjects show that thediscriminative power of the adapted HRV spectral features are significantly increased when classifying sleep and wake. Additionally, this method also provides a significant improvement of the overall classification performance when used in combination with some other (non-spectral) HRV features.

By illuminating the skin, a photoplethysmograph can measurea patient’s heart rate and blood oxygenation. The optical signals measured (PPGs) are highly susceptible to motion, which can distort the PPG derived data. It is hypothesized that motion induced opticalartifacts in PPGs correlate to movement of the sensor with respect to the skin. To investigate this correlation, a displacement measuring method using the self-mixing interferometric effect of a laser diode has been designed and tested in a laboratory setup. It is shown that displacement between the laser diode and a skin phantom can be measured accurately using the proposed method. Therefore the proposedmethod can be applied to measure displacement between a PPG sensorand skin and used to determine whether sensor displacement correlates to optical motion artifacts in PPGs. Conclusion - It has been demonstrated that displacement between a laser diode and a Delrin skinphantom can be accurately measured using the SMI effect of a laser diode of which the driving current is amplitude modulated. Therefore,this method can be applied to measure displacement between a PPG sensor and skin, and used to determine whether sensor displacement correlates to optical motion artifacts in PPGs.

Currently, photoplethysmograms (PPGs) are mostly used to determine apatient's blood oxygenation and pulse rate. However, PPG morphologyconveys more information about the patient's cardiovascular status.Extracting this information requires measuring clean PPG waveformsthat are free of artifacts. PPGs are highly susceptible to motion, which can distort the PPG derived data. Part of the motion artifactsare considered to result from sensor-tissue motion and sensor deformation. It is hypothesized that these motion artifacts correlate withmovement of the sensor with respect to the skin. This hypothesis has been proven true in a laboratory setup. In-vitro PPGs have been measured in a skin perfusion phantom that is illuminated by a laser diode. Optical motion artifacts are generated in the PPG by translating the laser diode with respect to the PPG photodiode. The optical motion artifacts have been reduced significantly in-vitro, by using anormalized least-mean-square algorithm with only a single coefficient that uses the laser's displacement as a reference for the motion artifacts. Laser displacement has been measured accurately via self-mixing interferometry by a compact laser diode with a ball lens integrated into the package, which can be easily integrated into a commercial sensor.

Pulse oximeters measure a patient’s heart rate and blood oxygenationby illuminating the skin and measuring the intensity of the light that has propagated through it. The measured intensities, called photoplethysmograms (PPGs), are highly susceptible to motion, which candistort the PPG derived data. Part of the motion artifacts are considered to result from sensor deformation, leading to a change in emitter-detector distance. It is hypothesized that these motion artifacts correlate to movement of the emitter with respect to the skin. This has been investigated in a laboratory setup in which motion artifacts can be reproducibly generated by translating the emitter with respect to a flowcell that models skin perfusion. The top of the flowcell is a diffuse scattering Delrin skin phantom under which a cardiac induced blood pulse is modeled by a changing milk volume. By illuminating the flowcell, a PPG can be measured. The emitter’s translation has been accurately measured using self-mixing interferometry (SMI). The motion artifacts in the PPG as a result of emitter motion are shown to correlate with the emitter’s displacement. Moreover, it is shown that these artifacts are significantly reduced by a least-mean-square algorithm that uses the emitter’s displacement measured via SMI as artifact reference.