Martin Ouwerkerk

Optical switches based on magnesium lanthanide alloy hydrides

It is shown that thin layers of palladium coated magnesium lanthanide alloys reversibly go through an optical transition by variation of the hydrogen concentration, just as has recently been shown for pure lanthanides. With these layers optical switches can be constructed that exhibit three different optical states: a color-neutral transparent state at high hydrogen concentration, a nontransparent dark absorbing state at intermediate hydrogen pressures, and a highly reflective metallic state at low hydrogen pressures. The ratio in transmission between the transparent state and the reflecting state is more than 1000.

Smart technologies for long-term stress monitoring at work

Due to the growing pace of life, stress became one of the major factors causing health problems. We have developed a framework for measuring stress in real-life conditions continuously and unobtrusively. In order to provide meaningful, useful and actionable information, we present stress information, derived from sensor measurements, in the context of persons activities. In this paper, we describe our framework, discuss how we address arising challenges and evaluate our approach on basis of the field studies we have conducted. The main results of the evaluation are that the results of long-term measurements of stress reveal people information about their behavioral patterns that they perceive as meaningful and useful, and trigger their ideas about behavioral changes necessary to achieve a better stress balance.

Emotion measurement platform for daily life situations

The growing interest in affective computing is expected to have its beneficial impact on consumer lifestyle products. Especially emphatic applications — applications that make you feel they really understand you — will serve the current consumer interest in enhanced and meaningful experiences. To do so, the applications will have to measure the users emotional experience. Well-established psychophysiological techniques bear promise, but so far have mainly been validated in laboratory situations. To also apply them in real-life situations, we built an emotion measurement platform. This platform shows that emotional experiences can be measured in a relatively unobtrusive way, while at the same time it enables us to gather knowledge on emotional experiences in everyday-life and it offers the opportunity to prototype emphatic application concepts and test them in relevant situations.

SAND: a modular application development platform for miniature wireless sensors

A modular application development platform for miniature wireless sensor/actuator devices called small autonomous network devices (SANDs) is described. As an application example a system power breakdown of a real-time ECG analysis is presented. The application development SANDs have a volume of about one cubic centimeter. Based upon testing and optimization the schematics and specifications are obtained for the mass-production SANDs. Utilizing system in package (SiP) technology the volume can be reduced up to five times. These devices can be used in a truly unnoticeable and unobtrusive way to serve as the smallest components of a personal health care monitoring system or an ambient intelligence system

Wireless multi sensor bracelet with discreet feedback

A novel wireless multi sensor bracelet has been developed. The design choices of the bracelet - based on insights obtained with a predecessor sensor bracelet -, as well as the rationale for the choice of sensors, are presented. The hardware and software architecture are described. An example of obtained sensor data is shown. The limited battery life of the performance optimized product software fell short of the one week design target. A power optimization of the software has been made, which meets the battery life design target. It is based on current consumption measurements, and optimized sensor timing. The tradeoffs between high performance - short battery life, and low performance - long battery life are analyzed. The learnings from recent field studies on work-related stress and affective health are discussed.

Unobtrusive Emotions Sensing in Daily Life

The measurement of human emotions in a daily life setting is reviewed in this chapter. In detail the hardware aspects of the Philips Research emotion measurement platform are described. The platform contains a wireless skin conductance wristband, a wireless chest strap ECG sensor and a wireless ear clip blood volume pulse sensor, which together with an internet tablet as hub form a personal wireless network. Two examples of applications, which have been evaluated in the form of concepts are presented.

Can mobile skin conductance assessments be helpful in signalling imminent inpatient aggression

Background: A well-known technique to assess (psychological) arousal is to measure the skin conductance level (SCL). Although widely used in experimental psychological research, this technique has not been used often in (locked) psychiatric admission settings on patients who are at a high risk of engaging in aggressive behaviour. One of the obvious reasons for this is that measuring skin conductance, until recently, required a substantial amount of equipment. Methods: As technology developed, it became possible to develop small wearable devices in the form of regular watches to measure the SCL as well as other psycho-physiological parameters. To illustrate the potential this may have for the prevention of aggressive behaviour, a case description is provided of a patient in crisis who became physically aggressive while wearing a skin conductance measurement device. Results: Interestingly, the SCL of the patient had been rising sharply before the first signs of aggressive behaviour were visible. Conclusion: Although it concerns an anecdotal case study, this finding suggests that measuring SCL on a continuous basis in patients who are at a high risk of becoming violent, without this procedure having to interfere with their daily life, may open new avenues for preventing aggression at an earlier stage. A large-scale empirical study in a substantial number of (potentially aggressive) patients is needed, however, to investigate the predictive validity of mobile skin conductance assessments on imminent inpatient aggression in a reliable way.

Mapping facial expression recognition algorithms on a low-power smart camera

Recent developments in the field of facial expression recognition advocate the use of feature vectors based on local binary patterns (LBP). Research on the algorithmic side addresses robustness issues when dealing with non-ideal illumination conditions. In this paper, we address the challenges related to mapping these algorithms on smart camera platforms. Algorithmic partitioning taking into account the camera architecture is investigated with a primary focus of keeping the power consumption low. Experimental results show that compute-intensive feature extraction tasks can be mapped on a massively-parallel processor with reasonable processor utilization. Although the final feature classification phase could also benefit from parallel processing, mapping on a general purpose sequential processor would suffice.

Unobtrusive Sensing of Psychophysiological Parameters

The quantification of the human perception of experiences can be achieved by the sensing of specific psychophysiological parameters. A growing interest develops for the daily life use of these quantification techniques by unobtrusive and unnoticeable data collection. Remote and non invasive sensing technologies are discussed for the sensing of the following psychophysiological parameters: heart rate variability, and muscle stress. A generic miniature platform for miniature wireless sensing applications is described as an important enabler for unobtrusive and unnoticeable sensing. The technology no longer seems to be a limiting factor for unobtrusive and unnoticeable sensing. Initially the sensors will be worn on the body, but ultimately implantable sensors will become widely accepted, allowing access to new parameters, such as hormone levels and body core temperature.

Heart Rate Variability, Sleep, and the Early Detection of Post-traumatic Stress Disorder

Measures of heart rate variability (HRV) are sensitive indices of autonomic nervous system functioning, capable of distinguishing activity of its two constituent branches, the sympathetic and parasympathetic nervous systems. As such, these measures are possibly useful as early markers of post-traumatic stress disorder (PTSD). We review the anatomical and physiological background of the cardiovascular system and provide guidelines for measuring the electrocardiogram and for deriving HRV measures. In addition, normative values for various HRV measures are provided, both in the time domain and in the frequency domain. We then review literature linking these HRV measures to PTSD, to sleep, and to the combination of PTSD and sleep. From this review, it appears that during awake resting states, PTSD patients are characterized by low parasympathetic tone, relative to healthy controls, resulting in elevated mean heart rates and reduced cardiac reactivity. By contrast, during sleep PTSD patients appear to be characterized by increased sympathetic activation, mainly observed during REM sleep, again with elevated mean heart rate and reduced reactivity as a consequence. We advocate the use of HRV measures in studies aimed at identifying individuals at risk for developing PTSD symptoms.