Scientific Publications "Sensor + Actuator Technology"

We analyse the influence of reflective photoplethysmography (PPG) sensor positioning relative to blood vessels. A voxel based Monte Carlo simulation framework was developed and validated to simulate photon-tissue interactions. An anatomical model comprising a multi-layer skin description with a blood vessel is presented to simulate PPG sensor positioning at the volar wrist. The simulation framework was validated against standard test cases reported in literature. The blood vessel was considered in regular and dilated states. Simulations were performed with 10 8 photon packets and repeated five times for each condition, including wavelength, relative position of PPG sensor and vessel, and vessel dilation state. Statistical weights were associated to photon packets to represent absorption and scattering effects. A symmetrical arrangement of the PPG sensor around the blood vessel showed the maximum AC …

 

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We compare performances of an expert model-based approach and a data-based baseline for eating event detection using proximity sensor data of smart eyeglasses. Proximity sensors in smart eyeglasses can provide dynamic distance estimates of cyclic temporalis muscle contraction during chewing without skin contact. Our expert model is based on proximity signal preprocessing and two-threshold grid search. In contrast, baseline data models were based on One-class Support-Vector-Machines. We evaluate both models with in-lab and free-living data from 15 participants. Free-living data were obtained across one day of wearing smart eyeglasses with temple-integrated proximity sensors in unconstrained settings. Overall, the retrieval performance F1 score of the two-threshold-based algorithm for free-living data ranged between 0.6 and 0.7, and outperformed all tested SVM model configurations. While SVM …

 

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We investigate non-contact sensing of temporalis muscle contraction in smart eyeglasses frames to detect eating activity. Our approach is based on infra-red proximity sensors that were integrated into sleek eyeglasses frame temples. The proximity sensors capture distance variations between frame temple and skin at the frontal, hair-free section of the temporal head region. To analyse distance variations during chewing and other activities, we initially perform an in-lab study, where proximity signals and Electromyography (EMG) readings were simultaneously recorded while eating foods with varying texture and hardness. Subsequently, we performed a free-living study with 15 participants wearing integrated, fully functional 3Dprinted eyeglasses frames, including proximity sensors, processing, storage, and battery, for an average recording duration of 8.3hours per participant. We propose a new chewing sequence …

 

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PURPOSE: To examine parent perceptions of young children’s acceptability of different methods for wearable sensor placement and the feasibility of a free-living 3 to 7-day wear protocol.
METHODS: This study was conducted in three phases. During phase 1, parents of 3 to 8-year-old children (n= 105) and child care providers (n= 56) completed an online survey to rate aspects of fitting and likelihood of wear for 7 methods (headband, eyeglasses, skin adhesive patch, shirt clip/badge, mask, necklace, vest). During phase 2, parent/child (3-8 years old) dyads (n= 30) were asked to wear one of the top 5 prototypes of each wearable for three days (n= 6 children per method; no active sensor). During phase 3, parent/child (3-8 years old) dyads (n= 22) were recruited to wear prototypes of the top 3 wearables (from phase 2; n=~ 7 children per method; no active sensor) for 7 days. In phases 2 and 3, parents completed wear …

 

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In the first part of this talk, I will review the hunt for sensors that started of the field of automated dietary monitoring (ADM) and continues to play a role in shaping current research. Moreover, I will describe the eyeglasses-based sensors that we currently develop and their perspectives for free-living monitoring. Moving on, in part two, I will discuss digital twin-based co-simulation as a novel system design approach for wearable devices and their relevance for supporting machine learning algorithm development. Finally, in part three, I will extend the scope into technology-based dietary intervention, i.e., how ADM can support users in their daily life when targeting a diet change or body weight reduction. I will show examples from our work to create digital twins that model individual behavior, identify behavior changes, and interaction strategies to integrate in everyday life.

 

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We present a framework for IMU-based joint angle estimation during activities of daily living (ADL). Personalised musculoskeletal models were created from anthropometric data. Three sensor fusion algorithms were optimised to estimate orientation from IMU data and used as input for the simulation framework. Four ADLs, involving upper and lower limbs were simulated. Joint kinematics of IMU-based simulations were compared to optical marker-based simulations. Results for IMU-based simulations showed median RMSE of 0.8 − 15.5 ° for lower limbs and 1.5 − 33.9 ° for upper limbs. Median RMSE were 4.4 °, 5.8 °, 6.9 °, 6.5 ° for ankle plantarflexion, knee-, hip flexion, and hip rotation, respectively. For upper limbs, elbow flexion showed best median RMSE  ∼ 3.7 °, whereas elevation angles (∼ 24.5 °) and shoulder rotation (∼ 12.5 °) performed worst. Increased RMSE at upper limbs was attributed to the degrees of freedom at the shoulder region compared to the hip. Overall, transversal plane movements (rotations) showed higher median RMSE compared to sagittal plane movements  (flexion/extension). Optimisation of orientation estimators improved performance considerably depending on ADL (up to ∼ 20 °). Comparing sensor fusion algorithms, Madgwick and Mahony produced comparable joint kinematics, whereas the Extended Kalman Filter performance showed larger variability depending on the ADL. Our approach offers a realistic representation of joint kinematics and can be supported by optimising parameters of sensor fusion algorithms.

 

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Monitoring dietary intake is essential to providing user feedback and achieving a healthier lifestyle. In the past, different approaches for monitoring dietary behavior have been proposed. In this position paper, we first present an overview of the state-of-the-art techniques grouped by image-and sensor-based approaches. After that, we introduce a case study in which we present a Wizard-of-Oz approach as an alternative and non-automatic monitoring method.

 

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We present a modelling and simulation framework to synthesise body-worn inertial sensor data based on personalised human body surface and biomechanical models. Anthropometric data and reference images were used to create personalised body surface mesh models. The mesh armature was aligned using motion capture reference pose and afterwards mesh and armature were parented. In addition, skeletal models were created using an established musculoskeletal dynamic modelling framework. Four activities of daily living (ADL), including upper and lower limbs were simulated with surface and skeletal models using motion capture data as stimuli. Acceleration and angular velocity data were simulated for 12 body areas of surface models and 8 body areas of skeletal models. We compared simulated inertial sensor data of both models against physical IMU measurements that were obtained simultaneously …

 

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In the aftermath of COVID-19 and with an increased awareness of health issues, the use of precisely targeted technological
methodologies for the solution of specific healthcare problems is becoming increasing important in medical applications. The use of MEMS technology for the development of an efficient sterilisation cycle counter by Hahn-Schickard is a simple but very effective example of such an application. Surface micromachining is applied utilizing vapor HF (vHF) etching and subsequent polymer anti-stiction coating as an efficient technique to remove sacrificial buried oxide layers and to release micro structure without stiction. The vHF etching process has been optimized and reaches etch rates of 900 nm/min for the buried oxide with a uniformity of more than 95 % across a 100 mm wafer.

 

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In this paper a novel fabrication technology for thermoelectric infrared sensors is presented. For the first time, the thermal insulation of the absorber structure is achieved by self-assembling multilayer thermocouples. After removal of a sacrificial oxide layer by vapor hydrogen fluoride (vHF) etching, the thermocouples lift off due to residual stress gradients. This provides the necessary distance between the absorber and the substrate. Compared to state-of-the-art sensors, this implementation does not require extensive bulk processing such as grinding and cavity etching to achieve a thermally isolated absorber structure. The deflection of the realized structures has shown high agreement with an analytical model which is also presented in this paper.

 

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Cryptographic protection of messages requires frequent updates of the symmetric cipher key used for encryption and decryption, respectively. Protocols of legacy IT security, like TLS, SSH, or MACsec implement rekeying under the assumption that, first, application data exchange is allowed to stall occasionally and, second, dedicated control messages to orchestrate the process can be exchanged. In real-time automation applications, the first is generally prohibitive, while the second may induce problematic traffic patterns on the network. We present a novel seamless rekeying approach, which can be embedded into cyclic application data exchanges. Although, being agnostic to the underlying real-time communication system, we developed a demonstrator emulating the widespread industrial Ethernet system PROFINET IO and successfully use this rekeying mechanism.

 

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It is mandatory for manufacturers of reusable medical devices to specify the maximum of allowed sterilization cycles. This work focuses on the fabrication of an autonomous sterilization cycle counter in MEMS technology. Surface microm-achining is applied utilizing vapor HF (vHF) etching and subsequent polymer anti-stiction coating as an efficient tech-nique to remove sacrificial buried oxide layers and to release micro structure without stiction. The vHF etching process has been optimized and reaches etch rates of 900 nm/min for the buried oxide with a uniformity of more than 95 % across a 100 mm wafer. Based on this process a compatible design with perforated structures is implemented. Finally, devices of the sterilization cycle counter are successfully tested by a simulated sterilization cycle temperature test.

 

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Piezoresistive accelerometers are a popular and widely used method of acceleration sensing due to their simplicity in fabrication, packaging and inherent ruggedness. These devices usually have simpler electronics for example compared to capacitive sensors. There are products available without ASICs as well. [1] This work takes an existing high-g piezoresistive accelerometer as a reference sensor and works on optimizing this design. The work delves into different design and optimization techniques to deliver novel high-performance piezoresistive acceleration sensor prototypes. These techniques exploit the device physics and mechanics to point towards the new designs. The sensor is designed and optimized to have higher bandwidth. The adaptation of SOI wafers instead of currently used epitaxial wafers, results in smaller chip size, enabling more chips/wafer and reducing the sensor cost. Extra emphasis has been laid to maintain high sensitivity, for specified doping of the piezoresistors, while still not compromising much on the resonance frequency. Finite element analysis with ANSYS Workbench offers insights into the device performance and helps in the determination of some key sensor parameters for the new designs. It also helps to establish trends and this provides an idea for the successive models. After several iterations and incorporating different optimization techniques, new models are achieved.

 

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In this paper we present a hybrid microsystem for acquisition and counting of sterilisation cycles. The device includes a micromechanical counter mechanism and a thermal actuator based on a shape memory alloy (SMA). The device is designed to count 100 sterilization cycles. The basic functionality is investigated on a hotplate using a thermal temperature profile with a peak temperature of 135 deg C. In this manner, counting of thermal cycles is demonstrated.

 

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This work provides an analytical non-linear model for the capacitive transduction in MEMS transducers with perforated counter-electrodes, especially applicable to capacitive MEMS microphones. Starting from an electrostatic description of a perforated unit cell of the transducer, analytical formulations of the variable capacitance and electrostatic forces are derived, accounting for the deflection profile of a clamped circular plate. A lumped implementation into conventional circuit simulations tools is enabled via behavioral modeling based on hardware description languages, such as Verilog-A. Therefore, the analytical model is approximated via Taylor series expansions, allowing for a stable and non-linear behavioral implementation. The resulting model finally enables both a small- and large-signal analysis of capacitive MEMS microphones, precisely accounting for non-linearities in the capacitive transduction. This allows to simulate the harmonic distortion of the microphone's output signal and to account for electrostatic spring-softening in simulations of its bias voltage dependent sensitivity.

 

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