Christian Bolzmacher

Morphing Tactile Display for Haptic Interaction in Vehicles

This work describes the design, fabrication and characterization of a morphing (actuated) tactile display based on an array of 32 electromagnetic actuators and a capacitive touch deformable layer. A two-stage locking device allows for reliable pattern creation when the users’ finger is placed on the interface. Taxel (tactile pixel) displacements up to 1.9 mm and a holding force of 1.25 N at 9 W electrical power have been measured. This device integrated in the centre console of vehicles is designed to work in combination with a LCD display mounted in the dashboard to control secondary vehicle systems.

Robust superelastic, metallic amplification unit for piezoelectric microactuators

In this work, a robust metallic amplification unit for piezoelectric microactuators is presented. The mechanism which is implemented with a sliced membrane structure made from a superelastic nickel titanium alloy is based on a mechanical lever in order to amplify the small piezoelectrically induced deformation. Therefore, increased stroke can be provided up to high frequencies. The fabrication process using laser ablation, the assembly process, the static and dynamic simulations and experimental measurements are reported. An amplification factor of 9 has been achieved for a specific load transmission point position. The dynamic response shows a quality factor of 25 at 11.97 kHz for the first mode. Compared to silicon, nickel titanium shows enhanced properties against failure and facilitates the integration process.

Electrovibration: Influence of the applied force on tactile perception thresholds

We present a study on the influence of the applied force on tactile perception thresholds, during exploration of tactile textures generated with electrovibration. Combined with screen-integrated force detection this could lead to more realistic texture feedback on touch screens while exploring a virtual surface. From a first user study, three force levels corresponding to the light (0.2 N–1.5 N), medium (1.5 N–3.0 N), and high force (3.0 N–7.0 N) categories were deduced. In a second study, the users were asked to apply these force levels while following a line on the screen. We determined the perception thresholds of 10 participants for specific electrovibration stimuli (100 Hz, 160 Hz, 240 Hz, 360 Hz, and 540 Hz sine signals) using a staircase method. No force effect on the perception threshold has been measured for 100 Hz and 160 Hz, while it decreased with increasing applied force at 240 Hz, 360 Hz, and 540 Hz.

Numerical modeling of a MEMS actuator considering several magnetic force calculation methods

Purpose – The purpose of this paper is to investigate the accuracy of different force calculation methods and their impact on mechanical deformations. For this purpose, a micrometer scaled actuator is considered, which consists of a micro‐coil and of a permanent magnet (PM) embedded in a deformable elastomeric layer.Design/methodology/approach – For the magnetic field evaluation a hybrid numerical approach (finite element method/boundary element method (FEM/BEM) coupling and a FEM/BEM/Biot‐Savart approach) is used, whereas FEM is implemented for the mechanical deformation analysis. Furthermore, for the magneto‐mechanical coupling several force calculation methods, namely the Maxwell stress tensor, the virtual work approach and the equivalent magnetic sources methods, are considered and compared to each other and to laboratory measurements.Findings – The numerically evaluated magnetic forces and the measured ones are in good accordance with each other with respect to the normal force acting on the PM. Neve...

Directional Identification of Sirens and Warnings in a Simulated Driving Task: Comparison of Two Loudspeaker Technologies

The hearing perturbation affecting the elderly called presbycusis is characterized by the degradation of the perception of high tones and impacts the capacity of drivers in localizing warnings and sirens while driving. We present the results of a user study performed to compare the capacity of traditional and car glass loudspeakers in providing directional alarms inside the car. The experiment compares the number of directional errors and subjective perception of alarms. It was performed in lab, in a real stationary car while the participant was engaged in a driving task on a driving simulator inside the car. Both technologies provide directional sounds with difficulties in perceiving sounds from the back mainly due to the anatomy of the ear as well as the wrap-around shape of the seats. Glass panes performed slightly better than traditional loudspeakers with regard to left/right confusion due to the position next to the ear.

Parameters influencing focalization spot in time reversal of acoustic waves

Time reversal is an approach that can be used to focus acoustic waves in a particular location on a surface, allowing a multitouch tactile feedback interaction. The spatial resolution in this case depends on several parameters, such as geometrical parameters, frequency used and material properties, described by the Lamb wave theory. This paper highlights the impact of frequency, geometrical parameters such as plate thickness and transducer’s surface on the focused spot dimensions. In this paper a study of the influence of the plate’s thickness and the frequency bandwidth used in the focusing process is presented. It is also shown that the dimension of the piezoelectric diaphragms used has little influence on the spatial resolution. Resonant behavior of the plate and its implication on focus point dimension and focalization contrast were investigated.

Car glass microphones using piezoelectric transducers for external alarm detection and localization

This work describes the potential use of car windows as a long range acoustic sensing device for external alarm signals. The goal is to detect and localize siren signals (e.g. ambulances and police cars) and to alert presbycusic drivers of its presence by visual and acoustic feedback in order to improve individual mobility and increase the sense of security. The glass panes of a Renault Zoé operating as an acoustic antenna have been equipped with large 50 mm outer diameter piezoceramic rings, hidden in the lower part of the door structure and the lower part of the windshield and the rear window. The response of the glass to quasi-static signals and sweep excitation has been recorded. In general, the glass pane is acting as a high pass filter due to its inherent stiffness and provides only little damping. This effect is compensated by using a charge amplifier electronic circuit. The detection capability up to 120 m as well as a dynamic test where the car is moving towards the sound source is reported.

Tunable Membrane for Electromagnetic Devices Using Dielectric Elastomers

The amplitudes of miniaturized electromagnetic actuators are clearly enhanced if the eigenfrequencies of the membrane are used for actuation. However, the bandwidth for such operation is very limited. This can be overcome to some extent by the employment of membranes with electrically tunable stiffness. In this context we investigated membranes of dielectric elastomer materials and present experimental results on the ability to change their pre-strain to shift the eigenmodes to lower frequencies upon activation. Furthermore, the viscoelastic properties of an acrylic and a silicone membrane are investigated and compared to dynamic experiments. The parameters for the stiffness and viscoelasticity are derived from the experimental creep data and incorporated in a hyperelastic material model. Using this adapted stress-strain relationship the membrane behavior over time can be evaluated for different loading as well as pre-strain conditions.