Are you developing a new device based on electromagnetic phenomena? Or do you want to improve operation of already developed elements that beside electromagnetic include also thermal and/or structural mechanic phenomena? Or even fluid flow? Advances of numerical methods for solving differential equations and increasing computer power is resulting in augmented use of numerical simulation for virtual device prototyping and also optimizations of already developed structures. In the Laboratory for Bioelectromagnetics at the Faculty of Electrical Engineering (University of Ljubljana) we have several years of experiences with numerical simulations of electromagnetic structures and phenomena. Use of simulations is manifold: it is used for improved and in-depth explanation of electromagnetic phenomena for pedagogic purposes, research & development of new structures and optimization of already developed electromagnetic devices. In the recent years we have broadened our research interests in ever more challenging field of multiphysics where coupled electro-thermal-structural mechanic and fluidic phenomena are studied by numerical simulations. In the following we provide information on some R&D achievements and interests of our laboratory. With this we invite you in collaboration.

Simulations EMstructuresOur main field of research is related to simulations of electromagnetic phenomena. The problems we are dealing with are very diverse and include all areas from electrostatic, magnetostatic and electrodynamic. Here are some examples:

Figure 1: Detection of airborne nanoparticles is a demanding task. In the study we have analyzed possible principle of nanoparticle counting by the use of a capacitive sensor. Nanoparticles serve as condensation cores and form small water droplets that are impinging on water filled parallel-plane capacitor and change its capacitance.

Figure 2: Dielectrophoresis enables manipulation of small electrically neutral particles with alternating electric field. This method is in particular interesting for contactless movement of biological cells. Numerical simulation enables study of the influence of different shapes of the electrodes on the development of electric field and forces on the particles at different amplitudes and frequencies of the applied signal.

Figure 3: Transcranial magnetic stimulation is gaining importance as a noninvasive electromagnetic stimulation of brain cells. It can be used as a method for treatment of various neurological and psychiatric disorders such as migraines, strokes, Parkinson's disease, depression, etc. Numerical simulation enables study of magnetic field distribution and optimization of current coils for focused stimulation of specific parts of the brain.

Figure 4: Four probe bioimpedance method can be used to analyze muscle changes (for instance muscle atrophy). Numerical simulation has been used to study current density distribution in the cross-section of a hand during stimulation with alternating current signal for various electrode placements. This enabled optimal positioning of the electrodes for bioimpedance measurements and determination of impedance changes of a particular muscle.

Figure 5: Design of new electromagnetic structures can be very demanding due to complex structure designs. Simulations have been used to analyze forces in an electromagnetic circuit breaker that is strongly depending on nonlinear magnetic properties (B(H) curve) of the ferromagnetic parts of the structure.

Electromechanicacal simulationSimulation of a cantilever type force sensor has been performed as shown in figure 2. Four resistors made of a semiconductor are placed on a thin strip of steel (cantilever) and electrically connected in a Wheatstone bridge configuration. Bending of a strip at a far end (see red arrow in the figure) results in a deflection of a strip and mechanical stresses. Due to piezoresistive properties of the resistors their resistivity is modified by stretching. By applying a voltage signal to a Wheatstone bridge a measurable (and also simulated) voltage change is obtained depending on the deflection of the cantilever. 

Numerical simulation enables modeling of piezoresistive elements by coupling of electrical and structural mechanics phenomena. Figure 2 (right) presents distribution of stresses along a thin steel cantilever and changes in specific resistivity of piezoresistive elements (left) due to their mechanical deformation. By electrically connecting the four resistors in a Wheatstone bridge configuration and applying a voltage bias it is possible to directly model device operation and thus perform virtual prototyping and optimizations of device parameters. 

electro fluid simulationMicrofluidic systems are becoming an essential part of so called Lab-on-a-chip devices that can incorporate a system for fluid transfer, heating, mechanical treatment and sensing. Most often such systems are fabricated using MEMS (micro-electro-mechanical systems) technologies on silicon substrates. Such microsystems are complex and several parameters influence device operation. Numerical device simulation plays an important role in virtual prototyping of a device in particular in the early stage of verification of new concepts of device operation. Development of such models requires knowledge of physical phenomena of fluidics, thermal management, electromagnetics and structural mechanics. We performed analysis of operation of a throttle type micropump actuated by a piezoelectric driven by a sinusoidal voltage signal. A particular interesting part of such pumps are the throttles that are designed as obstacles in the channel that close and open the channel in a similar way as the valves. One possible advantage of such an approach is nondestructive pumping of biological cells.