Pasi Kallio

Small and Flexible Metal Mountable Passive UHF RFID Tag on High-Dielectric Polymer-Ceramic Composite Substrate

A small and flexible metal mountable UHF RFID tag antenna, utilizing a high-permittivity substrate material is presented. The tag is composed of a small single-layer T-matched dipole antenna, on a flexible ceramic (BaTiO3) polymer (polydimethylsiloxane) composite substrate, with a thickness of 1.5 mm. The flexibility of the substrate allows it to be mounted on flat and cylindrical metallic surfaces. The performance of the developed tag is evaluated through simulations and measurements on both flat and cylindrical metallic platforms of various sizes. The results show that the tag achieves state-of-the-art size-performance ratio while meeting the key requirements of an affordable RFID tag with a simple and flexible structure.

PDMS and its Suitability for Analytical Microfluidic Devices

Poly(dimethylsiloxane) also known as PDMS is used in a wide range of biomedical applications. These range from implants through catheters to soft contact lenses. Therefore, it is understandable that PDMS has been extensively tested for these purposes. In past years, the microfluidics has moved from predominantly silicon and glass structures towards polymers due to their ease of manufacturing and moderate cost. PDMS has gained a lot of attention in various analytical applications. However, the testing of its suitability for such applications has not been as thorough as in the biomedical applications, perhaps relying on the experiments from that field. Microfluidic PDMS structures are more and more popular in various analytical devices. Such devices consume less reagents and can work with lower sample volumes. On the other hand, the surface-to-sample-volume ratio becomes larger. That increases the influence of material properties on the actual measurement. Some of the challenges include adsorption, diffusion, surface roughness, permeability and elasticity of PDMS, which are discussed in this paper

Displacement Control of Piezoelectric Actuators Using Current and Voltage

This paper introduces a feedforward charge control scheme, which controls the velocity of a piezoelectric actuator by the current fed to the actuator. The velocity-current relation, however, is not linear over the entire motion range, and therefore, information about the actuator voltage is also utilized. The required current is estimated using an actuator model, which is separated in two phases combining individual models for a motion phase and a static phase. The method is verified by a series of experiments, where a piezoelectric actuator is moved with variable velocities and displacements. During the experiments, the current is fed to the actuator using a current driver consisting of a voltage amplifier, a precise current meter, and a controller. The results show a significant improvement in comparison to open-loop voltage control; the hysteresis is less than 2% and the drift approximately 1%. This indicates that the motion of piezoactuators is a function of current and voltage, and does not depend considerably on the motion history. Therefore, a sensorless control scheme to overcome the hysteresis and drift would be feasible.

Challenges in capillary pressure microinjection

Capillary pressure microinjection is a popular method for the delivery of samples into cells. Needs for automatic reliable microinjection systems are growing, but the current systems do not possess ideal characteristics and many researchers do not even recognize the limits of the current systems. In many cases for example, the experiments are influenced by so called influx or efflux. This paper discusses the limits and challenges related to the automatic microinjection of single adherent cells. The discussion focuses on the reasons for the variability of the injected volume and shows the complexity of the problem. Solutions are outlined and future steps sketched. Future developments in the field of microinjection are proposed.

A 3-DOF piezohydraulic parallel micromanipulator

The paper presents a new parallel micromanipulator that is composed of three piezohydraulic actuation systems. The basic elements of the actuation system are a piezoelectric actuator, a bellows and hydraulic oil. The use of the flexible bellows results in a new type of parallel structure, where the joints are integrated into actuator links. The joint-free tripod-like micromanipulator is controlled using a real-time control software that is based on a multi-level architecture. Control is organised in four levels for nonlinearity compensation, position feedback control, supervision and tackling of automatic operations. The micromanipulator presented provides an exceptional combination of submicrometer resolution, large work space, miniature size and advanced control.

Multi-purpose impedance-based measurement system to automate microinjection of adherent cells

This paper presents a multi-purpose measurement system developed to automate cellular microinjection. The system is based on measuring impedance between an injection solution in an injection capillary and cell culture medium where cells grow. The system can be used for detecting a contact between a cell and the injection capillary, a broken capillary, a clogged capillary, an aged measurement electrode and faulty injection solution. The measurement system facilitates the development of an expert system for guiding cellular injections, and later a fully automatic microinjection system.

Microrobotic platform for manipulation and flexibility measurement of individual paper fibers

This paper introduces a microrobotic platform to manipulate and characterize individual paper fibers. Mechanical characterization of individual paper fibers determines the key parameters which affect the quality of paper sheets. Current laboratory tests are based on bulk paper fiber measurements. This paper presents a microrobotic platform which is able to characterize the flexibility of individual paper fibers directly, not in bulk amount and using indirect estimations. The flexibility of three different pulp samples is measured and the experimental results are reported.

Capillary pressure microinjection of living adherent cells: challenges in automation

This paper is divided into two parts. The first part describes the current status and the general challenges of developing automatic microrobotics systems for microinjection of adherent mammalian cells. The discussion covers applications and the review and challenges of the components of a capillary pressure microinjection system: a micromanipulator, a microinjector, a microcapillary, a vision system and an environment control system. The second part of the paper describes the research performed on the automatic capillary pressure microinjection at Tampere University of Technology. The advanced microinjection system includes two micromanipulators, a microinjector, a vision system and a control system. The control system comprises motion control schemes for the micromanipulators to accurately position a microcapillary, to precisely penetrate a cell membrane and to deliver information on the injection to the operator. A novel injection guidance system, being part of the control system, comprises an impedance measurement device and a user interface which provide information on the detection of the capillary–membrane contact, capillary clogging and capillary breakage. Results show a remarkable increase of the injection success from 40 to 65% when the injection guidance system is used.

Three-dimensional position control of a parallel micromanipulator using visual servoing

This paper presents a computer-vision based position controller for a highly non-linear parallel piezohydraulic micromanipulator: in addition to its non-linear kinematics the micromanipulator experiences hysteresis and drive induced by piezoelectric actuators. The controller consists of a decoupling matrix that provides the decoupled translations (xyz) in the task frame and three Single Input Single Output (SISO) PI controllers for the translations. Position measurement is performed by a vision system that determines the x and y coordinates of the end- effector using a modified Hierarchical Chamfer Matching Algoritm (HCMA) and the z position using a depth-from-defocus method. Experiments show that the proposed controller is capable of serving the parallel micromanipulator with a sub-micron accuracy at a sampling rate of 18 Hz.

A flexible microrobotic platform for handling microscale specimens of fibrous materials for microscopic studies

One of the most challenging issues faced in handling specimens for microscopy, is avoiding artefacts and structural changes in the samples caused by human errors. In addition, specimen handling is a laborious and time‐consuming task and requires skilful and experienced personnel. This paper introduces a flexible microrobotic platform for the handling of microscale specimens of fibrous materials for various microscopic studies such as scanning electron microscopy and nanotomography. The platform is capable of handling various fibres with diameters ranging from 10 to 1000 μm and lengths of 100 μm–15 mm, and mounting them on different types of specimen holders without damaging them. This tele‐operated microrobotic platform minimizes human interaction with the samples, which is one of the main sources contributory to introducing artefacts into the specimens. The platform also grants a higher throughput and an improved success rate of specimen handling, when compared to the manual processes. The operator does not need extensive experience of microscale manipulation and only a short training period is sufficient to operate the platform. The requirement of easy configurability for various samples and sample holders is typical in the research and development of materials in this field. Therefore, one of the main criteria for the design of the microrobotic platform was the ability to adapt the platform to different specimen handling methods required for microscopic studies. To demonstrate this, three experiments are carried out using the microrobotic platform. In the first experiment, individual paper fibres are mounted successfully on scanning electron microscopy specimen holders for the in situ scanning electron microscopy diagonal compression test of paper fibres. The performance of the microrobotic platform is compared with a skilled laboratory worker performing the same experiment. In the second experiment, a strand of human hair and an individual paper fibre bond are mounted on a specimen holder for nanotomography studies. In the third experiment, individual paper fibre bonds with controlled crossing and vertical angles are made using the microrobotic platform. If an industrial application requires less flexibility but a higher speed when handling one type of sample to a specific holder, then the platform can be automated in the future.