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Hot embossing with and without ultrasound are compared in this paper with respect to several properties of the fabricated samples. The same mold was employed for both processes and process parameters have been chosen adapted to each process such that to the best knowledge of the authors good moldings were achieved. Shrinkage is similar for both processes. Better mold filling is achieved without ultrasound and the polymer structures correspond better to the mold after demolding. Undesired sample curvature is also much less. With ultrasound required investment costs and energy consumption are significantly less, and the cycle time is reduced to seconds.

Strain : the journal of the British Society for Strain Measurement 12387 (2021). doi:10.1111/str.12387, Published by Wiley- Blackwell, Oxford [u.a.]

Ultrasonic welding of polymer micro structures is an economic and fast joining process but is also limited by the high need for geometrical accuracy required for tight and well-aligned joints. Melting of energy directors by ultrasound is nonhomogeneous especially when large parts are to be welded because the vibration amplitude is not the same everywhere under the sonotrode. This paper shows that the homogeneity of welding is improved by inserting metal parts between the joining partners.

Micro and nano structures and systems are generated in polymer surfaces with cycle times of a few seconds by ultrasonic processes such as ultrasonic hot embossing, welding and thermoforming paving the way for a variety of new products. However, measuring temperature and pressure during these processes is very difficult because the polymer is enclosed between an anvil and a sonotrode. Temperature and pressure distribution during ultrasonic processing now have been measured inside of a stack of thermoplastic polymer layers by sensor foils from polyvinylidene fluoride, 55 µm in thickness. The measurements are based on the piezoelectric and pyroelectric effect of polyvinylidene fluoride allowing to achieve resolutions in temperature and pressure of up to ± 1 °C and ± 0.5 kPa, respectively. The achieved resolutions in time and in normal and lateral direction are approximately 1 µs, 60 µm and 1 cm, respectively. The maximum temperature inside a foils stack that could be measured was 73 °C because the sensor foils lost sensitivity when heated up more. Every single oscillation of the polymer was measured as a pressure change. The difference in temperature change and ultrasonic pressure amplitude measured in lateral direction below a sonotrode with outer dimensions of 8 × 12 cm are approximately 12 °C and 4 kPa, 25 and 60%, respectively, indicating the width required for process windows of ultrasonic processing. Moreover, phase shifts are measurable and thus analysis of oscillation characteristics of sonotrodes were investigated.

Energy Harvesting and Systems 4(3), 137-141 (2017). doi:10.1515/ehs-2017-0004, Published by De Gruyter, Berlin ; Boston, Mass.

Microsystem technologies (2020). doi:10.1007/s00542-020-04818-5, Published by Springer, Berlin

Journal of magnetism and magnetic materials : MMM 506, 166694 (2020). doi:10.1016/j.jmmm.2020.166694, Published by North-Holland Publ. Co., Amsterdam

Microsystem technologies (2020). doi:10.1007/s00542-020-04834-5, Published by Springer, Berlin

Micro channels from polyether ether ketone (PEEK), 1 mm in width and depth and 1.6 cm in length, have been fabricated by ultrasonic hot embossing and ultrasonic welding. Micro channels from PEEK enable constructing chemically inert microfluidic systems suitable for applications at temperatures of more than 200 °C. Besides this, a new design can be realized within one working day, investment costs are only a few 10,000 €, and the cycle time of fabricating a microfluidic system is a few seconds. Maximum temperature and pressure difference over a micro channel are not limited by the material properties of semicrystalline PEEK but by difficulties in producing them and by their change of morphology during manufacturing. To ultrasonically fabricate a microchannel two ultrasonic processes need to be combined. The channel itself is fabricated in a first ultrasonic hot embossing process and then sealed with a lid foil in a second ultrasonic welding step. This paper shows that, PEEK changes its morphology when it is ultrasonically hot embossed to produce a microfluidic channel. Moreover the degree of crystallinity varies according to the local position in the micro channel. It turned out that successful sealing of a micro channel by ultrasonic welding is facilitated by energy directors from semicrystalline PEEK. Therefore, semi-finished PEEK channels need being exposed to a temperature of at least 170 °C for 30 min before ultrasonic welding. This way, the amorphous PEEK is recrystallized resulting in hardened polymer micro structures. Such a heat treatment is also necessary after welding to achieve the desired stability at high temperatures. Tests show that the PEEK channels remain tight at a pressure difference of up to 700 kPa at a temperature of up to 220 °C.

We present a polycarbonate-based microfluidic device that was rapidly manufactured by ultrasonic hot embossing and welding. The fabrication of microstructures using ultrasonic processing allowed the embossing of micrometer-sized structures in polymer films by molding from a master die; this process was completed within seconds. The short manufacturing time required using this process and its ease of reproducibility allows rapid prototyping of custom-made microfluidic devices. Through ultrasonic fabrication, disposable microfluidic devices were newly designed and manufactured within a working day. The feasibility of these devices was demonstrated by cultivating yeast cells. The cells remained viable within this system for at least 22 h. Enhanced green fluorescent protein (eGFP) expression was initiated by providing the cells with a supply of the inducer galactose. The present study not only shows the potential of microfluidic devices fabricated by ultrasonic processing but also discusses their capability for use in microbial analysis.

Microstructures are fabricated from polymer foils in seconds by a new process called ultrasonic hot embossing. This process allows to realize new designs within a day and is suitable both for large- and small-scale production. The required investment costs are in the order of some 10,000 ź. In this paper, heat generation and distribution in ultrasonic hot embossing is investigated with piezo-electric and pyro-electric foils from the polymer polyvinylidene fluoride (PVDF) placed into a stack of polymer layers. This way, the influence of pre-structures on and powders between polymer layers is revealed.

Calcification is a pathological accumulation of calcium phosphate in soft tissues including blood vessels [1] where it can cause cardiovascular morbidity and mortality e.g. heart attack [2] . Mixing blood serum with supersaturated calcium and phosphate results in colloidal calcium protein particles (CPPs) undergoing a typical ripening process. The conversion time can be optically determined by light scatter measurements of smaller primary and larger secondary CPPs (Fig 1). The half-maximal conversion time T 50 is a measure of the calcification risk in the patient. Here we report the miniaturization of the experimental setup on a polymer microchip fabricated by ultrasonic processing. Compared to the usual measurement of light scatter in a nephelometer, the analysis was accelerated by increasing the temperature. Furthermore, better reproducible results were obtained by using a staggered herringbone mixer to mix the reactants [3] . A Peltier element is employed to heat the chip. Using this setup, the analysis was shortened to 16.1 ± 1.1 min compared to 279 ± 9 min obtained in a nephelometer by increasing the temperature from 38 °C to 52 °C (Fig. 4).

Nozzles with circular cross-section and a diameter varying in axial direction have been fabricated in a microfluidic channel from polyvinylidene fluoride as chemically resistive thermoplastic polymer. Smallest diameter and length of the nozzle are approximately 150 µm and 3.4 mm, respectively. The nozzle and the entire channel system have been fabricated from two halves generated by ultrasonic hot embossing and bonded to each other by ultrasonic welding. Alignment during ultrasonic welding was assisted by a fit of energy directors and an accuracy of 35 and 10 µm in normal and lateral direction, respectively, was obtained. Thermoplastic molding of the two halves of the channel structures was performed by ultrasonic hot embossing with a cycle time of a few seconds. The development was significantly accelerated by milling the tools directly into aluminum plates. This way, new designs were realized within a day. The micro nozzles have been proven generating liquid/liquid dispersions of different flow patterns as a function of flow velocity and Capillary number.

Verkurzte Entwicklungszeiten chemischer Prozesse sind durch Laborexperimente und Erkenntnisse daraus moglich. Dies wird durch modulare Mikrosysteme und deren Standardisierung der Apparate vereinfacht. Kunststoffe bieten durch ihre variablen Materialeigenschaften die Anpassung an die jeweiligen Prozesse sowie kostengunstige Herstellung. Das modulare Konzept besteht aus ultraschallheisgepragten PVDF-Folien. Zwei mogliche Anordnungsvarianten werden bezuglich ihrer Charakteristiken und der Verbindungsarten einzelner Module diskutiert. Die Durchfuhrung einer Neutralisationsreaktion zeigt die Flexibilitat dieses modularen Systems hinsichtlich Prozessanforderungen. A reduction of developmental periods is possible by laboratory experiments and their insights. This is simplified by modular microsystems and the related standardization of equipment. Beside a more cost-effective fabrication, plastic materials as an alternative to commercial available systems made from glass and metals offer variable properties making an adaption on process demands possible. The modular system consists of ultrasonic hot embossed PVDF foils. Two arrangement concepts are discussed regarding their characteristics and connection techniques of single modules. Running a neutralization reaction shows the flexibility of this modular concept concerning process demands.

Current directions in biomedical engineering 4(1), 367-370 (2018). doi:10.1515/cdbme-2018-0088, Published by De Gruyter, Berlin

Ultrasonic fabrication of fiber reinforced plastics made from thermoplastic polymer films and carbon or glass fibers enables cycle times of a few seconds and requires investment costs of only some 10,000 &euro, Besides this, the raw materials can be stored at room temperature. A fiber content of 33 vol % and a tensile strength of approximately 1.2 GPa have been achieved by ultrasonic welding of nine layers of foils from polyamide, each 100 &micro, m in thickness, and eight layers of carbon fibers, each 100 &micro, m in thickness, in between. Besides unidirectional carbon fiber reinforced polymer composite (CFRP) samples, multi-directional CFRP plates, 116 mm, 64 mm and 1.2 mm in length, width and thickness respectively, were fabricated by processing three layers of carbon fiber canvas, each 300 &micro, m in thickness, and eight layers of polyamide foils, each 100 &micro, m in thickness. Furthermore, both the discontinuous and the continuous ultrasonic fabrication processes are described and the results are presented in this paper. Large-scale production still needs to be demonstrated.

Fabrication of micro devices from thermoplastic polymers by ultrasonic processing has become a promising new technology in recent years. Microstructures are generated on polymer surfaces with cycle times of a few seconds and are tightly sealed in even shorter times. Investment costs and energy consumption are comparatively low and processes are very flexible enabling economic fabrication even for small-scale production. For large-scale production role-to-role fabrication has been shown reducing costs even more. A variety of micro devices have been introduced up to now mostly for microfluidic applications. Besides this, electronic circuit boards are fabricated by ultrasonic processing.

Ultrasonic hot embossing of polymers is an alternative to reduce fabrication costs of microreactors. An ultrasonic welding machine is used to melt a stack of thermoplastic foils and adapting them to a short-time milled aluminum mold showing the inversed design of the desired microfluidic cavities. Two micromixers were fabricated this way providing a low degree of axial dispersion and pressure loss. Stability analysis is successfully performed for a wide temperature range and high pressure. Mixing of colored aqueous solutions and neutralization reactions are implemented to both systems for defined volume flow rates and optically investigated via microscope. Reaction progress is automatically determined with a MATLAB script by reference to the consequential color change of the neutralization reaction with a color indicator. Typical mixing characteristics are identified for both mixers.

Electronic circuit boards have been fabricated in cycle times of a few seconds by ultrasonic fabrication. A stack of thermoplastic polymer foils with a copper layer, 20 μm in thickness, on top is transformed into a polymer carrier with separated conductor paths. This process is accomplished in cycle times of a few seconds and the required equipment is just a commercially available ultrasonic welding machine and a metal tool micro patterned, e.g., by milling.Since soldering is often not possible on a thermoplastic carrier, electronic components are joined to the conductor paths by ultrasonic welding. This is achieved by employing an anisotropic conductive foil containing metal particles providing the electrical contact normal to the foil and showing no conductivity in lateral direction. The anisotropic conductive foil also serves as glue between circuit board and electronic components.

Ultrasonic hot embossing has been developed in recent years enabling quick and flexible fabrication of micro structures from thermoplastic polymers. This paper describes many possibilities of the fabrication, use, and limits of tools for this process. Tools have been produced by milling, drilling, silicon etching, photo and X-ray lithography, and electroplating and by combining these processes.

This paper describes the design and detection of mechanically actuated micro whistles not equipped with any electronics. When actuated, the micro whistle generates an ultrasonic tone above the audible range. A set of three or more microphones in the near record this tone and the position of the whistle is calculated from the differences of the arrival times of the acoustic signals at the microphones. In experiments the positions of whistles were measured in a 2 m × 2 m area with an accuracy of less than 10 cm. Besides this, micro whistles have been employed as remote controls such as switches for room light or air conditioning. The micro whistles have been fabricated by ultrasonic hot embossing of thermoplastic foils at low-cost and their overall size is approximately 1 cm. The paper also describes how to overcome obstacles such as accidentally generated ultrasonic noise, frequency shifts due to changing activation forces of the whistles, and distinguishing the signals of different whistles.

Vortex whistles generate a tone with a frequency which is a monotonically increasing function of the flow rate. This effect can be employed for flow sensors which do not need any lead-through into the fluidic channel because the frequency can be measured outside with a microphone. Flow measurements with vortex whistles can be performed both with gases and liquids. For comparatively small flow velocities the frequency is proportional to volume flow and only a weak function of temperature and fluid properties. The investigations presented here show that at high flow rates the frequency increases with the density of the gas. Micro whistles designed similar to organ pipes were also investigated. However their frequency is not proportional to flow velocity but is bowed similar as a root function. Therefore it is not very sensitive as vortex whistle at larger flow rates.

A polyvinylidene fluoride (PVDF) micro-sensor channel with integrated gold wires was developed and manufactured by ultrasonic hot embossing and welding. The sensor channel was employed to detect the slug length distribution in a liquid–liquid Taylor-flow by conductivity measurements. The sensor channel was also tested regarding its usability for the detection of blockages by hot wire anemometry.

Background Small-scale micro-bioreactors have become the cultivation vessel of choice during the first steps of bioprocess development. They combine high cultivation throughput with enhanced cost efficiency per cultivation. To gain the most possible information in the early phases of process development, online monitoring of important process parameters is highly advantageous. One of these important process parameters is the oxygen transfer rate (OTR). Measurement of the OTR, however, is only available for small-scale fermentations in shake flasks via the established RAMOS technology until now. A microtiter plate-based (MTP) μRAMOS device would enable significantly increased cultivation throughput and reduced resource consumption. Still, the requirements of miniaturization for valve and sensor solutions have prevented this transfer so far. This study reports the successful transfer of the established RAMOS technology from shake flasks to 48-well microtiter plates. The introduced μRAMOS device was validated by means of one bacterial, one plant cell suspension culture and two yeast cultures. Results A technical solution for the required miniaturized valve and sensor implementation for an MTP-based μRAMOS device is presented. A microfluidic cover contains in total 96 pneumatic valves and 48 optical fibers, providing two valves and one optical fiber for each well. To reduce costs, an optical multiplexer for eight oxygen measuring instruments and 48 optical fibers is introduced. This configuration still provides a reasonable number of measurements per time and well. The well-to-well deviation is investigated by 48 identical Escherichia coli cultivations showing standard deviations comparable to those of the shake flask RAMOS system. The yeast Hansenula polymorpha and parsley suspension culture were also investigated. Conclusions The introduced MTP-based μRAMOS device enables a sound and well resolved OTR monitoring for fast- and slow-growing organisms. It offers a quality similar to standard RAMOS in OTR determination combined with an easier handling. The experimental throughput is increased 6-fold and the media consumption per cultivation is decreased roughly 12.5-fold compared to the established eight shake flask RAMOS device. Electronic supplementary material The online version of this article (doi:10.1186/s13036-016-0034-3) contains supplementary material, which is available to authorized users.

An acceleration sensor from polymer has been developed which balances a proof mass by magnetic forces. The sensor is fabricated from a polyimide membrane with conductor paths from gold patterned by photolithography and etching, a frame manufactured by ultrasonic hot embossing, and permanent magnets fixed to the frame. Except the conductor path and permanent magnets, all components are made of polymers on a planar substrate, and then the frame is kinked forming the desired three-dimensional structure. In a first try, a sensitivity of 0.46 V/(m/s²) was achieved, and cross axis sensitivity error was less than 3 %.

Filamentary polymer sensors with predetermined breaking points have been developed. These sensors are produced by radial micro patterning of conductive polymer filaments by ultrasonic hot embossing. Micro structures in the filaments are generated by this fabrication process in less than a second. The dimensions of radial micro grooves in a filament tune the strain at which the filament breaks. This way, overload sensors for ropes or fuses can be realized. For example the discard status or the residual life time of ropes can be controlled with a simple measurement of the electric resistance of sensor filaments. By using different sensors in one rope it is possible to indicate different load cases of the rope.

A flow parallel wire (FPW) with a center tap is used in a sensor for measuring the time of flow. A heater is placed upstream of the sensor. The upstream and downstream parts of the FPW are combined to a half bridge resulting in a large output peak when a heat pulse passes the FPW. The time between generating the heat pulse and recording the peak maximum is insensitive to the properties of the fluid.

An acceleration sensor from polymer has been developed which balances a proof mass by magnetic forces. The sen- sor is fabricated from a polyimide membrane with conductor paths from gold patterned by photolithography and etch- ing, a frame manufactured by ultrasonic hot embossing, and permanent magnets fixed to the frame. All components are assembled on a planar substrate and then the frame is kinked forming the desired three-dimensional structure.

Ultrasonic hot embossing allows fabrication of metal patterns onto a polymer film with a low cost and rapid process. A polymer layer with a thin metal film on top is welded onto the polymer substrate where there are protruding micro structures on the tool. Edges around the protruding structures cut the metal layer and ensure electrical insulation. The entire process performs in a few seconds. The non-welded areas are mechanically removed after this process. An antenna of a radio frequency identification device (RFID) and a flexible membrane keyboard were fabricated by embossing 10- mum-thick conductive paths from an aluminum foil onto polypropylene films, 150 and 250 mum in thickness. Antenna circuits have been proven to show the expected resonance frequencies and the keyboard was successfully employed as an input device for a PC.

A new low-cost polymer pressure sensor has been developed. A piezoelectric polyvinylidenefluoride (PVDF) film is used in this sensor as the sensing element. The design of the sensor and the manufacturing are described in detail. The properties of the sensor have been investigated experimentally. The cross-sensitivity to temperature and humidity and the response time were measured and changes of the characteristic curve due to aging were investigated. The influence of different chemicals on the output signal of the pressure sensor are reported and discussed.

The hot embossing process is a flexible molding technique to produce delicate microstructures with high aspect ratios on thin layers. Large-scale hot embossing is one effective way to meet future requirements and produce high-quality microstructures at low costs. For this, however, principal changes of the molding process and molding tool design will be required. In the present paper, constructive solutions for large-scale hot embossing shall be described. Based on a simulation of the hot embossing process, solutions shall be presented that are aimed at reducing shrinkage of the molded parts and demolding forces and, hence, at avoiding damages of microstructures during demolding.

Metal strain gauges need to be designed differently from strain gauges made from silicon. In this paper equations are derived that allow us to calculate the resistance change of metal strain gauges as a function of the position on a thick diaphragm, a thin membrane and a disc simply supported at the rim. The results of finite element calculations presented reveal that large deviations from these equations occur for strain gauges on thin membranes made of soft materials.

A normally-closed piezo-driven micro valve for gases and liquids has been developed. Due to the small deflection of piezo-actuated bending disks made of PZT a hydraulic transmission was constructed, which increases the displacement of the piezo disk up to the 25-fold. The switching times of the valve are shorter than 1.8 ms. Silicone gel serves as a transition medium in the hydraulic. It simplifies the manufacturing process and allows a flexible adaptation to different pressure requirements up to a differential pressure of 150 kPa switched with 300 V. Additionally, this silicone gel supports the sealing of the valve so it achieves an open-to-close ratio of 1:150,000 or higher. The overall dimensions of the valve are 13 mm ×13 mm ×3 mm , the dead volume is 0.33 μl, and the inner diameter of the valve seat is 200 μm. A transformer as small as the micro valve is able to produce driving voltages of up to 300 V with a response time of 2 ms. Therefore, the valve could be integrated into hand-held systems which are battery powered with 5–15 V.

A polymer valve with a small dead volume in the range of 6 nl and a response time faster than 1 ms is presented. The valve structure is simple and therefore easy to fabricate by injection molding or hot embossing. A layer of silicone rubber applied by a stamping technique not only promotes the sealing of the valve but also defines the gluing area during assembly. The fabrication is based on the AMANDA-process, which allows low-cost batch production of polymer micro devices.

We present a dosing system, which consists of four microvalves (presented by Rogge et al in the Proceedings of Eurosensors XVI, Prague, 2002, pp 109–110) for controlling and a movable membrane for flow measurement that divides a cavity into two chambers. The flow rate is determined from the straining of the membrane caused by the entering fluid. The displaced volume is detected by strain gauges integrated in the membrane. The overall dimensions of the membrane and the entire system are 2 mm and 10 × 50 × 6 mm3, respectively. A simple control was coded for dosing a certain amount of volume. This simple system has already achieved an accuracy of about 10%. The dosing system is manufactured with the AMANDA process, which allows for low-cost production of microcomponents from polymers.

A new manufacturing method has been used to produce a magnetically driven micro ball valve. The micro ball valve consists of three hot-embossed polymer layers and three metal layers. The layers are bonded with adhesive films which are microstructured by a punching process. The valve uses iron balls with a diameter of 3 mm as moving parts driven by a commercially available coil. The valve switches up to 200 kPa differential pressure with an initial current of 300 mA. The on–off switch frequency investigated was up to 30 Hz. In addition, the valve can operate as a proportional valve regulating the outlet pressure range from 0 to 112.5 kPa at an input pressure of 200 kPa. A switching time of 10 ms was measured.