Christof Gerhardy

Review on ultrasonic fabrication of polymer micro devices

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

Ultrasonic hot embossing is a new process for fast and low-cost production of micro systems from polymer. Investment costs are on the order of 20.000 € and cycle times are a few seconds. Microstructures are fabricated on polymer foils and can be combined to three-dimensional systems by ultrasonic welding.

Coded ultrasonic remote control without batteries

A concept for battery-less remote controls has been developed based on mechanically actuated beams and micro whistles generating ultrasound signals. These signals need to be frequency or time coded to increase the number of signals which can be distinguished from each other and environmental ultrasound. Several designs for generating coded ultrasonic signals have been investigated.

Ultrasonic Hot Embossing and Welding of Micro Structures

Ultrasonic hot embossing allows the fabrication of micro structures from polymer films by moulding from a master tool. The fabrication process is completed within seconds and the investment costs are low. With micro patterned tools, structured surfaces can be created on one or both sides of polymer films. For micro whistles and micro fluidic devices such as micro mixers or flow sensors, sealed structures are created by welding a cover film on embossed structures. Furthermore, moulded interconnection devices can be fabricated by welding polymer coated metal films onto polymers.

Time of Flight Sensor with a Flow Parallel Wire

A time of flight sensor has been equipped with a sensing wire parallel to the flow direction (flow parallel wire, FPW). A heat pulse is generated with a coil in the flow channel. The FPW has a center tap allowing its upstream and downstream parts to join in a half bridge. When a heat pulse passes the FPW, a large output peak is generated. The time between heat pulse generation and recording the peak maximum is only marginally affected by the properties of the fluid. With a combination of two FPWs, a measuring range of approximately 0.01–0.5 m/s can be achieved.