Polydimethylsiloxane as an elastic material applied in a capacitive accelerometer

Polydimethylsiloxane is a silicone rubber. It has a unique flexibility, resulting in one of the lowest glass-transition temperatures of any polymer. Furthermore, it shows a low elasticity change versus temperature, a high thermal stability, chemical inertness, dielectric stability, shear stability and high compressibility. Because of its high flexibility and the very low drift of its properties with time and temperature, polydimethylsiloxane could be well suited for mechanical sensors, such as accelerometers. A novel capacitive accelerometer with polydimethylsiloxane layers as springs has been realized. The obtained measurement results are promising and show a good correspondence with the theoretical values

On the design of a triaxial accelerometer

Up to now, mainly uniaxial accelerometers are described in most publications concerning this subject. However, triaxial accelerometers are needed in the biomedical field. Commercially available triaxial accelerometers consisting of three orthogonally positioned uniaxial devices do not meet all specifications of the biomedical application. Therefore, a new highly symmetrical inherently triaxial accelerometer is being developed, the advantages of which are higher sensitivity and reduction of off-axis sensitivity

Integrated pressure sensing using capacitive Coriolis mass flow sensors

The cross-sectional shape of microchannels is, dependent on the fabrication method, never perfectly circular. Consequently, the channels deform with the pressure, which is a non-ideal effect in flow sensors, but may be used for pressure sensing. Multiple suspended channels with different lengths were modeled, fabricated, and characterized to verify the use and the scalability of this effect for pressure sensing. Furthermore, it is shown that the pressure dependence can be distinguished from the Coriolis effect in microfabricated Coriolis mass flow sensors, enabling the measurement of the pressure next to flow and density with only the flow sensor itself. In addition, this allows for further improvement in the accuracy of the flow measurement by correcting for the small pressure dependence

Theory, technology and assembly of a highly symmetrical capacitive triaxial accelerometer

A highly symmetrical cubic easy-to-assemble capacitive triaxial accelerometer for biomedical applications has been designed, realized and tested. The outer dimensions of the sensor are 5×5×5 mm 3 and the device is mounted on a standard IC package. New aspects of the sensor are an easy assembly procedure, the use of the polymers polydimethylsiloxane (PDMS) as spring material between the capacitor plates and the mass and polyimide (PI) as flexible interconnection layer between the capacitor plates, and the highly symmetrical cubic structure. The mathematical model, technology and assembly procedure of the sensor are described. The measurement results show a good linearity in the output voltage for accelerations up to at least 5 g and a bandwidth of DC >50 Hz. In the x-axis the sensitivity was found to be 175 mV/g which is in good correspondence with the theory. The sensitivity can be increased when the PDMS layer is patterned, which was shown in previous versions of the highly symmetrical triaxial acceleromete

Polydimethylsiloxane, a photocurable rubberelastic polymer used as spring material in micromechanical sensors

Polydimethylsiloxane (PDMS) is a commercially available physically and chemically stable photocurable silicone rubber which has a unique flexibility (G≈250 kPa) at room temperature. Further properties of PDMS are a low elasticity change versus temperature (1.1 kPa/°C), no elasticity change versus frequency and a high compressibility. PDMS is an interesting polymer to be used as spring material in micromechanical sensors such as accelerometers. The spring constant of the PDMS structures was theoretically calculated and measurements were done on accelerometers with PDMS springs to validate the theory. The measured and calculated spring constants showed a good correspondence, so the measurement results showed that the PDMS structures can successfully be used as mechanical springs

Miniature proportional control valve with top-mounted piezo bimorph actuator with millisecond response time

In this paper we demonstrate the realization of a micro control valve with a top-mounted piezoelectric bimorph actuator, to obtain a high-bandwidth proportional control valve for gases in the range of several grams per hour. Dynamic fluidic and mechanical characterization shows that the valve is suitable for high-speed flow control with response times on the order of milliseconds. The microvalve contains an integrated capacitive displacement sensor for position-based control, which can be used to improve the control precision. The microvalve is realized in a straight-forward fabrication process based on a single SOI wafer. A high level of integration of the piezo actuator is achieved using a flexible silicone rubber support between the bimorph and the silicon. This leads to a small volume, high speed device

Velocity-independent thermal conductivity and volumetric heat capacity measurement of binary gas mixtures

In this paper, we present a single hot wire suspended over a V-groove cavity that is used to measure the thermal conductivity ($k$) and volumetric heat capacity ($\rho c_p$) for both pure gases and binary gas mixtures through DC and AC excitation, respectively. The working principle and measurement results are discussed

Single chip flow sensing system with a dynamic flow range of more than 4 decades

We have realized a micromachined single chip flow sensing system with an ultra-wide dynamic flow range of more than 4 decades, from less than 0.1 up to more than 1000 μl/h. The system comprises both a thermal and a micro Coriolis flow sensor with partially overlapping flow ranges

Optimization of a micro Coriolis mass flow sensor using Lorentz force actuation

In this paper we present Finite Element models to optimize the Lorentz force actuation of a micro Coriolis mass flow sensor. These models specify six different configurations for the permanent magnets used to create the magnetic field for the actuation. The models are used to compare the various configurations in terms of the strength of the Lorentz force used for actuating the vibrational modes, and in terms of the sensitivity to misalignment of the magnetic field of the magnets. The simulations show that the Lorentz force actuation can be increased significantly by improving the placement of the magnets and that the actuation is insensitive to misalignment of the tube in relation to the magnetic field. By applying the models to a fabricated sensor, the magnetic field outside the sensor area has been reduced by 6 orders of magnitude. Due to the smaller size of the new permanent magnets, the footprint of the chip, including actuation, has been reduced by a factor 3. The models of two magnet configurations without misalignment have been validated with measurements