J.J.J. van Baar

Artificial sensory hairs based on the flow sensitive receptor hairs of crickets

This paper presents the modelling, design, fabrication and characterization of flow sensors based on the wind-receptor hairs of crickets. Cricket sensory hairs are highly sensitive to drag-forces exerted on the hair shaft. Artificial sensory hairs have been realized in SU-8 on suspended SixNy membranes. The movement of the membranes is detected capacitively. Capacitance versus voltage, frequency dependence and directional sensitivity measurements have been successfully carried out on fabricated sensor arrays, showing the viability of the concept.

Micromachined structures for thermal measurements of fluid and flow parameters

In this paper thermal sensor-actuator structures are proposed that can be used to measure various fluid parameters such as thermal conductivity, flow velocity, heat capacity, kinematic viscosity and pressure. All structures are designed in such a way that they can be realized in the same fabrication process and therefore they can be easily combined in a single device. All structures are based on the principle of thermal measurements: resistive structures are used for both heating and temperature measurements. For accurate measurements the temperature coefficient of resistance (TCR) must be well known. Therefore, a special structure, which can be used for auto-calibration, was designed to measure the TCR. A first device containing structures for the combined measurement of flow velocity, thermal conductivity and TCR has been fabricated. Measurements show promising results.

Arrays of cricket-inspired sensory hairs with capacitive motion detection

This paper presents the fabrication of flow-sensors based on the drag-force induced motion of artificial hairs connected to capacitive read-out. Artificial hairs were made either out of moulded silicon-nitride structures or by SU-8. The SU-8 hairs were suspended on membranes containing electrodes to form the variable capacitors. Silicon-rich-nitride hairs were made using a silicon wafer as a dissolvable mould. The longest SU-8 hairs were fabricated using a 470 /spl mu/m thick photoresist layer. Capacitance versus voltage, frequency dependency and directional sensitivity measurements have been carried out on entire arrays and are reported in this paper.

Fabrication of arrays of artificial hairs for complex flow pattern recognition

We present monolithically integrated high-density arrays of artificial hairs for flow pattern measurements based on drag force. A combined bulk/surface micromachining process has been developed to integrate the artificial hairs with capacitive read-out. First fabrication results show the possibility to fabricate out-of-plane hairs without reverting to micro-assembly technologies. This enables realisation of high-density arrays of symmetrical sensors with two-dimensional sensitivity.

Sensitive thermal flow sensor based on a micro-machined two dimensional resistor array

A two-dimensional resistor structure is presented, which opens the way for advanced flow measuring techniques. In this paper we demonstrate the application as a sensitive flow sensor. The temperature distribution along a heated segmented beam due to a parabolic flow profile has been calculated and experimentally confirmed. The temperature distribution allows measurement of the flow independent of the temperature coefficient of resistance (TCR).

Micromachined two dimensional resistor arrays for determination of gas parameters

A resistive sensor array is presented for two dimensional temperature distribution measurements in a micromachined flow channel. This allows simultaneous measurement of flow velocity and fluid parameters, like thermal conductivity, diffusion coefficient and viscosity. More general advantages of measuring temperature distributions are the inherent compensation of heat losses to the support and the insensitivity to variations in the temperature coefficient of resistance.

AC-Driven Temperature-Balance Flow Sensor

A micro fluid thermal flow sensor with an intrinsic offset-free DC-flow specification is presented. The flow sensor is based on a recently defined “Temperature-Balance-Anemometer” (TBA) concept. The thermal actuators are AC-driven and the dynamic temperature sensor is read-out by a phase-lock technique which results in a measurement signal which is insensitive to thermo-electric, DC-offset and l/f-noise signals. Also the system output signal is independent from the dynamic temperature-sensor sensitivity.

Pirani pressure sensor with distributed temperature measurement

Surface micromachined distributed Pirani pressure gauges, with designed heater-to-heat sink distances (gap-heights) of 0.35 /spl mu/rn and 1.10 /spl mu/m, are successfully fabricated, modeled and characterized. Measurements and model response correspond within 5 % of the measured value in a pressure range of 10 to 2*10/sup 4/ Pa. The distributed nature of the sensor facilitates pressure measurement to be independent of the Temperature Coefficient of Resistance of the resistors. This also provides an inherent compensation for heat loss via the membrane supporting the heater, extending the lower pressure range.

Drag Force Actuated Bistable Microswitches for Flow Sensing

This paper presents bistable microswitches with Au contacts with the aim to combine them with artificial hairs for flow sensing. The Au contacts are applied on both ends of a silicon nitride beam, suspended by a torsional bar at its center. The beam is provided with electrodes for electrostatic actuation, which were used for characterization and can also be used for adaptive control of the mechanical properties of the flow sensor. The electrodes have been actuated in anti-phase to drive the microswitch similarly to an astable multivibrator. Single-sided switching has been measured up to 10 kHz actuation frequency.

Pressure sensor based on distributed temperature sensing

A differential pressure sensor has been realized with thermal readout. The thermal readout allows simultaneous measurement of the membrane deflection due to a pressure difference and measurement of the absolute pressure by operating the structure as a Pirani pressure sensor. The measuring of the temperature distribution makes it possible to take the heat transfer to the support in to account and make the measurements independent of the temperature coefficient of resistance of the sensing elements.