Page 233 - MEMS Mechanical Sensors

222 Flow Sensors

Table 9.2 Data for Calorimetric Type Flow Sensors
Author; Year Flow Range Sensitivity Response Time Fluid Chip Size
Häberli et al. 0–40 m/s — — Air —
[54]; 1997
Lyons et al. 0–3.5 m/s — 2.5 ms — —
[49]; 1998
Kaltsas et al. 0.41–40 cm/s 6.0 (mV/W)/(m/s) — Nitrogen 1.1 × 1.5 mm 2
[52]; 1999
de Bree et al. 100 µm/s to 1 — A few Air —
[68]; 1999 m/s milliseconds
Ashauer et al. 0.1–150 mm/s — 2 ms Liquids and —
[41]; 1999 gases
Glaninger et al. 0.01–200 m/s; — 20 ms Air 2 × 4 × 0.3
[50]; 2000 0.6 ml/h to 150 mm 3
l/h
Oda et al. [53]; <12,000 l/h — — Air 2 × 2mm 2
2002
Ernst et al. [47]; >100 nl/h — — Water —
2002
Makinwa et al. 2–18 m/s — — Air 4 × 4mm 2
[28]; 2002
Park et al. [29]; 5–10 m/s — — Air 6.2 × 6.2 mm 2
2003

aluminum/polysilicon thermopiles up- and downstream. A sensor for very small
flow rate detection down to 100 nl/h in water was developed by Ernst et al. [47] for
biomedical applications like micro dialysis systems or drug infusion systems.
Some sensors are able to measure both the flow velocity and the direction
of the flow over 360°. A wind sensor has been realized in a standard CMOS
process, consisting of four heaters (polysilicon resistors) and four thermopiles (alu-
+
minum/p -doped silicon) [28]. The sensor electronics are integrated in the silicon
chip. Wind speed and direction were measured in a wind tunnel with an accuracy of
±4% and ±2° over a range of 2 to 18 m/s. Earlier work from that group is described
in [69–71]. Another flow sensor for direction-sensitive measurements was presented
by Park et al. [29]. This sensor is circular with one platinum heater and four plati-
num detectors arranged in a circle around the heater over a silicon membrane. The
sensor was tested between a flow rate of 5 to 10 m/s with an accuracy of 5°. Flow
direction and flow velocity were not yet measured at the same time with this sensor.
Schematics of both sensors are shown in Figure 9.8.
The calorimetric sensor has a higher sensitivity compared to the anemometer,
but at larger flow velocities the anemometer becomes advantageous. Hence, de Bree
et al. [68] developed a flow sensor operated by using both principles. The flow
sensor, comprised of two resistors, has a very large dynamic range. It measures air
flow rates from 100 µm/s to 1 m/s. Also a combination of two operating principles
is published by Ashauer et al. [41]. The considerable increase in the measuring
range, from 0.1 to 150 mm/s, was done by combining the calorimetric sensing mode
and the time of flight mode (described later). Twenty thermocouples are placed in a
row on each side of the heater. Measurements were taken for gases and liquids.
Another sensor designed to use this same operating principle was proposed by
Rodrigues et al. [56].