Page 310 - Microsensors, MEMS and Smart Devices - Gardner Varadhan and Awadelkarim
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290 MICROSENSORS
200
100 200 300 400
(a) Temperature above ambient (°C)
250
200 300 400 500
(b) Operating temperature (°C)
Figure 8.57 Power consumption of a microhotplate-based resistive gas microsensor (SRL108)
(a) observed against a simple analytical model and (b) relative contributions of conductive, convec-
tive, and radiative heat losses. From Pike (1996)
in every second and thus achieve an average power consumption of below 12 mW for
SRL108 or below 1 mW for smaller hot plates. An interesting and alternative approach is
to modulate the heater temperature with a sinusoidal AC drive voltage 26 and then relate
the harmonic frequency content of the AC tin dioxide resistance signal to the gas present.
This approach has been successfully demonstrated by researchers (Heilig et al. 1997; Al-
Khalifa et al. 1997); in this approach, the coefficients of a Fourier analysis are learnt in
Strictly speaking, the temperature rise is not a sine wave but is periodic.
