Developing
a facile, cost-saving, and environment-friendly method
for fabricating a multifunctional humidity sensor is of great significance
to expand its practical applications. However, most humidity sensors
involve a complex fabrication process, resulting in their high cost
and narrow application fields. Herein, a multifunctional paper-based
humidity sensor with many advantages is proposed. This humidity sensor
is fabricated using conventional printing paper and flexible conductive
adhesive tape by a facile pasting method, in which the paper is used
as both the humidity-sensing material and the substrate of the sensor.
Owing to the moderate hydrophilicity of the paper and the rational
structure design of the paper-based humidity sensor, the sensor exhibits
an excellent humidity-sensing response of more than 103 as well as good linearity (R
2 = 0.9549)
within the humidity range from 41.1 to 91.5% relative humidity. Furthermore,
the paper-based humidity sensor has good flexibility and compatibility,
endowing it with multifunctional applications for breath rate, baby
diaper wetting, noncontact switch, skin humidity, and spatial localization
monitoring. Although the resistance of the paper-based humidity sensor
is relatively large, the humidity-sensing response signals of the
sensor can be conveniently processed by the designed signal processing
system. The readily available starting materials and facile fabrication
technique provide useful strategies for the development of multifunctional
humidity sensors.
The vibration-rotation-tunneling absorption spectra of the formic acid dimer (HCOOH)2 have been measured in the C-O stretch region at 1215-1240 cm(-1) using a rapid-scan tunable diode laser spectrometer in conjunction with a slit supersonic expansion. The ν5 fundamental band of the HCOOH monomer is identified and the perturbed band-center is 1220.83329(10) cm(-1). Three vibrational bands centered at 1219.71, 1225.35, and 1233.95 cm(-1) are assigned to the two combination bands and the ν22 fundamental band of (HCOOH)2 unambiguously. The transition frequencies of these three vibrational bands are fitted together using a standard Watson A-reduced Hamiltonian, yielding precise rotational and centrifugal distortion constants for each tunneling level in the ground and excited vibrational states. The fitting results of the vibrational band centered at 1225.35 cm(-1) are in good agreement with a previous high resolution study [M. Ortlieb and M. Havenith, J. Phys. Chem. A. 111, 7355 (2007)]. The tunneling splittings in the vibrationally excited states are -0.00304(16), -0.01023(11), and -0.00318(12) cm(-1), respectively, where the minus indicates that the upper tunneling component lies energetically below the lower tunneling component. A three-state deperturbation analysis using the Fermi coupling constants obtained from a previous vibrational analysis [F. Ito, Chem. Phys. Lett. 447, 202 (2007)] fails to get the normal order of the tunneling levels for all the three excited vibrational states simultaneously.
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