Gas sensor based on semiconducting polymer to determine molecular fingerprint|directs microwave radiation to polymer in magnetic field and detects variations in polymer absorption characteristic in presence of gas to be detected

The sensor includes at least one semiconducting polymer (10) and an electromagnet (12) for applying a homogeneous magnetic field across the polymer in the electron spin resonance (ESR) cavity (18) of a commercial X band ESR spectrometer. Microwave radiation from a klystron (14), backward wave generator or Gunn diode is directed to the polymer by a waveguide (20).A detector (16), such as a standard crystal detector, detects variations in an absorption characteristic of the polymer in the presence of a gas or a mixture of gases to be detected. The output of the crystal is detected with a phase sensitive amplifier (22) and the spectrum obtained is displayed (24). One mode of operation, analogous to conventional ESR spectroscopy, involves modulating the magnetic field strength whilst employing a constant frequency microwave source. Alternatively, a constant magnetic field may be applied, the combination of field and microwave frequency being selected to probe within the ESR line-shape.ADVANTAGE - Variation in attenuation of microwave radiation by semiconducting polymer may be detected. Variations in absorption characteristic may be measured with respect to that measured in presence of reference gas.