Emerald Group Publishing Limited
Copyright © 2008, Emerald Group Publishing Limited
Electromagnetic radiation sensors
Article Type: Viewpoint From: Sensor Review, Volume 28, Issue 3
Ahmed Al-Shamma’a General Engineering Research Institute, Liverpool John Moores University, Liverpool, UK
Radio waves, microwaves, infra-red, visible light, ultraviolet, X- and γ-rays are all examples of electromagnetic radiation. They are waves with electric and magnetic components which travel at the speed of light in a vacuum, approximately 300 million m/s. The electric and magnetic fields oscillate at right angles to each other and combined waves move in a direction perpendicular to both of the electric and magnetic field oscillations. Like all waves, they have a frequency, which is the number of crests per second, and a wavelength, which is the distance between successive crests. These values are used to categorise the radiation into the types shown above. The examples here are given in order of increasing frequency and decreasing wavelength. FM radio, for instance, is transmitted at frequencies around 100 MHz, have wavelengths of 3 m and can be detected by an aerial. The eye can detect wavelengths in the region of 380-750 nm, less than a thousandth of a millimetre. Electromagnetic radiation, with even higher frequencies, and therefore smaller wavelengths, is ionising, which means that a large enough exposure can damage DNA and cause cancer. The frequency of UV radiation is around ten million times higher than that of FM radio.
A variety of sensors are required for detecting the different ranges of electromagnetic radiation. Aerials are suitable for detecting radio waves and microwave transmissions as used by WiFi and Bluetooth devices for example. Optical sensors such as photodiodes and charge-coupled devices are used for the infra-red and visible wavelengths. Geiger-Müller tubes use the ionising properties of the higher frequencies to produce a current pulse which can be used to generate an audible click Scintillators fluoresce when they detect ionising radiation. Microwave sensors are recently proven successfully over the range of 1-300 GHz to suit various industrial applications including non-invasive real-time monitoring of the oil and water pipe line constituents, passive radiometer and radar applications for mapping, imaging and tomography. Recent and future development of such sensors having high accuracy and reliability in health care applications including detection of tumours, alcohol, drugs and sugar in the blood stream. A new development has emerged in the use of optical imaging in radiotherapy that by measuring the patient movements very accurately which will have a tremendous potential for the health care industry. Future sensors will emerge in the form of nanoscale with hybrid multi-functionality sensors meeting the demands of many challenging applications.