Abstract: A method and apparatus for continuous and contactless grading and counting in which the articles or products to be surveyed are passed beneath a microwave radiometer antenna on a conveyor belt or the like, so as to measure the frequency spectrum of the radiation temperature emitted by the articles at a convenient temperature and relating the "signature" thus obtained to a non-electrical parameter such as weight or size.

Abstract: Apparatus for detecting the presence of an underwater object measures variations in the input impedance of a monopole antenna to provide data on the object. A sweep generator supplies a first electrical signal of varying frequency for transmission as an electromagnetic signal propagated through water from the antenna, and means are provided for detecting reflections of the electromagnetic signal to provide a second electrical signal, which is compared with the first electrical signal to provide an output signal. Preferably, the monopole antenna is one of three such antennas, which are provided with means for comparing input impedances of the antennas to provide an output signal representing the bearing of the object.

Abstract: A method and device for absorbing microwave energy avoid the expense and bulk of prior art arrangements, and provide greater efficiency, by forming a flame in the path of the microwave and supplying a seeding substance into the flame to produce a plasma flame column which absorbs the microwave. The seeding substance is preferably an alkali salt solution, e.g. KNO.sub.3.