Abstract: A system for the detection of wing icing by monitoring variations in flexural waves transmitted through the outer plate material of an aircraft airfoil. The flexural waves in the plate of the wing airfoil are more subject to variation from the accumulation of ice on the wing than the compressional waves. The flexural waves are detected apart from the compressional waves, which tend to remain relatively constant, to provide an indication of icing. Changes in amplitude, phase or dispersion characteristics of the flexural waves are detected to indicate ice buildup, and, in one embodiment, these values are ratioed to the corresponding levels in the compressional wave in order to provide compensation for variations other than ice buildup. The ultrasonic waves may be coupled directly from a transducer to the airfoil plate or via an ultrasonic waveguide interposed between the transducer and the plate.

Abstract: A vibrating wire placed in the humidity duct of a standard radiosonde is used to measure vertical profiles of the concentration of supercooled liquid water in clouds. An electronic circuit is provided for monitoring the natural frequency of vibration which varies according to the mass of ice accumulated on the wire by contact freezing. The time rate of change of ice accumulation is related to the supercooled liquid water concentration. By monitoring the natural frequency, the supercooled liquid water concentration can be found.

Abstract: A frost sensor for detecting the presence of frost uses an acoustic device having an acoustic transmitting medium made of a magnetostrictive material, particularly an amorphous metal alloy, of a ribbon shape, as means for detecting the frost.

Abstract: A detecting transmitter device installed in operative proximity with a surface to be observed includes an ultrasonic waveguide installed in such surface. Electronic equipment electrically connected to the ultrasonic waveguide transmits ultrasonic waves to the waveguide. The ultrasonic waves proceed in the waveguide. The equipment also receives the ultrasonic waves from the waveguide. The degree of attenuation of the waves in the waveguide depend upon the difference in viscosity and other mechanical properties of water and ice, whereby the detecting transmitter device and the electronic equipment detect freezing of the surface by attenuation of the waves in the waveguide.

Abstract: A frost detector comprises a piezoelectric element secured on a metal diaphragm and inside an air-tight space formed by the diaphragm, a base and a bellows which air-tightly and resiliently connects the diaphragm and the base, the base being secured on a fin of a heat exchanger, the piezoelectric element being connected to an oscillation circuit and an oscillation detection circuit; resonance frequency and impedance characteristic of the piezoelectric element being changed by frosting on the outside face of the diaphragm, and the frosting being detected through a change or stopping of the oscillation and resultant output signal by the oscillation detection circuit.