JPH0339589B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for detecting the presence of ice on a surface, in particular an aircraft wing.

In winter, aircraft are likely to encounter rain and snow,
Ice layers tend to form on aircraft wings. These ice layers are dangerous to the safe operation of aircraft and can cause the aircraft to crash during takeoff, for example.

In accordance with the present invention, a method is provided for detecting ice formation on the surface of a thin solid sheet, the method comprising energizing a transducer to transmit ultrasound waves having a predominant component parallel to the surface of the sheet to a portion of the sheet. detecting these waves by a second transducer, measuring the amplitude of the waves received by the second transducer, and measuring the amplitude of the waves received by the second transducer;
detecting the presence of an ice layer on the surface of that portion of the sheet by the amplitude of the waves received by a transducer of the sheet.

If an ice layer forms on the surface, waves with a predominant component parallel to the surface will dissipate energy into the ice layer but not into the atmosphere or liquid layer. Therefore, the amplitude and intensity of the wave detected by the second transducer will be reduced.

According to the invention there is also provided an ice detector for detecting ice on the surface of a thin solid sheet, the ice detector comprising transmitting an ultrasound wave having a predominant component parallel to the surface of the sheet through a portion of the sheet. an ultrasonic transducer, another ultrasonic transducer that receives these waves and generates a signal representative of their amplitude, and in response to this reception the presence of an ice layer on the surface of the portion of the sheet; It is equipped with a means to detect.

Said wave is a guided horizontal shear
It may be a wave, or it may be a Lamb wave mode in which the predominant component is horizontal. Incidentally, "horizontal" means parallel to the surface, and "perpendicular" means perpendicular to the surface.

These transducers are placed opposite (back) the surface of the part of the sheet where an ice layer may develop.
It can be attached to the side surface and can generate and receive ultrasound by piezoelectric or electromagnetic means.

Embodiments of the ice detector according to the present invention will be described below with reference to the accompanying drawings.

As shown in FIG. 1, the icing detector includes a first transducer 10 mounted on a surface 12 of the mold sheet 14 opposite (back) from the surface 16 where icing is expected to form. There is. The transducer 10 is connected to a signal generator 22 by a coaxial cable 20, and when the signal generator 22 is energized, the transducer 10 vibrates at a frequency and is horizontally polarized through the sheet 14. Propagates shear wave pulses. Since the wavelength of the waves is comparable to the thickness of sheet 14, shear waves become guided by surfaces 12 and 16.
A second transducer 30 of the same type as the first transducer 10 is mounted to the surface 12 of the sheet 14 at a distance from the transducer 10. A second transducer 30 is connected to a signal receiver and discriminator 34 by a coaxial cable 32. A signal receiver and discriminator 34 determines whether an ice layer is present on the surface 16 from measurements of the amplitude of the signal from the second transducer 30.

As shown in FIG.
comprises six transducer strips 40 extending parallel to each other and perpendicular to the surface and spaced apart by a distance equal to the wavelength of the ultrasonic shear waves in the sheet 14; It is held within the base material 42. Each strip is 30 mm long and is bonded to surface 12 by a conductive layer 44. Each strip 40 is made of piezoelectric material and has contacts (not shown) on both the top and bottom surfaces by which it can be excited to vibrate parallel to its length. These vibrations are in phase with the other strips 40 and cause horizontally polarized shear waves to propagate into the sheet 14.

The structure of transducer 30 is the same as transducer 10. The shear waves propagating through the sheet 14 drive each strip 40 of the transducer 30 to vibrate parallel to its length, inducing voltages between the contacts on both the top and bottom surfaces of the strips 40 of the transducer 30.

The operation of this ice detector is as follows. When the signal generator 22 is energized, it generates a chopped continuous wave, but since the number of cycles in each burst is approximately equal to the number of transducer strips 40 in the transducers 10 and 30, the signal generator 22 generates a chopped continuous wave. One transducer 10 propagates horizontally polarized ultrasonic shear wave pulses through the sheet 14 . These pulses are received by a second transducer 30 which provides a signal representative of the amplitude of the pulses to a signal receiver and discriminator 34. In order to cause the signal receiver and discriminator 34 to respond only to signals for pulses that traveled directly from the first transducer 10 to the second transducer 30, the signal receiver and discriminator 34 responds to the predicted arrival of the pulse. It is gated to operate only about 5% of the time before and after the time. If the surface 16 is dry or covered with water (because horizontally polarized shear waves cannot propagate in water), the amplitude of the pulse will be different if the surface 16 is covered with an ice layer (the shear wave cannot propagate through water). waves can propagate). This is because some of the energy of the shear waves within sheet 14 dissipates into and propagates through the ice. As described above, this ice detector can detect ice adhering to the surface 16 and is insensitive to the presence of ice.

The frequency of the continuous wave generated by signal generator 22 depends on the mode of the wave desired to propagate through sheet 14. For example, for zero-order symmetric horizontally polarized shear waves, frequencies in the range of 250 KHz to 1 MHz are used. The pulse repetition frequency is limited by pulse reverberation, but may conveniently be 50 Hz. The distance along the sheet 14 between the first transducer 10 and the second transducer 30 is between 5 and 10 m, depending on the material from which the sheet 14 is made and the sensitivity of the signal receiver and discriminator 34. It would be about that.

The sensitivity of the ice detector to ice of different thicknesses depends on the frequency (and hence wavelength) of the ultrasound. It has been shown that an ice detector generating zero-order symmetric horizontally polarized shear waves and operating at 1 MHz is sensitive to ice layers approximately half as thick as a similar ice detector operating at 500 KHz. Ivy. Therefore, the operating frequency of the ice detector can be selected to provide the required sensitivity.

Other types of transducers may be used to generate horizontally polarized shear waves; an electromagnetic transducer 50, shown in FIG. 3, is used in place of transducers 10 and 30 on metal sheet 14. It is something that can be done. Six electromagnetic transducers 50 are arranged parallel to each other and 30 mm perpendicular to the plane of the paper.
A strip 52 of soft ferromagnetic material extending a length of
, which are separated by spacers 56 of non-magnetic material at a distance equal to the wavelength of the ultrasonic shear waves within sheet 14 . Two ceramic magnets 58, one on each side of the sheet 14, generate a magnetic field perpendicular to the surface of the sheet 14, with the magnetic field being strongest near the ferromagnetic strip 52. A ten-turn coil 60 is wound around the ferromagnetic strip 52 and spacer 56, with a portion of each turn located near one surface 12 of the sheet 14 and parallel to the plane of the paper. The ferromagnetic strip 52 and the nominal coil 60 are located near the surface 12 of the sheet 14, but are not bonded thereto.

Applying an alternating current to the coil 60 (its source not shown) induces eddy currents in the surface 12 of the sheet 14 parallel to the plane of the paper, so that the portion of the surface 12 near the ferromagnetic strip 52 experiences a force perpendicular to the plane of the paper. As a result, shear waves are allowed to propagate within the sheet 14. Similarly, a shear wave propagating through sheet 14 near ferromagnetic strip 52 generates an alternating electromotive force in coil 60.

An ice detector using two transducers 50 in place of transducers 10 and 30 operates in the same manner as described with respect to the ice detector of FIGS. 1 and 2.

Although transducers 10, 30 and 50 have been described as having six strips 40 or 52, it should be understood that different numbers of strips may be used. Although one strip may be used for each transducer, it is preferred to use five or more strips to provide sufficient selectivity for the ultrasound mode.

Further, the length of each strip 40 or 52 determines the directivity of the transducer 10, 30 or 50, but this length may also be determined by implementation constraints. For transducers 10, 30 and 50, the strip length is 30 mm, but lengths of eg 10 mm to 50 mm may be convenient. The width of the strip is preferably equal to about one-fifth of the wavelength of the ultrasonic waves being generated, but any width up to about half a wavelength is acceptable.

It should be understood that other modes of wavelength may be propagated within sheet 14. For example, a Lamb wave mode with a predominant component parallel to the surface can be used.

It is also noted that the ultrasound is guided by the surface of the sheet as long as the wavelength of the ultrasound is comparable to the thickness of the sheet and that the transducer 10, 30 or 50
It should also be understood that the can be placed on either side of the sheet.

Additionally, if an ice layer is detected on the surface 16 of the sheet 14, a conventional thickness gauge monitor ( It is also to be understood that the thickness of the ice layer can be measured by the method (not shown).

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an ice detector mounted on a gold layer sheet, FIG. 2 is a cross-sectional view of one of the transducers of the ice detector, and FIG. 3 is a diagram of the transformer of FIG. FIG. 3 is a cross-sectional view of another transducer different from the transducer. DESCRIPTION OF SYMBOLS 10... First transducer, 12... Surface of sheet, 14... Sheet, 16... Surface where ice formation is expected, 20, 32... Coaxial cable, 2
2... Signal generator, 30... Second transducer, 34... Signal receiver/discriminator, 40... Piezoelectric strip, 42... Base material, 44... Conductive layer,
50... Electromagnetic transducer, 52... Ferromagnetic strip, 56... Nonmagnetic spacer, 58...
...Ceramic magnet, 60...coil.

Claims (1)

[Claims] 1. Force the transducer 10 to move the sheet 14
transmitting ultrasonic waves through a portion of the ultrasonic wave, detecting the ultrasonic waves by a second transducer 30;
The amplitude of the ultrasound received by the second transducer 30 is measured and the amplitude of the ultrasound received by the second transducer 30 determines the amplitude of the In a method of detecting ice formation on the surface of a thin solid sheet 14, said ultrasound waves are
Surface 1 of said sheet 14 perpendicular to the direction of propagation
A method characterized in that the guided ultrasound wave has a predominant component parallel to 6 and larger than the other components. 2. The method according to claim 1, wherein the ultrasound waves are guided horizontally polarized shear waves. 3. The method according to claim 1, wherein the ultrasonic wave is a Lamb wave mode with a horizontal predominant component. 4 an ultrasonic transducer 10 for propagating ultrasonic waves through a portion of the sheet 14, another ultrasonic transducer 30 for receiving these ultrasonic waves and generating a signal representative of their amplitude, and responsive to this signal; In a detector for detecting ice formation on a surface 16 of a thin solid sheet 14, the transducer 10, 30
are transducers capable of respectively propagating and receiving guided ultrasound waves having a predominant component larger than the other components, perpendicular to the direction of propagation and parallel to the surface 16 of said sheet 14. Features an ice detector. 5. The ice detector according to claim 4, wherein the ultrasonic waves are guided horizontally polarized shear waves. 6. The ice detector according to claim 4, wherein the ultrasonic wave is in a Lamb wave mode with a horizontal predominant component. 7. Claims 4 to 6 in which the ultrasonic transducer 10, 30 is acoustically coupled to a surface 12 of the portion of the sheet 14 opposite the surface 16 on which an ice layer may form. The freezing detector according to any one of. 8. The ice detector according to claim 4, wherein the ultrasonic transducers 10, 30 are piezoelectric transducers. 9. The ice detector of claim 8, wherein each transducer 10, 30 includes five or more piezoelectric strips 40. 10. The ice detector according to claim 4, wherein the ultrasonic transducer 50 is an electromagnetic transducer. 11. The ice detector of claim 10, wherein each transducer 50 comprises five or more ferromagnetic strips 52 and one excitation coil 60.