1. Field of the Invention
The present invention relates to a method of and system for threatening noxious animals and insects such as rats or mice, pigeons, cockroaches and the like (hereinafter referred generally to as "pests") and more particularly to those which use a mechanical oscillation of acoustic signal or the like to get rid the pests from a sonifying area and to prevent same from entering thereto.
2. Prior Arts
The pests, more particularly the rats not only stealingly eat a human food reserved in a storehouse or the like but also are often a carrier of infectious desease. Therefore, various measures for getting rid of those have been taken.
The most common technique is set out a poison but this has obvious drawbacks.
In recent years, it has been found that the pests are quite averse to an acoustic signal of a certain frequency range, so that in case of the rats, an emission of such acoustic signal to an inhibiting area thereof such as a storehouse, ceiling or the like and an entrance or passage thereto is effective for getting rid same therefrom and preventing same from entering thereto. Therefore, various system for utilizing the finding have been developed and actually employed. Such a system emits the acoustic signal of a specific frequency in an ultrasonic range of 18 to 40 KHz, since some pests are sensitive only to frequencies at the low end while other pests are sensitive to frequencies at the high end but said range covers the frequencies, in which almost all of pests will be affected.
Such a conventional system is certainly effective in an early period after its installation but the pests eventually and gradually adapt themselves the sonified circumstance, so that a threatening effect of the system shall be lost in an early stage. Of course, the effect can be sustained in some extent by increasing an output level or intensity of the ultrasonic energy but this technique may give an injury to pet and domestic animals as well as human body.
An emission of ultrasonic signal, a frequency of which varies regularly with time has also been tried but the pests eventually obtain an immunity against such signal, when they are exposed to the ultrasonic energy for a prolonged period.
As measures to give no immunity to the pests while avoiding the increase of output intensity, various methods have been proposed. For instance, Jap. Examined Pat. Appln. Gazette No. 38 588/1975 teaches a use of AM ultrasonic pulse wave of 25 KHz which is emitted under an output range of 380 to 600 mw synchronizedly with a flashing light pulse wave. Jap. Unexamined Pat. Appln. Gazette No. 86 376/1978 (corresponding to U.S. Ser. Nos. 738,807 and 840,061) discloses an alternative emission of two kinds of ultrasonic pulse signals, wherein a frequency randomly varies in the range of about 18 to 25 KHz and about 23 to 30 KHz, respectively. Further, Jap. Unexamined Pat. Appln. Gazette No. 5 128/1982 proposes to emit an ultrasonic signal containing a plurality of frequency components, which signal is prepared by making modulation of a pulse width on a carrier wave (100 to 250 KHz) with various frequencies, to which the pests are sensitive, namely about 25 KHz (aversing frequency for rats), about 24 to 25 KHz (communication frequency between female and male rats) and about 37 to 43 KHz (usual communication frequency range for rats), so as to make unable normal communication of the exposed pest and accelerate its madness.
Turning now to that I, the inventor had found that a sustaining threatening effect similar to that in said methods can be obtained by emitting intermittently an ultrasonic signal which is irregular in emitting time period and interval of the signals and randomly varies in frequency thereof and then filed a patent application in Japan [Jap. Pat. Appln. No. 23 673/1982 (Jap. Unexamined Pat. Appln. Gazette No. 141 742/1983 issued Aug. 23, 1983)].
As a result of various studies and experiments having been made with use of a system which embodies the invention as disclosed in my said Japanese patent application (Jap. Pat. Appln. No. 23 673/1982), it has been found that there is a distinctive interrelation between a curve showing fluctuation in frequency and a pest threatening effect.