| 摘要 |
A resonator for use in a marker in a magnetomechanical electronic article surveillance system is composed of an amorphous magnetostrictive alloy containing iron, cobalt, nickel, silicon and boron in quantities for giving the resonator a quality Q which is between about 100 and 600. The amorphous magnetostrictive alloy is annealed in a transverse magnetic field for giving it a B-H loop which is linear up to about 8 Oe and an anisotropy field strength of at least 10 Oe. The resonator is incorporated in a marker in combination with a bias element which produces a bias field, and when the resonator is excited to resonate by a signal emitted by the transmitter in the surveillance system, it produces a signal at a mechanical resonant frequency which can be detected by the receiver of the detection system. The receiver is operated so as to look for the signal from the resonator at the resonant frequency in a first detection window which begins at approximately 0.4 ms after excitation of the resonator, and in a second detection window which begins at approximately 6 ms after excitation of the resonator. Due to the resonator having a quality Q in the above range, the signal produced by the resonator in the first window has a high amplitude in the first detection window which is no more than 15 dB below its amplitude immediately after excitation, but drops to a level in the second detection window which is at least approximately 15 dB below its level in the first detection window. The signal from the resonator can thus be reliaby detected as well as distinguished from spurious signals.
|
