METHOD AND APPARATUS FOR DETECTING MULTIPLEX DOCUMENT USING PHASE SHIFT AND AMPLITUDE OF ULTRASONIC WAVE

摘要

PROBLEM TO BE SOLVED: To provide improved method and apparatus for detecting multiplex documents accurately and at a relatively lower cost. SOLUTION: In one embodiment, an apparatus for detecting multiplex documents has an ultrasonic transmitter (14) for transmitting an ultrasonic signal (16). An ultrasonic wave receiver (20) receives the ultrasonic wave signal (17) after it (17) passes through at least one multiplex document part (18). A phase comparator (24) compares the transmitted ultrasonic signal (16) with the received ultrasonic signal (17) and a amplitude measuring circuit (26) compares the received ultrasonic signal (17) with a reference. A microprocessor (23) compares an information signal (28) from the phase comparator and an information signal (30) from the amplitude measuring circuit (26) with a specified threshold to determine that any multiplex document exists.