EMAT TRANSMIT/RECEIVE SWITCH

• Main Authors: MACLAUCHLAN, DANIEL T, OVERBY, CHARLES B
• Format: Patent
• Language: English; French
• Published: 30.12.2003
• Edition: 7
• Subjects: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIRCHEMICAL OR PHYSICAL PROPERTIES; MEASURING; PHYSICS; TESTING

A transmitting and receiving switch assembly for an electromagnetic acoustic transducer (EMAT) and a method for selectively switching an EMAT between transmit mode and receive mode both use a particular circuit. This circuit contains an EMAT coil (20) coupled to a tuning capacitor (10), which allows the EMAT to be operated at a desired frequency when transmitting. A set of capacitors (40, 42) separates the EMAT coil (20) from a set of diode strings (70, 72) (preferably containing at least one fast switching diode), which ar e joined by a resistive connection (61, 62, 63, 64). A transformer (50), which is center tapped at its primary winding, is coupled to the other end of the diode strings (70, 72). Finally, a receiver input (95) is connected to the transformer (50). In operation, the frequency of the EMAT (20) is set by appropriately energizing and tuning the tuning capacitor (10). A voltage is then applied in the center tapped transformer (50) and in the resistive link (61, 62, 63, 64) between the diode strings (70,, 72). The current automatically switches the conductivity of the diodes and permits the EMAT (20) to switch modes as desired. Likewise, the method disclosed also utilize s this circuit, as described above, and involves several steps. First, the EMA T frequency must be selected and set, using the tuning capacitor (10). Then, a voltage is applied within the circuit to induce transmission by the EMAT (20 ). Next a sinusoidal toneburst is given within the circuit to switch the transmit/receive capabilities of the EMAT (20), and then observing the input received by the EMAT (20) - thereby permitting the alternate switching of th e EMAT (20) from receive to transmit mode in a matter of nanoseconds.