Ultrasonic Tomography (UT)

Ultrasonic sensors have been successfully applied in flow measurement, non-destructive testing and it is widely used in medical imaging (Hoyle and Xu, 1995). The method involves in using ultrasonic is through transmitting and receiving sensors that are axially spaced along the flow stream. The sensors do not obstruct the flow. It is sensitive to the density of sound changes and has the potential for imaging component flows such as oil/gas/water mixtures, which frequently occur in the oil industry (Ruzairi et al., 2004). Ultrasonic sensors’ systems are based upon interactions between the incident ultrasonic waves and the object to be imaged. For example, the incident waves may be reflected from boundaries; the reflections may be sensed and their data combined to indicate the location of the boundary (Volodymyr Koshovyy et al., 2004).

There are two types of ultrasonic signals that are usually used. They are the continuous signal and the pulsed signal (Hoyle, 1996). The pulsed system will be used to avoid the standing wave patterns that can exist within the pipes. Using the ultrasonic method in air is very inefficient due to the mismatch of the sensors’ impedance as compared with air’s acoustic impedance (Abdul Rahimet al., 2004). New types of sensor are continually being developed but the effective ones are expensive. The design of this sensor is critical when it need to reduce sensor’s ringing (Kevin et al., 2002). Both the transmitter and the receiver electronics are relatively sophisticated compared to the electrical charge sensor.

In ultrasonic tomography, the required equipments includes ultrasonic generator, transducers to transmit and receive ultrasonic waves and computerized image processing system (Ng et al., 2004). The cost of this type of tomography system is relatively higher compared with some other tomography methods due to the fact that the ultrasonic transmitters and receivers are expensive. Besides that, ultrasound transmitters are often driven by voltage of hundreds of volts which makes an intrinsically safe system hard to develop (Leong, 2005).