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The Characteristics of Sequenced Array Transducers

A transducer is any device that converts one form of energy into another. Sequenced array transducers refer to an array of transducers that convert sequences of sound waves into light and dark signals that can be used to build pictures. These arrays are used with ultrasound devices.

  1. History

    • Ultrasound technology is thought to have been developed during WW II. This cannot be known for sure because WW II technology is still classified. Originally, sonar technology mimicked radar technology---transmitting out a single signal and seeing what bounced back. Sound, however, is different from microwave signals and a single broadcast does not work well for sound. For sonar (and later ultrasound), it is best to send out a sequence of focused signals and then use the echoes that come back to construct a picture. This requires an array of transducers that work with a sequence of focused sound beams---a sequenced array of transducers.

    Structure

    • The sequenced array of transducers consists of approximately 500 transducers equally spread over an area of about 100 mm. In most systems, a few of these transducers respond at a time, and then another few transducers are chosen. This continues until all of the transducers are used to scan an area. The transducers can be focused to different depths by varying the time delay before a particular transducer contributes its signal to the picture. If a few transducers in a row have short delays on the end transducer and increasing longer delays until the middle transducer, these few transducers act like a lens that can be focused to a certain depth by varying the time delays. The sequences are repeated so quickly that the array can produce a movie---like the way a motion picture camera can make a movie out of a sequence of still pictures.

    Applications

    • Ultrasound is any sound outside the range of human hearing (20 to 20,000 hertz). Industrial ultrasound machines usually operate in the 50,000 to 100,000 hertz range, depending on the material being examined. Industrial ultrasound looks for cracks or other defects in glass, plastic, concrete and metals. Biological ultrasound is usually around 1,000,000 hertz. Medical ultrasound has the sequenced array of transducers in the handheld unit that the physician applies to the patient. Medical ultrasound lets a doctor look at movies of the body at selected depths. Ultrasound is less destructive than X-rays, so watching an ultrasound movie for hours is less destructive than a single X-ray photograph. Ultrasound is used to look at blood flow in veins and arteries, to watch the heart operate and---the most common use of all---to give new parents the first glimpse of their child.

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