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TRANSDUCER Converts the one form of energy into another. Process of…

- - - - Do not require any power source for their operation
    - - Require an external power source for their operation
- - - - This ultrasonic subassembly is mounted in a case with appropriate electrical connections.
        All common contact, delay line, and immersion transducers utilize this basic design.
        Dual element transducers, commonly used in corrosion survey applications, differ in that they have separate transmitting and receiving elements separated by a sound barrier, no backing, and an integral delay line to steer and couple the sound energy, rather than a wearplate or lens.
  - - - Note the thickness of the PZT is generally 1/2 the wavelength of the ultrasound produced.
        In front of the PZT is a thin layer of material on the surface of the probe called the matching layer.
        Note that the thickness of the matching layer is generally 1/4 the wavelength of the ultrasound produced.
        
        The purpose of the matching layer is to try to maximize transmission of ultrasound from the PZT to the patient.
        Recall that when there is a large difference in impedance between two media, most sound wil be reflected and little will be transmitted at the interface.
         There is a large difference in impedance between the PZT and skin.
        
        The matching layer and ultrasound gel have an impedance in between that of the PZT and the skin to reduce the amount of reflection at this interface and improve transmission into the patient.
        On many diagnostic ultrsound transducers, the PZT is mounted on a backing material (also sometimes called a damping material).
         The backing material has several effects on the properties of the transducer.
        The backing material has the effect of decreasing ringing of the PZT crystal.
        
        It therefore shortens the spatial pulse length and so improves axial resolution (this is why the backing material is used).
         The backing material also has the effect of widening the bandwidth and therefore decreasing the quality factor.
        Thus, diagnostic transducers are wide bandwidth, low quality factor transducers.
        
        By way of contrast, therapeutic ultrasound transducers typically do not have a backing material as they require a narrow bandwidth of frequencies around the central frequency.
         Similarly, dedicated continuous wave transducers such as the Pedoff probe have no need to improve axial resolution and therefore do not have acking materials.
- - - - Detect any changes in physical quantity (Temperature, Speed, Flow,etc.)
        Detected by a Sensor and reflected as changes in output quantity.
    - - Non-electrical output quantity of the Sensor
         Used to convert the physical output (or non-electrical output) of the sensor to an electrical quantity
        Example: Analog to Digital Converters, Amplifiers