Xray

1. THE TRANSDUCER/PROBE OPERATION PRINCIPLES
Transducer
• Refers to a device which converts one type of energy into
another.
• Ultrasound/ Piezoelectric transducers convert electrical
energy into ultrasonic energy and vice versa.
• Elements, with their associated case and damping and
matching materials are called a transducer assembly,
probe, scanhead, or, simply, transducer.

2. THE TRANSDUCER/PROBE OPERATION PRINCIPLES
Transducer; construction and operation
• Main part of US transducer is the piezoelectric element. Eg.
ceramics like PZT (lead-zirconate-titanate), quartz, etc.
• Various formulations of lead zirconate titanate are used
commonly as materials in the production of modern
ultrasound transducer elements.
• US transducers operate on the principle of piezoelectricity;
conversion of electrical energy(voltage) into
mechanical(sound) energy and vice versa.
• This principle states that some materials, when deformed by
an applied pressure, produce a voltage.
• Based upon the pulse-echo principle occurring with
ultrasound piezoelectric crystals, ultrasound transducers
convert;
1. Electrical energy into sound = pulse
2. Sound energy into electricity = echo

3. THE TRANSDUCER/PROBE OPERATION PRINCIPLES
Transducer; construction and operation
• The voltage applied is often several hundred volts which
causes the crystal to momentarily change shape; thus
increasing and decreasing the pressure infront of the
transducer, hence producing ultrasound waves.
• The returning echoes are converted back into electrical
energy signals (inform of alternating voltage pulse) using
either the same transducer or another.
• Transducers typically are driven by one cycle of alternating
voltage for sonographic imaging. This single-cycle– driving
voltage produces a two- or three-cycle ultrasound pulse.
• The frequency of the sound produced is equal to the
frequency of the driving voltage, which must be reasonably
near the operating frequency (fo) of the transducer.

4. THE TRANSDUCER/PROBE OPERATION PRINCIPLES
Transducer; construction and operation
• Operating frequency is determined by the following:
1. The propagation speed of the element material (ct).
2. The thickness (th) of the transducer element.
• Typical diagnostic ultrasound elements are 0.2 to 1 mm
thick and have propagation speeds of 4 to 6 mm/μs.
• Because wavelength decreases while frequency
increases, thinner elements operate at higher
frequencies.

5. THE TRANSDUCER/PROBE OPERATION PRINCIPLES
Transducer modes of operation
Shock-excited mode:
• Excitation of transducer by a brief driving voltage impulse.
• Produces US pulses within the range of the element’s
resonant/nominal frequency.
• Resonance freq.: preferred specific frequency of
operation(natural frequency).
• Element thickness  resonant frequency
• Resonant frequency also depends on sound velocity within
the element, typically 4 to 6 mm/s.
• Thin materials have a higher frequency and thicker ones have
a low frequency.
• Typical values are 0.2 to 1 mm thick.

6. THE TRANSDUCER/PROBE OPERATION PRINCIPLES
Transducer modes of operation
Burst- excited mode:
• Excitation of transducer by a cycle of alternating driving
voltage.
• Burst: a cycle or two of voltage variation.
• Produces US pulses of one or two or three selected
frequencies(multi-hertz) within range of resonant
frequency.

7. THE TRANSDUCER/PROBE OPERATION PRINCIPLES
Transducer modes of operation
Continuous mode (cw):
• Transducer excitation by repeating cycles of alternating
driving voltage.
• Produces a non pulsed wave with cycles that repeat
indefinitely at the transducer’s resonant frequency.

8. THE TRANSDUCER/PROBE OPERATION PRINCIPLES
Damping material
• Damping (also called backing) material, a mixture of
metal powder and a plastic or epoxy resin, is attached to
the rear face of the transducer elements to reduce the
number of cycles in each pulse.
• Damping reduces pulse duration and spatial pulse length
and improves resolution.
• Transducers intended for continuous wave Doppler
ultrasound use are not damped because pulses are not
used in this application.
• These transducers have higher effeciencies because
energy is not lost to damping material.