Transducers Flashcards
Direct Piezoelectric Effect
When acoustic PRESSURE is applied to some materials, they will deform and create ELECTRICAL energy.
DIRECT RECEPTION!
Matching Layer ideal thickness:
1/4 wavelength
Purpose of Damping Material:
Improves AXIAL, SPACIAL, DETAIL resolution.
The main frequency is the:
Center or Operating Frequency.
Broad bandwidth:
Pulse with MANY frequencies present.
Narrow bandwidth:
Pulse with FEW frequencies present.
The SHORTER the PULSE, the ______ frequencies that are present, the ______ the bandwidth.
MORE, WIDER
Quality Factor
Number that indicates the extent that transducer can operate at the center or main frequency.
UNITLESS NUMBER!
Pulsed transducers = _____ Q Factor
LOW
Continuous wave transducers = ______ Q Factor
HIGH
Quality Factor Equation:
Q FACTOR = OPERATING (MAIN) FREQUENCY/
BANDWIDTH
(EST of Q Factor - # of cycles in pulse)
Can operate at more than one center frequency:
Multihertz Transducer.
The _____ _______ can be chosen w/Multihertz Transducers w/broad bandwidth.
Operating frequency
Multihertz Transducers Pro:
Able to switch frequency w/o changing transducers. (User adjustable)
The TWO factors that determine Operating Frequency:
- Propagation speed in piezoelectric material.
2. Thickness of crystal.
Operating Frequency Equation:
Fo = SPEED/ (2x THICKNESS)
Operating Frequency =
Propagation speed in Piezoelectric Material/
2x Thickness of the Piezoelectric Material
RELATIONSHIP:
Propagation speed and Operating Frequency.
DIRECTLY RELATED.
RELATIONSHIP:
Thickness of material and Operating Frequency.
INVERSELY RELATED.
Typical thickness of piezoelectric material:
1/2 wavelength of sound in material.
.2 - 1 mm
A shorter dampened pulse has a LOWER/HIGHER Q-factor.
LOWER.
Q-factor is:
INVERSELY related to: _______ &
DIRECTLY related to _______.
BANDWIDTH.
PULSE LENGTH.
Transducer w/3 MHz main freq. produces a sound pulse w/freq. ranging from 1 MHz - 5 MHz. The BANDWIDTH (RANGE OF FREQ) in this pulse is:
4 MHz
5 MHz - 1 MHz = 4 MHz
Short duration events are usually _______ bandwidth (broadband).
WIDE.
The ______ the Q-factor, the _______ the images (OR ______ ______).
LOWER.
BETTER
AXIAL RES.
Electrical frequency =
Acoustic frequency.
Speed of sound in PZT and the frequency of sound are _______ related.
DIRECTLY.
Thinner active elements create pulses:
w/HIGHER frequency and SHORTER wavelength cycles. (and vise versa)
PZT thickness and frequency are:
INVERSELY related.
NZL is also called:
FOCAL DEPTH.
