Page 416 - Sensors and Control Systems in Manufacturing

370
Cha p te r
Se v e n

Fiber to the
LDV instrument

Micromanipulator
Nylon clad
Inlet

Heparin

Optical fiber
Needle

Holder

Θ
Artery
Blood

FIGURE 7.44 Special probe for measurement of blood velocity.

Interestingly, the LDV system proved useful in the measurement
of arterial blood velocity (Fig. 7.44), thereby providing valuable med-
ical information. Another application in medical research is the study
of motion of the tympanic membrane in the ear.

7.27 Ultrasonic/Laser Nondestructive
Evaluation Sensor
Ultrasonic/laser optical inspection is a relatively new noncontact tech-
nique. A laser system for generating ultrasound pulses without distor-
tion of the object surface is shown in Fig. 7.45. A laser pulse incident on
a surface will be partly absorbed by the material and will thus generate
a sudden rise in temperature in the surface layer of the material. This
thermal shock causes expansion of a small volume at the surface, which
generates thermoelastic strains. Bulk optical systems have been used
previously to generate the laser pulse energy. However, the omnidirec-
tionality of bulk sources is completely different from other well-known
sources, and is regarded as a serious handicap to laser generation.
To control the beamwidth and beam direction of the optically
generated ultrasonic waves, a fiber phased array has been developed.