Coherent light generators – Particular beam control device – Modulation
Reexamination Certificate
2001-05-18
2003-07-15
Ip, Paul (Department: 2828)
Coherent light generators
Particular beam control device
Modulation
Reexamination Certificate
active
06594290
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for detecting dynamic change in ultrasonic wave or the like propagating through a medium. Further, the present invention relates to an ultrasonic diagnostic apparatus having such a dynamic change detecting apparatus.
2. Description of a Related Art
In an ultrasonic diagnostic apparatus for a so-called ultrasonic echo observation or the like, it is the general practice to use piezoelectric materials typically represented by PZT (Pb (read) zirconate titanate) for an ultrasonic sensor portion (probe).
FIGS. 12A and 12B
schematically show the structure of a conventional probe.
FIG. 12A
is a whole perspective view of the probe, and
FIG. 12B
is an enlarged perspective view of array vibrator included in the probe.
As shown in
FIG. 12A
, the probe
301
has a thin box shape as a whole, and has a slender rectangular probing surface
302
. The probing surface
302
is brought into contact with a human body and an ultrasonic wave is transmitted so as to receive an ultrasonic echo reflected from the depths of the body. A cable
307
, which transmits a drive signal for transmitting an ultrasonic wave and a detection signal of the ultrasonic wave, is connected to the upper side of the probe
301
.
A comb-shaped array vibrator
303
serving as both a transmitter and a receiver of ultrasonic wave is housed in the probing surface
302
. As shown in
FIG. 12B
, the array vibrator
303
is provided a number of slits
306
(having a width of, for example, 0.1 mm) in a thin strip-shaped PZT sheet (having a thickness of, for example, 0.2 to 0.3 mm) so as to form a number of (for example, 256) comb-teeth-shaped individual vibrator
305
(having, for example, a width of 0.2 mm and a length of 20 mm).
An electrode is formed in each individual vibrator
305
, and a signal line is connected thereto. An acoustic lens layer or an acoustic matching layer made of resin material such as rubber is attached to the surface side (lower side in the drawing) of the array vibrator
303
, and a backing material is attached to the back side. The acoustic lens layer converges the transmitted ultrasonic waves effectively. The acoustic matching layer improves the transmission efficiency of ultrasonic waves. The backing material has a function of holding the vibrator and causes vibration of the vibrator to be finished earlier.
Such ultrasonic probe and ultrasonic diagnostic apparatus are described in detail in “Ultrasonic Observation Method and Diagnostic Method”, Toyo Publishing Co., or “Fundamental Ultrasonic Medicine”, Ishiyaku Publishing Co.
In the field of ultrasonic diagnostic, it is desired to collect three-dimensional data in order to obtain more detailed information about the interior of an object's body. In order to comply with such a demand, it is required to make ultrasonic detecting elements (ultrasonic sensors) into a two-dimensional array. In the aforementioned PZT, however, it is difficult to fine the devices down and integrate them in the present conditions for the following reasons. That is, processing technology of PZT materials (ceramics) is almost on a limit level, and further fining down leads to an extreme decrease in processing yield. Moreover, if the number of wires increases, electrical impedance of the element and crosstalk between the elements (individual vibrators) would increase. It is therefore considered difficult to realize a two-dimensional array probe using PZT at the present level of the art.
On the other hand, Japanese patent application publication JP-A-10-501893 discloses an ultrasonic detecting apparatus including an array of vertical cavity surface emission laser (VCSEL) excited electrically (pumping). A cavity length of each laser is modulated by the acoustic field propagated from an object. As a result, the laser beam obtained thereby is frequency modulated by the acoustic field. The modulated laser beam is converted into amplitude modulation signal by a detector head, and thereafter, detected by a CCD array. Then, information of the signal is transmitted electrically to the signal processing assembly and processed. It is stated that this ultrasonic apparatus can achieve high level detection of frequency bandwidth, high resolving power of space and simplification of electric wiring.
Further, a paper entitled “High Frequency Ultrasound Imaging Using an Active Photodetector” by James D. Hamilton et al. appears in IEEE TRANSACTIONS ON ULTRASCONICS, FERROELECTRICS, AND FREQUENCY CONTROL, VOL. 45, NO. 3, MAY 1998. This paper discloses an ultrasonic detecting apparatus including laser and optical modulator having a waveguide made of neodymium doped glass.
However, the detection system using change in a length of the laser resonator due to the ultrasonic wave have no practicality without compensation for environmental changes such as temperature change because such a detection system has high sensitivity for displacement. In the case of arraying the sensors, since variance will be inevitably generated in oscillation frequencies at respective laser element, it would be difficult to put the sensors to practical use as an array, unless a measuring method which is not affected by the variance in oscillation frequencies of laser elements is used.
SUMMARY OF THE INVENTION
The present invention has been accomplished in view of these problems. A first object of the present invention is to provide a dynamic change detecting method and apparatus for detecting dynamic change stably by canceling influence of environmental change or an individual difference between a plurality of laser elements. A second object of the present invention is to provide an ultrasonic diagnostic apparatus using such a dynamic change detecting apparatus and appropriate for collection of three-dimensional data.
In order to solve the aforementioned problems, a dynamic change detecting method according to the present invention comprises steps of: (a) emitting a laser beam while causing frequency modulation to the laser beam to be generated in accordance with change in a size of a laser resonator by propagating the dynamic change to a total reflection mirror included in the laser resonator to cause dynamic displacement to the total reflection mirror; (b) separating the laser beam into a plurality of split-beams and guiding the plurality of split-beams to a plurality of optical paths having mutually different optical path lengths, respectively; (c) causing frequency shift in at least one of the plurality of split-beams; (d) combining the plurality of split-beams with each other to obtain interference light, and detecting the interference light to obtain an intensity signal corresponding to intensity of the interference light; (e) demodulating the intensity signal to generate a demodulated signal; and (f) obtaining a signal corresponding to the dynamic change on the basis of the demodulated signal.
Moreover, a dynamic change detecting apparatus according to the present invention comprises a laser including a laser resonator having a total reflection mirror where a dynamic perturbation is generated by propagation of dynamic change, the laser emitting a laser beam while causing frequency modulation to the laser beam to be generated in accordance with change in a size of the laser resonator; first means for separating the laser beam emitted from the laser into a plurality of split-beams and guiding the plurality of split-beams to a plurality of optical paths having mutually different optical path lengths, respectively; second means for causing frequency shift in at least one of the plurality of split-beams; third means for combining the plurality of split-beams with each other to obtain interference light; a photodetector for detecting the interference light to obtain an intensity signal corresponding to intensity of the interference light; fourth means for demodulating the intensity signal to generate a demodulated signal; and fifth means for obtaining a signal corresponding to the dynamic change on the ba
Fuji Photo Film Co. , Ltd.
Ip Paul
Vy Hung T
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