Communications – electrical: acoustic wave systems and devices – Signal transducers – Underwater type
Reexamination Certificate
2000-04-21
2001-11-13
Pihulic, Daniel T. (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Signal transducers
Underwater type
Reexamination Certificate
active
06317389
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for radiating an ultrasound-signal into a liquid by means of using an assembly composed of a piezoelectric substrate, a first input-, a second input-, and an output interdigital transducers.
2. Description of the Prior Art
In constructing an acoustical system, a transducer for emitting and detecting an acoustic wave has a key role. A thickness mode piezoelectric transducer is usually used, whose operation frequency is dependent on the thickness of the piezoelectric substrate. Such a conventional type of transducer has a difficulty in high-frequency operation. A surface acoustic wave (SAW) propagates in the form of a leaky wave, when the piezoelectric substrate, sufficiently thicker compared with the wavelength, is in contact with a liquid. In this time, the leaky wave is mode-converted to a longitudinal wave into the liquid. This means that an interdigital transducer (IDT) on the piezoelectric substrate operates at a liquid-solid boundary as a leaky wave transducer for bulk wave radiation into the liquid. The leaky SAW traveling on a sufficiently thick substrate compared with the wavelength has only one mode without velocity dispersion. Thus, conventional transducers such as the thickness mode piezoelectric transducer and the IDT for the leaky SAW have the problem of the limited ultrasound-radiation angle.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an ultrasound-signal radiating device capable of a multi-modes operation with a quick response and a high efficiency at a high frequency.
Another object of the present invention is to provide an ultrasound-signal radiating device capable of adjusting ultrasound power.
Another object of the present invention is to provide an ultrasound-signal radiating device capable of adjusting radiation angle.
Another object of the present invention is to provide an ultrasound-signal radiating device capable of a low electric power consumption.
Another object of the present invention is to provide an ultrasound-signal radiating device excellent in durability and manufacturing.
Another object of the present invention is to provide an ultrasound-signal radiating device which is not affected by a change in circumstances, for example, a change in temperature.
A still other object of the present invention is to provide an ultrasound-signal radiating device easy in use and having a small size which is very light in weight and has a simple structure.
According to one aspect of the present invention there is provided an ultrasound-signal radiating device comprising a piezoelectric substrate, a first input interdigital transducer, a second input interdigital transducer, an output interdigital transducer, a cap, an amplifier, and a modulator with an input terminal. All the interdigital transducers are formed on one end surface of the piezoelectric substrate. The cap is mounted on a surface part of the other end surface of the piezoelectric substrate. The surface part corresponds to a surface part, including the first input- and the output interdigital transducers, of the one end surface of the piezoelectric substrate.
If an input electric signal is applied to the first input interdigital transducer, a non-leaky elastic wave is excited in the piezoelectric substrate, The non-leaky elastic wave is transmitted to the output interdigital transducer, and detected at the output interdigital transducer as a delayed electric signal, which is amplified via the amplifier. A signal part of an amplified electric signal is fed back, as the input electric signal, to the first input interdigital transducer, again. A remaining signal part of the amplified electric signal is transmitted to the modulator as a carrier signal. If an input message-signal is applied to the modulator through the input terminal, an amplitude of the carrier signal is modulated according to the input message-signal. And then, an amplitude modulated (AM) signal is generated. When the AM signal is applied to the second input interdigital transducer, a leaky elastic wave is excited in the piezoelectric substrate, and radiated in the form of a longitudinal wave into a liquid kept in contact with a remaining surface part of the other end surface of the piezoelectric substrate.
According to another aspect of the present invention there is provided a voltage controller controlling a voltage of the carrier signal. Thus, the longitudinal wave is radiated, by an intensity corresponding to the voltage of the carrier signal, into the liquid kept in contact with the remaining surface part of the other end surface of the piezoelectric substrate. Accordingly, it is possible to adjust an ultrasound power into the liquid.
According to another aspect of the present invention there is provided a filter for adjusting a frequency of the input electric signal. A radiation angle &thgr; into the liquid depends on an operation frequency. Therefore, it is possible to adjust the radiation angle &thgr; into the liquid.
According to another aspect of the present invention there is provided a polymer film, with which at least the remaining surface part of the other end surface of the piezoelectric substrate is coated. Thus, the longitudinal wave is effectively radiated into a liquid in contact with an outside surface of the polymer film.
According to another aspect of the present invention there are provided another output interdigital transducer formed on the one end surface of the piezoelectric substrate and corresponding to the second input interdigital transducer, and a modulator with an output terminal. If a material exists in a liquid, the longitudinal wave radiated into the liquid is reflected at the material, and detected at the output interdigital transducer, corresponding to the second input interdigital transducer, as a delayed output signal, of which an amplitude is demodulated via the demodulator. And then, an output message-signal is delivered from the output terminal.
According to another aspect of the present invention there are provided another piezoelectric substrate, another output interdigital transducer formed on one end surface thereof and corresponding to the second input interdigital transducer, and a demodulator with an output terminal. If a material exists in a liquid, the longitudinal wave radiated into the liquid is reflected at the material, and detected at the output interdigital transducer, corresponding to the second input interdigital transducer, as a delayed output signal, of which an amplitude is demodulated via the demodulator. And then, an output message-signal is delivered from the output terminal.
According to another aspect of the present invention there is provided a piezoelectric substrate made of a piezoelectric ceramic thin plate, the polarization axis thereof being parallel to the thickness direction thereof. Thus, the elastic wave is effectively excited in the piezoelectric substrate.
According to other aspect of the present invention there is provided a piezoelectric substrate made of a piezoelectric polymer thin plate. Thus, the elastic wave is effectively excited in the piezoelectric substrate.
According to a further aspect of the present invention there is provided an ultrasound-signal radiating device, wherein the electrode-finger direction of the first input interdigital transducer is orthogonal to that of the second input interdigital transducer.
REFERENCES:
patent: 4399387 (1983-08-01), Kohji
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