HU190757B - With piezoelectric ceramic operating transducer of the ultrasonic sound - Google Patents

Abstract

The present invention relates to a piezoelectric ceramic ultrasonic transducer having a unimorphic type of piezoceramic transducer (1) covered with armor (3) and a thicker metal plate (2). The essence is that the thickness of the metal plate (2) is at least five times that of the ceramic plate (1). 190757 -1-

Description

BACKGROUND OF THE INVENTION The present invention relates to an unimorphic ultrasonic transducer with piezoelectric ceramic for use as a transmitter and receiver in air and equipped with a piezoceramic transducer of unimorphic type with an armored ceramic plate and a thicker metal plate.

Unlike ultrasonic transducers operating in solid and liquid media, airborne transducers perform bending vibrations. These provide a better fit for air with a much lower acoustic impedance than solid and liquid materials.

In known solutions of air-operated ultrasound transducers, two plates of similar thickness are bonded together. If both are made of piezoceramics, then a bimorph element, while one is made of piezo-ceramic and the other is metallic, is called an unimorphic active element of the ultrasound transducer. Unimorphic battery converters can be found in Nos. 3,849,679 and 3,638,052. U.S. Patents; and Arch. of Acoust. 1982/7, An improved piezoelectric ceramic transducer (by V.N. Bindal and Chandra). The essence of its operation is that when it is applied to the ceramic, it tends to resize, but the other adhesive plate i interferes with this, shear forces awaken, so the plate bends. Applying alternating voltage at the same frequency as the mechanical resonance frequency of the bonded sheet pair to the piezoceramic produces vibrations of much greater amplitude, thereby producing a much higher sound pressure in the air than, for example, only thickness vibrations.

A known disadvantage of known unimorphic elemental ultrasonic transducers is that the resonance frequency may vary greatly depending on the size, and the efficiency of the converter is not always adequate.

The object of the invention is to eliminate the above disadvantages.

It has now been discovered that the means of achieving the desired goal is to select the appropriate proportions of the unimorph element. The literature, Thus the above article, or N.T. Adelman and Y. Stavsky, Flexural-exteneural behavior of composite piezoelectric circular plates, J. Acoust. An article by Soc. Am., Published in March 1980, page 819, shows that the ratio of the thickness of the ceramic to the metal is usually in the range of 0.35 to 0.5, i.e. the thickness of the metal plate is up to three times that of the ceramic plate. It has been found that the most preferred way of designing the ultrasonic transducer is a unimorphic element in which the thickness of the ceramic is small compared to the thickness of the metal plate.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a highly efficient, unimorphic ultrasonic transducer, characterized by a more manageable resonance frequency, utilizing recognition.

To accomplish this object, we have provided an piezoelectric ceramic ultrasonic transducer provided with an unimorphic type piezoceramic transducer comprising an armored ceramic plate and a metal plate thicker and, according to the invention, at least five times the thickness of the metal plate.

An oscillator with high precision at the resonant frequency of the transmitter can be constructed by dividing the armament on one side of the ceramic plate into two separated parts, which are connected to a feedback circuit.

In the ultrasonic transducer according to the invention, the use of a thin ceramic plate has three advantages.

During manufacture, the resonant frequency of the converter can be adjusted with great precision and compared to known solutions. In this case, the standard deviation of the metal plate is the standard deviation of the values, which is a parameter that can be maintained with high accuracy during production. For example, in the case of a disc, the resonance frequency is directly proportional to the thickness of the disc and vice versa to the square of its diameter.

The mechanical strength coefficient of the metal sheet is higher than that of a ceramic, and converters of greater goodness, lower bandwidth, and higher efficiency can be made if the converter is largely made of metal.

Finally, the use of a thin ceramic plate offers two advantages. Since the size change of the ceramic is proportional to the applied electric field strength, the small voltages used in the conventional transistor and integrated circuits for drive and sensor electronics can achieve relatively large dimensional changes due to the increased field strength. The higher capacity due to the low ceramic thickness results in a transmitter / receiver with a lower impedance; so, for example, the receiver will be less susceptible to interference.

The voltage sensitivity of the receiver (the voltage produced at a given sound pressure is directly proportional to the thickness of the ceramic) will be lower, but this voltage may be more heavily loaded due to the lower impedance of the receiver: thus the receiver sensitivity is not reduced.

The present invention will now be described in more detail with reference to the accompanying drawing, with reference to the accompanying drawings.

In the drawing it is Figure 1 the converter according to the invention is formed with a cover plate outline of version Figure 2 sketch of a resonant cone version of the transducer according to the invention, a

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Figure 3 is a schematic view of a piezoelectric ceramic plate, while Figure

Fig. 4 is an insertion of the ceramic plate of Fig. 3 into a feedback circuit.

The ultrasonic transducer according to the invention has a structure similar to those known in the art. Inside the housing 7, which is preferably formed of cavities, is fixed a ceramic plate 1 of piezoelectric material, to which flexible terminals 5 are connected. They are connected by 4 connectors. The ceramic plate 1 has a metal plate 2 which according to the invention is at least five times the thickness of the ceramic plate 1 below it.

Above the metal plate 2 there is a cover plate 6 (Fig. 1) or a resonant cone 8 (Fig. 2) similar to the known solutions. Above them are 9 screens for protection against environmental influences, which are secured by 10 rings.

The ceramic plate 1 has a male armor 3 (Figs. 1 and 2), which is preferably divided into two non-contacting portions (Fig. 3), thus having a coupling part 3a. The armor 3 may be undivided on both sides of the ceramic plate 1, but as shown in FIG.

As shown in Figure 3, one side is divided into two parts. The feedback produces an oscillator which always operates at the resonance frequency of the transmitter.

During the operation of the transducer according to the invention, it is fixed to the housing 7 at the first resonance frequency of the unimorph element and the efficiency of the transducer (Fig. 2) is improved by the cover plate 6 and (Fig. 3) by the cone 8.

The thickness-polarized piezoceramic discs 3 on both sides are polished with a conductive adhesive on the metal plate 2.

The piezoceramic arms 3 are joined by flexible terminals 5. When ac voltage is applied to the flexible terminals 5, the unimorph element performs bending vibrations. The amplitude of the vibration shows sharp maxima if the frequency of the excitation voltage is equal to one of its own mechanical resonance frequencies. When used as an ultrasonic transducer, an inverse process takes place: in the air, ultrasound causes the flexible terminals 5 to have alternating voltages of the same frequency as the ultrasonic frequency, which shows sharp maxima on the resonance frequency of the unimorph.

Claims (2)

PATENT CLAIMS 25 1 · Piezoelectric ceramic ultrasonic transducer equipped with a piezoceramic transducer of unimorphic type with an armored ceramic plate and a thicker metal plate, characterized in that the metal plate (2) is at least five times the thickness of the ceramic plate (1). An ultrasonic transducer according to claim 1, characterized in that on one side of the ceramic plate (1) the armature (3) is divided into two separate parts, which are connected to a feedback circuit.