KR20040064261A - Cylindrical ultrasound receivers and transceivers formed from piezoelectric film - Google Patents

Abstract

The ultrasonic receiver 20 is initially formed from a flexible piezoelectric film, and has a hollow cylinder 22 having a height of an outer circumferential surface 24, an inner circumferential surface 26, a central axis 28 and a length parallel to the central axis 28. It includes. The sensing electrode is formed from the conductive material applied to the inner circumferential surface 26 while the ground electrode 32 is formed from the conductive material applied to the outer circumferential surface 24. The hollow cylinder 22 is supported by a support structure formed to transmit vibration waves in the circumferential direction around the core portion of the hollow cylinder 22. The sensing electrode is formed like a strip extending in the diffusion direction substantially parallel to the central axis 28 along the central portion of the height, the strip being in an angular range not greater than 90 ° in the central axis 28.

Description

CYLINDRICAL ULTRASOUND RECEIVERS AND TRANSCEIVERS FORMED FROM PIEZOELECTRIC FILM

Circular ultrasonic transducers are being used to transmit ultrasonic signals in digitizer systems. The circular shape simplifies the calculation of the geometry of the emission time by providing signal transmission in all directions and by providing the same effect at one point (exactly, the line). This advantage is disclosed in US Patent No. 4,758,691, invented by De Bruyne. Another advantage of circular ultrasonic transducers is that they can focus the signal around the device at the location you want to measure. This is implemented in the figure of the digitizer system disclosed in PCT Publication No. WO98 / 40838.

Structurally, some other shape of the circular transducer has been proposed. The patent invented by De Bruyne proposes a "cell transducer" which is a capacitive device formed from a complex arrangement of circular layers provided to produce a circular air gap of about 20 μm. Such a structure is expensive to manufacture and is not reliable.

The second shape of the transducer, which has been proposed in the medical field, uses piezoelectric elements. One example of a medical transducer of this shape is disclosed in US Pat. No. 4,706,681, invented by Breyer, who published an ultrasound marker. Here, the circular piezoelectric collar is sandwiched between two electrodes. An alternating potential crossing the electrodes causes the collar to vibrate, thus radiating an ultrasonic signal radially.

In principle, any ultrasonic transducer can operate as both a transmitter and a receiver, but is in fact unsuitable as a receiver in many transmitter structures. This is the fact that while only one small position of the cylinder is correctly oriented to receive the complex signal from a given direction, the nearly complete circular cylinder operates at a relatively high voltage, causing wide angle transmission. In addition, the inherent capacitance of the large inactive area of the transducer, which can eliminate the amplitude of the received signal at a large rate, makes the transducer unresponsive as a receiver.

In general, much effort has been made in developing transducers using piezoelectric films such as PVDF. The conductive electrode is generally formed opposite the film by selectively printing the conductive ink in the surface area. Such films are inexpensive to manufacture and well tolerate a wide range of operating conditions, including moisture exposure.

Although the circular ultrasonic transducer is implemented relatively simply using piezoelectric film, the implementation of the receiver is difficult with additional problems other than the general problems of the circular receiver mentioned above. In particular, referring to FIGS. 1 and 2, a schematic of a floating cylinder 10 formed from a piezoelectric film is shown. 1 shows the relaxed state, and FIG. 2 shows the reaction of cylinder 10 when an ultrasonic signal 12 is received at the front. The piezoelectric film is flexible and generates a wavelength (abnormally extended) while the oscillation of signal 12 travels around cylinder 10. The direction and degree of flexibility of the piezoelectric film changes along the waveform generated around the cylinder and ends with the reversal of the sensing potential generated between the electrodes. As a result, a large amount of potential generated by the piezoelectric film is radiated with local eddy currents in the electrodes, and the total signal voltage measured between the electrodes is greatly reduced.

Another problem with the implementation of circular ultrasonic transducers using piezoelectric films is the tendency of the electrodes to act as antennas to capture unwanted electromagnetic radiation resulting from very low signals for noise ratios.

Therefore, there is a need for a circular ultrasonic receiver structure using a piezoelectric film.

FIELD OF THE INVENTION The present invention relates to ultrasonic transducers, in particular to circular ultrasonic receivers and transceivers formed from piezoelectric films, and to their application in digitizer systems.

1 is a schematic view of a floating cylinder freely formed from a piezoelectric film in a relaxed state;

2 is a schematic diagram when the cylinder of FIG. 1 is exposed to an ultrasonic signal;

3 is a configuration and operation diagram of a circular ultrasonic transceiver according to an embodiment of the present invention;

4A and 4B are shape views of electrode patterns applied to each of the inner and outer circumferential surfaces of the piezoelectric film applied to the circular ultrasonic transceiver of FIG. 1;

4C is a schematic diagram illustrating the film of FIGS. 4A and 4B in a circular shape;

5 illustrates a metal core device in the circular ultrasonic transceiver of FIG.

6 is a view showing a conductive foam core element that can be used in place of the core element of FIG.

7A and 7B are schematic diagrams showing one embodiment for forming electrical contact with the circular ultrasonic transceiver of FIG. 1 using a conductive adhesive;

8 is a schematic diagram illustrating a second embodiment for forming electrical contact with the circular ultrasonic transceiver of FIG. 1 using a spring connection;

9 is a schematic diagram illustrating a third embodiment for forming electrical contact with the circular ultrasonic transceiver of FIG. 1 using pins;

10A is a schematic diagram showing an alternative shape of a connection tab of a piezoelectric film used in the circular ultrasonic transceiver of FIG. 1;

10B is a schematic view showing the film of FIG. 10A wound into a circular shape;

11 is a block diagram illustrating the main components of a transceiver assembly including the circular ultrasonic transceiver of FIG. 1;

12A is a schematic operational explanatory diagram of a system for determining the position of a mobile device operating in a first mode of operation in accordance with an embodiment of the present invention;

12B is a schematic operational explanatory diagram of the system of FIG. 12A while performing a self calibration operation;

13A is a schematic operational explanatory diagram of an alternative system for determining the position of a moving component operating in a first mode of operation in accordance with an embodiment of the present invention;

13B is a schematic operational explanatory diagram of the FIG. 13A system while performing a self calibration operation;

14 is a schematic diagram of a protective grating for use with an ultrasonic transducer in accordance with an embodiment of the present invention;

The present invention is a circular ultrasonic receiver structure using a piezoelectric film.

Ultrasonic receiver according to the embodiment of the present invention, (a) a hollow cylinder initially formed from a flexible piezoelectric film, having a height of the outer peripheral surface, the inner peripheral surface, the central axis and the length parallel to the central axis; (b) a sensing electrode formed from a conductive material applied to the inner circumferential surface; (c) a ground electrode formed from a conductive material applied to the outer circumferential surface; And (d) a support structure configured to support the hollow cylinder in such a manner as to transmit a vibration wave in the circumferential direction around the core portion of the hollow cylinder, in order to support the hollow cylinder, wherein the sensing electrode is of the height. It is shaped like a strip extending along the core part in a diffusion direction substantially parallel to the central axis, characterized in that the strip is in an angular range not greater than 90 ° from the central axis.

In the present invention, the strip is characterized in that the angle range not greater than 30 ° from the central axis.

In addition, in the present invention, the ground electrode is characterized in that it extends above the core portion of the outer peripheral surface.

In the present invention, at least one additional electrode formed from a conductive material applied to the inner circumferential surface in a discontinuous pattern with the sensing electrode is further configured.

In the present invention, the at least one additional electrode is characterized in that it extends over the core portion of the inner peripheral surface.

In the present invention, the at least one additional electrode is grounded.

In addition, the ultrasonic receiver of the present invention comprises: (a) a receiver circuit electrically connected to the sensing electrode; (b) transmitter circuitry; And (c) a switching module associated with an operating electrode selected from the ground electrode and the additional electrode, the switching system being configured to alternately electrically connect the operating electrode to the transmitter circuit and ground. It is characterized in that the serving is configured to be used as an ultrasonic transmitter.

Further, in the present invention, the support structure includes a conductive core element deployed in the hollow cylinder in a manner to avoid electrical contact with the sensing electrode, the conductive core element is electrically grounded, and the conductive core element is a metal core element. And the conductive core element is formed from a conductive foam.

In addition, the flexible piezoelectric film in the present invention is characterized in that it is implemented as a PVDF film.

In addition, the sensing electrode and the ground electrode in the present invention is characterized in that substantially implemented as a transparent electrode.

In addition, a method of operating an ultrasonic transceiver for transmitting and receiving an ultrasonic signal according to an embodiment of the present invention is (a) (i) initially formed from a flexible piezoelectric film and parallel to an outer circumferential surface, an inner circumferential surface, a central axis, and the central axis. A hollow cylinder having a height of length and mounted circumferentially to transmit a vibration wave around the core portion, (ii) formed from a conductive material applied to the inner circumferential surface and substantially parallel to the central axis along the core portion of the height A sensing electrode formed like a narrow strip extending in the diffusion direction, a strip in an angular range not greater than 90 ° from the central axis, (i) formed from a conductive material applied as extending over the core portion of the inner circumferential surface in a discontinuous pattern with the sensing electrode From at least one additional inner electrode, (i) an electrically conductive material applied as extending over the core portion of the outer circumferential surface Generated the method comprising: providing an ultrasonic transceiver structure comprising at least one outer electrode; (b) (i) receiving the ultrasonic signal by connecting both the additional internal electrode and the external electrode to ground, and (ii) electrically connecting the sensing electrode to a receiver circuit; And (c) transmitting an ultrasonic signal by supplying a driving voltage to at least one of the additional internal electrode and the external electrode.

In addition, a method for driving a system for determining a position of a moving element according to an embodiment of the present invention is attached to a first group and a base unit of a moving ultrasonic transducer including at least one ultrasonic transducer coupled with the moving element. And a second group of fixed ultrasound transducers comprising at least two ultrasound transducers to maintain a fixed geometric relationship, wherein (a) (iii) one of the first and second groups of ultrasound transducers is at least one measurement Transmit a signal, the other of the first and second groups is received by an ultrasonic transducer, and (ii) the system is in a measurement mode to obtain the position of the moving element from the emission time measurement for the at least one measurement signal. Operating; (b) (iii) at least one ultrasonic transducer from the second group transmits a calibration signal, and at least another ultrasonic transducer from the second group receives the calibration signal, and (ii) the calibration information. Operating the system intermittently in a calibration mode obtained from the emission time measurement for the calibration signal.

In addition, in the present invention, at least one ultrasonic transducer from the second group may be implemented as the above-described circular ultrasonic transducer structure.

In addition, the present invention provides mechanical protection for an ultrasonic transducer used for a given frequency of the ultrasonic signal while minimizing interference of the ultrasonic signal, positioning a protective grating adjacent the transducer, and giving a given ultrasonic frequency wavelength in air. A method of constructing a grating having multiple open intervals at spatial frequencies of less than about ½, but rather less than about ¼, is provided.

The transducer is a circular transducer, characterized in that the grating is formed as a circular grating surrounding the transducer.

The present invention is a circular ultrasonic receiver or transceiver formed from a piezoelectric film. The present invention also provides for the application of the above-described transceiver in a digitizer system.

The principle and operation of the receiver and transceiver according to the present invention will be described more easily with reference to the drawings.

Various appearances of the ultrasonic receiver will be described with reference to FIGS. 3 to 11. Generally, reference numeral 20 is a coupling assembly constructed and operative in accordance with an embodiment of the present invention.

In other words, the receiver 20 is initially formed from a flexible piezoelectric film and includes a hollow cylinder 22 having a height h of length parallel to the outer circumferential surface 24, the inner circumferential surface 26, the central axis 28 and the axis 28. The sensing electrode 30 applied to the inner circumferential surface 26 is formed from a conductive material. The ground electrode 32 is formed from a conductive material applied to the outer circumferential surface 24.

The cylinder 22 is supported by a support structure (here indicated as core element 34) formed for supporting the hollow cylinder in a manner that transmits vibration waves circumferentially around the core portion of the cylinder 22.

A particular feature which should be implemented first of all in the present invention is that the sensing electrode 30 extends in the direction of diffusion substantially parallel to the central axis 28 along the central part of the height h, the strip being no greater than 90 ° at the central axis 28. It is shaped like a strip in angular range (shown in FIG. 4C). The dimensions of strip 30 are preferably chosen to match less than about ¼ oscillation wavelength in cylinder 22 induced by ultrasonic vibration at a given operating frequency. In most cases, cylinder 22 selects such dimensions that support only about one oscillation wavelength (rather than about three wavelengths schematically illustrated in FIG. 2) to minimize or equal the interference effect. As a result, the phase rejection problem can be largely avoided while strip 30 is in the α angle range less than about 90 ° on axis 28. Rather, however, the width of strip 30 is generally chosen in the α angle range between about 20 to 30 ° on axis 28.

The operating principle of the receiver 20 is as mentioned in FIGS. 1 and 2. As mentioned above, commonly occurring pressure waves tend to cause oscillating waves that propagate around the cylinder. As a result, sensors placed randomly on the surface of the cylinder experience the independence of the directions commonly encountered in the same vibration and pressure waves. At the same time, the degree of enclosing the periphery of the sensing electrode 30 is small in proportion to the wavelength of the vibration transmitted through the film, thereby avoiding the above-described problems due to phase removal and large capacitance. As a result, the wide-angle ultrasonic receiver is very effective. Various advantages of the shape of the invention will become more apparent in the following more detailed description.

Regarding the material, the present invention can be implemented using any piezoelectric film material and a suitable conductive electrode material. In particular, a preferred example of a film is PVDF. The direction of polarization is aligned circumferentially around the cylinder. The use of such films offers particular advantages depending on the wide frequency response. In particular, existing narrow frequency band receivers using piezo-ceramic for shifting signal noise into a measurement frequency range that significantly reduce the signal-to-noise ratio have been known. In contrast, the wide frequency band receiver of the present invention is used in combination with subsequent filtering to match the desired signal obtained to provide a greatly enhanced signal to noise ratio.

Suitable conductive materials for the electrode include, but are not limited to, compositions containing carbon, silver, and gold. Applications require transparent structures, and transparent conductive materials are used.

As mentioned earlier, one important problem associated with the implementation of circular ultrasonic transducers using piezoelectric films is that the electrodes act like antennas for electron (EM) radiation. To minimize or eliminate this problem, the present invention includes one or more features to shield the sensing electrode 30 from EM radiation and will now be described in detail.

First, the ground electrode 32 extends as much as possible over the core portion of the outer circumferential surface 24 of the film. This forms a conductive shell around the sensing electrode 30, thereby shielding the EM field from the volume contained therein. This is to say that the sensing electrode 30 is positioned on the inner circumferential surface of the film rather than from the outside.

An additional shield is shown by providing at least one additional ground electrode 36 formed from a conductive material applied to the inner circumferential surface in a discontinuous pattern with the sensing electrode. Rather, the additional electrode 36 extends over the core portion of the inner circumferential surface 26. Where two or more separation regions are required, they have the advantage of being electrically connected by the bridge position 38 of the conductive material, as shown in FIG. 4B.

An alternative contribution to the EM shield is provided by using a conductive core element 34 arranged in the cylinder 22 and electrically grounded in a manner that avoids electrical contact with the sensing electrode 30. Core element 34 is generally part of the support structure for cylinder 22, although not necessarily.

5 shows an example of a core element 34 embodied as a metal core element, which may be a solid as shown or hollow. In order for the film of the cylinder 22 to vibrate freely, the core component 34 is formed with the diameter position 38 reduced over the core part of the height. In some cases, the non-contact area is defined by a reduced diameter position 38 that is sufficient to avoid electrical contact with the sensing electrode 30. Alternately, the additional insulating layer can be inserted between the core element 34 and the sensing electrode 30.

6 shows an alternative implementation of core element 34 formed from a conductive foam. In this case, the contact between the core element 34 and the cylinder 22 does not significantly interfere with the transmission of vibration in the cylinder 22. In this case, an additional insulating layer is generally required between the core element 34 and the sensing electrode 30.

In order to make receiver 20, proper electrical connection must be made between the various electrodes and the electrical components of the circuit (as indicated below). The range of effective connection shapes is known in the design art of piezoelectric devices. If you implement, you will be able to easily create some of the connection shapes believed to have special advantages.

First, referring to Figs. 3, 4A and 4B, the shape of the cylinder 22 is formed with a tab 40 which carries all the electrical contacts and shoots from it. Three connection techniques of these contacts corresponding to the contacts of the PCB are illustrated in FIGS. 7A-7B, 8 and 9, respectively.

According to the technique of FIGS. 7A and 7B, the tab 40 is disposed with the PCB by dropping conductive glue 44 on each, and press-molded in correspondence with the contact 42 of the PCB.

According to the technique of FIG. 8, tab 40 is sandwiched between the PCB and one or more spring elements 46. Electrical contact is provided on one or generally two of the PCB and the spring.

According to the technique of FIG. 9, some of the conductive pins 48 are inserted through the contact positions of the tabs 40 and engaged corresponding to the contact sockets on the PCB.

10A and 10B show an alternative shape of the piezoelectric film contacting tab 40a and tab 40b extending axially from cylinder 22 rather than in contact. In other respects, this shape is very similar to the shape of FIGS. 3-4.

So far, device 20 has been described as an ultrasonic receiver, but such a construction is well suited for use in a transceiver system. That is, both the reception and transmission signals will now be described. 4B, the additional electrode 36 rather covers the opposite ground electrode 32 surface 26 in a large proportion. Thus, the operating potential applied between the two electrodes is very effective for generating an ultrasonic signal, and is similar to the operation of a conventional circular ultrasonic transmitter.

As mentioned earlier, both the ground electrode 32 and the additional electrode 36 have the advantage of being grounded for shielding purposes while receiving the ultrasonic signal. To maintain this advantage, a switching system is used to selectively switch one of the ground electrodes to the transmitter circuit when transmission is needed.

Thus, referring to FIG. 11, a transceiver assembly employing device 20 is shown. The transceiver assembly also includes a control module 50 having a receiver circuit 52 electrically connected to the sense electrode 30 via an amplifier 54. The control module 50 also includes a transmitter circuit 56, a switching system 58. The switching system 58 is coupled to a ground electrode 32 or an additional electrode 36 which acts like an active electrode which is alternately connected to ground with the transmitter circuit for transmission during the reception. The entire assembly is operated under the control of processor 60, and detailed description thereof will be omitted.

In the operation in which the assembly is used for reception, the EM shield is maximized by connecting both the additional electrode 36 and the external electrode 32 to ground. When transmission is required, the operating voltage is used to generate the desired signal at ground electrode 32 or additional electrode 36.

It should be considered that there are many variations and purifications made under the principles of the present invention. For example, the receiver 20 may use one or more sensing electrodes 30 spaced around the cylinder 22. This can be useful for some reason. First, by analyzing the individually detected signals and matching the phase difference between these signals, the proximity direction information measured in a single receiver can be obtained. For example, the wavelength is short compared to the size of cylinder 22, and it is possible to select an interval commonly connected to the sensing electrode to achieve receiver-specific tuning at the desired frequency. In other words, the spacing for a given frequency corresponds to the phase spacing around the cylinder, and the signal from each sensing electrode will have the same indication and have increased amplitude. Some degree of rejection at many different frequencies will occur as described in FIG.

As mentioned earlier, cylinder 22 is formed to support only a single wavelength of the oscillating wave in the piezoelectric film induced by the ultrasonic signal at the operating frequency. In more detail, half the circumference (πD / 2) is equal to the wavelength of the oscillating wave in the film. For this reason, the diameter of the cylinder is usually chosen to be inversely proportional to the specified operating frequency. For example, the cylinder diameter is approximately 5 mm for an operating frequency of 90 kHz.

Referring now to Figures 12A-13B, while implementing a self calibration mode in accordance with another aspect of the present invention, the transceiver function in the transducer of the present invention increases precision and reliability in a system for determining the position of a mobile device. Very useful.

Ultrasonic radiation using a digitizer system solves the problem of accuracy due to significant changes in the sound passing through the air with changes in temperature, pressure and humidity. To compensate for this change, the present invention provides the self calibration capability described below.

Referring to FIG. 12A, a mobile ultrasonic transducer 70 coupled with a mobile element 72, including at least two ultrasonic transducers 74,76 attached to the base unit 78 and maintaining a fixed geometric relationship, determines the position of the mobile component. A system for this is schematically shown. In the illustrated case, the normal measurement mode of the system includes transmitting at least one measurement signal at the moving ultrasound transducer 70 and receiving by the fixed ultrasound transducers 74,76. The position of the moving element 72 can be obtained using the radiation time measurement on the ultrasonic measurement signal.

According to the practice of the present invention, the system is also operated intermittently in a calibration mode in which the transducer 74 transmits from the normal receiving function and transmits a calibration signal received by the transducer 76. The distance between the transducers 74 and 76 is defined as a fixed value by the construction of the base unit 78, and the radiation time measurement for the calibration signal can be used to obtain a calibration information display on the speed of sound under the environment in which the system is currently operating. have. This calibration information can accurately derive the position of the mobile element 72.

Briefly described in FIGS. 13A and 13B, a mobile transducer 70 which acts as a receiver while receiving a signal transmitted by the fixed transducers 74, 76 embodies and describes this aspect of the present invention for the system. In this case, the calibration mode is implemented by using transducer 76 momentarily as a receiver to receive a calibration signal sent by transducer 74. In all other respects, the principles of the present invention remain as before.

14 shows a protective grating. Reference numeral 80 shows a configuration and operation according to another embodiment of the present invention, which is used for mechanical protection of the ultrasonic transducer.

Mechanical protection must often be provided for the transducers, especially those using piezoelectric films are easily damaged. Many current transducer structures allow for significant signal distortion and / or "reception points" (i.e., directions of significant drop in transmission strength or reception sensitivity) by various protective structures on the front of the transducer.

In order to minimize or eliminate this problem, the present invention provides a protective grating having a spatial period S in which the periodic open pattern does not exceed λ / 2, but rather λ / 4, when the wavelength of the ultrasonic operating frequency in the air is λ. Provide structure 80. A grating with grating spacing S can be used to obtain an ultrasonic signal that is significantly smaller than existing systems and has little directional interference. In practice, for example, an operating frequency of 90 kHz has a wavelength of about 4 mm in the atmosphere and a grating spacing of 1.9 mm causes minimal interference to the transmission and reception of signals.

In order to minimize the attenuation of the signal, the ratio of the grating is rather open to the maximum depending on the mechanical requirements for the structure. In the above example, the open area of the grating is at least about 70% of the total area within each grating step.

Although the present invention schematically illustrates a rectangular grid shape, the grid 80 can be implemented in a range of different shapes to suit each application. Thus, as described above in the circular transducer, the grating 80 can be embodied as a circular outer sleeve with periodic open spacing S.

In particular, the transducer combined with the recording point of the recording device is typically a transparent element (such as an electrode and a transparent plastic or grating 80) in a size such that the ultrasonic transducer can be placed very close to the surrounding so that the user's tip is clearly recorded. Consider all components of transducer 20 and grid 80 that are implemented as

What has been described above is merely an embodiment for carrying out the present invention, and the present invention is not limited to the above-described embodiments, and various modifications are naturally within the spirit and scope of the present invention.

Claims (18)

(Iii) a hollow cylinder initially formed from a flexible piezoelectric film, the hollow cylinder having an outer circumferential surface, an inner circumferential surface, a central axis, and a height parallel to the central axis; (Ii) a sensing electrode formed from a conductive material applied to said inner circumferential surface; (Iii) a ground electrode formed from a conductive material applied to the outer circumferential surface; And (Iii) a support structure configured to support the hollow cylinder in such a manner as to transmit a vibration wave in the circumferential direction around the core portion of the hollow cylinder to support the hollow cylinder; Consists of, And said sensing electrode is shaped like a strip extending in a diffusion direction substantially parallel to said central axis along a central portion of said height, said strip being in an angular range no greater than 90 ° from said central axis. The method of claim 1, And the strip is in an angular range no greater than 30 ° from the central axis. The method of claim 1, And the ground electrode extends over a central portion of the outer circumferential surface. The method of claim 3, wherein And at least one additional electrode formed from a conductive material applied to the inner circumferential surface in a discontinuous pattern with the sensing electrode. The method of claim 4, wherein And said at least one additional electrode extends over a central portion of said inner circumferential surface. The method of claim 5, And the at least one additional electrode is grounded. The method of claim 5, (Iii) a receiver circuit electrically connected to the sensing electrode; (Ii) transmitter circuits; And (Iii) a switching system associated with an operating electrode selected from the ground electrode and the additional electrode, the switching system being configured to alternately electrically connect the operating electrode to the transmitter circuit and ground; Ultrasonic receiver, characterized in that the serving as an ultrasonic transceiver further comprising a control module comprising a further used as an ultrasonic transmitter. The method of claim 1, And said support structure comprises a conductive core element deployed in said hollow cylinder in a manner to avoid electrical contact with said sensing electrode, said conductive core element being electrically grounded. The method of claim 8, And the conductive core element is a metal core element. The method of claim 8, And the conductive core element is formed from a conductive foam. The method of claim 1, The flexible piezoelectric film is an ultrasonic receiver, characterized in that implemented as a PVDF film. The method of claim 1, And the sensing electrode and the ground electrode are generally implemented as transparent electrodes. (Iii) a hollow cylinder, initially formed from a flexible piezoelectric film, having a height of an outer circumferential surface, an inner circumferential surface, a central axis and a length parallel to the central axis, and mounted to transmit a vibration wave in a circumferential direction around the core portion, A sensing electrode formed from a conductive material applied to the inner circumferential surface and formed like a narrow strip extending in a diffusion direction substantially parallel to the central axis along the central portion of the height, the strip in an angular range not greater than 90 ° from the central axis , At least one additional internal electrode formed from a conductive material applied along the core portion of the inner circumferential surface in a discontinuous pattern with the sensing electrode, Ⓓ providing an ultrasonic transceiver structure comprising at least one external electrode formed from an applied conductive material extending above a core portion of the outer circumferential surface; (Ii) both the additional internal electrode and the external electrode are connected to ground, Ⓑ receiving an ultrasonic signal by electrically connecting the sensing electrode to a receiver circuit; And (Iii) transmitting an ultrasonic signal by supplying a driving voltage to at least one of the additional internal electrode and the external electrode; Method for operating an ultrasonic transceiver for transmitting and receiving an ultrasonic signal, characterized in that consisting of. A first group of mobile ultrasound transducers comprising at least one ultrasound transducer coupled to a moving element and a second of a stationary ultrasound transducer including at least two ultrasound transducers attached to the base unit to maintain a fixed geometric relationship Group, (Iii) ⓐ one of the first and second groups of ultrasonic transducers transmits at least one measurement signal, the other of the first and second groups is received by the ultrasonic transducers, Operating the system in a measurement mode whereby the position of the mobile element is obtained from the emission time measurement for the at least one measurement signal; (Ii) at least one ultrasonic transducer from the second group transmits a calibration signal, and at least another ultrasonic transducer from the second group receives the calibration signal, Operating the system intermittently in a calibration mode where the calibration information is obtained from the emission time measurement for the calibration signal; A method of driving a system for determining a position of a mobile device comprising. The method of claim 14, At least one ultrasonic transducer from the second group, (Iii) a hollow cylinder initially formed from a flexible piezoelectric film, the hollow cylinder having an outer circumferential surface, an inner circumferential surface, a central axis and a height parallel to the central axis, and mounted to transmit a vibration wave in a circumferential direction around the core portion; (Ii) a sensing electrode formed from a conductive material applied to the inner circumferential surface and formed like a narrow strip extending in a diffusion direction generally parallel with the central axis along the central portion of the height, the angle range not greater than 90 ° from the central axis Strips of; (Iii) at least one additional internal electrode formed from a conductive material extending over the core portion of the inner circumferential surface in a discontinuous pattern with the sensing electrode; And (Iii) at least one external electrode formed from a conductive material extending above the core portion of the outer circumferential surface; Formed to a structure comprising a. Provides mechanical protection for the ultrasonic transducer used for the frequency of a given ultrasonic signal while minimizing interference of the ultrasonic signal, positioning a protective grating adjacent the transducer, and less than about ½ of a given ultrasonic frequency wavelength in air A method of constructing a grating having multiple open intervals at spatial frequencies. The method of claim 16, And the grating has a plurality of open intervals at spatial frequencies less than about ¼ of a given ultrasonic frequency wavelength in air. The method of claim 16, The transducer is a circular transducer, and the grating is formed as a circular grating surrounding the transducer.