WO2009046736A1 - Piezo-electric crystal - Google Patents

Piezo-electric crystal Download PDF

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Publication number
WO2009046736A1
WO2009046736A1 PCT/EP2007/008707 EP2007008707W WO2009046736A1 WO 2009046736 A1 WO2009046736 A1 WO 2009046736A1 EP 2007008707 W EP2007008707 W EP 2007008707W WO 2009046736 A1 WO2009046736 A1 WO 2009046736A1
Authority
WO
WIPO (PCT)
Prior art keywords
piezo
layer
electric
crystal
electric crystal
Prior art date
Application number
PCT/EP2007/008707
Other languages
French (fr)
Inventor
Morten Storgaard Nielsen
Original Assignee
Siemens Aktiengesellschaft
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Siemens Aktiengesellschaft filed Critical Siemens Aktiengesellschaft
Priority to PCT/EP2007/008707 priority Critical patent/WO2009046736A1/en
Publication of WO2009046736A1 publication Critical patent/WO2009046736A1/en

Links

Classifications

    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/80—Constructional details

Definitions

  • the present invention relates to piezo-electric crystals.
  • An ultrasonic wave also called ultrasound wave, is a cyclic sound pressure wave with a frequency greater than the upper limit of human audible range which is approximately 20 kHz. Ultrasonic waves are used in various applications including medical diagnosis, distance measurement, velocity calculation of fluids, etc.
  • Ultrasonic waves are used in an ultrasonic flowmeter to measure the velocity of a fluid through a pipe using ultrasonic sensors.
  • the most commonly used is the transit time flowmeter which works by measuring the time difference between an ultrasonic wave sent in the flow direction and an ultrasonic wave sent opposite the flow direction.
  • Ultrasonic flowmeters usually use piezo-electric ceramic crystals for generation of ultrasonic wave.
  • Certain single crystal materials exhibit the phenomenon that, when the crystal is mechanically strained, or when the crystal is deformed by the application of an external stress an electric charge appears on certain of the crystal surfaces, and when the direction of the strain reverses, the polarity of the electric charge is reversed. This is called the direct piezo-electric effect, and the crystals that exhibit it are classed as piezo-electric crystals.
  • piezo-electric crystal when a piezo-electric crystal is placed in an electric field, or when charges are applied by external means to its faces, the crystal exhibits strain, i.e. the dimensions of the crystal change. When the direction of the applied electric field is reversed, the direction of the resulting strain is reversed. This is called the converse piezo-electric effect.
  • piezo-electricity nowadays use polycrystalline ceramics instead of natural piezo-electric crystals.
  • Piezo-electric ceramics are more versatile in that their physical, chemical, and piezo-electric characteristics can be tailored to specific applications. Piezo-electric ceramic materials can be manufactured in almost any shape or size, and the mechanical and electrical axes of the material can be oriented in relation to the shape of the material.
  • Piezo-electric crystals are used in the sensors of ultrasonic flowmeters but when the piezo-electric crystal is disconnected from the sensor, a large voltage may build up due to thermal or mechanical loads. During assembly of the flowmeter or in case of cutting the transducer wires, the voltage may give rise to a spark or possibly an electric shock.
  • a piezo-electric crystal comprising:
  • the underlying idea of the present invention is to electrically connect the charged surfaces on the piezoelectric crystal.
  • the self-discharging property also aids in safer operation of the devices where piezo-electric crystals are used.
  • the piezo-electric crystal further comprises a protective layer on the layer of resistive material. This layer retains the resistive layer on the piezo-electric crystal and protects the layer from external damages.
  • the layer of resistive material is a vapor-deposited layer.
  • the vapor-deposition method used for attaching the resistive layer makes sure that the layer perfectly adheres to the surface of the piezo-electric crystal and gives a continuous structure to the layer across the connecting points.
  • the proposed piezo-electric crystal is used in an ultrasonic flowmeter.
  • the proposed piezo-electric crystal eliminates the external devices used for discharging the charged piezoelectric crystal. This makes the ultrasonic flowmeter safer and explosion proof. Also it makes custom designed mechanical contacting in connections of ultra-sonic transducers obsolete and allows use of standard contacts.
  • FIG 1 is a schematic overview of a conventionally used piezo- electric crystal and electrodes
  • FIG 2 is a schematic overview of a conventionally used piezoelectric crystal with electrodes as integral part
  • FIG 3 is a schematic overview of an ultrasonic flowmeter
  • FIG 4 is a schematic diagram of the charged piezo-electric crystal
  • FIG 5 is a schematic diagram of a piezo-electric crystal according to an embodiment of the present invention.
  • FIG 1 an overview of a conventionally used piezo-electric crystal 10 is shown.
  • the two opposite surfaces 12 and 14 on the crystal 10 serve as points of contact for connecting external electrodes 16.
  • the electrodes 16 can be connected to an external electric supply when needed.
  • the electrodes 16 can also be formed as integral part of the piezo-electric crystal 10 as shown in FIG 2. When an alternating current (AC) is applied across the electrodes, the crystal will vibrate at the frequency of the AC field.
  • AC alternating current
  • the ultrasonic flowmeter 18 has two piezo-electric crystals in the form of piezo-electric transducers 26 and 28 which are separated by a predetermined distance along the longitudinal direction and on opposite sides of the pipe 22. Ultrasonic waves are reciprocally transmitted between these two piezo-electric transducers as shown by the arrow 30.
  • the transducers are located such that when there is exchange of ultrasonic waves between them, one wave travels downstream (in the direction of the fluid) and the other wave travels upstream (in opposite direction of the fluid) .
  • the flowmeter 18 further comprises electronic circuit connected to the transducers, which is not shown in the figure for the sake of clarity.
  • Each transducer alternately transmits and receives ultrasonic waves from each other.
  • the difference in the transit times in the upstream vs. the downstream directions measured over the same path can be used to calculate the flow velocity of the fluid.
  • a large voltage may build up due to thermal or mechanical loads.
  • FIG 4 shows a charged piezo-electric crystal 10 with positive and negative charge on its opposite surfaces 12 and 14.
  • Normally piezo-electric crystals are mounted with either a mechanical switch or/and an external discharge resistor to short-circuit the crystal.
  • a layer of resistive material 34 electrically connects the surfaces 36 and 38 with each other, which are the two points of contact for connection of electrodes.
  • the layer of resistive material 34 provides a path for the charge to flow, i.e. a path for a discharging current.
  • the resistive layer 34 might be deposited on the crystal by vapor-deposition.
  • the material for the resistive layer can be C or ZnO or any other material having resistive properties.
  • the resistive layer is provided with a protective layer 40 over it.
  • the protective layer 40 can be formed by materials including TiN, AlTiN, etc.
  • the present invention relates to piezo-electric crystals used in ultrasonic flowmeters.
  • the proposed piezoelectric crystal comprises at least two contact points for connecting electrodes and a layer of a resistive material attached to the surface of the piezo-electric crystal such that the layer connects the contact points, wherein the layer of resistive material is adapted for discharging the piezoelectric crystal.

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Abstract

The present invention relates to a piezo-electric crystal (32). The proposed piezo-electric crystal (32) comprises at least two contact points (36, 38) for connecting electrodes (16) and a layer of a resistive material (34) attached to the surface of the piezo-electric crystal (32) such that the layer connects the contact points (36, 38), wherein the layer of resistive material (34) is adapted for discharging the piezo-electric crystal. The resistive layer (34) is covered with a protective layer (40).

Description

Description
Piezo-electric crystal
The present invention relates to piezo-electric crystals.
'An ultrasonic wave, also called ultrasound wave, is a cyclic sound pressure wave with a frequency greater than the upper limit of human audible range which is approximately 20 kHz. Ultrasonic waves are used in various applications including medical diagnosis, distance measurement, velocity calculation of fluids, etc.
Ultrasonic waves are used in an ultrasonic flowmeter to measure the velocity of a fluid through a pipe using ultrasonic sensors. The most commonly used is the transit time flowmeter which works by measuring the time difference between an ultrasonic wave sent in the flow direction and an ultrasonic wave sent opposite the flow direction. Ultrasonic flowmeters usually use piezo-electric ceramic crystals for generation of ultrasonic wave.
Certain single crystal materials exhibit the phenomenon that, when the crystal is mechanically strained, or when the crystal is deformed by the application of an external stress an electric charge appears on certain of the crystal surfaces, and when the direction of the strain reverses, the polarity of the electric charge is reversed. This is called the direct piezo-electric effect, and the crystals that exhibit it are classed as piezo-electric crystals.
Conversely, when a piezo-electric crystal is placed in an electric field, or when charges are applied by external means to its faces, the crystal exhibits strain, i.e. the dimensions of the crystal change. When the direction of the applied electric field is reversed, the direction of the resulting strain is reversed. This is called the converse piezo-electric effect. Most of the applications of piezo-electricity nowadays use polycrystalline ceramics instead of natural piezo-electric crystals. Piezo-electric ceramics are more versatile in that their physical, chemical, and piezo-electric characteristics can be tailored to specific applications. Piezo-electric ceramic materials can be manufactured in almost any shape or size, and the mechanical and electrical axes of the material can be oriented in relation to the shape of the material.
When piezo-electric crystals are subjected to Direct Current (DC) then there is tension or compression in the crystal depending on the polarity of the charge applied. Whereas applying an alternating current (AC) across the piezoelectric crystals causes them to vibrate. An array of piezo- electric crystals are simultaneously used to produce high frequency sound waves.
Piezo-electric crystals are used in the sensors of ultrasonic flowmeters but when the piezo-electric crystal is disconnected from the sensor, a large voltage may build up due to thermal or mechanical loads. During assembly of the flowmeter or in case of cutting the transducer wires, the voltage may give rise to a spark or possibly an electric shock.
It is an object of the present invention to provide a solution to the above mentioned problem.
The above object is achieved by a piezo-electric crystal, comprising:
- at least two contact points for connecting electrodes, and
- a layer of a resistive material attached to the surface of the piezo-electric crystal such that the layer connects the contact points, wherein the layer of resistive material is adapted for discharging the piezo-electric crystal. The underlying idea of the present invention is to electrically connect the charged surfaces on the piezoelectric crystal. A resistive layer provided on the surface of the crystal connecting the two points, thus discharges the piezo-electric crystal when it is charged. This has an advantage over conventionally used piezo-electric crystals, that it does not require any external means for discharging. The self-discharging property also aids in safer operation of the devices where piezo-electric crystals are used.
In a preferred embodiment of the present invention, the piezo-electric crystal further comprises a protective layer on the layer of resistive material. This layer retains the resistive layer on the piezo-electric crystal and protects the layer from external damages.
In a further preferred embodiment of the present invention, the layer of resistive material is a vapor-deposited layer. The vapor-deposition method used for attaching the resistive layer makes sure that the layer perfectly adheres to the surface of the piezo-electric crystal and gives a continuous structure to the layer across the connecting points.
In a further preferred embodiment of the present invention the proposed piezo-electric crystal is used in an ultrasonic flowmeter. The proposed piezo-electric crystal eliminates the external devices used for discharging the charged piezoelectric crystal. This makes the ultrasonic flowmeter safer and explosion proof. Also it makes custom designed mechanical contacting in connections of ultra-sonic transducers obsolete and allows use of standard contacts.
The present invention is further described hereinafter with reference to preferred embodiments shown in the accompanying drawings, in which:
FIG 1 is a schematic overview of a conventionally used piezo- electric crystal and electrodes,
FIG 2 is a schematic overview of a conventionally used piezoelectric crystal with electrodes as integral part,
FIG 3 is a schematic overview of an ultrasonic flowmeter,
FIG 4 is a schematic diagram of the charged piezo-electric crystal, and
FIG 5 is a schematic diagram of a piezo-electric crystal according to an embodiment of the present invention.
Referring to FIG 1, an overview of a conventionally used piezo-electric crystal 10 is shown. The two opposite surfaces 12 and 14 on the crystal 10 serve as points of contact for connecting external electrodes 16. The electrodes 16 can be connected to an external electric supply when needed. The electrodes 16 can also be formed as integral part of the piezo-electric crystal 10 as shown in FIG 2. When an alternating current (AC) is applied across the electrodes, the crystal will vibrate at the frequency of the AC field.
Referring to FIG 3, an overview of an ultrasonic flowmeter 18 is shown. A fluid 20 is flowing inside the pipe 22 in the direction shown by the arrow 24. The ultrasonic flowmeter 18 has two piezo-electric crystals in the form of piezo-electric transducers 26 and 28 which are separated by a predetermined distance along the longitudinal direction and on opposite sides of the pipe 22. Ultrasonic waves are reciprocally transmitted between these two piezo-electric transducers as shown by the arrow 30. The transducers are located such that when there is exchange of ultrasonic waves between them, one wave travels downstream (in the direction of the fluid) and the other wave travels upstream (in opposite direction of the fluid) . The flowmeter 18 further comprises electronic circuit connected to the transducers, which is not shown in the figure for the sake of clarity.
Each transducer alternately transmits and receives ultrasonic waves from each other. The difference in the transit times in the upstream vs. the downstream directions measured over the same path can be used to calculate the flow velocity of the fluid. When the piezo-electric transducers are disconnected from the circuit, a large voltage may build up due to thermal or mechanical loads.
FIG 4 shows a charged piezo-electric crystal 10 with positive and negative charge on its opposite surfaces 12 and 14. In case of high charges there is a risk of spark generation which may damage the equipment and/or harm the personnel handling it. Normally piezo-electric crystals are mounted with either a mechanical switch or/and an external discharge resistor to short-circuit the crystal.
Referring to FIG 5, an overview of an embodiment of a piezo- electric crystal 32 according to the present invention is shown. A layer of resistive material 34 electrically connects the surfaces 36 and 38 with each other, which are the two points of contact for connection of electrodes. The layer of resistive material 34 provides a path for the charge to flow, i.e. a path for a discharging current.
The resistive layer 34 might be deposited on the crystal by vapor-deposition. The material for the resistive layer can be C or ZnO or any other material having resistive properties. The resistive layer is provided with a protective layer 40 over it. The protective layer 40 can be formed by materials including TiN, AlTiN, etc.
Summarizing, the present invention relates to piezo-electric crystals used in ultrasonic flowmeters. The proposed piezoelectric crystal comprises at least two contact points for connecting electrodes and a layer of a resistive material attached to the surface of the piezo-electric crystal such that the layer connects the contact points, wherein the layer of resistive material is adapted for discharging the piezoelectric crystal.
Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternate embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that such modifications can be made without departing from the spirit or scope of the present invention as defined.

Claims

Patent claims
1. A piezo-electric crystal (32), comprising:
- at least two contact points (36,38) for connecting electrodes (16); and
- a layer of a resistive material (34) attached to the surface of the piezo-electric crystal such that the layer connects the contact points (36,38), wherein the layer of resistive material is adapted for discharging the piezo-electric crystal (32).
2. The piezo-electric crystal (32) of claim 1, further comprising a protective layer (40) on the layer of resistive material (34) .
3. The piezo-electric crystal (32) according to any of the preceding claims, wherein the layer of resistive material
(34) is a vapor-deposited layer.
4. An ultrasonic flow meter, comprising a piezo-electric crystal (32) as claimed in any of the preceding claims.
PCT/EP2007/008707 2007-10-08 2007-10-08 Piezo-electric crystal WO2009046736A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/EP2007/008707 WO2009046736A1 (en) 2007-10-08 2007-10-08 Piezo-electric crystal

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/EP2007/008707 WO2009046736A1 (en) 2007-10-08 2007-10-08 Piezo-electric crystal

Publications (1)

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WO2009046736A1 true WO2009046736A1 (en) 2009-04-16

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Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3027583A1 (en) * 1979-07-20 1981-01-29 Murata Manufacturing Co Piezoelectric filter in hermetically sealed housing - uses polarised ferroelectric plate cut so that polarisation axis intersects flat top and bottom surfaces
JPS56144624A (en) * 1980-04-14 1981-11-11 Murata Mfg Co Ltd Mechanical resonator device using piezoelectric transducer
JPS6148215A (en) * 1984-08-16 1986-03-08 Fujitsu Ltd Piezoelectric vibrator and its manufacture
US5052230A (en) * 1988-07-08 1991-10-01 Flowtec Ag Method and arrangement for flow rate measurement by means of ultrasonic waves
US6111339A (en) * 1998-08-12 2000-08-29 Ueda Japan Radio Co., Ltd. Porous piezoelectric ceramic sheet and piezoelectric transducer
US6227058B1 (en) * 1997-07-01 2001-05-08 Peus-Systems Gmbh High precision flow meter for measuring a gaseous volume flow in a pipe
DE10147666A1 (en) * 2001-09-27 2003-04-10 Bosch Gmbh Robert piezo element
US20040189147A1 (en) * 2003-03-27 2004-09-30 Kyocera Corporation Surface acoustic wave apparatus and communications device
DE102005057950A1 (en) * 2005-12-05 2007-06-06 Robert Bosch Gmbh Stacked type of piezo electric actuator is produced with a surface coating of low electrical conductivity lacquer to avoid surface charges

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3027583A1 (en) * 1979-07-20 1981-01-29 Murata Manufacturing Co Piezoelectric filter in hermetically sealed housing - uses polarised ferroelectric plate cut so that polarisation axis intersects flat top and bottom surfaces
JPS56144624A (en) * 1980-04-14 1981-11-11 Murata Mfg Co Ltd Mechanical resonator device using piezoelectric transducer
JPS6148215A (en) * 1984-08-16 1986-03-08 Fujitsu Ltd Piezoelectric vibrator and its manufacture
US5052230A (en) * 1988-07-08 1991-10-01 Flowtec Ag Method and arrangement for flow rate measurement by means of ultrasonic waves
US6227058B1 (en) * 1997-07-01 2001-05-08 Peus-Systems Gmbh High precision flow meter for measuring a gaseous volume flow in a pipe
US6111339A (en) * 1998-08-12 2000-08-29 Ueda Japan Radio Co., Ltd. Porous piezoelectric ceramic sheet and piezoelectric transducer
DE10147666A1 (en) * 2001-09-27 2003-04-10 Bosch Gmbh Robert piezo element
US20040189147A1 (en) * 2003-03-27 2004-09-30 Kyocera Corporation Surface acoustic wave apparatus and communications device
DE102005057950A1 (en) * 2005-12-05 2007-06-06 Robert Bosch Gmbh Stacked type of piezo electric actuator is produced with a surface coating of low electrical conductivity lacquer to avoid surface charges

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