Patent Publication Number: US-2007119257-A1

Title: Vibration detection method and system, battery-less vibration sensor and interrogator therefor

Description:
BACKGROUND OF THE INVENTION  
      This invention relates to a vibration detection method as well as a vibration detection system comprising a vibration sensor and an interrogator.  
      There are proposed and known various vibration sensors, which are used for, for example, earthquake-proof diagnosis of structures or buildings, detection of glass or pane breakage events, or detection of abnormal vibration in facilities or machine tools.  
      JP-A 2000-48268 discloses a system that detects momentary and periodical fluctuation such as vibration generated when a glass or pane is broken. The disclosed system includes a vibration sensor fabricated by using a piezoelectric material to transform, into electric signals, vibration generated upon a glass breakage event.  
      However, the disclosed sensor is too large in size because of its structure. There is a need for a new structure which can reduce a size of a vibration sensor.  
     SUMMARY OF THE INVENTION  
      One aspect of the present invention applies a radio frequency identification (RFID) scheme to a vibration detection method or system to enable a battery-less vibration sensor.  
      According to one aspect of the present invention, a method for detecting a vibration status of a target object comprises: attaching to the target object a battery-less vibration sensor provided with a single port surface acoustic wave (SAW) resonator, the battery-less vibration sensor being configured to sense the vibration status as mechanical vibration of the battery-less vibration sensor; continuously transmitting a carrier wave signal to the single port SAW resonator; continuously monitoring a wave signal reflected from the single port SAW resonator; and acknowledging the vibration status from fluctuation which is included in the reflected wave signal and is caused by the mechanical vibration.  
      According to another aspect of the present invention, a vibration detection system comprising: a battery-less vibration sensor comprising a single port surface acoustic wave (SAW) resonator, the battery-less vibration sensor being attached to a target object upon actual use thereof and being configured to sense a vibration status of the target object as mechanical vibration of the battery-less vibration sensor; and an interrogator configured to perform: continuously transmitting a carrier wave signal to the single port SAW resonator; continuously monitoring a wave signal reflected from the single port SAW resonator; and recognizing the vibration status from fluctuation which is included in the reflected wave signal and is caused by the mechanical vibration.  
      An appreciation of the objectives of the present invention and a more complete understanding of its structure may be had by studying the following description of the preferred embodiment and by referring to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS:  
       FIG. 1  is a view schematically showing a vibration detection system according to one embodiment of the present invention;  
       FIG. 2  is a perspective view schematically showing a battery-less vibration sensor of  FIG. 1 ;  
       FIG. 3  is a sectional view schematically showing a sensor chip of  FIG. 2 ;  
       FIG. 4  is a top plan view schematically showing a single port SAW resonator of  FIG. 3 ;  
       FIG. 5  is an enlarged view showing a detail of an oval part indicated in  FIG. 4 ;  
       FIG. 6  is a block diagram schematically showing an interrogator of  FIG. 1 ;  
       FIG. 7  is a flowchart showing an exemplary processes carried out in a judgment section of  FIG. 6 ; and  
       FIG. 8  is a view schematically showing an example application of the system of  FIG. 1 . 
    
    
      While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.  
     DESCRIPTION OF PREFERRED EMBODIMENTS:  
      With reference to  FIG. 1 , a vibration detection system according to one embodiment of the present invention comprises a battery-less vibration sensor  100  and an interrogator  200 . The battery-less vibration sensor  100  is attached to a target object such as a glass pane upon its actual use. The interrogator  200  interrogates the battery-less vibration sensor  100  by transmitting a carrier wave signal continuously and receives a reply from the battery-less vibration sensor  100 . If the battery-less vibration sensor  100  senses a vibration status or a vibration event of the target object as mechanical vibration of the battery-less vibration sensor  100 , its reply to the interrogator  200  includes fluctuation in accordance with the mechanical vibration of the battery-less vibration sensor  100  so that the interrogator  200  can detect the vibration status of the target object.  
      As shown in  FIG. 1 , the battery-less vibration sensor  100  comprises an antenna  10  and a sensor chip  20 . In the sensor chip  20 , a single port SAW resonator  30  is included. The antenna  10  is electrically connected to the single port SAW resonator  30 .  
      As shown in  FIG. 2 , the battery-less vibration sensor  100  according to the present embodiment is of tag type. In detail, the battery-less vibration sensor  100  further comprises a tag base  40 . The tag base  40  of the present embodiment is made of synthetic resins, but the present invention is not limited thereto. For example, the tag base may be made of paper, metal, ceramics, wood or concrete. On the tag base  40 , the antenna  10  is formed and the sensor chip  20  is mounted. The illustrated antenna  10  is a set of conductive thin film antennas  11  and  12 . The antenna  10 , i.e. thin film antennas  11 ,  12  may be embedded in the tag base  40 . Likewise, the sensor chip  20  may be embedded in the tag base  40 .  
      With reference to  FIG. 3 , the sensor chip  20  comprises a supporter substrate  22  and a cap or lid member  23 . The supporter substrate  22  and the cap member  23  define a cavity  24 , within which the single port SAW resonator  30  is supported by the supporter substrate  22  so that the single port SAW resonator  30  is vibratable in the cavity  24 . In detail, the supporter substrate  22  comprises a main portion  22   a  of a general plate shape and a side wall portion  22   b  standing from the main portion  22   a . The main portion  22   a  is formed with a depressed portion  22   c . The supporter substrate  22  and the cap member  23  are made of, for example, silicon or ceramics.  
      The cap member  23  is adhered to a brim of the supporter substrate  22 , i.e. a top edge of the side wall  22   b , by means of an adhesive agent. Thus, the supporter substrate  22  and the cap member  23  are sealed off so that the cavity  24  is hermetically enclosed.  
      As shown in  FIGS. 3 and 4 , the single port SAW resonator  30  of the present embodiment comprises a piezoelectric substrate  32 , an inter-digital transducer (IDT)  34  and reflectors  37 ,  38 . The piezoelectric substrate  32  has a plate-like shape. On one surface of the piezoelectric substrate  32 , the IDT  34  and the reflectors  37 ,  38  are formed: The piezoelectric substrate  32  of the present embodiment is made of a langasite (La 3 Ga 5 SiO 14 ) single crystal but may be made of another single crystal of, for example, quartz, lithium niobate (LiNbO 3 ), lithium tantalate (LiTaO 3 ), lithium borate (LBO 2 ) or zinc oxide.  
      As shown in  FIG. 3 , the piezoelectric substrate  32  is supported in cantilever form by the supporter substrate  22  so that the IDT  34  is positioned over the depressed portion  22   c . In other words, the piezoelectric substrate  32  has a supported portion and a projecting portion; the supported portion is supported by the supporter substrate  22  while the projecting portion projects over the depressed portion  22   c ; the IDT  34  is formed on the projecting portion. In this embodiment, the IDT  34  faces the depressed portion  22   c . In addition, the IDT  34  is positioned close to the supported portion of the piezoelectric substrate  32 . In other words, the IDT  34  is positioned on a root section of the projecting portion of the piezoelectric substrate  32 .  
      As shown in  FIGS. 3 and 4 , the IDT  34  is formed with connection portions  35 ,  36 , which are connected through solder bumps  25 ,  26  to a pattern (not shown) formed on the supporter substrate  22 ; the pattern is further connected to terminals  27  through via holes (not shown) formed in the supporter substrate  22 . The terminals  27  are connected to the antennas  11 ,  12  through wires or traces  42  formed on the tag base  40  (see  FIG. 2 ). Thus, electrical paths are formed between the IDT  34  of the single port SAW resonator  30  and the antennas  11 ,  12  so that a wave signal received at the antennas  11 ,  12  is supplied to the IDT  34  through the electrical paths; the IDT  34  reflects the received wave signal, and the reflected wave signal is transmitted through the electrical paths and the antennas  11 ,  12  to the interrogator  200 . In this embodiment, an impedance-matching is ensured at every boundary on the electrical paths so that undesirable reflection is not included in the reflected wave signal.  
      The piezoelectric substrate  32  of the present embodiment has a specific shape in accordance with which a resonant frequency of the single port SAW resonator  30  belongs to an exemplary frequency band of mechanical vibration of a detection target object, ex. a frequency band representative of a glass breakage event in a case of detection of glass breakage. The thus adjusted resonant frequency results in continuing vibration of the piezoelectric substrate  32  even after vibration of the target object ceases. In this embodiment, the piezoelectric substrate  32  has a constant thickness so that its resonant frequency is adjustable by changing a length of the projecting portion of the piezoelectric substrate  32 .  
      The reflectors  37 ,  38  of the present embodiment are arranged in proximity to the IDT  34  to serve as an energy blocker blocking or preventing energy of the received carrier wave signal from escaping from the IDT  34  or surroundings of the IDT  34 . In this embodiment, two reflectors  37 ,  38  are used. In consideration of the magnitude of allowable energy loss, any one or both of them may be omitted.  
      As shown in  FIG. 5 , the IDT  34  comprises two base portions, only one of which is shown with a reference numeral  34   a , and two set of fingers  34   b ,  34   c . Each of the fingers  34   b  projects from the base portion  34   a  upwardly in  FIG. 5 . Each of the other fingers  34   c  projects downwardly from the other base portion that is not shown in  FIG. 5 . The fingers  34   b  and the other fingers  34   c  are alternately arranged at regular intervals. Each finger  34   b ,  34   c  has a width W 1  and extends along a vertical direction in  FIG. 5 . Neighboring two fingers  34   b  and  34   c  are positioned away from each other by a distance D. In this embodiment, the width W 1  is equal to the distance D 1 .  
      The reflector  37  also comprises a base portion  37   a  and a plurality of fingers  37   b  extending from the base portion  37   a  along the vertical direction in  FIG. 5 . The illustrated finger  37   b  has a width W 2  equal to the width W 1  of the finger  37   b ,  37   c . An end one of the fingers  37   b  is positioned away by a distance D 2  from an end one of the finger  37   b ,  37   c . In other words, the reflector  37  is positioned away from the IDT  34  by the distance D 2  in a horizontal direction in  FIG. 5 . Preferably, the distance D 2  is equal to an integral multiple of the distance D 1 . In this embodiment, the distance D 2  is equal to the distance D 1 . The distance D 2  may be equal to two or more times of the distance D 1 . The other reflector  38  of the present embodiment has a shape same as that of the reflector  37  and is arranged in a manner similar to that of the reflector  37 .  
      The distance D 1  has an influence on the resonant frequency at the single port SAW resonator  30 . In this embodiment, the distance D 1  is determined and designed so that the resonant frequency at the single port SAW resonator  30  is equal to a frequency of the carrier wave signal transmitted from the interrogator  200 .  
      With reference to  FIG. 6 , the interrogator  200  comprises a transmitter/receiver  210 , a judgment section  220 , an output section  230  and an interface (I/F) section  240 .  
      The transmitter/receiver  210  has a function to continuously transmit a carrier wave signal to the battery-less vibration sensor  100  and another function to receive a wave signal reflected from the battery-less vibration sensor  100 . The exemplary transmitter/receiver  210  comprises a transmitter for continuously transmitting the carrier wave signal, a circulator, an antenna, and a receiver for receiving the reflected wave signal. In this embodiment, the transmitter/receiver  210  continues to transmit the carrier wave signal even when receiving the reflected wave signal. In other words, the transmitter/receiver  210  of the present embodiment carries out the transmission of the carrier wave signal and the reception of the reflected wave signal.  
      The carrier wave signal of the present embodiment consists of a single frequency component, namely, is shown in a simple sinusoidal wave signal. However, the carrier wave signal may comprises multiple frequency components, provided that the carrier wave signal is not a momentary pulse but has a periodical change. Preferably, the carrier wave signal has a periodical, smooth change to make it easy to recognize a difference between the carrier wave signal and the reflected wave signal.  
      The judgment section  220  is connected to the transmitter/receiver  210  and has a function to monitor the reflected wave signal to judge whether the target object is in the vibration status. When the battery-less vibration sensor  100  senses a vibration event of the target object, the single port SAW resonator  30  reflects the received carrier wave signal with vibration information included therein. For example, the vibration information is at least one of an amplitude, a frequency and a phase which are not of the carrier wave signal. In other words, the single port SAW resonator  30  modulates the received carrier wave signal in accordance with the sensed vibration event. Therefore, the judgment section  220  judges that the target object is in vibration status, when recognizing the above-mentioned modulation.  
      The output section  230  is coupled to the judgment section  220  and serves to, if the judgment section  220  judges that the target object is in vibration status, notify a user of the judgment. In this embodiment, the output section  230  comprises a buzzer.  
      The I/F section  240  is connected between the judgment section  220  and an upper apparatus or section/unit not shown. The I/F section  240  serves to, if the judgment section  220  judges that the target object is in vibration status, notify the upper apparatus of the judgment.  
      The exemplary judgment processes by the judgment section  220  are shown in  FIG. 7 ; the judgment section  220  of this example comprises a timer. When detecting a precaution condition under which the reflected wave signal includes modulated components which are not of the carrier wave signal (S 101 ), the judgment section  220  sets its timer for 50 ms (S 102 ). Then, the judgment section  220  monitors whether the precaution condition continues (S 103 ). If the precaution condition continues for 50 ms (S 104 ), the judgment section  220  judges that the target object is in vibration status. After the judgment, the judgment section  220  turns the buzzer on and notifies the upper apparatus of the detection of the vibration status by means of the I/F section  240 .  
      Although the system of the present embodiment comprises a single battery-less vibration sensor, the present invention is not limited thereto. A vibration detection system may comprise a plurality of battery-less vibration sensors. Especially, as shown in  FIG. 8 , a vibration detection system may comprise a single interrogator  200   a  and a plurality of battery-less vibration sensors  100   1 ,  100   2 , which include single port SAW resonators  30   1 ,  30   2 , respectively. The single port SAW resonators  30   1 ,  30   2  have similar structure to that of the above-explained resonator  30 . The single port SAW resonators  30   1 ,  30   2  have different resonant frequencies from each other by, for example, selecting suitable lengths of projecting portions of their piezoelectric substrates. The interrogator  200   a  identifies the battery-less vibration sensors  100   1 ,  100   2  on the basis of the different resonant frequencies of their single port SAW resonators  30   1 ,  30   2 .  
      The present application is based on Japanese patent applications of JP2005-327855, JP2006-025852 and JP2006-197678 filed before the Japan Patent Office on Nov. 11, 2005, Jan. 11, 2006 and Jul. 20, 2006, respectively, the contents of which are incorporated herein by reference.  
      While there has been described what is believed to be the preferred embodiment of the invention, those skilled in the art will recognize that other and further modifications may be made thereto without departing from the sprit of the invention, and it is intended to claim all such embodiments that fall within the true scope of the invention.