Vibration displacement sensing device

• US 6,340,347 B1
• Filed: 04/21/2000
• Issued: 01/22/2002
• Est. Priority Date: 04/21/2000
• Status: Expired due to Fees

• Current Assignee: Toda, Kohji
• Original Assignee: Toda, Kohji
• Inventors: Toda, Kohji
• Primary Examiner(s): Jaworski, Francis J.
• Application Number:
  US09/557,056
• Time in Patent Office: 641 Days
• Field of Search: 600/437, 600/438, 600/459, 73/614.5, 73/617.5, 73/617.8, 735/70, 735/73--75, 735/79, 735/84, 736/44, 736/49, 73D/IG.4
• US Class Current: 600/438
• CPC Class Codes: A61B 8/02 Measuring pulse or heart rate

Abstract

A vibration displacement sensing device comprises a piezoelectric substrate, an input interdigital transducer, a first output interdigital transducer, a second output interdigital transducer, and a signal analyzer. All the input-, the first output-, and the second output interdigital transducers are formed on one end surface of the piezoelectric substrate. If an input electric signal is applied to the input interdigital transducer, an elastic wave is excited in the piezoelectric substrate. A leaky component of the elastic wave is radiated effectively in the form of a longitudinal wave toward a first material located inside a second material which is in contact with the other end surface of the piezoelectric substrate and has an acoustic impedance different from that of the first material. The longitudinal wave is reflected by the first material. A reflected longitudinal wave is detected at the first output interdigital transducer as a first delayed electric signal. A non-leaky component of the elastic wave is detected at the second output interdigital transducer as a second delayed electric signal. A vibration displacement caused by the first material is sensed by the signal analyzer from a difference between the first- and second delayed electric signals.

Claims

1. A vibration displacement sensing device comprising:

a piezoelectric substrate having two end surfaces;

an input interdigital transducer;

a first output interdigital transducer;

a second output interdigital transducer, all said input-, said first output-, and said second output interdigital transducers being formed on one end surface of said piezoelectric substrate; and

a signal analyzer,

said piezoelectric substrate, said input interdigital transducer, said first- and second output interdigital transducers forming a sensing assembly,

said input interdigital transducer receiving an input electric signal, exciting an elastic wave, composed of a leaky- and a non-leaky components, in said piezoelectric substrate, radiating said leaky component of said elastic wave in the form of a longitudinal wave toward a first material located inside a second material which has an acoustic impedance different from that of said first material and is in contact with the other end surface of said piezoelectric substrate, and making said first material reflect said longitudinal wave back,

said first output interdigital transducer detecting a reflected longitudinal wave as a first delayed electric signal,

said second output interdigital transducer detecting said non-leaky component of said elastic wave as a second delayed electric signal,

said signal analyzer sensing a vibration displacement caused by said first material from a difference between said first- and second delayed electric signals.

2. A vibration displacement sensing device as defined in claim 1, wherein said second material is a cellular tissue, and said first material is a blood vessel.

3. A vibration displacement sensing device as defined in claim 1 further comprising an amplifier connected between said input interdigital transducer and said second output interdigital transducer,

said amplifier amplifying said second delayed electric signal, and

said input interdigital transducer, said second output interdigital transducer and said amplifier forming a delay-line oscillator.

4. A vibration displacement sensing device as defined in claim 1 further comprising an amplifier connected between said input interdigital transducer and said first output interdigital transducer,

said amplifier amplifying said first delayed electric signal, and

said input interdigital transducer, said first output interdigital transducer and said amplifier forming a delay-line oscillator.

5. A vibration displacement sensing device as defined in claim 1, wherein said signal analyzer comprises a phase comparator, which compares an acoustic phase delay of said first delayed electric signal with that of said second delayed electric signal, and senses said vibration displacement in terms of a phase difference between said first- and second delayed electric signals.

6. A vibration displacement sensing device as defined in claim 1, wherein all said input-, said first output-, and said second output interdigital transducers have an arch-shape, respectively, and are arranged to have one concentric center.

7. A vibration displacement sensing device as defined in claim 1, wherein said piezoelectric substrate is made of a piezoelectric ceramic thin plate, the polarization axis thereof being parallel to the thickness direction thereof.

8. A vibration displacement sensing device as defined in claim 1, wherein said piezoelectric substrate is made of a piezoelectric polymer thin plate.