Object characteristics measurement apparatus

1. An object characteristics measurement apparatus, comprising a surface acoustic wave device,

the surface acoustic wave device comprising:

an interdigitated electrode that is formed on a first surface on a piezoelectric substrate for exciting an elastic wave and for receiving at least one reflection based on the elastic wave;

a reflector that has a third surface and a fourth surface between the interdigitated electrode and a second surface orthogonal to the first surface of the piezoelectric substrate in a propagation direction of the elastic wave, the third surface being formed at a position different from that of the first surface in a normal direction of the first surface, the fourth surface connecting an end of the first surface, which is formed perpendicular to the normal direction of the first surface, to the third surface;

a reaction field that is formed between the interdigitated electrode and the reflector, in which a measured object is to be loaded; and

a propagator that is formed between the reflector and the second surface, wherein

a surface acoustic wave is separated and extracted from a bulk wave, and characteristics of the measured object are determined based on the extracted surface acoustic wave, the surface acoustic wave propagating along the reaction field from the interdigitated electrode, the surface acoustic wave being reflected by the fourth surface of the reflector, the surface acoustic wave propagating along a surface of the piezoelectric substrate which is included in the elastic wave that is received by the interdigitated electrode, the bulk wave being reflected by the second surface of the piezoelectric substrate, the bulk wave propagating through an inside of the piezoelectric substrate which is included in the elastic wave that is received by the interdigitated electrode.

2. The object characteristics measurement apparatus according to claim 1 , wherein

the reflector has a wall, and a height d of the wall thereof in a direction from the surface of the piezoelectric substrate toward the inside of the piezoelectric substrate is a value satisfying a relationship represented by the following formula.

λ/2 ≦d≦H/ 2

λ: Wavelength of the elastic wave

H: Thickness of the piezoelectric substrate.

3. The object characteristics measurement apparatus according to claim 1 , wherein

the interdigitated electrode includes a plurality of electrode fingers which is N pairs of electrode fingers (N is an integer greater than or equal to 1), and

a length L 2 from the fourth surface of the reflector to the end of the piezoelectric substrate is a value satisfying a relationship represented by the following formula.

L 2 ≧N×λ/ 2

λ: Wavelength of the elastic wave

N: Number of a plurality of pairs of electrode fingers constituting the interdigitated Electrode.

4. The object characteristics measurement apparatus according to claim 1 , wherein

the reflector has the third surface, and the third surface is parallel to the first surface of the piezoelectric substrate.

5. The object characteristics measurement apparatus according to claim 1 , wherein

the reflector has the third surface, and at least one portion of the third surface is a curved surface.

6. The object characteristics measurement apparatus according to claim 1 , wherein

the reflector has the third surface, and at least one portion of the third surface is an inclined face that is inclined with respect to a normal direction of the first surface of the piezoelectric substrate at a predetermined angle.

7. The object characteristics measurement apparatus according to claim 1 , wherein

a resin fills the reflector without protruding above the first surface of the piezoelectric substrate.

8. The object characteristics measurement apparatus according to claim 1 , wherein

a plurality of interdigitated electrodes are formed on the piezoelectric substrate in a direction perpendicular to the propagation direction of the elastic wave, and

a plurality of reaction fields, which correspond to the respective interdigitated electrodes are formed between the interdigitated electrodes and the third surface of the reflector.