# US 7,021,141 B1 · Beam-type accelerometer

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- Number: US 7,021,141 B1
- Document ID: US7021141B1
- Status: Granted
- Kind: B1
- Application number: 09/423,383
- Filed: 1998-05-04
- Granted: 2006-04-04
- Earliest claimed: 1997-05-07
- Assignees: Pacesetter, Inc.
- Inventors: Kenth Nilsson; Eva Nilsson
- Web page: https://patentgrep.com/patent/US7021141B1

## CPC

- G01P 15/0922: {of the bending or flexing mode type}
- G01P 1/023: {for acceleration measuring devices}
- G01P 15/18: in two or more dimensions
- G01P: MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT (measuring or recording blood flow A61B5/02, A61B8/06; monitoring speed or deceleration of electrically-propelled vehicles B60L3/00; vehicle lighting systems adapted to indicate speed B60Q1/54; determining position or course in navigation, measuring ground distance in geodesy or surveying G01C; combined measuring devices for measuring two or more variables of movement G01C23/00; measuring velocity of sound G01H; measuring velocity of light G01J7/00; measuring direction or velocity of solid objects by reception or emission of radiowaves or other waves and based on propagation effects, e.g. Doppler effect, propagation time, direction of propagation, G01S; measuring speed of nuclear radiation G01T; measuring acceleration of gravity G01V; {measuring or recording the speed of trains B61L23/00; speed indicators incorporated in motor vehicles B60K35/00; measuring frequency or phase G01R; traffic control G08G})

## Abstract

An accelerometer has a cantilever beam supported at one end and having an opposite free end with a longitudinal direction between the supported end and the free end, the beam being formed of a piezoelectric layer and a supporting layer. An inertial, sensing mass is mounted at the free end of the beam, and is located eccentrically relative to the longitudinal direction of the beam. The accelerometer has a primary direction of sensitivity to acceleration forces, and a secondary direction of sensitivity, which is orthogonal to the primary direction and in which the sensitivity is negligible. The secondary direction forms an angle relative to the longitudinal direction of the beam such that a line coinciding with a force proceeding through the center of gravity of the inertial mass, and which is directed in the secondary direction, also intersects the beam.

## Claims

### Claim 1

An accelerometer comprising:
a cantilevered beam having a fixed end and a free end with a longitudinal direction proceeding between said fixed end and said free end;
said cantilevered beam being composed of at least one piezoelectric layer and at least one supporting layer;
an inertial mass mounted at said free end of said cantilevered beam, said inertial mass being disposed eccentrically relative to said longitudinal direction and having a center of gravity; and
said cantilevered beam and said inertial mass, in combination, having a primary direction of sensitivity to acceleration forces, and a secondary direction of sensitivity to acceleration forces which is orthogonal to said primary direction and in which sensitivity to acceleration forces is negligible, said secondary direction forming an angle α relative to said longitudinal direction so that a line coinciding with a force proceeding through said center of gravity of said inertial mass, and which is directed in said secondary direction, also intersects said cantilevered beam.

### Claim 2 (depends on 1)

An accelerometer as claimed in claim 1 wherein said center of gravity of said inertial mass is M and has coordinates XT and YT in an X-Y coordinate system, wherein said piezoelectric layer has a modulus of elasticity of E1 and a thickness t1, wherein said supporting layer has a modulus of elasticity E2 and a thickness t2, and wherein said cantilevered beam has as deformable length l, wherein Y′ represents said primary direction of sensitivity and wherein X′ represents said secondary direction of sensitivity, and wherein 0.7 F≦α≦1.2 F, wherein
F=arctan
{
E
1
2
⁢
t
1
2
⁡
(
4
⁢
t
1
2
-
6
⁢
t
1
⁢
t
2
+
3
⁢
t
2
2
)
-
E
1
⁢
E
2
⁢
t
1
⁢
t
2
⁡
[
6
⁢
Y
T
⁡
(
t
1
+
t
2
)
-
t
1
2
-
13
⁢
t
2
2
]
+
E
2
2
⁢
t
2
2
⁡
[
t
2
2
-
6
⁢
Y
T
⁡
(
t
1
+
t
2
)
]
3
⁢
E
2
⁢
t
2
⁡
(
E
1
⁢
t
1
+
E
2
⁢
t
2
)
⁢
(
2
⁢
X
T
-
l
)
⁢
(
t
1
+
t
2
)
}
.

### Claim 3 (depends on 1)

An accelerometer as claimed in claim 1 wherein 5°≦α≦30°.

### Claim 4 (depends on 1)

An accelerometer as claimed in claim 1 wherein 10°≦α≦16°.

### Claim 5 (depends on 1)

An accelerometer as claimed in claim 1 wherein 13.5°≦α≦14.5°.

### Claim 6 (depends on 1)

An accelerometer as claimed in claim 1 wherein α=14°.

### Claim 7 (depends on 1)

An accelerometer as claimed in claim 1 wherein said piezoelectric layer has a modulus of elasticity and a thickness and wherein said supporting layer has a modulus of elasticity and a thickness, and wherein a ratio of the thickness of said piezoelectric layer relative to the thickness of said supporting layer is in a range between 2 and 4 and wherein a ratio of the modulus of elasticity of said supporting layer relative to the modulus of elasticity of said piezoelectric layer is in a range between 8 and 12.

### Claim 8 (depends on 7)

An accelerometer as claimed in claim 7 wherein said ratio of said thickness of said piezoelectric layer relative to said thickness of said supporting layer is 3.

### Claim 9 (depends on 7)

An accelerometer as claimed in claim 7 wherein said ratio of said modulus of elasticity of said supporting layer relative to said modulus of elasticity of said piezoelectric layer is 10.

### Claim 10 (depends on 1)

An accelerometer as claimed in claim 1 wherein said supporting layer has a modulus of elasticity ≧400 GPa.

### Claim 11 (depends on 1)

An accelerometer as claimed in claim 1 wherein said supporting layer has a modulus of elasticity which is ≧500 GPa.

### Claim 12 (depends on 1)

An accelerometer as claimed in claim 1 wherein said supporting layer is comprised of electrically conducting material.

### Claim 13 (depends on 1)

An accelerometer as claimed in claim 1 wherein said supporting layer is comprised of tungsten carbide.

### Claim 14 (depends on 1)

An accelerometer as claimed in claim 1 wherein said supporting layer is comprised of binderless tungsten carbide.

### Claim 15 (depends on 1)

An accelerometer as claimed in claim 1 wherein said supporting layer and said inertial mass are integrally formed of the same material.

### Claim 16 (depends on 1)

An accelerometer as claimed in claim 1 wherein said piezoelectric layer is comprised of PZT.