Optomechanical pressure measurement system and method using the vibrational modes of a membrane

Patent metadata

Field	Value
Publication number	US-11287334-B1
Application number	US-201916445583-A
Country	US
Kind code	B1
Filing date	Jun 19, 2019
Priority date	Jun 19, 2018
Publication date	Mar 29, 2022
Grant date	Mar 29, 2022

Abstract

An optomechanical pressure-measurement system measures pressure in the range of 10−6 Pa-10−2 Pa by measuring various properties of a vibrational mode of an ultra-thin membrane member. With independent measurements of the thickness and density of the membrane, in addition to the measured vibration mode properties, the system can operate as a primary pressure sensor. The membrane member is mounted on a vibration-isolated mount and is excited by a drive force. A laser beam impinges on the excited membrane, and an optical phase detector detects the amplitude of the oscillations, as well as parameters of the laser beam affected by the membrane vibration. In one embodiment, a mechanical damping is computed based on the amplitude or frequency shift (depending on the pressure range), and the pressure based on the ring-down time of the membrane vibration mode.

First claim

What is claimed is:

1. An optomechanical pressure measuring system, comprising:
a membrane member,
a vibration-isolated mounting sub-system, said membrane member being mounted in a vacuum chamber in contact with said vibration-isolated mounting sub-system,
a light source generating a light beam impinging on said membrane member,
a mechanical drive operatively coupled to said membrane member and imparting a force thereon to excite a vibration mode therein,
an optical phase detector operatively coupled to said membrane member and configured to detect at least one property of the excited vibration mode in said membrane member, said at least one property being selected from a group consisting of an amplitude of said vibration mode, a resonant frequency shift, a phase shift, and an angular deviation of the light beam reflected from or transmitted through said membrane member, a mechanical ring-down time of said vibration mode excited in said membrane member, and a combination thereof, and
a computer system operatively coupled to said optical phase detector to compute a pressure in said vacuum chamber based on said at least one property of said vibration mode excited in said membrane member, said at least one property being computed as a function of: a molecular mass of a gas in said vacuum chamber, a density of the membrane member material, a thickness of the membrane member, a temperature within the vacuum chamber, an intrinsic mechanical decay rate of the membrane member, and the Boltzmann constant.

2. The system of claim 1 , wherein said membrane member is an ultra low intrinsic damping rate membrane fabricated from a material supporting discrete vibration modes in said membrane member and transmissive or reflective of said light beam.

3. The system of claim 1 , wherein said membrane member is fabricated from at least one material selected from a group consisting of silicon nitride, silicon, gallium arsenide, silicon carbide, silicon dioxide, gold, aluminum, and a combination thereof.

4. The system of claim 1 , wherein said membrane member is fabricated from silicon nitride.

5. The system of claim 1 , wherein said membrane member is dimensioned with a thickness in a nanometer range and length and width each ranging from μm range to mm range.

6. The system of claim 1 , wherein said vibration-isolated mounting sub-system is selected from a group consisting of a phononic bandgap structure, a wire, a cantilever, a spring suspension, and a combination thereof.

7. The system of claim 1 , wherein said light source is selected from a group consisting of a single-frequency diode laser, a fiber laser, a fiber-coupled light-emitting diode, and a combination thereof.

8. The system of claim 1 , wherein said optical phase detector is selected from a group consisting of a Fabry-Pérot interferometer, Mach-Zehnder interferometer, Michelson-Morley interferometer, a spatial-mode interferometer, and a combination thereof.

9. The system of claim 1 , wherein said mechanical drive is selected from a group consisting of a piezoelectric drive, optical radiation pressure drive, photothermal drive, photoacoustic drive, electrostatic drive, magnetic drive, thermal expansion drive, and a combination thereof.

10. The system of claim 1 , wherein said computer system is further configured to compute the mechanical ring-down time of said vibration mode excited in said membrane member responsive to the application of the force from said mechanical drive to said membrane member, as a time between detection of an initial amplitude of said vibration mode and detection of an amplitude reduced to approximately 1/e of the initial amplitude, wherein e is approximately 2.718281828459046.

11. The system of claim 1 , wherein said computer system is further configured to compute the pressure in said vacuum chamber in accordance with

1

τ
rd

=

Γ

t
⁢
o
⁢
t

=

Γ
i

+

3
⁢
2

π

⁢

m
m

k
B

⁢
T

⁢

1

ρ
⁢
h

⁢
p

where τ rd is a ring-down time of said vibration mode in the membrane member, m m is the molecular mass of a gas in said vacuum chamber at pressure p, ρ is the density of the membrane member material, h is the membrane member thickness, T is the temperature, Γ i is the intrinsic mechanical decay rate of the membrane member, and k B is the Boltzmann constant.

12. The system of claim 1 , measuring the pressure in the vacuum chamber ranging between 10 −6 Pa to 10 −2 Pa.

13. A method for high vacuum pressure measurements using vibrational modes of a membrane, comprising:
(a) establishing a pressure sensor system by mounting an ultra-thin membrane member in a vacuum chamber on a vibration-isolated mounting structure, coupling a mechanical drive to said membrane member, impinging a light beam generated by a light source to said membrane member, and operatively coupling an optical phase detector with said membrane member to detect a light beam transmitted therethrough or reflected therefrom;
(b) applying a drive force by said mechanical drive to said membrane member sufficient to excite a vibration mode in said membrane member having a magnitude exceeding ambient thermal modulations of said membrane member;
(c) detecting, by said optical phase detector, at least one property of the vibration mode excited in said membrane member, said at least one property being selected from a group consisting of an amplitude of said vibration mode, a resonant frequency shift, a phase shift, and an angular deviation of the light beam transmitted through, or reflected from, said membrane member caused by said vibration mode excited in said membrane member;
(d) measuring a mechanical damping characteristic of said vibration mode based on said detected amplitude; and
(e) computing, by a computer, the pressure based on a combination of said mechanical damping characteristic, the thickness of said membrane member, a molecular mass of a gas in said vacuum chamber, a density of the membrane member material, a temperature, an intrinsic mechanical decay rate of the membrane member, and the Bolt

Assignees

• Univ Maryland
• National Institute Of Standards And Tech
• Government Of The Usa As Represented By The Secretary Of Commerce National Institute Of Standards An

Inventors

• Eckel Stephen
• Fedchak James
• Purdy Thomas
• Singh Robinjeet

Classifications

• G01L21/22 Primary

  using resonance effects of a vibrating body; Vacuum gauges of the Klumb type · CPC title

• G01L9/0017

  Optical excitation or measuring · CPC title

• G01L1/103 Primary

  optical excitation or measuring of vibrations · CPC title

• G01L1/106

  Constructional details · CPC title

• G01L27/005

  Apparatus for calibrating pressure sensors · CPC title