US 11,287,334 B1Granted

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

AssigneesUniversity of Maryland, College Park, Government of the USA, as represented by the Secretary of Commerce, National Institute of Standards and Technology

InventorsStephen Eckel, James Fedchak, Thomas Purdy, Robinjeet Singh

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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.

Claims20

Dependent claims

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.

4 more elements

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 Boltzmann constant.

3 more elements

Dependencies are inferred from the claim text.

Facts

Application: 16/445,583Filed 19 Jun 2019 · us provisional application
Priority: 19 Jun 2018
Granted: 29 Mar 2022
Term ends: Not estimatedThe source records don’t support an estimate.

Classification6 codes

G01L 1/103
By measuring variations of frequency of stressed vibrating elements, e.g. of stressed strings: optical excitation or measuring of vibrations
G01L 21/22
By measuring variation of frictional resistance of gases: using resonance effects of a vibrating body; Vacuum gauges of the Klumb type
G01L 1/106
By measuring variations of frequency of stressed vibrating elements, e.g. of stressed strings: constructional details
G01L 9/0017
Of a diaphragm: optical excitation or measuring