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Case studies

Characterising vapour cells for ultra-accurate atomic clocks

NPL helped Inex Microtechnologies design and calibrate components used in the production of atomic clocks

Case study

The Need

Atomic clocks are ultra-accurate timing devices whose use is vital in applications such as telecommunications and finance, and also used for quantum measurements such as of magnetic fields, motion and laser properties, and as quantum gyroscopes. Their accuracy is derived from measuring the oscillations of atoms in gases, including metals in a gaseous state, which are contained in tiny cavities etched into solid silicon, called vapour cells. Inex Microtechnologies makes vapour cells and supplies them to manufacturers of atomic clocks and magnetometers.

Inex had a variety of measurement challenges concerning these cells. There are very tight specifications for the cells around gas composition, pressure and temperature, and Inex needed assistance to improve their quality control processes during manufacture, to ensure the cells were meeting these specifications. Inex turned to NPL for assistance with cell design, to determine the correct properties of the cells required for different applications, and assuring that the cell performance was correct.


As the design authority for vapour cells, NPL was ideally placed to assist Inex with its goals. NPL conducted detailed modelling and measurements of Inex’s vapour cells using radio-frequency spectroscopy to understand specifications of parameters including gas composition, pressure and temperature of the cell, to deliver performance that industry requires.

Through the work, Inex gained an understanding of how to use these measurement tools, and acquired technical data on measurements of cells that they could use to better understand the cells, and develop new quality control processes. The measurements also helped Inex to understand how design affected cell lifetime.


Using the project data and acquired measurement expertise, Inex were able develop a bench top cell measurement device they could use for quality control in their manufacturing line. The ability to carry out in-house quality control is likely to reduce manufacturing costs by 20% by reducing the number of rejected items.

Inex were also able to refine their design of a vapour cell by controlling the cell environment so that it had greater functionality, making it suitable for a new application in inertial sensors.

This improved capability also means customers can request custom performance parameters for their cells. Inex now have the knowledge to deliver these specifications in ways that could be repeated and with consistent quality for volume production.

As a result of the collaboration, Inex has successfully received an Innovate UK grant to further the Q-Cell work. As well as opening up other possibilities to bid for new projects with NPL and others. It is hoped this will provide funds for the development of a new saleable product.

We now have the possibility of being able to carry out functional measurements as well as just QC. We also have a much better understanding of how to design a vapour cell with multiple functionalities. The project exceeded expectations; we got all we had wanted out of it and more.

Roger Carline, acting business development, strategy and performance director - Inex

About Inex

Founded in Newcastle-upon-Tyne in 2014, Inex provides contract manufacturing and development of micro-electromechanical and semiconductor electronic devices, and also develops power and radiofrequency gallium nitride devices. Its products are used in specialised sensing equipment for sectors including space, defence, energy and electric mobility.

INEX      Saturated Abs Spectroscopy


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