Aerospace Testing InternationalAerospace Testing International
  • News
    • A-E
      • Acoustic & Vibration
      • Avionics
      • Data Acquisition
      • Defense
      • Drones & Air Taxis
      • Electric & Hybrid
      • EMC
      • Engine Testing
      • Environmental Testing
    • F-L
      • Fatigue Testing
      • Flight Testing
      • Helicopters & Rotorcraft
      • High Speed Imaging
      • Industry News
    • M-S
      • Materials Testing
      • NDT
      • Simulation & Training
      • Software
      • Space
      • Structural Testing
      • Supplier News
    • T-Z
      • Technology
      • Telemetry & Communications
      • Weapons Testing
      • Wind Tunnels
  • Features
  • Magazines
    • March 2025
    • Dec 2024/Jan 2025
    • Showcase 2025
    • September 2024
    • June 2024
    • Archive Issues
    • Subscribe Free!
  • Opinion
  • Webinars
  • Events
    • All Events
    • Aerospace Test & Development Show
  • Podcasts
  • Videos
  • Suppliers
    • Supplier Spotlights
    • Press Releases
    • Technical Papers
  • Jobs
    • Browse Jobs
    • Post a Job – It’s FREE!
    • Manage Jobs (Employers)
LinkedIn YouTube X (Twitter)
LinkedIn YouTube X (Twitter)
Subscribe to magazine Subscribe to email newsletter Media Pack
Aerospace Testing InternationalAerospace Testing International
  • News
      • Acoustic & Vibration
      • Avionics
      • Data Acquisition
      • Defense
      • Drones & Air Taxis
      • Electric & Hybrid
      • EMC
      • Engine Testing
      • Environmental Testing
      • Fatigue Testing
      • Flight Testing
      • Helicopters & Rotorcraft
      • High Speed Imaging
      • Industry News
      • Materials Testing
      • NDT
      • Simulation & Training
      • Software
      • Space
      • Structural Testing
      • Supplier News
      • Technology
      • Telemetry & Communications
      • Weapons Testing
      • Wind Tunnels
  • Features
  • Magazines
    1. March 2025
    2. Dec 2024/Jan 2025
    3. Showcase 2025
    4. September 2024
    5. June 2024
    6. March 2024
    7. Archive Issues
    8. Subscribe Free!
    Featured
    19th March 2025

    In this issue: March 2025

    Online Magazines By Ben Sampson
    Recent

    In this issue: March 2025

    19th March 2025
    contents and front cover of magazine

    In this issue: December / January 2025

    19th December 2024
    Showcase 2025

    In this issue – Showcase 2025

    6th November 2024
  • Opinion
  • Webinars
  • Events
    • All Events
    • Aerospace Test & Development Show
  • Podcasts
  • Videos
  • Suppliers
    • Supplier Spotlights
    • Press Releases
    • Technical Papers
  • Jobs
    • Browse Jobs
    • Post a Job – It’s FREE!
    • Manage Jobs (Employers)
LinkedIn YouTube X (Twitter)
Aerospace Testing InternationalAerospace Testing International
Features Materials Testing

Masterclass: How measuring microvibrations makes clearer Earth observation possible

Ben SampsonBy Ben Sampson19th June 20186 Mins Read
Share LinkedIn Twitter Facebook Email
Google image map of London
Clearer satellite imagery is made possible by attenuating micro vibrations in satellites (Image: Google)

In recent years, there have been major advances in terrestrial observation – accompanied by a dramatic increase in the need to measure Earth’s surface and atmosphere with greater precision. Cameras on the latest Earth observation satellites, such as WorldView 3, feature resolution of up to 0.5m. They are used for the images on Google Earth that are familiar to us all.

The quality of these pictures would have been unimaginable only a few years ago. A critical step in achieving these images has been the reduction of microvibrations on satellites.

Every satellite requires numerous drives, position controls, actuators and cryocoolers. These devices consist of mechanical components that cause vibrations when they operate. With increased camera resolution, these vibrations cause blurring of the images or ‘jitter’.

There are basically two paths to a solution – engineers either have to reduce microvibrations at source, or attenuate the microvibrations. Either way requires the measurement of microvibrations, which is done with the help of piezoelectric dynamometers.

 

Piezoelectric dynamometers

Microvibrations consist of extremely small accelerations of very low intensity. Measuring them is a challenging task, and methods for doing so have only become known in the last few years.

Piezoelectric force sensors and dynamometers are suited to this purpose and are in widespread use for measuring microvibrations. The very high resolutions achievable in these devices are advantageous because it becomes possible to measure dynamic force changes down to 0.01N, even if the object being measured weighs more than 10kg. The static weight can also be ‘eliminated’ by resetting the charge amplifier. Another factor is their high rigidity. This permits very high natural frequencies of 1,000Hz or more.

The dynamometer is mounted on a vibration-insulated table to ward off any structure-borne sound and external vibrations. External influences of this sort can distort measurements severely because the dynamometer, together with the mass of the object being measured, constitutes a large acceleration sensor. With correct setup, the interference signal is in the range of less than 0.01N and 0.003Nm (RMS; 3-350Hz).

The measurable frequency range is typically 1-350Hz. The lower limit is defined by the natural frequency of the vibration-insulated stone table. The upper limit is determined by the natural frequency of the dynamometer with the mass of the object being measured.

Correct mounting of the measured object and the dynamometer is critical for a good measurement result. It is important that the dynamometer as well as the measured object are mounted with plenty of bolts so as to ensure a clean mechanical coupling.

Sound and EMI (electro-magnetic interference) should also be avoided in or near the measurement setup. The dynamometer is connected to the charge amplifier with a special high-insulation cable. Data recording is handled by a laptop and an analog-to-digital convertor.

A waterfall chart is used to visualize the measured data, so targeted elimination of the causes of disruptive vibrations is possible.

 

Restriction on upper cut-off frequency

The maximum measurable frequency for microvibrations is currently about 350Hz. There has recently been increasing demand for the higher cut-off frequencies needed to measure larger objects.

Modern dynamometers consist of four three-component force sensors with a base plate and top plate, each made of steel. The dynamometer behaves like a second-order spring/mass system with a dominant natural frequency. Measurements must be taken well below the natural frequency.

Additional mass lowers the natural frequency, so a heavy object to be measured can have a major influence if the dynamometer is small. The dynamometer’s size also has a considerable effect on the natural frequency. The larger the dynamometer, the heavier the top plate will be – thereby reducing the natural frequency. This effect cannot be entirely compensated by using more rigid sensors.

There is also a trend emerging toward measuring higher frequencies, which makes it possible to reduce microvibrations even further.

Another trend is for larger dynamometers. The testing of complete subsystems and small satellites require larger dynamometers. However, the maximum size of dynamometers had been reached with existing materials. Further enlargements were only possible with a large investment in R&D.

 

 

Dynamometer

 

 

Dynamometers with ceramic top plates

As shown above, the dynamometer’s size has a critical impact on natural frequency. The heavy weight of the top plate is especially unfavorable in this regard. A search for new materials for the top plate at Kistler revealed that ceramics offer highly advantageous properties for dynamometers, including a low specific gravity and a high modulus of elasticity. Low tensile strength and low thermal expansion were found to be the drawbacks of ceramics.

Finite element modeling (FEM) calculations showed that the natural frequency is increased by 40% with the same sized dynamometer, enabling significant improvements to be achieved when measuring microvibrations. The lower strength can be accepted because the forces and loads in microvibration measurement are very small. To allow correct mounting of the dynamometer, the steel base plate was retained.

Low thermal expansion proved to be a problem. Despite the FEM calculation, full validation of this behavior was not possible. An extended investigation with experimental specimens was needed to show that the difference in thermal expansion between the steel base plate made of steel and the Al2O3 top plate does not lead to fractures, thanks to the special structural design.

By using ceramic instead of steel for the top plate, it has been possible to manufacture a dynamometer specifically for measuring microvibrations. Thanks to significantly increased rigidity and a lower weight for the top plate, natural frequency could be increased by 40%. This allows microvibration measurements at higher frequencies. In parallel, the size of the dynamometer could be increased to accept complete subsystems or small satellites.

 

Sentinel 4 satellite

Testing of the optical calibration system of the Sentinel 4 satellite

 

A great example of the use of a piezoelectric dynamometer in a testing application is the recent development of the Sentinel 4 (Ultraviolet Visible Near-infrared) UVN satellite at the Centre Spatial de Liège (CSL) in Belgium.

The Sentinel 4 satellite, which is part of the EU’s Copernicus program, will provide information on the atmosphere by monitoring air quality, stratospheric ozone, solar radiation, and the climate.

Engineers at CSL required a dynamometer with a natural frequency of less than 1,500Hz to characterize the optical calibration system for of the Sentinel 4. They selected Dynamometer type Z21492 with a ceramic top plate because of its large dimensions and high natural frequency. The dynamometer is set up on an insulated stone table and in a sound-insulated area.

The next step will be validation measurements with subassem- blies for Sentinel -4 satellite. After completion of validation, the CSL will be able to offer the space community a superior test facility for characterization of microvibration measurements down to a noise floor of 0.01mN (narrow band noise ΔF=1Hz).

 

Written by Marine Dumont, business development manager, Kistler Instruments

Share. Twitter LinkedIn Facebook Email
Previous ArticleA330neo starts function and reliability tests
Next Article Updated real-time test data system saves time and costs at Arnold lab
Ben Sampson

Ben has worked as a journalist and editor, covering technology, engineering and industry for the last 20 years. Initially writing about subjects from nuclear submarines to autonomous cars to future design and manufacturing technologies, he was editor of a leading UK-based engineering magazine before becoming editor of Aerospace Testing in 2017.

Related Posts

Features

NDT: Robotics and software spur innovation

21st May 20258 Mins Read
Features

How new computing advances have reignited alternative rocket engine design

14th May 20258 Mins Read
Materials Testing

Glasgow NextSpace facility to test 3D printed space materials

14th May 20253 Mins Read
Latest Posts

AIR cargo eVTOL completes night flight testing

22nd May 2025

Astrolight raises €2.8m to build optical space communications network

22nd May 2025

Industry Adoption of 3D Optical Surface Gauges

21st May 2025
Supplier Spotlights
Our Social Channels
  • Twitter
  • YouTube
  • LinkedIn
Getting in Touch
  • Subscribe To Magazine
  • Contact Us
  • Meet the Team
  • Media Pack
Related Topics
  • Aircraft Interiors
  • Business Jet Interiors
FREE WEEKLY NEWS EMAIL!

Get the 'best of the week' from this website direct to your inbox every Wednesday

© 2023 Mark Allen Group Ltd | All Rights Reserved
  • Cookie Policy
  • Privacy Policy
  • Terms & Conditions

Type above and press Enter to search. Press Esc to cancel.