Sensor Systems

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We make sensor systems for our clients that gather relevant information about the world around them, ensuring that the information is timely, unambiguous, accurate and easy to interpret.

We have engineered systems to measure a great range of different parameters, from radar sensors that provide spatial information about the world, through to contact sensors that detect electrical signals on the human body or buried sensors that detect the presence of a parked car. These often require a carefully crafted combination of sensor physics, analogue signal manipulation and digital signal processing.

Glenn Wilkinson

Senior Consultant, Sensor Systems

“A sensor is the means by which some aspect of the physical world can be rendered into useful information. Practical sensors typically operate in realms beyond the reach of human senses, providing information that is key to functions from industrial control and monitoring systems, through healthcare, to remote sensing of human activity for security applications. At times, working with systems that allow us to perceive unfamiliar aspects of the world around us in new ways can provide insights which seem almost magical”

Glenn wilkinson headshot

A few of the skills we employ

  • Radar – mm-wave, SAR, FMCW, high-resolution, Doppler, e-scan, low SWaP, micro radar, imaging, harmonic radar
  • Biomedical sensors – ECG, blood pressure, ABR, ECOGH, EEG, respiratory, nerve signals, heart rate, driven right leg
  • Inertial sensors – accelerometers, gyroscopes, pedestrian dead-reckoning, gps-denied
  • Environmental sensors – Magnetometers, barometers, temperature, humidity, gas
  • Wireless monitoring – sensor integration into COTS or custom communications infrastructure
  • RF Spectroscopy – materials analysis and identification, reflectometry
  • Integrated sensor systems – low power data acquisition, processing, communications, user interface
  • System simulation and modelling, fusion algorithms
  • Analog signal conditioning and digitisation – low noise, high-bandwidth, high CMRR, high dynamic range, wide-bandwidth
  • Approvals – CE, FCC, EMC, Medical (EN60601)
Smart Sensors, manhole cover

Tinnitus Detection System

tinnitus sensor clean

We live in a world where there is noise all around us, from loud equipment in the workplace, to loved but powerful music at concerts. Whether enjoyable or not this constant noise is leading to an ever growing number of people with tinnitus; a condition where a person will hear an array of phantom noises; buzzing, humming, whistling etc. For some, these phantom sounds are barely noticeable, but for others they can be seriously debilitating with a significant and prolonged impact on peoples’ lives.

The challenge then was to develop a method to help detect and diagnose tinnitus from an early stage. Currently, most patients are only diagnosed after the symptoms have become well developed, by which stage little can be done to mitigate the condition. One way of detecting the initial stages of tinnitus is by studying the AEP (Audio Evoked Potentials) that are produced in the cochlear nerve when an audio stimulus is provided to the ear.

At the moment, this is done by a clinician placing a needle into the ear canal to measure the resulting AEP in a controlled environment. Our goal was to measure the AEPs in a non-invasive way in a normal (i.e. non-clinical) environment. Measuring these signals through electrode contact with the skin is very difficult because the AEP waveforms are of the order of 1µV; whereas, other detectable signals nearby (for example those generated by muscles) are around a 1000 times larger. Ambient electrical noise present in the environment (generated by computers, power systems, etc.) is also a significant obstacle.

A whole range of strategies were employed in order to enable the tiny AEP signals to be measured on the surface of the skin. These included custom electrode design, optimised analogue signal processing and advanced digital processing methods. The system was then measured on multiple subjects against a reference system in order to provide confidence in the results gained.

By combining standard headphones, adapted to carry our electrode design with analogue electronics and processing software, Plextek was able to demonstrate an innovative method for detecting the onset of tinnitus. The final system allows quick testing to gain results in a non-clinical environment and in that way improve the health of our ears.

Micro Radar Sensor

Flooded City Street sensor

Our major strength is the ability to bring together specialist expertise across many disciplines to engineer something very special. Plextek’s current micro-radar project is an excellent example of this. The project was funded through Autonomous Systems Underpinning Research (ASUR), with the aim of investigating how radar might be applied to the problem of collision avoidance in small-sized UAVs. In just a few months, our engineers have taken the initial concept through detailed system performance and design calculations, to an integrated, highly manufacturable single-board radar sensor head, suitable for use in airborne trials.

Given the application, it was apparent from the outset that size, weight and power would all need to be ruthlessly minimised. In order to facilitate navigation through closely spaced obstacles, the sensor must achieve high angular resolution – to only a few degrees. To achieve this from an antenna only centimetres across dictated the use of millimetre-wave frequencies. Initial systems engineering calculations concentrated on selecting a waveform that would maximise the detection performance achievable with only milliwatts of transmitted power, aiming for compatibility with an emerging generation of highly integrated commercial millimetre-wave ICs.

Having identified candidate active devices, the next problem to solve was that of the antenna. Although radar antenna gain requirements may be similar to those of demanding communications applications, radar applications typically also mandate that very narrow beamwidths and ultra-low sidelobe levels are achieved across very wide bandwidths. In this particular case, size and weight must also be kept to a minimum. Plextek’s antenna engineers evolved a novel printed design, which was verified and refined using advanced EM simulation software tools.

Through the creative use of state-of-the-art PCB design and manufacturing techniques, it proved possible to integrate the transceiver circuitry and antenna onto the same PCB, not only minimising size and weight, but also eliminating the need for bulky waveguide or lossy coaxial cable interconnects. 3D printing was employed to realise supporting mechanical components. Throughout the design process, input from Plextek’s manufacturing engineers ensured that this advanced design would be readily manufacturable.

Plextek’s signal processing expertise was brought to bear in providing real-time display of the sensor output, along with raw data logging to facilitate refinement of detection algorithms off-line. Code has been designed to be compatible with a variety of platforms, with a view to enabling the efficient use of pre-existing processing resource, if required.

Trials of the complete radar have demonstrated the ability to detect relevant obstacles at up to 100 metres with an update rate of several Hertz, in a lightweight low-SWaP package. The successful outcome of the micro radar development highlights the benefits of bringing together systems design, millimetre-wave engineering, antenna design and EM simulation, mechanical design and digital signal processing skills in the realisation of a uniquely capable low-SWaP sensor. Future work will concentrate on further development of algorithms for UAV collision avoidance as well as for ground vehicle and static applications, and also the analysis of target micro-Doppler.

Demonstrations have strayed beyond the originally intended application, with one particular favourite being a real-time, high update rate display of a game of catch with a golf ball!

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