Wireless Miniature Piezoelectric Accelerometers – The Holy Grail?
DJB Instruments UK Ltd have been on a journey…there’s an underused phrase these days!!.... along with their development partners at Loughborough University, DJB have been working on the holy grail of customer desires, a miniaturized wireless piezoelectric accelerometer.
Over the last few years RF wireless connections have come a long way and have replaced physical wiring in many industrial applications. These include engine testing, landing gear in-flight or test status monitoring all of which require continuous acquisition of system parameters, collection and transmission of data for further analysis. Such industrial applications often require sensors to be installed at remote, difficult to access or hostile locations and clearly, in such cases, cabling can be impractical. Wireless sensors offer many benefits for simplified installation and avoid the need for long cables which can cause signal degradation and noise.
Although wireless sensors would seem to have many benefits there are challenges to be considered due to data bandwidth, power and whilst wireless communication for static and quasi-static sensing is relatively simple, it is far less straight forward for dynamic signal measurement.
Making an informed choice about the wireless communication standard requires a comprehensive understanding of the technology and the application. There is no ‘ideal’ wireless sensor that could be used for all plausible applications. Development of any wireless sensor requires an in-depth understanding of the environment, usage and expectations from the device.
The need for wireless accelerometers has been identified in many industries and manufacturers have begun to respond to customer demands for such a dynamic wireless device. These wireless accelerometers predominantly use MEMS (Microelectromechanical Systems) for sensing. They are often designed with the intention of allowing a number of devices to be networked together, each operating as a node. Each of these nodes consist of processor, memory and radio. The manufacturers have devised a complete sensor network system which includes gateway and a software program with simple user interface.
However, all the wireless MEMS accelerometers suffer from similar disadvantages related to MEMS technology; these include low measurement range, low sensitivity, susceptibility to noise and limited frequency bandwidth. In addition, many of them are large and heavy making them unsuitable for test and measurement applications.
DJB Instruments UK Ltd is focused in the manufacture of test and measurement accelerometers and is already a world leader in miniaturisation and high temperature devices. It has dedicated itself to developing Piezoelectric wireless accelerometers. The target product will be miniature in size (using proven DJB technology) with high sensitivity and measurement range and enabled with Bluetooth Low Energy for wireless transmission.
The proposed accelerometer, which uses DJB’s unique Konic shear piezoelectric ceramic design, will have a measurement range of up to 5000g and can measure a signal with frequency content from 0.5 to 8000Hz. High speed sampling will be provided giving the user a much higher usable bandwidth when compared to MEMS devices whilst on board storage of 2MB provides excellent data storage prior to transmission.
The signals will be transmitted in packets by the RF transmitter to minimise the risk of data loss. The radio will be a Bluetooth low energy module which has high speed data transfer, very low power consumption and extremely robust connection.
The wireless sensor will be easy to use for the operator with functions for initiating and terminating the transfer, connectivity check and basic diagnosis on board, in addition to an alarm system for any connection loss.
Power consumption is a critical challenge while using wireless sensors. The wireless accelerometer could be installed at remote locations where the battery may be expected to work for months. In such cases, power management is an important issue to be dealt with. Power consumption is at its highest while transmitting data, so management of wireless communication is essential to extend battery life.
The DJB solution is an event-driven product that transfers data only when requested by the user, otherwise it stays in a low power mode. Power consumption is significantly reduced in such systems.
Bandwidth is also an important decision factor. Wireless communications must share bandwidth in the radio spectrum. There are many competing wireless standards that are candidates for such a device. To make intelligent use of the bandwidth available, and to account for the possibility that the radio channel may not be available continuously, a strategy must be adopted for the selective transfer of information; which requires a detailed understanding of the application.
Many other limitations and challenges are being dealt with by researchers across the globe and techniques such as energy harvesting are being explored to make the wireless sensors more efficient and usable.
DJB’s journey down the wireless accelerometer road has only just begun but the significant benefits and potential are already very clear. The options for packaging wireless communication alongside DJB’s existing range of microminiature accelerometers offers significant advances for testing in fields such as human vibration, sports science, medicine and many others.