Wireless for extreme environments
Continually our business counterparts in Aviation, Energy and Oil & Gas ask: how can we increase efficiency? Use less fuel? Reduce emissions? Reduce downtime and maintenance? Some of the answers to these questions lie in sensors. I work in the Device Integration lab at Global Research in Niskayuna and my research focus has been in the area of sensors for harsh environments.
Sensors are an important part of any GE system because the information they deliver can be used for advanced controls and in health monitoring and management. However, in systems such as jet engines and gas turbines, harsh environments decrease sensor options, increase sensor costs, and accelerate the probability of sensor failure. Harsh environments challenge sensor designers in electronics selection, performance, cost, reliability, and packaging. In a previous article, Vinny Tilak told you about Global Research’s innovations addressing high temperature electronics and showed you a sensor working at 300 degrees Celcius—or a temperature “hot enough to fry an egg.” However, what happens when you go to temperatures beyond that where electronics are practical? We know that leakage currents grow with temperature in any electronic technology. Therefore, what other sensor technologies are available in this regime? There are certainly areas in a gas turbine or jet engine where temperatures reach beyond 350C, yet important information can be gathered about the state of health of components or engine cycle performance, if you have a sensor that can take the heat.
As my colleague and Micro and Nano Structures Technology principal engineer, Ertugrul Berkcan, has mentioned to me many times, “sometimes you have to leave the p-n junction at home”. While the sensor options do dwindle at these temperatures, there are some interesting and growing research areas trying to address this need. One method that we have investigated is wireless. Now this isn’t wireless in the traditional notion of a sensor with active electronics radioing a signal back to a receiver. This is transmission based on inductive coupling between two coils where the sensor is part of a LC tank. Now this is a well proven method to get data transmission from a sensor but unfortunately, the sensor still requires a method to receive power. At elevated temperatures, batteries are a reliability risk and add weight and bulk to the assembly.
Recently, I was at IEEE Sensors 2010 presenting a paper representing a team composed of my colleagues David Vernooy, Faisal Ahmad, Dan Sexton, and myself. We showed feasibility of a novel sensor communication method using inductive coupling to power and read a resonant based sensor, which are some of the highest accuracy and most stable sensors today. Using a MEMS resonator such as a comb drive, we were able to demonstrate a fully wireless link where power was inductively coupled into the sensor at 1 RF frequency. Then information on the frequency of the resonator was read back at a separate RF frequency. The idea would be that the frequency of the resonator would be a function of the measurand of interest. This concept does not use p-n junctions but two separate LC tank circuits that serve as the method of receiving power and transmitting data on the state of the sensor.
The limiting temperature for such a system isn’t set by the electronics, but rather the onset of creep in silicon affecting the frequency of the resonator. This work demonstrated a read distance of 9cm which could allow a lower temperature reader to be used to interrogate the system. Certainly, there are other ways beyond this one to read and drive power into a resonant device without the use of the p-n junction. In the coming months, I hope to tell you about some of those other efforts.
Hi Aaron,
It is good to learn that GE is also developing passive wireless sensors for extreme environment. We at Acree Technologies are also developing similar wireless sensor concept, i.e. using LC tank circuit but not MEMS resonator. We have thus far demonstrated operation up to 1260C in air. Let me know if you are interested in further discussion or potential collaboration.
Thanks,
Kelvin