Pressure sensor miniaturisation: No space, no problem

In November 2017, the Food and Drug Administration approved the first digital pill for use by US doctors. The pill includes not just a drug but also an electronic sensor. The device communicates with a patch worn by the patient to track whether they are on course with their treatment regimen.

The sensor uses the combination of electrolytes in the stomach fluid and two metals embedded in the pill to send a signal to the patch when the outer shell breaks down and dissolves. The digital pill demonstrates the progress electronic sensor technology has made in miniaturisation. Other larger pills have integrated sensors such as MEMS-based cameras to take pictures of the digestive system as they descend through the body. Although they are not yet being ingested as pills, miniaturised pressure sensors are enabling other medical treatments.

Developed by Silicon Microstructures (SMI), the IntraSense pressure sensor is small enough to fit into the tiny catheters used for keyhole surgery and endoscopic investigations. Laparoscopic surgery has many advantages. The procedures require far less pain medicine than is needed for conventional surgery and the wounds are also less likely to suffer from infections. But there are challenges in performing the operations. Surgeons lose the benefit of being able to sense issues through touch. A further issue is making sure that the fluid or atmospheric pressure around the target is controlled properly.

Sometimes the surgical procedure involves applying additional pressure or suction. Without a clear feeling of the effect of that pressure, complications can arise. By being able to put a tiny sensor at the target, surgeons can gain much better information on how pressure is changing. The IntraSense device can measure ambient pressure in different body environments, from the cranial cavity to inside veins and arteries.

 In addition to medical devices such as IntraSense, SMI makes die-sized pressure sensors that can go into many other applications. Measuring a little over 1mm across, the tiny sensors make it possible to point pressure sensors into mechanical systems where size and weight are critical or where it is vital the devices do not interfere with flow. With backside-sensing versions designed for harsh environments, the sensors can go into applications where chemicals would degrade the internal electronics but where larger products would hinder the flow of fluids.

Using products such as the EB100 pressure transducer, one of the smaller sensors produced by TE Connectivity, Andretti Technologies is working hard to push the endurance of its Formula E racing cars. For these vehicles, reliability is just as important as performance. The car cannot win if it breaks down halfway through a race. The TE pressure sensors go into chambers such as the gearbox to monitor oil pressure. Dropouts in the pressure reading, particularly under high-g conditions when going round sharp bends, can indicate problems with oil levels or with temperature. The sensor can flag up those problems so race technicians can take action.

By reducing the size of pressure sensors, other applications in more benign environments are opening up. Smart watches and fitness monitors are taking advantage of tiny gel-filled pressure sensors made by TE. They use the signals to help determine altitude and so provide a much more accurate indication of location in combination with other sensors such as GPS receivers and accelerometers.

Such miniature sensors are also helping people sleep. Pressure sensors can monitor breathing to detect problems such as the apnea that interrupts restful sleep. These sensors need to be small and light so that they can be worn on a harness or sleeping clothes without introducing discomfort. It is another reason why pressure sensors are continuing to scale down and using novel packaging techniques to get there.

Are you developing a new device or application that requires pressure measurement? Read our design guide on choosing pressure sensors and explore a range of additional pressure sensor resources to help you find the right solution for your design. Alternatively, if you’re ready to take the next step, contact our team of technical specialists who are on hand to discuss your design and assist with product selection.