Introduction
Micro-hotplates, MEMS and manufacturing
Welcome to our latest newsletter and the first in a series of articles explaining key innovations behind the company’s sensor technology platform. In this article, Professor Florin Udrea, CTO at Flusso talks about micro-hotplates and micro-wires.
Micro-hotplates and micro-wires are unusual MEMS structures where movement is a parasitic measurand. In other words, unlike MEMS-based pressure sensors, gyros and accelerometers with movable parts that rely on physical displacement, hotplate structures need to remain stable and to avoid any physical displacement or mechanical effects (such as stress).
They also don’t make use of standard semiconductor technologies because they’re typically standalone devices without any built-in intelligence. But they do rely on semiconductor substrates (mostly silicon) for mechanical support and for ease of manufacturing.
Using standard microelectronics processing to manufacture MEMS in CMOS foundries has several advantages including high quality and yield, low cost and being readily scalable for high volume production.
Micro-hotplates and micro-wires are used for a diverse range of applications including chemical sensors, infra-red emitters, thermal conductivity sensors and flow sensors. They feature a metal resistor as a micro-heater embedded in a dielectric membrane formed within a semiconductor substrate and where the resistor can have different shapes as shown above.
The heat produced by the micro-heater can be conductive through the membrane, conductive through the medium or chemical elements around or above the heater, convective or radiation-based.
Heat loss through the membrane is always undesirable so the thinner and larger the membrane the better the sensor. Bridge type structures are good at minimising those conductive heat losses but their structures are fragile. Whereas full dielectric membranes with slots or holes near the micro-heaters give a better trade-off between performance and robustness. The convective loss can be used in a calorimetric or anemometric mode to measure flow.
Micro-heaters are typically implemented in nickel or platinum. Platinum has a high and stable temperature coefficient of resistance (TCR), meaning it can be used as a micro-heater as well as a temperature sensor. But it’s expensive and not compatible with CMOS or standard microelectronic technologies. Tungsten is an excellent alternative with the advantage of being totally compatible with the CMOS process too.
Flusso was the first company to launch flow sensors using tungsten micro-wire technology, and has also developed a proprietary package using standard microelectronic-qualified materials. As a result, our flow sensor products are highly reliable, scalable and can operate in both anemometric and calorimetric modes (as shown above).
The next step for the company is to develop gas sensors on a similar micro-hotplate technology and using its proprietary differential structures for very high signal-to-noise ratio. Wait for our next announcement! It will not disappoint you.
Florin Udrea | Chief Technology Officer
Product news
FLS122 evalkit helps deliver new sensor design-ins
Flusso has secured a number of major design-ins for its FLS122 thermal air velocity as a direct result of its easy-to-use evaluation kit that was launched in October last year.
The flow sensor evaluation kit allows customers to fully assess the FLS122’s performance and capabilities within their own system. It provides air velocity, temperature and optionally pressure measurements and comprises:
- an FLS122 velocity sensing module on an extended PCB (with an optional pressure sensor);
- an extended sensor module adapter PCB; and
- a USB adaptor and I2C cable.
Further technical support documents for Flusso products are available from Flusso customer portal.
The FLS122 evaluation kit can be used to acquire air velocity readings either in continuous mode or at 60 second intervals. Pressure measurements are acquired directly from the (optional) pressure sensor or a single value can be manually inserted.
Real-time air velocity, temperature and pressure measurements are displayed on-screen (as shown above) and the parameters can be recorded and retrieved for further analysis and manipulation.
The FLS122 module within the evaluation kit is delivered with factory offsets and a calibration curve for its factory-calibrated air velocity and temperature sensors. The GUI gives the option to amend these parameters or to restore the factory default values if needed. Air flow calibration accommodates for bidirectional scenarios with a maximum positive velocity of up to 20 ms-1.
Denis Lemaire | Global Product Manager
Applications
Miniaturised flow sensors improve patient monitoring at home
There are more than 340 million people globally who suffer from chronic respiratory diseases such as asthma, COPD and cystic fibrosis.
In the US alone, 25% of all ER visits are caused by asthma attacks and in China and India asthma rates are increasing by double digit percentages annually. It’s estimated that more than 10% of the world's population aged between 30 and 79 years old is affected by COPD.
At home tracking of peak flow enables patient to know how their lungs are doing day to day and could provide advance notice to them and their doctors when more attention is needed to keep symptoms under control and avoid an emergency.
Miniaturised flow sensors make it possible to capture lung function values using a low-cost, home healthcare device. This device provides an important piece of evidence that patients can use to gain better insights on their condition and which physicians can use to drive better health outcomes.
Virgilant is a New York-based R&D team that’s been studying the application of mobile technologies to the care and management of chronic respiratory diseases for more than a decade. In the last few years, they’ve been specifically looking at the role miniaturised flow sensors such as the FLS110 could play in the remote treatment and management of these long-term conditions.
Jonathan Tarpy, founder and product lead at Virgilant said:
“We have seen some very promising initial results from implementing micro sensors into our proprietary remote monitoring devices and a patient usability study is planned for the first half of 2023. We expect to have some strong efficacy data on our remote patient monitoring platform that we will present to the FDA later this year.”
Events
Are you heading to AHR Expo 23?
If you are, then we hope you’ll come along to booth C7655 to meet the Flusso team and to see our FLS122 thermal air velocity sensor in action.
AHR Expo 23 is taking place Monday 6 to Wednesday 8 February at the George World Congress Center in Atlanta, US. It’s one of the world’s largest trade exhibitions for air conditioning, heating and refrigeration with over 20,000 visitors expected to attend this year.
At our booth we’ll be showcasing how the FLS122 can provide active air filtration and improved air quality within HVAC systems. We’ll also show how it can be integrated into a new generation of smarter, handheld flow test instruments to help more accurately pinpoint leaks and other energy inefficiencies within systems.
Amazing facts about flow
First mechanical ventilators invented in 1800s
Although the first negative-pressure ventilators to help patients breathe were developed over 200 years ago, it wasn’t until the late 1920s that the machines started to be widely used for mechanical ventilation.
The Drinker and Shaw ‘iron lung’ was developed in 1929 to treat polio patients who were unable to breathe independently because the virus had paralysed their chest muscles. The machine was powered by an electric motor with air pumps from two vacuum cleaners. The pump changed the pressure inside a rectangular, airtight metal box, pulling air in and out of the lungs.
This idea found widespread use in the treatment of polio in the first half of the 20th century, with most patients typically being treated for two to three weeks. However, it has since been replaced by modern positive-pressure ventilators. These systems use flow and pressure sensors to deliver the correct amount of air into the patient’s lungs, and they are so accurate they can dose a few hundreds of a litre for each breath of a premature baby.
While polio has been virtually eradicated thanks to the global vaccination programme, there are still some patients who rely on an iron lung to breathe. Paul Alexander is one of the last two survivors in the US: despite living inside an iron lung since 1952, he has graduated and worked as a lawyer, and written a book about his experiences.
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