Wireless medical temperature sensor sets new standards for precision

8th July 2009
ES Admin
Cambridge Temperature Concepts has designed a wireless temperature sensor that can measure body temperature to within a thousandth of a degree – current solutions typically have precision of a tenth of a degree. The coin sized unit also uses innovative power saving techniques to extend the battery life to in excess of six months rather than the usual life of a few days. The sensor’s unprecedented precision and long life open up many new applications in the medical field, and the company has already used it to create a device called DuoFertility to assist women in getting pregnant.
Dr Shamus Husheer, CTC’s CEO, explained, “The various technologies that we have used to create our sensor did not exist 5-10 years ago. Companies had basically given up trying to create sensors with a high precision for consumer use. Fortunately, as a bunch of recent graduates, we didn’t know it couldn’t be done! Also, being a startup, meant we had to use ingenuity to solve problems. Custom ASICs were out so we used standard parts and hacked them to perform in novel ways. For example, the RF chips for wireless download are standard Atmel parts that we modified so that instead of pulsing data we use frequency modulation, reducing sensor current consumption.”

The sensor uses a Microchip PIC 8-bit microprocessor to process and compress the temperature readings which are taken every few seconds. Up to a month of data can be stored on the on-board 2Mbyte memory, which is downloaded via RF by a reader when required. Average sensor power consumption is less than 1uA, providing for months of continuous use off a tiny battery.

The sensor’s high degree of accuracy and long life are key to the company’s first commercial product, DuoFertility, which is designed to inform couple of the optimal time to try and conceive a baby. When an egg is released, the woman’s body temperature increases by around half a degree but this is easy masked by variations that naturally occur by walking, sitting up, etc so the recommended method is to use a thermometer to take a reading early in the morning just after waking and before getting up. This is inconvenient and has to be manually recorded, charted and then interpreted to try and determine exactly when the temperature change has occurred. Often it is not clear for a day or so by which time the best time for conception has passed. By contrast, the sensor’s temperature readings taken every few seconds are statistically processed alongside additional physiological parameters, and compared with previous readings from other women who have similar patterns to predict the optimal time for conception a few days ahead so that couples can plan for a romantic evening.

The incredibly precise temperature measurements allow calculation of skin surface heat flow, which in turn allow calculation of core body temperature. This, combined with a movement sensor, can indicate when the user is in deep sleep and when unconscious movement occurs, causing more blood to circulate and disturbing the body's thermal equilibrium. The result is data giving a dramatically improved measurement of body temperature during deep sleep, which is precisely what is required for the accurate detection of ovulation.

“We are currently in the middle of a user trial,” added Dr Husheer, “and we are getting tremendous feedback from users. They really love the prediction element as it enables them to plan ahead and relax rather than stress and worry about whether they have got the timing right from their reading of the points on a graph. It is also tremendously rewarding as the trial is with couples who have problems with having babies and are contemplating or have undergone expensive IVF treatment. We have already had couples on the trial becoming pregnant. Basically we are enabling them to have the best possible shot at getting pregnant the way nature intended.”

Cambridge Temperature Concepts is based in the Cambridge Science Park in the UK. It was founded in 2007 and its first commercial product, DuoFertility, took only 18 months from seed funding to product on the market. The company is currently investigating other medical applications for its sensors such as infection response monitoring where the ultra sensitive temperature readings can open up new treatment regimes.

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