Objective: Currently, capturing and quantifying subjective health relevant data, such as pain, pain-profiles, well-being, etc., is routinely done by visual analog scales, i.e., the patient rates by associating the considered parameter with a numerical value, e.g., between 0 and 10. In most cases this is still done, on a paper-pencil basis, requiring wasteful (manual) post-processing and at the same time being susceptible to errors. In order to overcome these problems, an analog scale integrated into a smart NFC transponder has been developed.

Methods: The developed NFC analog scale (Austrian patent application A504/2010, PCT application pending) can be realized with dimensions of typically 2.5 cm (width) x 12 cm (length) and less than 0.3 mm thickness. It consists of the following elements: a 13.56 MHz resonant coil antenna and an ISO 14443 transponder chip, extended by an electronic circuit for A/D conversion of two analog voltages Us (sensor voltage) and Uc (compensation voltage) provided by two corresponding coils, also realized in the smart transponder. The sensor coil is distributed along the longer axis of the transponder in a special way in order to provide the voltage Us induced by an external reader device (mobile phone with NFC interface and corresponding software application) and at the same time Us being a measure for the position of the reader device along the longer axis of the transponder. The reference coil runs along the outer boundaries of the sensor coil and produces the voltage Uc, required to compensate for the reader device's magnetic field strength variations. From the voltages Us and Uc the position of the reader device in relation to the longer axis of the transponder can be determined and via the ISO 14443 transponder chip the position can be wirelessly transmitted to the reader device. The whole system can be realized purely passive, i.e., all the electronic circuits inside the NFC analog scale can be powered solely by the reader device's magnetic field and no additional power supply is required.

Results/Conclusion: The NFC analog scale described above enables an easy-to-use, comfortable and robust way for capturing and quantifying subjective health relevant parameters, such as pain, pain-profiles, well-being, etc. Equipped with such a device, a patient needs not more than a mobile phone with NFC interface and corresponding software application, to be able to rate the considered health parameter anywhere, at any time, by just placing the mobile phone at the corresponding position above the NFC analog scale. Real time feedback about the current position on the mobile phone's display ensures accurate data capturing and the acquired data can easily be forwarded wirelessly to a telemonitoring, therapy or compliance management centre. Especially for home-monitoring of patients with chronic pain, this passive NFC analog scale could be a big improvement for monitoring the efficacy of different therapy methods and medications.