“…A variety of alterative, non-invasive approaches have been investigated in the past 40 years, such as infrared spectroscopy (including absorption and Raman spectroscopy), bioimpedance spectroscopy, and radio wave sensing [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ]. It is well known that any such non-invasive technique must overcome significant challenges to obtain clinical sensing accuracy, such as the weak signature of the glucose molecule compared to other tissue components and water, the signal interference from other substances, and the effects of environmental factors such as ambient temperature and skin moisture.…”