It has been found advantageous to deploy coiled antennas as transmitters and receivers for acquiring the dielectric spectrum of materials. This method of impendence spectroscopy has been used to determine the concentration of glucose and other small polar molecules in vitro, as well as in vivo by placement on the antennas so that transmission is through the tissue, as for example on opposite sides of an organ or body part. The optimum selection of antenna coils permits deeper penetration into tissue for glucose detection, improves the SNR as well as expands the spectral range for greater accuracy and precision, to enable continuous non-invasive monitoring for either improved patient or automated management of diabetes.