Microwave needle dielectric sensors

A needle-like microwave reflection resonator sensor for measuring or monitoring the dielectric properties of materials, comprising:

• a coaxial cable having a metal shield and center conductor;
• an electrically short circumferential gap in the metal shield of the coaxial cable, the center conductor of the coaxial cable extending immediately beyond the gap, and then shorted to the cable shield, the gap defining a transverse input plane;
• an electrically thin dielectric substrate sheath covering the cable shield;
• one or more thin conductive dipole resonators having different resonant frequencies, placed on the substrate sheath and positioned near the gap to facilitate inductive coupling between the gap and all of the resonators simultaneously so that the impedance matching factor r.sub.o of the cable at the transverse input plane lies in the range 0.5<r.sub.o <2.0 at the resonant frequency of one or more resonators when the sensor is exposed to the material being measured or monitored.

A microwave reflection resonator sensor for measuring or monitoring the complex dielectric properties of materials, comprising:

• a coaxial cable having a metal shield and a center conductor;
• an electrically short circumferential gap in the metal shield of the coaxial cable, the gap defining a transverse input plane;
• an electrically thin dielectric substrate sheath covering the cable shield;
• a thin conductive resonator placed on the substrate sheath near the gap to facilitate inductive coupling between the resonator and the gap;
• an electrical feed means for coupling microwave power to and reflected from the gap, said feed means operating with an impedance matching factor r.sub.o of the cable at the transverse input plane in the range 0.5<r.sub.o <2.0 at the resonant frequency of the resonator when the sensor is exposed to a material being measured or monitored.

A method for in vivo or in vitro sensing the complex dielectric properties of lossy dielectric materials, comprising:

• forming an electrically short circumferential gap in the shield of a coaxial cable, the gap defining a transverse input plane;
• extending the cable center conductor immediately beyond the gap and then shorting the center conductor to the cable shield;
• enclosing the gap and the cable with a thin dielectric substrate sheath;
• placing a thin conductive resonator on the dielectric sheath;
• positioning the resonator near the gap to facilitate inductive coupling between the gap and the resonator such that the impedance matching factor r.sub.o of the cable at the transverse input plane lies in the range 0.5<r.sub.o <2.0 at the resonant frequency of the resonator when the sensor is exposed to the material being measured or monitored;
• exposing the sensor to a dielectric material being measured or monitored;
• detecting a wave reflected from the transverse input plane;
• measuring the resonant frequency and impedance matching factor of the sensor at the resonant frequency.