Inductive sensing with left-handed antenna for biomedical applications

-May 15, 2014


Presenting one of the runners-up in the TI LDC1000 inductive sensor design contest.

A left-handed (LH) antenna based biosensor is developed to investigate the near-field electromagnetic interaction between antenna and sample with different dielectric properties. These dielectric properties can be determined by analyzing the electromagnetic coupling between the antenna and the test samples without labeling or chemical reaction. It has the advantages of real-time detection, small feature size, reduced sample volume, and minor environmental disturbance. Such an antenna sensor can be effectively used to measure both liquid and solid biological samples.

We propose to use this new inductive to digital sensor (LDC1000) to further enhance the performance by using the measured signal for precise distance and volume control in the sample chamber, and to integrate the antenna-LDC1000 unit into a handheld device. We will be able to demonstrate its potential uses in water contents of biological tissues, biomarkers of in-vitro diagnostics, and content differences in food industry.

The antenna biosensor’s LH capacitance (CL) is attributed to the interdigital capacitors coupling between the patch, and LH inductance (LL) is due to the shorted-stub inductances to ground. The LH effects are due to the capacitive (CR) coupling between the patch and ground plane, and the current flow atop the patch. The proposed antenna-based biosensor is made on FR4 PCB substrate. All simulations in this work were carried out using Ansoft HFSS 12.0. The measurement instrument was an RF network analyzer, Agilent E5071B. The different concentrations of ethanol solution ranged from 3% to 100%, and the values of equivalent permittivity are 79 to 14. Currently, the measurement done by using a network analyzer has hindered its practical clinical and home sensing applications.

Our preliminary results from the LDC1000 indicates the feasibility of such a coupling sensing mechanism. As shown in the uploaded video, the readings from water samples on the coil antenna do have significant changes compared to a control experiment. However, our fabricated left-handed antenna exhibits a characteristic resonance frequency near 1GHz, which is significantly higher than the LDC nominal specifications. We are currently trying to redesign a new antenna for further exploration.

Sensing Design Challenge 2013 winners:

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