Electrical Near-Field Imager with Sub-Cellular Resolution at Millimeter-wave Frequencies

Ali Niknejad

Rapid characterization and analysis of biological specimen is increasingly important in medical diagnosis for point-of-care health monitoring as well as biological research and clinical studies. Several bio-detection methods have been developed including optical, chemical, electrical, magnetic, and mass. However, most require cell labeling with specific chemicals or molecules that can alter cell properties, change their physiological states, and even damage the cells. Though such labeling enhances the SNR, complicated and time-consuming sample preparation procedures increase not only costs but also the hazards caused by contamination. Therefore, a direct, real-time, label-free, non-destructive, non-invasive, and sensitive detection technique will be the most promising approach for medical diagnosis and biological studies. A near-field imager using electric fields at microwave/millimeter-wave frequencies for dielectric spectroscopy measurements is proposed. To reduce costs, sensor electrodes are implemented using upper-level metallization in a commercial IC process. The sensing is performed using fringing fields between two selected strips in a multi-electrode sensor. To alleviate the tradeoff between spatial resolution and sensitivity, an interleaving detection technique is proposed. Instead of using adjacent metal strips, sensing is performed with every other one. To enhance the sensitivity and facilitate the circuit design, a narrowband coherent receiver, which is widely used in instrumentation and wireless communication systems, is adopted. The first step is to embed the capacitance-under-test into a resonator such that the capacitance change can be measured through the impedance change of the resonator in a narrowband fashion. A coupled resonator array with RF switching network is proposed to simultaneously measure multiple capacitors. Conventionally, 2D imaging is performed using scanners. To avoid such bulky mechanical equipment and further confine the fields into a smaller sensing “spot”, active shielding on top of the sensing electrodes is proposed (Fig.1). Fig. 2 shows the block diagram of the near-field imaging system at mm-wave frequency.

Figure 1
Figure 1: Fig. 1. Near-field imager.

Figure 2
Figure 2: Fig. 2. System block diagram.