A design of a microwave noninvasive continuous blood glucose monitoring sensor and its interference test results are presented. The novelty of the proposed sensor is that it comprises two spatially separated split-ring resonators, where one interacts with the change in glucose level of a sample under test while the other ring is used as a reference. The reference ring has a slightly different resonant frequency and is desensitized to the sample owing to its location, thus allowing changes in temperature to be calibrated out. From an oral glucose tolerance test with two additional commercially available sensors (blood strip and continuous glucose monitor) in parallel, we obtained encouraging performance for our sensor comparable with those of the commercial sensors. The effects of endogenous interferents common to all subjects, i.e., common sugars, vitamins (ascorbic acid), and metabolites (uric acid) have also been investigated by using a large Franz cell assembly. From the interference test, it is shown that the change in sensor response is dominated by changes in glucose level for concentrations relevant to blood, and the effects of interferents are negligible in comparison.

We will demonstrate an alternative topology for the feedforward amplifier. This amplifier does not use a delay element, thus providing an efficiency enhancement and a size reduction by employing a distributed-element negative group-delay circuit. The insertion loss of the delay element in the conventional feedforward amplifier seriously degrades the efficiency. Usually, a high-power coaxial cable or a delay-line filter is utilized for a low loss, but the insertion loss, cost, and size of the delay element still act as a bottleneck. The proposed negative group-delay circuit removes the necessity of the delay element required for a broadband signal suppression loop. With the fabricated two-stage distributed-element negative group-delay circuit with 30 MHz of bandwidth and -9 ns of group delay for a wideband code-division multiple-access downlink band, the feedforward amplifier with the proposed topology experimentally achieved 19.4% power-added efficiency and -53.2-dBc adjacent channel leakage ratio with 44-dBm average output power.

In this paper, a microwave non-invasive blood glucose monitoring system operating at around 1.4 GHz is designed and its performance in terms of accuracy and repeatability is evaluated by a clinical trial involving 24 human subjects, with and without diabetes. Direct comparison with the most accurate benchtop glucose analyzer shows the exceptional accuracy and repeatability of the proposed system.

In this letter, a novel design for a dual-band negative group delay circuit (NGDC) is proposed. Based on the topology of a single-band reflection type NGDC, composite right/left handed λ/4 short stubs are employed to obtain a negative group delay (NGD) at two separate frequency bands simultaneously. In order to achieve a bandwidth extension, the proposed structure consists of a two-stage dual-band NGDC with different center frequencies connected in a cascade. According to the measurements performed for wide-band code division multiple access and worldwide interoperability for microwave access, an NGD of -3.0 ± 0.4 ns and -3.1 ± 0.5 ns are obtained at 2.12-2.16 GHz and 3.46-3.54 GHz, respectively.

In this letter, the application of a variable characteristic impedance transmission line that can be used to design a dual-band bandpass filter (BPF) is presented. The proposed filter offers a fixed first passband and a controllable second passband. The tuning of the second passband is achieved by varying the characteristic impedance of the shunt open stub of stub loaded resonator (SLR) with the help of a defected ground structure (DGS) transmission line and varactor diodes. In order to validate the theoretical predictions and simulated results, a two stage dual-band BPF with three transmission zeros was implemented and experimentally verified.