The sensitivity curves of a long helix antenna covering the whole cylinder placed at different orientations is shown in. Another interesting fact is that, under certain scenarios, the drug container may be placed at different angles, and the impact of the helix orientation must be identified. It can be seen that the antenna sensor is much less sensitive when the liquid-air interface is out of the helix coil covered region. Shows the simulation result of an antenna that only covers half of the cylinder, and is placed at three different spots alongside the cylinder. When the helix antenna is not long enough to cover the cylinder completely, the relative position of the antenna is critical to optimize the sensor performance. It is important to point out that when the number of turns or the pitch gap is large enough to make the helix antenna cover the whole cylinder body, the sensor is mostly linear in the middle range, but globally it is not linear, due to the reason that has been discussed in. Even though the size and cost of drug delivery system are continuously going down, most of the existing monitoring methods still involve bulky equipments and expensive test process. During the past decade, various drug delivery monitoring technologies have been developed such as photoacoustic tomography, electron paramagnetic resonance, and fluorescence based imaging. In addition, dosage monitoring will also benefit the RFID (Radio Frequency Identification) platform enabled personalized medical tracking and chronic disease management. Drug delivery systems may have different control mechanisms –, but no matter what control mechanism is adopted, drug dosage monitoring is crucial to provide feedback as well as prevent unexpected in-vivo fluctuation and leakage. Instead of injecting drugs at the maximum tolerable dose (MTD) once in a treatment period, contemporary drug delivery paradigms maintain the constant release and administer it within some desired therapeutic range, providing minimized side effects and increased therapeutic efficacy. I. Introduction DRIVEN by the rise of micro and nano technologies, controlled rate and micro-patterned drug deliveries have been playing major roles to overcome the limitations of conventional burst-release dosage forms. The in vitro experiment on two prototypes of antenna sensor-drug reservoir assembly have shown the ability to monitor the drug dosage by tracking antenna resonant frequency shift from 2.4–2.5-GHz ISM band with realized sensitivity of 1.27 for transdermal drug delivery monitoring and 2.76- sensitivity for implanted drug delivery monitoring.
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