However, when the amount of test sample is limited (which is common in biosensor application), the operating frequency tends to be much higher, which brings challenges in resonance excitation and frequency measurement. To conquer these deficiencies, sensing architecture based on Helmholtz resonance was proposed in our previous paper as a new type of biosensor, which shows a higher sensitivity at a similar operating frequency compared with the sensor using a cantilever beam.

This kind of sensor mostly detects the resonant frequency shift induced only by the added mass effect, so sensitivity improvements are usually realized by decreasing the size or operating at higher order modes, which may bring manufacturing complexities and frequency measurement difficulties. In addition, with the development of microfabrication technology, high sensitivity and resolution are realized. Over the past several decades, dynamic-mode cantilever sensors have been studied extensively with broad applications in various fields due to their fast response and low fabrication cost. Prospective results of the proposed HR after miniaturization show an operating frequency around 3 kHz when the amount of test sample is 0.1 mL, which will facilitate use of the common acoustic power source and acoustic pressure sensors in the sensing system. The experiment was done using test solutions with different glucose concentrations, whose results showed consistency with the analytical results and noticeable frequency increases with the glucose concentration. Based on the underlying theory, the measurement principle was proposed and the experiment setup was established using a 3D-printed structure. An analytical example was calculated and verified by acoustic finite element analysis, and the results clearly showed that the frequency decreases in comparison to that of the conventional HR. The resonant frequency of the proposed HR was derived by treating it as an HR with a straight neck with the equivalent length.

In this paper, a modified HR was proposed for biosensor application at a lower frequency, by designing the neck of the HR as a type of an Archimedes spiral, which can increase the neck length as much as possible without occupying much space. However, for biosensor application, when the amount of test sample is limited, the operating frequency tends to be very high, which may bring challenges of resonance excitation and frequency measurement. Helmholtz resonators (HR) have been proven to have feasibility for sensor applications with good performance.

Archimedes principle labs