Mikhail Zubtsov

Sub-wavelength phononic crystal liquid sensor

We introduce an acoustic liquid sensor based on phononic crystals consisting of steel plate with an array of holes filled with liquid. We both theoretically and experimentally demonstrate sensor properties considering the mechanism of the extraordinary acoustic transmission as underlying phenomenon. The frequency of this resonant transmission peak is shown to rely on the speed of sound of the liquid, and the resonant frequency can be used as a measure of speed of sound and related properties, like concentration of a component in the liquid mixture. The finite-difference time domain method has been applied for sensor design. Ultrasonic transmission experiments are performed. Good consistency of the resonant frequency shift has been found between theoretical results and experiments. The proposed scheme offers a platform for an acoustic liquid sensor.

Phoxonic crystals—a new platform for chemical and biochemical sensors

A new sensor platform is based on so-called phoxonic crystals. Phoxonic crystals are structures designed for simultaneous control of photon and phonon propagation and interaction. They are characterized by a periodic spatial modulation of the dielectric constant as well as elastic properties on a common wavelength scale. Multiple scattering of photons and phonons results in a band gap where propagation of both waves is prohibited. The existence of photonic and phononic band gaps opens up opportunities for novel devices and functional materials. The usage of defect modes is an advantageous concept for measurement. The defect also acts as point of measurement. We show theoretically that the properties of the defect mode can be tailored to provide very high sensitivity to optical and acoustic properties of matter confined within a defect cavity or surrounding the defect or being adsorbed at the cavity surface. In this paper, we introduce the sensor platform and analyze the key features of the sensor transduction scheme. Experimental investigations using a macroscopic device support the theoretical findings.

Towards a SAW based phononic crystal sensor platform

A Surface Acoustic Wave (SAW) sensor platform based on phononic crystals specifically designed for chemical and biosensing will be introduced. The unique feature of this sensor concept is the possibility to determine volumetric properties of analytes at volume as low as 1 nl. The sensor platform has the capability paving the way to study chemical reactions in microreactors or biomaterials directly in their physiological environment without any label.

Phoxonic crystal sensor

The concept of photonic and phononic crystal sensors is based on the measurement of changes in the transmission properties of the devices caused by changes of material properties of one of the materials building the crystal. It has been demonstrated that in the optical case the key parameter is the refractive index, i.e. speed of light, in the acoustic case it is sound velocity. Both parameters can be measured with accuracy competitive with other optical and acoustic sensor principles. A phoxonic crystal sensor combines both concepts in one device, therefore allowing for a dual parallel determination of two independent material properties. Such a sensor is especially attractive for complex analytes as common in chemistry and biochemistry. We have designed and modeled a phoxonic crystal consisting of a solid matrix and holes where the central cavity acts as analyte container. We especially concentrate on the generation of a characteristic feature within the transmission spectrum like a transmission peak within the phoxonic band gap where the respective wavelength or frequency of maximum transmission is sensitive to material properties of the analyte. We could show theoretically that a (geometric) defect is required in photonics whereas in phononics separation of the sensitive peak is the challenge. The respective wavelength/frequency of maximum transmission moves in accordance to the resonance conditions. We further analyze the transmission of light and sound through a phoxonic crystal plate at normal incidence.

Determining liquid properties by extraordinary acoustic transmission through phononic crystals

This contribution shows how a resonance-induced extraordinary acoustic transmission through a phononic crystal structure can be used as sensor for liquid properties. The phononic crystal consists of a metal plate with a periodic array of holes. Ultrasound propagates in a way that the incidence direction of sound is perpendicular to the plate. A characteristic transmission peak has been found to strongly depend on liquid sound velocity. The respective peak maximum frequency serves as measure for liquid composition. Numerical calculations based on FDTD and FEA reveal more insides to the propagation characteristics, in particular the presence of specific plate modes. Experimental investigations using a laser vibrometer and the Schlieren method support the theoretical findings.

Liquid sensor utilizing a regular phononic crystal with normal incidence of sound

A phononic crystal device is investigated as a sensor platform combining bandgap engineering with resonant transmission. Here we apply a regular phononic crystal with a solid matrix and liquid filled holes, fully immersed into the liquid with incidence direction of sound normal to the plate.

A novel method for tuning the band gap structure of 2D phononic crystals

Our study encompasses the phenomena associated with gradual symmetry reduction in phononic crystals (PnC). As the lattice of the PnC is deformed, transmission spectrum shows a change in the shape, position and the size of the band gaps. More important, a pass band inside the stop band develops. The practical feasibility of the phenomena for a sensor application of a PnC is demonstrated for the 2D case of a solid matrix and liquid inclusions. A distinct pattern of the pass band build-up and its alteration induced by both the lattice deformation and the change of the material properties of inclusions are demonstrated.

Phononic cystal sensor for medical applications

We report on first steps towards a phononic crystal sensor for biomedical applications. Phononic crystal sensors are a new concept following the route of photonic crystal sensors. Basically, the material of interest constitutes one component of the phononic crystal. Here a liquid analyte is confined in a disposable element which acts as defect in a phononic crystal. In an application as biomedical sensor the concentration of a compound in liquid must be related to speed of sound of the liquid in the cavity. A change in the concentration e.g. caused by the appearance of a toxic compound or as a result of a biochemical reaction, results in measurable changes in the transmission coefficient, specifically a shift of a resonance induced transmission peak. Three additional key design challenges for a medical sensor are the strong restriction coming from limitations to approved materials for the analyte container, geometric dimensions in the mm-or sub-mm-range common in hospital or point-of-care environment and acoustic coupling between sensor platform and the analyte container.

Phononic crystal sensor for liquid property determination

Acoustic band gap materials, so-called phononic crystals, provide a new sensor platform. Phononic crystals are periodic composite materials with spatial modulation of elasticity, mass density as well as longitudinal and transverse velocities of elastic waves. When utilized as sensor, the input parameter to be measured changes characteristic properties of the phononic crystal in a distinct manner. These changes can be detected by measuring the transmission behavior of ultrasonic waves through the phononic crystal. The most optimal feature for detection is a sharp isolated transmission peak which corresponds to the input parameter. When applying as liquid property sensor one component building the phononic crystal is the liquid to be analyzed. Here we present recent results gathered from different sensor realizations. In the second part we report on experimental investigations based on laser vibrometry which provide deeper insides to the so-called extraordinary transmission. These analyses reveal that structural resonance effects are responsible for the smart properties of the device.

Disposable phononic crystal liquid sensor

Phononic crystals (PnC) consist of two or more materials arranged in a spatially periodic manner. Introduction of a defect into the crystal lattice is a technique to create resonant modes. The idea behind the application of a PnC as sensor element is the dependence of the characteristic features of those modes on speed of sound. Currently the sensor designs are based on common 2D phononic crystal geometries. A liquid-filled defect in the crystal lattice creates a resonant mode used for the determination of sound velocity of the confined analyte. This (complex) value allows the determination of thermodynamic values which are linked to molecular properties of (bio)chemical samples. The objective of our current research is two-fold: a new geometry considering disposable elements containing the analyte while keeping the high sensitivity of the acoustic sensor signal and suppressing influences of unavoidable inaccuracies when replacing the analyte container.