Articles you may be interested inSimultaneous determination of density and viscosity of liquids based on quartz-crystal resonators covered with nanoporous alumina J. Appl. Phys. 98, 014305 (2005); 10.1063/1.1942646 Simultaneous liquid viscosity and density determination with piezoelectric unimorph cantilevers Simultaneous measurement of liquid density and viscosity using remote query magnetoelastic sensors Rev. Sci. Instrum. 71, 3822 (2000)We studied theoretically the properties of a vibrating sensor, constituted of a cylindrical tip partly immersed in a liquid. The tip is driven axially by a stepped horn and by a piezoelectric element. Equations of the fluid flow around the tip are solved and show that longitudinal and transverse waves are emitted in the fluid. This allows the device to be sensitive to the density and viscosity of the fluid. It is shown that the properties of the fluid can be deduced by measuring the frequency shift at resonance and the corresponding electric impedance. The precision of the actual device is still low for several reasons, which are discussed. Then our apparatus seems to be more convenient to in situ reaction monitoring rather than for rheological precise measurements.

We have studied the relationship between the acoustic properties of a near-field acoustic sensor and the properties of a liquid. An acoustic stepped horn is driven by two piezoelectric elements. The generated acoustic waves cause the solid horn to resonate and an acoustic load at the tip modifies these oscillation modes. This leads to a change in electric impedance at the piezoelectric elements. This sensitivity to acoustic load allows a study of semi-infinite liquids. We found a relation between the resonance frequency and the liquid density and a relation between the electric impedance and the viscosity.

It is well known that the damping effect observed in non-contact vibrating AFM is due mainly to the viscoelasticity of the fluid clenched between the tip and the object. Similar effects can be reproduced in near-field ultrasonic microscopy and can be used to monitor the tip-sample distance or to characterize the properties of the fluid. Two techniques are compared. The AFM technique uses a tip coupled to a piezoelectric transducer whereas the second technique uses a solid horn driven directly by a transducer. The sizes of the vibrating tips vary from millimetric to submicrometric scale. The approach of these two new techniques has been validated and leads to cross results, the first one in terms of equivalent acoustic impedances, the second in terms of spring-dashspot constants. Both concepts can be useful for characterization.One usual problem in scanning probe microscopy is to keep the probe distance constant. Different high accuracy techniques have been developed to image the surface of the sample. After the well known tunneling current [1] and atomic forces [2], several authors imagined techniques to characterize the sample and to keep the tip-sample interaction constant [3][4][5][6][7][8]. Because near field acoustics is very sensitive to the interaction distance, we have chosen the near field acoustic coupling to accurately sense the distance. Two techniques are used: one technique uses a solid horn driven directly by a transducer whereas the other technique uses a tip directly coupled to a piezoelectric transducer. The first technique is described in terms of equivalent acoustic impedances, the second in terms of spring-dashspot constants. A solid horn driven directly by a transducerThe acoustic horn consists of two piezoelectric elements sandwiched between two metal rods. One rod -the front section -is a stepped horn which is often referred as a Mason horn [9][10][11][12]. A change in cross section gives a velocity amplification operating in a resonance mode of the small cylinder of the front section. The back section is used to transmit the acoustic waves into the front section (see Fig. 1). These sensors are mainly used for an operation in contact mode [10]. A large range of applications can be found in the field of soldering plastics and machining like drilling and sticking [13]. Here, we used these horns in non-contact mode with a coupling fluid between tip and sample. The electrical impedance Z e of the sensor is sensitive for an acoustic load Z load at the tip of the horn. The Z load is the result of the mechanical interaction between the tip and the volume where it is immersed. This load can be expressed by a general relation:with a the radius of the tip, V 0 the amplitude of the movement of the tip (considered sinusoidal, V(t) = V 0 sin(ωt)) and F the amplitude of the force acting on the liquid. This force F is also sinusoidal for a linear system what results in a complex expression for the acoustic load impedance. The acoustic load at the tip perturbs the oscillation modes in the small front sect...