A system is provided that can include a first tube for communicating a fluid through a wellbore. The system can also include a gap between the first tube and a first electromagnetic acoustic transducer (EMAT). The first EMAT can be positioned to magnetically couple with the first tube. The first EMAT can include a magnet and a wire coil positioned around the magnet. The first EMAT can coupled to a power source and positioned to, responsive to receiving a power from the power source, apply a first magnetic force to the first tube for determining a density or viscosity of the fluid.

A method for estimating a specific gravity of a gaseous fuel is described. The gaseous fuel may power an engine and the engine may include a cylinder, a gas valve configured to supply an intake port of the cylinder with the gaseous fuel, a gas rail configured to deliver the gaseous fuel to the gas valve, and a microprocessor adapted to perform the method. The method may comprise establishing a pressure wave in the gas rail by opening and closing the gas valve, wherein the pressure wave travels at the speed of sound in the gaseous fuel. The method may further comprise determining a frequency of the pressure wave in the gas rail, and estimating the specific gravity of the gaseous fuel based on the frequency of the pressure wave.

A method of measuring a material property of a viscoelastic fluid using one or more vibratory transducers, the method comprising: vibrating one or more vibratory transducers in the viscoelastic fluid to generate a first wave propagating from a first surface of the one or more vibratory transducers and a second wave propagating from a second surface of the one or more vibratory transducers, wherein the first and second surfaces are spaced and oriented relative to each other such that, during vibration of the one or more vibratory transducers, the first and second waves combine with each other to provide a net constructive or destructive interference; and determining a material property of the viscoelastic fluid based on the vibrating of the one or more vibratory transducers in the viscoelastic fluid.

Determining a physical property of a fluid by: vibrating a vibratory transducer element in a fluid at a vibration frequency, wherein the vibratory transducer element comprises a fluid-contacting elongate member characterised by a width, a half width that is equal to half of the width, and a length that is greater than the width, wherein the half width is less than a propagation depth of a shear wave in the fluid at the vibration frequency; making a measurement of the vibration of the vibratory transducer element in the fluid at the vibration frequency; and determining, based on the measurement of the vibration, a physical property of the fluid such as a viscosity, a viscoelasticity, a density, a fluid stiffness, a loss tangent, a storage modulus, a loss modulus, or a yield stress.

A method for determining a process anomaly in a fluid flow system, the system having a meter with immersed elements immersed in a fluid of a fluid flow is disclosed. The method includes determining, using a data processing circuit (132), a measured density of the fluid in the fluid flow system, determining, using the data processing circuit (132), whether the fluid flow system is experiencing a density anomaly based on a relationship between the measured density and an expected density of the fluid in the fluid flow system, determining, using the data processing circuit (132), a measured phase difference of vibrations of the immersed elements of the meter, determining, using the data processing circuit (132), whether the fluid flow system is experiencing a phase anomaly based on a relationship between the measured phase difference and a target phase difference of the vibrations of the immersed elements in the fluid flow, and identifying an anomaly of the fluid flow system based on the determination of whether there is a density anomaly and the determination of whether there is a phase anomaly.