Apparatus and method for characterization of ductile films, surfaces, and subsurface properties

Abstract

Apparatus and methods for characterization of ductile films, surfaces, and subsurface properties are provided. In one embodiment, an ultrasound signal processor uses an excitation generator to cause displacement of a membrane or surface while a series of ultrasound pulses are applied to the membrane or surface. The phase difference between the transmitted and received signals is examined to determine the movement of the membrane or surface in response to the applied excitation. Examination of the membrane or surface phase response provides a determination of whether the fluid type behind the membrane or surface is one of no fluid, serum fluid, or purulent fluid.

Description

[Technical field]

[0001] The present invention relates to a device for characterization of ductile membranes, surfaces, and / or subsurface material properties. In particular, the present invention relates to non-contact characterization of ductile membranes, surfaces, or subsurface regions by stimulating the surface or membrane using low frequency excitation, such as audio excitation, and measuring the displacement behavior using relatively higher frequencies, such as ultrasound. [Background technology]

[0002] Measurements of ductile surfaces or membranes are traditionally performed by applying external forces to develop an understanding of the surface or membrane's response to the applied force. For the case of elastic surface or membrane behavior, an exemplary characterization can be drawn for the spring constant for short range motions, or for a displacement in one direction followed by a nonlinear displacement in the opposite direction, hysteresis effects can also be observed for lossy systems. There are several noteworthy conditions associated with the relationship between the membrane and the adjacent fluid or gel. In one condition, the ductility of the membrane dominates the measurement, and the influence of the material adjacent to the membrane, such as air, fluid, or gel, does not affect the measurement, as the properties of the membrane dominate the measurement. In another condition, the membrane provides an interface and challenge surface for surface stimulation, and the properties of the fluid or gel adjacent to the membrane are measured using the membrane, which does not change the property that is otherwise being measured. Because the membrane is closely coupled to the surface and the underlying fluid, a displacement to the underlying fluid can be made through the surface or membrane without changing the property to be measured. Such characterization is widely practiced in the food industry using mechanical (stirring paddles) or other means to measure stiffness or other mechanical properties of various liquid or semi-solid foods, such as those with hardening or incubation times. For example, in the food science prior art, it is desired to know when yogurt has reached a certain incubation level by its mechanical properties, whereas bacterial growth intervals can be determined from previous batches or fixed intervals used. Similarly, the maturity of a fruit or vegetable can be determined by its surface softness, elasticity, or other mechanical properties, which can be performed by applying forces small enough to generate measurable deflections, or by inducing surface or shear waves across the surface of the fruit or vegetable and measuring the minute surface or subsurface deflections in response to the surface forces.

[0003] It is therefore desirable to measure the mechanical properties of food products using non-contact measurement methods applied to the surface of the article to be characterized.

[0004] In the medical field, it may be desirable to measure the elasticity of a skin surface, a movable membrane, or an organ surface. In one example, the eye may be measured by using contact or optical methods to determine the deflection when a puff of air is applied. In the prior art, the optical reflectance properties of the eye may be measured as deflection versus applied force. However, the optical interfaces and various underlying structures of the eye may have motion-limited resolution that is a result of optical measurement systems characterizing light-transmitting structures, and the intended target (such as the cornea) and the surrounding tissues (the eye lens and vitreous humor) have similar optical properties and are therefore difficult to resolve from one another. It is desirable to use remote sensing and interrogation, such as through air, to measure the elasticity of the surface of the eye or other organs.

[0005] Ultrasonic measurements are typically performed using a liquid medium as a coupling fluid, whereby ultrasonic energy propagates from the transducer through the fluid as a traveling acoustic wave, creating reflected ultrasonic energy that originates from a target interface, which has an acoustic refractive index difference due to the transmission impedance mismatch between the coupling fluid and the target. The use of ultrasound has not been possible for non-contact displacement measurements that resolve distances on the order of millimeters (mm) and sub-mm distance ranges due to the traditional requirement for a coupling fluid between the transducer and the target.

[0006] A method for non-contact surface characterization of a surface through remote sensing of displacement in combination with application of a surface stimulus is desired. Additionally, it is further desired to use air as a medium for stimulation and measurement without direct contact of the surface or membrane by the stimulation or measurement device. Summary of the Invention [Problem to be solved by the invention]

[0007] Object of the Invention A first object of the present invention is an apparatus and method for the generation of a pulsating mechanical stimulus for application to a surface or membrane, the mechanical stimulus being combined with ultrasonic measurement of the response of the surface or membrane to the stimulus by examination of a reflected ultrasonic signal, and characterization of the reflected response to determine the mechanical properties of the surface or membrane.

[0008] A second object of the present invention is the measurement of the ductility and elasticity of a surface, subsurface, or film by probing ultrasonic signals reflected from the surface, subsurface, or film.

[0009] A third object of the present invention is an apparatus and method for the application of force to a food product, where the force generates a deflection of a surface or membrane with a time response comprising a shear wave or surface wave, the deflection of the surface or membrane being characterized by a change in phase or amplitude of an ultrasonic signal being reflected from the surface or membrane.

[0010] A fourth object of the present invention is the characterization of a substantially homogeneous fluid with respect to its elasticity or viscosity by applying a non-contact displacement force, and characterizing its response to the non-contact displacement force by measuring the phase and amplitude of reflected ultrasound from a transmitted ultrasound wave applied to the surface of the fluid.

[0011] A fifth object of the present invention is an apparatus and method for the measurement of elasticity of animal and human organs whereby an air puff is applied to an organ such as a human eye, an intraocular pressure measurement is performed, the response of the organ is measured, and during the response time of relaxation from the air puff, the air puff response of the organ results in a characteristic phase change in reflected ultrasonic energy which is compared to the phase of ultrasonic energy applied over a continuous wave (CW) ultrasonic interrogation or a series of pulsed ultrasonic interrogations. [Means for solving the problem]

[0012] The present invention utilizes ultrasonic transducers such as capacitive micromachined ultrasonic transducers (cMUTs) that provide a diaphragm structure with a thin diaphragm that provides good impedance matching of the gaseous medium for the propagation of ultrasonic energy through air from the displacement of the diaphragm. Thus, cMUTs are suitable for coupling through air and for overlapping in planar 2D hexagonal filled arrays, such as on a substrate, for the generation of plane waves of desired spatial characteristics and lateral extent. In one exemplary embodiment, a material, optionally on the far surface of the membrane, can be characterized by applying a pulsating challenge displacement force, such as by air puffs, and the ultrasonic transducer measures the dynamic displacement characteristics of the membrane or surface. In one example, the membrane provides a physical barrier to the material to be characterized transparently and therefore does not significantly change the properties of the material as seen by the ultrasonic transducer. The ultrasonic transducer transmits or receives ultrasonic energy through a medium such as air to the surface or membrane to be characterized, and the ultrasonic transducer is operable during an interval when a relatively low frequency excitation source is coupled to the surface or membrane. The low frequency excitation source generates a slight movement of the surface or membrane during an interval that coincides with an ultrasonic transmitter delivering acoustic ultrasonic energy to the surface or membrane in either CW or pulsed form. A receiver for the ultrasonic waves reflected from the surface or membrane measures the displacement of the surface or membrane as a phase change in the received signal when compared to the transmission frequency, thereby indicating the temporal displacement of the surface or membrane. Analysis of the temporal displacement of the surface or membrane is used to determine mechanical properties of the surface or membrane by combination with a comparison with the temporal displacement, as measured by a phase shift of the reflected ultrasonic waves in response to a pneumatic excitation coupled to the surface or membrane, or from a template or metric associated with the delay in response or its amplitude between an excitation stimulus to the surface or membrane and the ultrasonic response therefrom. The mechanical properties measured may include ductility, elasticity, or hardness. In this way, a non-contact measurement of the mechanical properties of the fluid below a surface or film can be determined.

[0013] Aspects of the present disclosure provide a non-contact characterization system. The non-contact characterization system may include an excitation generator that generates a non-contact displacement force that is directed at a remote object to be characterized. The non-contact characterization system may include an ultrasonic transducer that directs ultrasonic energy at the remote object, and a transmit waveform generator coupled to the ultrasonic transducer. The non-contact characterization system may include a receive signal processor coupled to the ultrasonic transducer that receives ultrasonic energy reflected from the remote object, the receive signal processor comparing an amplitude or phase of the received ultrasonic signal to a transmit signal formed by the transmit waveform generator, thereby forming an estimate of the displacement of the remote object in response to the non-contact displacement force.

[0014] The excitation generator may form a puff of air that is directed toward the remote object. The puff of air may include a non-oxidizing gas. The non-oxidizing gas may be at least one of nitrogen, argon, CO2, and helium. The ultrasonic transducer may be a capacitive micromachined ultrasonic transducer (cMUT). The transmit signal generator may be either a continuous wave (CW) generator or a pulsed signal generator operable at a fundamental or harmonic frequency of the ultrasonic transducer transmit frequency. The receive signal processor performs baseband demodulation of the received signal and forms a displacement estimate from a series of phase estimates, each of which may be determined from a phase displacement of the received signal compared to the transmitted signal. The series of phase estimates may form an elasticity metric.

[0015] Another aspect of the present disclosure provides a method for non-contact measurement of an elastic surface. A non-contact force event may be provided. An excitation generator may provide a non-contact force to the surface to be characterized or to a volume of material adjacent to the surface. A series of displacement measurements may be formed for each applied excitation generator non-contact force event. Ultrasonic energy may be directed from a transducer to the surface to be characterized or to a volume of material adjacent to the surface. The transducer may receive ultrasonic energy reflected from the surface or volume to be characterized. A phase of the transmitted ultrasonic energy may be compared to the received ultrasonic energy to form a displacement estimate. A plurality of such displacement measurements may be used to estimate elasticity or viscosity.

[0016] The non-contact force of the excitation generator may be a puff of air released from a nozzle directed onto or at the surface of the material to be characterized. The puff of air may be an inert gas including at least one of nitrogen, argon, CO2, or helium.

[0017] The transducer may be at least one of a cMUT or a piezoelectric transducer. The ultrasonic energy may be continuous wave (CW) ultrasonic energy by a transmitting transducer. Comparing the phase of the transmitted ultrasonic energy to the received ultrasonic energy may form a phase displacement that is converted to a non-contact displacement of the material to be measured. An estimation of elasticity or viscosity may be performed by comparing a series of measured phase displacements to a series of measurements of a template. An estimation of elasticity or viscosity may be performed by examination of the rise or fall time of the displacement compared to the rise or fall time of the excitation source.

[0018] The excitation may be a step pressure or an impulse pressure. An estimation of the elasticity or viscosity may be performed by inspection of the ring-down characteristics. The ring-down characteristics may be at least one of an exponential decay time, or a ring cycle interval or frequency. The excitation may propagate to the surface or volume to be characterized as a surface wave, a shear wave, or a combination of surface and shear waves.

[0019] The surface or volume to be characterized may include a film on a fluid. The surface or volume to be characterized may include a fluid having elastic or viscous properties. The surface or volume to be characterized may include an animal or a human.

[0020] Another aspect of the present disclosure may provide a non-contact material characterization system. The non-contact material characterization system may include an excitation generator. The non-contact material characterization system may be configured to generate a non-contact displacement force directed to the elastic surface or a volume of material adjacent to the elastic surface. The non-contact material characterization system may include an ultrasonic transducer. The ultrasonic transducer may be configured to direct a transmission signal to the surface or volume. The ultrasonic transducer may be configured to receive a Doppler ultrasonic signal reflected from the surface or volume. The non-contact material characterization system may include a processor coupled to the ultrasonic transducer. The processor may be configured to determine a displacement of the surface or volume responsive to the non-contact displacement force and the reflected Doppler ultrasonic signal.

[0021] The processor may be configured to determine the displacement by comparing at least one of an amplitude or phase of the reflected Doppler ultrasound signal with at least one of an amplitude or phase of the transmitted signal. The non-contact displacement force generated by the excitation generator may include a puff of air. The excitation generator may be configured to generate a non-contact displacement force with a frequency of at least 20 Hz. The non-contact displacement force generated by the excitation generator may include an impulse excitation. The ultrasound transducer may include a capacitive micromachined ultrasound transducer (cMUT) or a piezoelectric transducer.

[0022] The non-contact material characterization system may include a waveform generator coupled to an ultrasonic transducer. The waveform generator may include either a continuous wave (CW) generator or a pulsed signal generator. The waveform generator may be operable at a fundamental or harmonic frequency of the transmission signal.

[0023] The processor may be configured to determine the displacement by performing a series of comparisons of the phase of the reflected Doppler signal and the phase of the transmitted signal. The processor may be further configured to perform baseband demodulation of the reflected Doppler signal. The processor may be configured to determine at least one of an elasticity or viscosity of the elastic surface or volume based on the series of phase estimates. The processor may be configured to determine at least one of an elasticity or viscosity of the elastic surface or volume based on the determined displacement.

[0024] Another aspect of the present disclosure provides a method for measurement of an elastic surface. A non-contact displacement force may be provided to the elastic surface or a volume of material adjacent to the elastic surface (step (a)). Ultrasonic energy may be transmitted from a transducer to the surface or a volume adjacent to the elastic surface (step (b)). A reflected Doppler ultrasound signal may be received at the transducer (step (c)). At least one of the amplitude or phase of the transmitted ultrasonic energy may be compared to at least one of the amplitude or phase of the reflected Doppler ultrasound signal to form a displacement measurement (step (d)). Elasticity or viscosity may be calculated from the displacement measurement in response to the non-contact displacement force.

[0025] Providing a non-contact force to the elastic surface or to a volume of material adjacent to the elastic surface may include directing a puff of air to the elastic surface or to a volume of material adjacent to the elastic surface. The non-contact displacement force may include an impulse excitation. The transducer may include a capacitive micromachined ultrasonic transducer (cMUT) or a piezoelectric transducer. Transmitting ultrasonic energy may include transmitting continuous wave (CW) ultrasonic energy.

[0026] The method may include repeating steps (a)-(d) to perform a series of displacement measurements and comparing the series of displacement measurements to a series of displacement measurements of a template of known material. Calculating the elasticity or viscosity may include comparing a rise or fall time of the displacement measurements to a rise or fall time of a non-contact displacement force.

[0027] Providing a non-contact force may include providing a step pressure or an impulse pressure. Calculating the elasticity or viscosity may include analyzing ring-down characteristics of the reflected Doppler ultrasound signal. The ring-down characteristics may include at least one of an exponential decay time, a ring cycle interval, or a ring cycle frequency.

[0028] The non-contact displacement force may propagate to a surface or volume as at least one of a surface wave or a shear wave. The surface or volume may include a membrane over a fluid. The elastic surface may include animal or human tissue. The elastic surface may include a solid or semi-solid food product. The non-contact displacement force may be provided at a frequency of at least 20 Hz. The present invention further provides, for example, the following: (Item 1) 1. A non-contact characterization system, comprising: an excitation generator that generates a non-contact displacement force that is directed at a remote object to be characterized; an ultrasonic transducer for directing ultrasonic energy at a remote object; a transmit waveform generator coupled to the ultrasonic transducer; a receive signal processor coupled to the ultrasonic transducer; Equipped with The receive signal processor receives ultrasonic energy reflected from a remote object, the receive signal processor compares the amplitude or phase of the received ultrasonic signal with a transmit signal formed by the transmit waveform generator, and the receive signal processor thereby forms an estimate of the displacement of the remote object in response to the non-contact displacement force. (Item 2) 2. The non-contact characterization system of claim 1, wherein the excitation generator forms a puff of air that is directed toward a remote object. (Item 3) 3. The non-contact characterization system of claim 2, wherein the puff of air comprises a non-oxidizing gas. (Item 4) 4. The non-contact characterization system of item 3, wherein the non-oxidizing gas is at least one of nitrogen, argon, CO2, and helium. (Item 5) 2. The non-contact characterization system of item 1, wherein the ultrasonic transducer is a capacitive micromachined ultrasonic transducer (cMUT). (Item 6) 2. The non-contact characterization system of claim 1, wherein the transmission signal generator is either a continuous wave (CW) generator or a pulsed signal generator operable at a fundamental or harmonic frequency of the ultrasonic transducer transmission frequency. (Item 7) 2. The non-contact characterization system of claim 1, wherein the receive signal processor performs baseband demodulation of the received signal and forms a displacement estimate from a series of phase estimates, each phase estimate being determined from a phase displacement of the received signal compared to the transmitted signal. (Item 8) 8. The non-contact characterization system of claim 7, wherein the series of phase estimates form an elasticity metric. (Item 9) 1. A method for non-contact measurement of an elastic surface, the measurement method comprising the steps of: a non-contact force event, whereby the excitation generator provides a non-contact force to a surface to be characterized or to a volume of material adjacent to said surface; forming a series of displacement measurements for each applied excitation generator non-contact force event; Including, Each displacement measurement is directing ultrasonic energy from a transducer to a surface to be characterized or to a volume of material adjacent said surface; the transducer receiving ultrasonic energy reflected from the surface or volume to be characterized; comparing a phase of the transmitted ultrasonic energy with the received ultrasonic energy to form a displacement estimate; Including, A method whereby a plurality of said displacement measurements are used to estimate elasticity or viscosity. (Item 10) 10. The method of claim 9, wherein the non-contact force of the excitation generator is a puff of air released from a nozzle directed onto or at the surface of the material to be characterized. (Item 11) 11. The method of claim 10, wherein the puff of air is an inert gas comprising at least one of nitrogen, argon, CO2, or helium. (Item 12) 10. The method of claim 9, wherein the transducer is at least one of a cMUT or a piezoelectric transducer. (Item 13) 10. The method of claim 9, wherein the directed ultrasonic energy is continuous wave (CW) ultrasonic energy from a transmitting transducer. (Item 14) 14. The method of claim 13, wherein comparing the phase of the transmitted ultrasonic energy to the received ultrasonic energy forms a phase displacement that is converted to a non-contact displacement of a material to be measured. (Item 15) 10. The method of claim 9, wherein the estimation of the elasticity or viscosity is performed by comparing a series of measured phase displacements with a series of measurements of a template. (Item 16) 10. The method of claim 9, wherein the estimation of the elasticity or viscosity is performed by inspection of the rise or fall time of the displacement compared to the rise or fall time of the excitation source. (Item 17) 10. The method of claim 9, wherein the excitation is a step pressure or an impulse pressure and the estimation of the elasticity or viscosity is performed by inspection of ring-down characteristics. (Item 18) 20. The method of claim 17, wherein the ring-down characteristic is at least one of an exponential decay time, or a ring cycle interval or frequency. (Item 19) 10. The method of claim 9, wherein the excitation propagates to the surface or volume to be characterized as a surface wave, a shear wave, or a combination of surface and shear waves. (Item 20) 10. The method of claim 9, wherein the surface or volume to be characterized comprises a film on a fluid. (Item 21) 10. The method of claim 9, wherein the surface or volume to be characterized comprises a fluid having elastic or viscous properties. (Item 22) 10. The method of claim 9, wherein the surface or volume to be characterized comprises an animal or a human. (Item 23) 1. A non-contact material characterization system, comprising: an excitation generator configured to generate a non-contact displacement force directed at a resilient surface or a volume of material adjacent to the resilient surface; an ultrasound transducer configured to direct a transmission signal towards the surface or the volume, the ultrasound transducer configured to receive a Doppler ultrasound signal reflected from the surface or the volume; a processor coupled to the ultrasonic transducer; Equipped with The processor is configured to determine a displacement of the surface or the volume in response to the non-contact displacement force and the reflected Doppler ultrasound signals. (Item 24) 24. The non-contact material characterization system of claim 23, wherein the processor is configured to determine the displacement by comparing at least one of an amplitude or a phase of the reflected Doppler ultrasound signal to at least one of an amplitude or a phase of the transmitted signal. (Item 25) 24. The non-contact material characterization system of claim 23, wherein the non-contact displacement force generated by the excitation generator comprises a puff of air. (Item 26) 24. The non-contact material characterization system of claim 23, wherein the excitation generator is configured to generate the non-contact displacement force with a frequency of at least 20 Hz. (Item 27) 24. The non-contact material characterization system of claim 23, wherein the non-contact displacement force generated by the excitation generator comprises an impulse excitation. (Item 28) 24. The non-contact material characterization system of claim 23, wherein the ultrasonic transducer comprises a capacitive micromachined ultrasonic transducer (cMUT) or a piezoelectric transducer. (Item 29) 24. The non-contact material characterization system of claim 23, further comprising a waveform generator coupled to the ultrasonic transducer, the waveform generator comprising either a continuous wave (CW) generator or a pulsed signal generator, the waveform generator operable at a fundamental or harmonic frequency of the transmission signal. (Item 30) 25. The non-contact material characterization system of claim 24, wherein the processor is configured to determine the displacement by performing a series of comparisons between the phase of the reflected Doppler signal and the phase of the transmitted signal. (Item 31) 31. The non-contact material characterization system of claim 30, wherein the processor is further configured to perform baseband demodulation of the reflected Doppler signal. (Item 32) 31. The non-contact material characterization system of claim 30, wherein the processor is configured to determine at least one of an elasticity or a viscosity of the elastic surface or volume based on the series of phase estimates. (Item 33) 24. The non-contact material characterization system of claim 23, wherein the processor is configured to determine at least one of an elasticity or a viscosity of the elastic surface or volume based on the determined displacement. (Item 34) 1. A method for the measurement of an elastic surface, the method comprising the steps of: (a) providing a non-contact displacement force to the resilient surface or to a volume of material adjacent to the resilient surface; (b) transmitting ultrasonic energy from a transducer to the surface or to a volume adjacent to the elastic surface; (c) receiving a reflected Doppler ultrasound signal at the transducer; and (d) comparing at least one of an amplitude or a phase of the transmitted ultrasonic energy to at least one of an amplitude or a phase of the reflected Doppler ultrasonic signal to form a displacement measurement; (e) calculating elasticity or viscosity from the displacement measurements in response to the non-contact displacement force; A method comprising: (Item 35) 35. The method of claim 34, wherein providing the non-contact force to the elastic surface or to the volume of material adjacent to the elastic surface comprises directing a puff of air at the elastic surface or to the volume of material adjacent to the elastic surface. (Item 36) Item 35. The method of item 34, wherein the non-contact displacement force comprises an impulse excitation. (Item 37) 35. The method of claim 34, wherein the transducer comprises a capacitive micromachined ultrasonic transducer (cMUT) or a piezoelectric transducer. (Item 38) 35. The method of claim 34, wherein transmitting the ultrasonic energy comprises transmitting continuous wave (CW) ultrasonic energy. (Item 39) Item 35. The method of item 34, further comprising repeating steps (a)-(d) to perform a series of displacement measurements and comparing the series of displacement measurements to a series of displacement measurements of a template of known material. (Item 40) (e) calculating the elasticity or viscosity includes comparing a rise time or fall time of the displacement measurement to a rise time or fall time of the non-contact displacement force. (Item 41) 35. The method of claim 34, wherein (a) providing the non-contact force comprises providing a step pressure or an impulse pressure, and (e) calculating the elasticity or viscosity comprises analyzing ring-down characteristics of the reflected Doppler ultrasound signal. (Item 42) Item 42. The method of item 41, wherein the ring-down characteristics include at least one of an exponential decay time, a ring cycle interval, or a ring cycle frequency. (Item 43) 35. The method of claim 34, wherein the non-contact displacement force propagates to the surface or to the volume as at least one of a surface wave or a shear wave. (Item 44) 35. The method of claim 34, wherein the surface or the volume comprises a film on a fluid. (Item 45) 35. The method of claim 34, wherein the elastic surface comprises animal or human tissue. (Item 46) 35. The method of claim 34, wherein the resilient surface comprises a solid or semi-solid food product. (Item 47) 35. The method of claim 34, wherein the non-contact displacement force is provided at a frequency of at least 20 Hz. [Brief description of the drawings]

[0029] The novel features of the invention are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings.

[0030] [Figure 1] FIG. 1 is a block diagram of a signal processor system for estimating surface or film properties.

[0031] [Diagram 2] FIG. 2 is a block diagram as in FIG. 1 in which the signal processor operates directly on the received ultrasound echoes.

[0032] [Diagram 3] FIG. 3 shows waveforms for the system of FIG.

[0033] [Figure 4A] FIG. 4A shows a plot for a sinusoidal excitation applied to a deformable surface or membrane with a reflected response signal having a certain phase delay and amplitude level.

[0034] [Figure 4B] FIG. 4B shows a plot of a step excitation applied to a deformable surface or membrane and the response to the step excitation with a phase delay and amplitude level.

[0035] [Figure 4C-1] FIG. 4C-1 shows a plot of the displacement of a sinusoidal surface or membrane producing a phase shift of more than + / -180°.

[0036] [Figure 4C-2] FIG. 4C-2 shows the data obtained where the phase has been wrapped from the large phase shift of FIG. 4C-1.

[0037] [Figure 4C-3]FIG. 4C-3 shows a plot of the unwrapped phase estimate from FIG. 4C-2.

[0038] [Diagram 5] FIG. 5 shows a CW signal processor for continuous interrogation of a membrane or membrane surface in response to an excitation generator.

[0039] [Figure 6] FIG. 6 shows waveforms for the CW system of FIG.

[0040] [Figure 7A] FIG. 7A is a plot of the displacement response of a sinusoidal excitation source and an associated membrane or membrane surface.

[0041] [Figure 7B] FIG. 7B is a plot of the displacement response of a step excitation source and an associated membrane or membrane surface. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] FIG. 1 shows a signal processor for an exemplary embodiment of a non-contact gas-coupled surface, subsurface, or film characterization system. The surface 150 can be a film or compressible surface with elastic properties. The surface 150 is interrogated by an ultrasonic beam 128 from an ultrasonic transducer 160, optionally mounted adjacent to a source of applied non-contact force (such as a puff of gas, such as an air puff), which is delivered through a hose 122 to a nozzle 124, or by other means to provide a non-contact pressure stimulus to the film or surface, whereby the response of the film or surface to the non-contact force can be observed. The nozzle 124 can be coupled to an internal volume that provides dynamic pressure coupling from a surface excitation generator 120 through a hose 122 to the surface 150, where the air pressure results in a displacement of the surface 150. This displacement may also be the result of a pressure differential, whereby one side of the membrane or surface is temporarily above or below the other side, and the response of the surface or membrane is characterized after the pressure differential is at steady state. The excitation generator 120 may generate static or dynamic pressure fluctuations that are coupled to the surface 150. As described above, the excitation generator 120 may generate any suitable static or dynamic pressure modulation for the displacement of the surface, including sub-audio frequencies below 20 Hz, audio frequencies between 20 Hz and 20 KHz, or super-audio frequencies above 20 KHz. The nature of the pressure excitation generated by the excitation generator may be impulse-like step or delta (impulse) generation, sinusoidal pressure excitation, square wave excitation, or any combination of these, and the excitation may be gated burst or continuous. Pressure excitation may be provided with or without a static positive or negative pressure bias. The pressure nozzle 124 also has an adjacent ultrasonic transducer 160 with electrical leads 162 and 164 coupled to the transmit-receive switch 118. The ultrasonic transducer 160 generates an ultrasonic beam 128 that is directed toward a central region of the surface 150. The controller 148 generates various control signals that are distributed throughout the signal processor 100. The system reference clock 110 may be derived from a time-stable clock source, and the reference clock 110 may also be used for demodulation of the received signal.The system reference clock 110 is coupled to a transmit waveform generator 112 which generates a pulse train at or near the center frequency of the transducer 160, and the transmit transducer interface 114 performs voltage level shifting and any required amplification before coupling to a transmit / receive switch 118 which couples the waveform from the transmit interface 114 to the ultrasonic transducer 160 via conductors 162 and 164. The ultrasonic transducer 160 generates ultrasonic energy and directs it in a beam 128 towards the surface 150. Energy reflected from the surface 150 is coupled back from the transducer 160 through conductors 162 and 164 to the transmit / receive switch 118 where it is directed to the receive preamplifier 116 which boosts the signal level, isolates the signal using frequency filtering, removes out of band frequency components, and optionally provides automatic gain control via a gain control input from the controller 148. The output of the receive preamplifier 116 is applied to quadrature mixers 140 and 142, and a quadrature clock from the clock generator 110 at the ultrasound transmission frequency generates a quadrature output comprising an I (in-phase) baseband channel and a Q (quadrature, or separated by 90 degrees) baseband channel, which are coupled to the same low pass filters 136 and 138, each of which has a respective analog-to-digital converter 132 and 134, whose outputs are stored in one data buffer, data buffer 144, for each of the I and Q channels. It is also possible to provide multiple gate samples over time, so that if the target moves outside of a particular gate, the system can adaptively use samples associated with subsequent depths. For example, for an ultrasound propagation speed of 2 MHz transducer center frequency (0.33 mm / μs, c / f=170 ns), an eight cycle burst at 2 MHz would be 4 μs, ct / 2=1 / 3 of 2 μs=600 u. If the speculum is adjusted 1 mm, the signal will move away from where the TM appears as a peak signal and may reach the edge of the sample volume with a 0.5 mm movement of the TM, i.e., only twice the desired perturbation range.A number of adjacent sample volumes should be included to use the I and Q of adjacent signal samples to use the maximum reflected amplitude of the various samples. The gain control applied to the preamplifier 116 is set to place the I and Q signals within the optimum converter range for the A / D converters 132 and 134. When the received signal is mixed with the reference clock in this manner, each transmit pulse generates a single phase value for each range-gated sample at a particular depth, and this sequence of phase differences over a series of transmit events is used by the phase and amplitude analyzer 146 to estimate the temporal displacement of the surface 150. In one embodiment of the present invention, the transmit clock coupled to the transducer during the transmit interval is derived from the system clock 110, which is substantially at the center frequency of the transducer. In an exemplary embodiment in which the phase and amplitude analyzer 146 primarily examines the phase of the return signal, the system clock provides synchronous clocking to the quadrature mixers 140 and 142 during the receive interval at the transmit rate, and compares the received signal phase with the system clock (at the original transmit frequency) to generate a phase difference between the transmitted and reflected pulses. The phase values ​​are compared over one or more cycles of the received signal to establish an average phase value over that particular receive interval, and then each phase value from each receive interval is summed to provide a continuous series of discrete estimates of the displacement of the surface 150 based on the wavelength of the acoustic wave and the measured phase values. In another exemplary embodiment, the phase and / or amplitude analyzer 146 may operate based on the amplitude of the received signal, where the amplitude of the received signal may be analyzed to provide information regarding the quality of the phase estimate made from the data (such as a signal to noise metric), or the amplitude of the signal may be analyzed to provide a metric such as db / MHz-cm attenuation, or the amplitude profile may provide an elasticity metric indicative of elasticity or other surface characteristics based on the reflection of ultrasonic energy from the surface in response to an instantaneous pressure perturbation provided by the excitation generator. In general, an elasticity metric is any phase or amplitude derived metric from the data presented to the amplitude and phase analyzer 146 that provides a measure of surface elasticity, where mobility is preferentially associated with the elasticity of the surface 150.The controller 148 which generates the excitation 122 also reads the output of the phase and amplitude analyzer 146, and optionally the amplitude of the reflected signal, over the duration of the activity of the excitation generator 120 to derive the temporal response of the surface 150 to the pneumatic excitation provided through the coupling tip 124. The pneumatic excitation can be any sub-audio, audio, or super-audio frequency, or pulsed, as described above.

[0043] FIG. 2 shows an alternative embodiment of the signal processor of FIG. 1, which implements direct sampling of the RF signal from the transducer rather than using quadrature mixing of the RF signal to baseband. A system clock 210 generates a transmit clock that is coupled to the transmit waveform generator 112. The operation of the transmit waveform generator 112, the transmit transducer interface 114, the transmit receive switch 118, the receive preamplifier 116, the surface excitation source 120, and the transducer 160 are as described above with respect to FIG. 1. The receive preamplifier 116 may be gain controllable, with a gain determined by the controller 248 to place the RF signal within an optimal A / D converter 232 range, as described above. The output of the receive preamplifier 116 is directed to a bandpass filter 236 for reduction of the noise bandwidth applied to the ADC 232, which samples at a Nyquist rate at least twice as fast as the applied signal. For the case of a 1.5 MHz transducer 160, the Nyquist sampling rate is at least 3 MHz plus the skirt attenuation associated with the bandwidth of the transducer 160, known in the art of signal sampling as the Nyquist sampling criterion. The single channel output of the ADC 232 is applied to a data buffer 244, and a signal analyzer 246 examines the phase shifts in the buffered signal to determine the phase changes of the RF signal and discern surface movement. The sequence of phase measurements used to form the phase measurement may be a series of measurements that are inverse time weighted to increase the effect of the most recently obtained measurements, or they may be weighted uniformly over a window of phase samples. The use of weighting factors applied to the stream of measurements over a window may provide favorable noise rejection properties, with weights chosen to favor signals within the excitation source bandwidth and filter and reduce the effects of noise outside the excitation source band.

[0044] FIG. 3 illustrates an exemplary operation of the ultrasonic processor of FIG. 1. In pulsed RF mode, the transmit / receive events provide an estimate of the surface position as a series of phase values ​​during a series of repeated interrogation intervals 340, each of which provides a single phase value. The system clock waveform 302 runs continuously and is provided by the system clock generator 110 of FIG. 1. The duration 340 of the event interval is determined by the flight time from the transducer 160 to the surface 130 and back to the transducer 160 of FIG. 1. The propagation speed of ultrasonic waves in air is 330 m / s (0.33 mm / μs). Thus, for a 1.5 MHz transducer, the resulting wavelength of this traveling wave in air is 0.22 mm. The total flight time for an ultrasonic signal of 10 mm in each direction is therefore 60 μs, and therefore the duration 340 may be 60 μs or more in this case. This time-of-flight interval for the transmitted pulse to return as a received signal after reflection is shown in FIG. 3 as interval 343. The time-of-flight provides an upper limit to the pulse repetition frequency (PRF) corresponding to the sum of the transmit and receive intervals. For this example, a transducer with a 1.5 MHz center frequency would have a wavelength of 220 u traveling in air. Displacement of the surface would result in a shortened path from the transducer to the surface, and the reflected signal returning from the surface to the transducer would return with a phase shift. Thus, a phase and amplitude analyzer observing a 180 degree phase offset between the transmit clock and the received signal compared to the datum phase offset would correspond to a 55 μm displacement of the surface. A transmit interval 342 for transmission of a longer pulse train may provide an improved signal-to-noise ratio of the received signal phase, at the expense of reduced axial resolution, and extended return flight time due to the duration 342 of the transmit pulse stream, which may be desirable for the case of a discrete moving target such as a surface. For a 10 cycle stream at 1.5 MHz, the transmission interval 342 is 6.6 μs, and for a signal to be reflected from a previous transmission burst so as not to interfere with a new transmission burst, the maximum interval 340 is 66.6 μs, implying a pulse repetition frequency (PRF) of 15 KHz or less.In the limiting case where the surface is 30 μs away in one-way flight time and most of the signal energy reflection is at the air / fluid interface of the surface with the fluid behind it and minimal signal energy reflected from structures beyond the surface, the shortest possible repeat cycle time is 30 μs (maximum transmit burst length) + 30 μs (outgoing flight time) + 30 μs (return flight time). In this idealized scenario, the transducer begins transmitting in the repeat cycle at t=0. At t=30 μs, the first cycle of transmit energy arrives at the surface at the same time that the transducer has transmitted the last of the transmit burst. At t=60 μs, the first reflected cycle arrives at the transducer and the last cycle of the burst has reflected from the surface, and at t=90 μs, the last cycle of the burst arrives at the transducer. In a real ultrasound system, the PRF would be much lower to account for the required attenuation of multipath reflected energy that would mix with the surface reflections. In a CW system, separate transmit and receive transducers are used and other path considerations can be ignored when the surface to be measured has signal energy that dominates the returned Doppler signal energy. It may be preferable for the system to operate in CW mode in some circumstances and in pulsed mode in others, depending on the nature of the reflected signal energy. With respect to pulsed mode, several parametric changes can be utilized to improve the SNR, including the use of shorter or longer bursts of transmit RF energy (307 in FIG. 3) that match the spatial extent of the diaphragm or fluid that is responding coherently to the excitation, such as by moving in a common direction, since a stronger reflected signal with a better SNR is provided when the sample volume that is the returning acoustic energy moves in the same direction. Alternatively, it is possible to use short transmit bursts 307 with a spatial extent that matches the region of the diaphragm or fluid that is moving in the same direction and to range gate or sample each region of the reflected signal separately and in succession to distinguish the movement or displacement of one region from the movement or displacement of another region, thereby processing each reflected region separately.This may provide the advantage that the membrane or surface moves in and out of one sampled region (such as the spatial range represented by waveforms 311 / 313 in FIG. 3). Alternatively, it may be possible to provide many cycles of transmit energy to improve the phase accuracy of each measurement, particularly if a clear surface reflection boundary exists and most of the signal energy is reflected from the surface. The combined transmit and receive intervals that determine the PRF may be in the repetition period range of 50 μs to 1 ms or more. Because multipath reflections may occur, it may be preferable to reduce the maximum PRF, for example to reduce the effect of ultrasound reflections from transmission events earlier than the current interval 340. For an ultrasound propagation speed of 0.33 mm / μs, when the transducer to surface separation is 15 mm, the round trip ultrasound path requires approximately 90 μs, and when the transducer to surface separation distance is 20 mm, the round trip path requires approximately 120 μs. As an example, for a separation distance of 20 mm, a transmit burst length of 15 cycles at 1.5 MHz would add an additional 10 μs, and adding 20 μs of settling time for multipath reflections would result in a 150 μs interval 340 corresponding to a PRF of approximately 6.67 KHz. Transducer waveform 306 shows the transmit waveform 307 including bias and amplitude correction during the transmit interval 342, and the reduced amplitude receive signal 309 from the surface. The received signal 309 also includes the effect of surface displacement in the form of phase change from the system clock, which must be subtracted from any static phase value that may be present. The outputs of the mixers I and Q after low pass filtering are shown as waveforms 308 and 310, respectively. Each 66 μs cycle provides a single phase estimate, which can be considered in polar coordinates using the I and Q outputs. This can be done using a range gate to select a time-of-flight interval corresponding to the region containing reflections from the surface, and taking each sample indicative of the instantaneous phase of the surface for a particular sample from the transmit event.Each of the values ​​obtained within a receive interval 344 is averaged or filtered in time over a time region corresponding to the surface reflection response to arrive at an average phase estimate shown as 311 and 313 for the I and Q waveforms 308 and 310. A series of such phase estimates is stored, each spanning a range of the receive interval 344, which range corresponds to reflections from a particular depth. Over multiple data acquisition receive intervals 344, the I and Q samples are concatenated to build a time series that describes the motion of the surface or surface reflection, since phase changes over time are due to changes in distance from the transducer. A succession of these sampled values ​​are collected and compared against the surface excitation waveforms used to form a characterization of the surface for that particular excitation waveform.

[0045] FIG. 4A illustrates an exemplary sinusoidal excitation applied to a surface, such as a sinusoidal waveform 321 applied using a voice coil diaphragm that displaces a sufficient volume to modulate a localized area of ​​membrane or surface pressure by pp of 100 daPa (decapascals). Subsonic frequencies (<20 Hz) may require sealing a localized area around the excited surface, but audio frequencies (20 Hz-20 kHz) and superaudio frequencies (>20 kHz) may be sufficiently propagated as audio waves without sealing the surface area. The sinusoidal pressure excitation 321 results in a modulation of the surface displacement, which is shown as a phase plot 332, since the modulation of the surface position corresponds to a change in the phase of the return signal. Each separate circle in the waveform 332 represents a sample point, such as a polar inversion of the average values ​​for I 311 and Q 313. In one exemplary embodiment of the invention, a series of exemplary sinusoidal modulation 321 frequencies are applied, each with a different period 322, and the delay 330 and peak phase amplitude of the response are used in combination to estimate the elasticity or ductility, or other surface or bulk fluid properties. Since each 360 degree phase change of a 1.5 MHz transmit pulse corresponds to lambda / 2=0.11 mm, a total of + / - 180 degree phase change as shown in plot 332 would correspond to a peak-to-peak displacement of the surface of 0.11 mm. By applying a series of audio and sub-audio tones with different cycle times 322 and measuring the phase response 330 as shown in plot 332, it is possible to estimate properties such as viscosity or elasticity of the fluid behind the surface. For example, exemplary elastometric measurements related to the changed density or viscosity of the fluid can be related to changes in the response time of the surface or film. In this manner, the frequency domain response of the surface can be performed using a series of excitations 321 and measuring a series of surface responses 332.

[0046] The series of Figs. 4C-1, 4C-2, and 4C-3 show the effect of reconstructed surface displacement when the received signal phase exceeds λ / 2 (180°, corresponding to λ / 4 surface displacement). Fig. 4C-1 shows a received signal 430 with a phase shift associated with a displacement exceeding λ / 2 (180°). Phase shifts above 180° wrap to -180°, so the series of samples in Fig. 4C-2 wraps and produces a series of samples shown with the samples of the individual segments 432, 434, 436, 438, and 440. If a sufficiently high sample rate is used that exceeds the Nyquist sampling rate, it is possible to "unwrap" the samples as shown in Fig. 4C-3 and provide the original phase information. These techniques are well known in the prior art of Doppler signal reconstruction.

[0047] FIG. 4A shows a sinusoidal excitation that may be provided in a series of such excitations to generate a phase versus frequency response plot of surface displacement values ​​from a series of measurements, while FIG. 4B shows a comparable time domain step response to FIG. 4A, where a 50 daPa peak surface step pressure excitation 362 is applied to the surface or membrane, which generates a phase response 372 of the return signal from the surface. Similarly, it is also possible to characterize the surface response based on the time delay 374 and the amplitude response (shown as 180 degrees) for the phase response plot 372 corresponding to a displacement of 0.11 / 2 mm. The phase unwrapping technique described in the series of FIGS. 4C-1, 4C-2, 4C-3 may similarly be applied to samples of the waveform 372 of FIG. 4B to reconstruct phase shifts in excess of + / - 180°.

[0048] The signal processing of Fig. 2 operates in a similar manner as described with respect to Fig. 3, however, the reflection 306 observed by the transducer is directly sampled and compared to a reference clock to determine the phase change associated with the surface movement, for example by integrating the signal received over the reference clock and the received signal averaging time, integrating this value over the duration of the received signal, and estimating the phase value over one receive interval. In a similar manner, this would result in the generation of a response waveform 332 from an excitation source 321 interacting with the surface, or a response waveform 372 from an excitation source 362 interacting with the surface, as described with respect to Fig. 4A. In an exemplary embodiment of the invention where a surface interface is being characterized, the phase analyzer 146 or signal analyzer 246 is operable to detect the maximum amplitude of the I or Q channel, or the maximum magnitude of the vector generated by IQ, associate the region of that large signal response as the surface to be characterized, and subsequently sample that region to form an estimate of the phase offset from which the displacement may be estimated.

[0049] Figure 5 shows another example of the invention for CW operation. The signal processor of Figure 5 operates as in Figure 1 and with the same operational block description as was present in Figure 1, however, the transmit interface 114 is directly coupled to the transmit transducer 524 via conductors 502 / 504 to generate a transmitted beam 526 that coincides in surface with the receive beam profile 528 of the receive transducer 530, which conveys the receive signal to the receive amplifier 116 using conductors 506 / 508, where signal processing occurs as previously described with respect to Figure 1, however, the system of Figure 5 operates continuously, with the transmitter transmitting continuously and the receiver baseband signal being received continuously. This operation is advantageous for detection of signal bandwidths that exceed the pulsed transmit configuration described in Figure 3. Because the CW transmit signal introduces a constant DC offset in the receive mixers 140 and 142, it is desirable to provide electronic isolation between the transmit element 524 and the receive element 530. For the CW processing case, the low pass filters 570 and 572 may be set to the Nyquist rate of half the transmit clock rate (Ftx / 2), or they may alternatively be set to the highest response frequency expected during measurement so as not to exceed Ftx / 2. The advantage of matching the low pass filters 570 and 572 bandwidth to the signal bandwidth is the reduction of excess noise from out-of-band noise frequency contributions.

[0050] The systems of Figures 1, 2, and 5 may require that the illumination pattern of the ultrasonic transmitter and receiver (128 in Figures 1 and 2 and 526 in Figure 5) be visualized at the sonicated surface of the film, so that the area of ​​sonication being characterized may be easily visually identified. An optical illumination system (such as a collimated LED, laser, or other beam source) may be added to indicate the area and characteristics being interrogated by the system, such as by adding a converging optical source, or an optical source that is colinear with the illumination pattern (128 in Figure 1 and 526 in Figure 5).

[0051] FIG. 6 shows waveform plots for the baseband CW system of FIG. 5. The system clock 110, the transmit waveform generator 112, and the transmit transducer interface 114 generate the DC biased transducer CW signal waveform 602 of FIG. 6, which is applied to the transmit transducer 524 of FIG. 5, and the receive transducer 530 of FIG. 5 generates the receive signal 608 of FIG. 6. While a DC bias may be required for a cMUT transducer, a piezoelectric transducer does not require a DC bias. The outputs of the I and Q channel low pass filters 136 and 138 are shown as waveforms 614 and 616, respectively. The phase unwrapping technique described above may be applied to these waveforms as well, where the detected phase crosses a + / -180° boundary and wraps to the opposite boundary.

[0052] Figures 7A and 7B show a CW output 714 for excitation 702, and sample points 332 and 372 of Figures 4A and 4B are not present because the CW system of Figure 5 is not subject to the baseband Nyquist sampling limit of the pulsed Doppler system of Figures 2 and 3, provided the mixer output is sampled at a high enough rate to satisfy the Nyquist criterion for phase changes at the mixer output.

[0053] The transducer types for 130 in Figures 1 and 2, and 524 and 530 in Figure 5, can be either capacitive micromachined ultrasonic transducers (cMUT) or piezoelectric transducers formed, for example, using the piezoelectric material PZT.

[0054] Exemplary embodiments for the signal processor include those for a pulsed Doppler system in Figures 1 and 2, and a CW Doppler system in Figure 5. Each of these systems can be implemented using direct RF sampling, as shown in Figure 2, where the bandpass filters are typically expressed as nanovolts per root Hertz.

number

[0055] K is the Boltzmann constant, 1.38*10 -23 It is.

[0056] T is the temperature of the system, assumed to be 300°K.

[0057] B is the bandwidth of the signal being sampled (either the bandwidth of bandpass filter 236 in FIG. 2, or the bandwidth of lowpass filter 136 / 138 in FIGS. 1 and 5).

[0058] R is the resistance that generates the Johnson noise, typically 50 ohms.

[0059] In an ideal system, Johnson noise is generated by the transducer 160 and preamplifier 120 of FIG. 1, and this noise is frequency limited to reduce its effect on the system measurements. The noise floor for a 50 ohm system is:

number

[0060] The invention can be practiced in many different ways. In one embodiment, the phase and amplitude analyzer generates an elasticity metric, which is a characterization of a series of phase measurements from ultrasonic reflections from a surface in combination with the displacement of the surface from a surface excitation source. The elasticity metric derived from the response of the surface can provide an indication of several different phenomena. The elasticity metric can indicate whether the surface adjacent to the membrane has a gaseous boundary (if the reflection is from the membrane itself) or a fluid boundary (if the reflection is from both the membrane and the fluid adjacent to the membrane). The elasticity metric can indicate the extent or properties of the fluid as it characterizes the fluid behind the membrane-fluid boundary, or alternatively, it can provide a means of measuring the properties of an elastic fluid with or without hysteresis in response, whereby the fluid has an offset, or "memory", in the displacement response, whereby the response behavior in one direction is similar to the response behavior in the opposite direction, but only after traveling a certain displacement distance. For a hysteretic response, it may be necessary to characterize the linear behavior of the response after a particular measured displacement that is associated with the hysteresis of the system. Fluid elastic metrics can be determined from the characteristic response of the surface or membrane to a surface excitation and the reflected ultrasonic characterization.

[0061] The components of the system are shown in block diagram form for clarity of understanding the invention. It is understood that the physical components of the invention can be located anywhere, including adjacent to the surface to be measured and at any distance from that surface. A specific arrangement of the elements relative to the surface or film to be measured is shown for clarity and to illustrate one example of the invention.

[0062] The excitation generator may be an air bladder, an alternating pressure, a step pressure, or an air displacement generator that produces an air puff that is manipulated by an operator to apply a force to the membrane or surface. The excitation generator output may be sealed to an enclosed area of ​​the surface or may be unsealed and may use a puff of gas, such as air or other suitable gas.

[0063] Estimates of surface deflection may be derived from measured estimates of velocity, acceleration, or any other metric associated with deflection over time. In one example of the invention, the excitation is a step or impulse response with a rising edge, a falling edge, or an impulse excitation that includes resolved frequency components above the expected response frequency of the system, and an estimate of elasticity or viscosity is performed by inspection of the ring-down characteristics. In another example of the invention, the ring-down characteristics include at least one of an exponential decay time or ring cycle interval or frequency, such as decomposing the response into a ring-down characteristic as follows: φ(t)=e -t / τ cos(2πft) During the ceremony, φ(t) is the phase captured for the sequence of measurements, τ is the exponential decay coefficient, f is the ring cycle frequency, t is time.

[0064] In one example of a non-contact elasticity measurement, the excitation generator is an air puff directed through a nozzle to the film surface, and the film has an underlying liquid to be characterized. The liquid may be a semi-solid food such as yogurt, cheese, or other fermented food, and the elasticity measurement may provide a measurement of the completion of fermentation or other time-dependent processes.

[0065] In another example of the invention, the excitation generator is an air puff coupled to the surface of a semi-solid food product being fermented or cured, such as using bacteria or other time-dependent processes, and an ultrasonic transducer periodically receives a signal reflected from an ultrasonic transmission event, and the amplitude or phase received during the relaxation time of the food product after the air puff excitation is compared to the original transmitted signal to characterize the time-dependent displacement characteristics of the food product and derive elasticity or other physical properties based on the relaxation time changes in response to the excitation.

[0066] In another example of the invention, an excitation generator applies an impulse pressure to a surface of a food product, such as a vegetable or fruit, and the ultrasonic energy applied to the food product is reflected and characterized to measure the time-dependent surface response of the fruit or vegetable, whereby using the phase or amplitude response reflected during the surface relaxation time determines elasticity or other physical properties that may be related to the ripeness of the fruit or vegetable. In one example of the invention, the food product is placed in a holder and the surface is excited with a puff of gas, such as air, and the surface deflection response can estimate ripeness and other properties. In another example of the invention, the excitation can be gas delivered at a supersonic speed and / or at a glancing angle to the surface of the food product, or one or more food products can be placed in a chamber with variable pressure to measure low frequency surface response to pressure, such as deflection versus pressure. In another aspect of the invention, the excitation can be applied to one surface and responses measured on different surfaces of the same article can be characterized, such as measuring propagating surface waves or shear waves traveling through the item.

[0067] In another example of the invention, an excitation generator applies an impulse pressure to an animal or human organ, such as the eye, for an interval when ultrasound energy is applied to the eye, and a phase change in the reflected ultrasound during application of the non-contact excitation or after removal of the non-contact excitation exhibits an elasticity that can be related to intraocular pressure for measuring or diagnosing glaucoma.

[0068] In another example of the present invention, the excitation can be an air puff containing nitrogen (N2) or a non-reactive gas such as argon, carbon dioxide (CO2), helium (He), or an inert gas to prevent oxidation of the film to be characterized. For these alternative gases, the acoustic wave velocity will have a different value compared to the velocity of air.

[0069] In another example of the invention, an ultrasonic transducer, such as a capacitive micromachined ultrasonic transducer (CMUT), is formed by a plurality of membrane surfaces, each of which is electrostatically excited by a transmit voltage waveform that causes the membrane surface to form and transmit acoustic waves. The applied voltage waveform may also include a direct current (DC) component to position the membrane within a desired range of motion, while an alternating current (AC) component of the applied voltage waveform may provide movement of the membrane for generation of ultrasonic energy.

[0070] In another example of the present invention, the ultrasonic transducer may be a ceramic piezoelectric transducer that changes mechanical shape based on the applied pressure.

[0071] Various aspects of the invention can be practiced as set forth below.

[0072] A signal processor for detection of air or fluid behind a surface, the signal processor further estimating an elasticity metric of the fluid, if present, the signal processor comprising: an ultrasonic transducer for coupling ultrasonic energy to the surface; an excitation generator that generates a sub-audio, audio, or super-audio excitation that is coupled into the surface to cause a measurable deflection in the surface; a transmitter coupled to the ultrasonic transducer during a transmission interval; a receiver coupled to the ultrasonic transducer during a receive interval following the transmit interval; a phase and / or amplitude analyzer for comparing the phase of the transmitted signal of the transmit interval with the phase and / or amplitude of the received signal during the receive interval to estimate the surface deflection; a signal processor that derives metrics from the phase and amplitude analyzer by comparing the surface deflection to an excitation generator output; an elasticity metric that indicates whether the received signal is a reflection from a surface, including reflections from air or fluid, and optionally characterizes the fluid from surface deflection characteristics; A signal processor comprising:

[0073] A signal processor, wherein the excitation generator generates at least one of a sinusoidal, impulse, steady state, or periodic sub-audio, audio, or super-audio excitation.

[0074] A signal processor, wherein the phase and amplitude analyzer is operable in response to receiving acoustic energy from the transducer at a natural center frequency of the transducer.

[0075] A signal processor, wherein the phase and amplitude analyzer is operable based on received acoustic energy from a transducer in a baseband frequency spectrum, the baseband frequency spectrum being formed by mixing the received signal with a carrier frequency substantially at a center frequency of the transmitter.

[0076] A signal processor, the transmitter generating a transmit waveform including an excitation voltage signal at a center frequency of the transducer during a transmit interval.

[0077] A signal processor, wherein the sum of a transmit interval and a receive interval is greater than 50 microseconds and less than 1 millisecond.

[0078] A signal processor, wherein the phase and amplitude analyzer determines a weighted or unweighted average phase relative to a transmit clock.

[0079] A signal processor, wherein the metric is derived from a temporal phase change between a signal received from a transducer during a receive signal interval and a transmit clock that is operational during the receive interval.

[0080] A signal processor, wherein a metric is derived from a phase relationship between an output baseband signal of a mixer and an output of an excitation generator.

[0081] A signal processor, wherein a metric is derived from temporal phase changes in the received signal and the output of the excitation generator.

[0082] A signal processor, wherein the ultrasonic transducer generates periodic bursts of transmitted signal energy.

[0083] A signal processor, wherein the ultrasonic transducer generates a continuous transmitted signal energy.

[0084] A signal processor, wherein the phase and amplitude analyzer is operable based on the received signal to identify an area of ​​a first reflection from the membrane or surface, and then characterizes the fluid behind the area, which is identified as either air or liquid.

[0085] A signal processor that uses a phase or amplitude response associated with the measurable deflection to determine surface elasticity or fluid viscosity when the fluid behind the identified region is liquid.

[0086] 1. A signal processor for characterizing a temporal response from a surface or film, the signal processor comprising: an excitation generator that generates a sub-audio, audio, or super-audio excitation for application to a surface or membrane to cause a displacement; a transducer for launching acoustic waves towards and receiving reflections from a surface to be characterized; a visual indicator to enable direction of the acoustic wave from the transducer to an area of ​​interest on the surface; an ultrasonic transmitter operable during a transmit interval to couple gated frequency bursts to the transducer; an ultrasonic receiver operable during a receive interval and coupled to the transducer; a phase and amplitude detector for comparing the phase of the transmit clock with a received signal from the ultrasonic receiver to generate a phase output; a response analyzer that compares the phase output with an output of the excitation generator, the response analyzer determining a viscosity of the fluid adjacent to the surface to be characterized by comparing the phase output with the output of the excitation generator; A signal processor comprising:

[0087] A signal processor, wherein the transducer is at least one of a capacitive micromachined ultrasonic transducer (cMUT) or a piezoelectric transducer.

[0088] The signal processor, wherein the excitation generator is at least one of a voice coil actuator or a moving diaphragm.

[0089] A signal processor, wherein the visual guide is at least one of a laser diode, a light emitting diode, or an optical indicator that illuminates an area corresponding to a beam profile from the ultrasound transducer.

[0090] A signal processor, wherein the ultrasonic transmitter has a repetition rate of less than 15 KHz.

[0091] A signal processor, wherein the phase and amplitude detector is a baseband mixer that generates an output after a low pass filter.

[0092] A signal processor, wherein the phase and amplitude detector is operable at a center frequency of the transducer.

[0093] A signal processor, wherein the response analyzer compares the phase output over a plurality of sample points over a duration with an output of the excitation generator when the excitation generator is operational.

[0094] A signal processor, wherein the receive interval and the transmit interval are simultaneous intervals.

[0095] A signal processor, wherein the receive interval and the transmit interval are exclusive intervals.

[0096] While preferred embodiments of the present invention have been shown and described herein, it will be apparent to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. It is understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. The following claims define the scope of the invention, and it is intended that methods and structures within the scope of these claims and their equivalents be covered thereby.

Claims

1. A non-contact medical diagnostic system, comprising: an excitation generator configured to generate a non-contact displacement force directed at an elastic surface or a volume of material adjacent to the elastic surface, the non-contact displacement force being a step pressure or an impulse pressure; an ultrasonic transducer configured to direct a transmitted ultrasonic signal through a gas phase medium to the elastic surface or the volume, the ultrasonic transducer configured to receive an ultrasonic signal reflected from the elastic surface or the volume; a processor coupled to the ultrasonic transducer; Equipped with The processor is configured to determine the non-contact displacement force and the displacement of the elastic surface or volume in response to the reflected ultrasound signal by analysis of ring-down characteristics of tissue motion in response to the step or impulse pressure.

2. 2. The non-contact medical diagnostic system of claim 1, wherein the processor is configured to determine the displacement by comparing at least one of an amplitude or a phase of the reflected ultrasound signal to at least one of an amplitude or a phase of the transmitted ultrasound signal.

3. 3. The non-contact medical diagnostic system of claim 2, wherein the processor is configured to determine the displacement by performing a series of comparisons of a phase of the reflected ultrasound signal and a phase of the transmitted ultrasound signal.

4. The non-contact medical diagnostic system of claim 3 , wherein the processor is further configured to perform baseband demodulation of the reflected ultrasound signal to obtain a baseband signal.

5. The non-contact medical diagnostic system of claim 3 , wherein the processor is configured to determine at least one of an elasticity or a viscosity of the elastic surface or the volume based on a series of baseband phase values.

6. The non-contact medical diagnostic system of claim 1 , wherein the non-contact displacement force generated by the excitation generator comprises a puff of air.

7. The non-contact medical diagnostic system of claim 1 , wherein the non-contact displacement force has a frequency of at least 20 Hz.

8. The non-contact medical diagnostic system of claim 7 , wherein the non-contact displacement force has a frequency between 20 Hz and 20 kHz.

9. The non-contact medical diagnostic system of claim 1 , wherein the non-contact displacement force has a frequency below 20 Hz.

10. The non-contact medical diagnostic system of claim 1 , wherein the ultrasonic transducer comprises a capacitive micromachined ultrasonic transducer (cMUT) or a piezoelectric transducer.

11. 10. The non-contact medical diagnostic system of claim 1, further comprising a waveform generator coupled to the ultrasonic transducer, the waveform generator comprising either a continuous wave (CW) generator or a pulsed signal generator, the waveform generator operable at a fundamental or harmonic frequency of the transmitted ultrasonic signal.

12. The non-contact medical diagnostic system of claim 1 , wherein the processor is configured to determine at least one of an elasticity or a viscosity of the elastic surface or the volume based on the displacement measurements.

13. The non-contact medical diagnostic system of claim 1 , wherein the excitation generator is separate from the ultrasound transducer.

14. The non-contact medical diagnostic system of claim 1 , wherein the processor is configured to determine a viscosity of a volume of fluid adjacent the elastic surface based on the displacement measurements.

15. A method for non-contact measurement of an elastic surface, the method comprising: providing a series of non-contact forces to a surface to be characterized or to a volume of material adjacent to said surface with an excitation generator, said series of non-contact forces being step pressures or impulse pressures; forming a series of displacement measurements for each non-contact force in the series of non-contact forces, each displacement measurement comprising: directing transmitted ultrasonic energy from a transducer to the surface or to a volume of the material adjacent to the surface, the transmitted ultrasonic energy comprising a transmit burst; receiving reflected ultrasonic energy from the surface or the volume of material adjacent to the surface with the transducer; setting a range gate for a first region of the reflected received ultrasonic energy; Distinguishing between the movement or displacement of the first region and the movement or displacement of a second region; forming a displacement estimate for the surface or the volume of the material adjacent to the surface by comparing a phase of the transmitted ultrasonic energy with the reflected and received ultrasonic energy; and forming an estimate of elasticity or viscosity based at least in part on the series of displacement measurements; and A method comprising:

16. The method of claim 15, wherein the transmission burst has a spatial extent that corresponds to a region of the surface or a region of the volume of the material adjacent to the surface that is moving in the same direction as the transmission burst.

17. The method of claim 15, wherein setting a range gate for each displacement measurement in the series of displacement measurements is based at least in part on at least one of a frequency of the transmitted ultrasonic energy, a propagation velocity of the transmitted ultrasonic energy, or a number of cycles of the transmitted ultrasonic energy included in the transmission burst.

18. The method of claim 15, further comprising adaptively forming a first displacement measurement of the series of displacement measurements based at least in part on utilizing other displacement measurements of the series that include a second range gate associated with a second depth when the surface or a volume of the material adjacent to the surface moves out of range of a first range gate associated with the second depth from a first depth.

19. The method of claim 15, wherein the transmitted ultrasonic energy is pulsed ultrasonic energy.

20. A method for non-contact measurement of an elastic surface, the method comprising: providing a series of non-contact forces to a surface to be characterized or to a volume of material adjacent to said surface with an excitation generator, said series of non-contact forces being step pressures or impulse pressures; forming a series of displacement measurements for each non-contact force in the series of non-contact forces, each displacement measurement comprising: directing transmitted ultrasonic energy from a transducer to the surface or to a volume of the material adjacent to the surface; receiving reflected ultrasonic energy from the surface or the volume of material adjacent to the surface with the transducer; forming a displacement estimate for the surface or the volume of the material adjacent to the surface by comparing a phase of the transmitted ultrasonic energy with the reflected and received ultrasonic energy; and forming an estimate of elasticity based at least in part on the series of displacement measurements; and characterizing the surface or the volume of the material adjacent to the surface based at least in part on the estimate of elasticity, the characterizing being based at least in part on a hysteretic response of the surface or the volume of the material adjacent to the surface; A method comprising:

21. The method of claim 20, wherein characterizing the hysteresis response is based at least in part on an offset in each displacement measurement.

22. The offset includes a first displacement response in a first direction and a second displacement response in a second direction; the first direction is opposite to the second direction; The method of claim 21 , wherein the first displacement response is similar to the second displacement response after the first displacement response has traversed a displacement distance.

23. The method of claim 20, further comprising characterizing a volume of the surface or material adjacent to the surface based at least in part on a series of hysteretic responses of the series of displacement estimates.

24. The method of claim 23, further comprising forming the series of hysteresis responses based at least in part on the linear behavior of each hysteresis response in the series.

25. The method of claim 20, wherein the surface or a volume of the material adjacent to the surface comprises an elastic fluid.

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