A method for designing ultrasonic transducers used in diagnostic ultrasonic imagers, in particular, transducers made up of at least one piezoelectric layer and at least one acoustic matching layer, plus various bonding and backing layers. The method of transducer design uses a particular family of spectra as the basis of the bandpass characteristic. The approach is to specify a transfer function from the Transitional Butterworth Thompson family of spectra. The specification is influenced by trade-offs in bandwidth, transient response and design feasibility. This family is indexed by a design parameter called M. Using the M factor, a designer can more readily make the engineering trade-offs needed. By adjusting this parameter, any dynamic response from maximally flat to Gaussian can be obtained. Since not all possible members of this spectral family are feasible as transducers, a design space (bandwidth versus band shape) is used to systematically represent the engineering trade-offs and to graphically represent the physical constraints on feasibility.

A miniature chemical sensor using a thin film acoustic resonator coated with a chemically sensitive sorbent coating. The thin film acoustic resonator has electrodes separated by a thin piezoelectric layer and is supported by a multilayer resonant acoustic isolator. The resonant acoustic isolator has alternating layers of high and low acoustic impedance material, each layer being one quarter acoustic wavelength thick or an odd multiple thereof at the resonant frequency. The resonant acoustic isolator is solidly mounted on a substrate but provides acoustic isolation between the thin film acoustic resonator and the substrate at a resonant frequency.

A resonator device includes a piezoelectric resonator having a detuning layer sequence arranged on the piezoelectric resonator. The detuning layer sequence includes at least a first layer having a high acoustic impedance and a second layer having a low acoustic impedance.

A megasonic transducer for generating and transmitting megasonic acoustic energy into a water based liquid solution for cleaning particles from substrates immersed in the solution, and having piezo crystals connected to a high frequency electrical power supply and generating 0.5 Megahertz to 2.0 Megahertz acoustic energy, a rigid backing layer secured to the back sides of the crystals by a bonding layer, both the backing layer and the bonding layer having thicknesses approximately equaling an odd number of one-quarter wavelengths of the megasonic frequency being propagated in the backing and bonding layers, a quartz isolation layer between the front faces of the piezo crystals and the liquid solution and having a thickness approximately equaling an even number of one-quarter wavelengths of the megasonic frequency propagated in the isolation layer, an encapsulation layer of an electrically insulating material with an acoustical impedance of less than water and free of air bubbles and applied onto the front faces of the piezo crystals, the encapsulation layer having a thickness substantially equaling an odd number of one-quarter wavelengths of the megasonic frequency propagated in the encapsulation layer, and a deionized water coupling layer flowing between the encapsulation layer and the isolation layer and having a thickness substantially equaling an even number of one-quarter wavelengths of the megasonic frequency propagated in the liquid coupling layer.

A resonant-type transducer providing a narrow band, high output or high sensitivity signal to a radiation medium, the resonant transducer comprising a vibrator body comprising piezoelectric or electrorestricitive material having a first acoustic impedance at a resonant condition, and a matching layer for acoustically matching the piezoelectric vibrator body at resonance to the radiation medium. Another type of a matching layer structure comprising a first layer of material of a first thickness t.sub.1 and acoustic impedance Z1 and having an inner surface coupled to a front surface of the vibrator body, and a second layer of material of thickness t.sub.2 and acoustic impedance Z2 and having an outer surface coupled to the radiation medium wherein the second layer has a high acoustic impedance relative to the first layer and wherein the second layer has a thickness of less than one quarter wavelength of the resonant frequency so as to cause a reflection from the high impedance layer to provide a combined impedance of the matching layer at the front surface of the vibrator body which is less than the acoustic impedance of the radiation medium. These matching layer structures provide increased output power and also higher receiving sensitivity for resonant type transducers.