Ultrasonics is concerned with sound frequencies above 16,000 cycles per second (16 KHz). Frequencies of this magnitude are used in a number of applications including:

• Sonar
• Echo Sounding
• Cleaning
• Welding
• Imaging
• Atomization
• Drilling and Machining

A brief discussion of several applications

SONAR 
Ultrasonic Cleaning
Measurement Transducers 
Medical Transducers 
Audio Transducers 
Filters and Resonators 
High Voltage Devices 
Piezoelectric Actuators 
Electro Optics

• SONAR is an acronym for Sound Navigation and Ranging and is used  for underwater observation, communication and detection in Antisubmarine Warfare, as well as the commercial and sport fishing industries.
  
  The transmitting and receiving in a sonar system is performed by transducers. The transmitting transducer converts electrical energy into mechanical energy, in this case frequency sound. which are beamed through the water, and the receiving transducer (generally the same transducer) converts the reflected energy into an electrical signal which is imaged on to a video screen or a marking on a chart recorder. The signal generation and display are all accomplished electronically.
  
  In antisubmarine warfare, the systems are either active or passive. An active system both sends and receives signals and are used mainly by surface ships. A passive system  only receives signals. Passive systems are used  by submarines to detect and evade surface vessels. In addition, passive systems are used in sonobuoys and hydrophones. The operating frequencies used for most sonar systems range from approximately 50 KHz to 200KHz.
   

• ULTRASONIC CLEANING is based on the cavitation effect. Cavitation occurs when high frequency sound waves are passed through liquids. The ultrasonic energy produces cavities, or microscopic bubbles that collapse and send out small but powerful shock waves. These high-energy ultrasonic waves loosen dirt, paint, scale, rust or other contaminants on the surface of the material being cleaned. Ultrasonic cleaners are widely used in the electronics industry, aircraft, automotive, as well as the medical and consumer market.

   

• MEASUREMENT TRANSDUCERS

  • Pressure Transducers are in common use in automotive applications such as knock sensors, strain gauges, and back-up proximity sensors, for measurement of pulse in a human body, and for die pressure change in a circuit breaker and contact pressure in a relay.
  • Vibrational Transducers sense acceleration forces and convert the force into corresponding electrical units as a measurement of change in velocity. Accelerometers are the major application and are commonly used in aircraft and guided missiles.
  • Ultrasonic Measuring Transducers include nondestructive testing which is used to evaluate materials for flaws, flow meters, thickness meters, and ranging devices.
     
• MEDICAL TRANSDUCERS utilize piezoelectric ceramic materials in both diagnostic and therapeutic ultrasound applications. The piezoelectric ceramic device is used as a single element or is diced for use as an array. Applications within medical diagnostic ultrasound include cardiology, neurology, prenatal, and optomology.
   

• AUDIO TRANSDUCERS, in the form of piezoelectric buzzers are now the most widely used audio transducers and are found in a number of products, including but not limited to:

• Fire alarms
• Gas detectors
• Electronic games
• Appliance timers
• Calculators
• Clocks
• Control systems
• Burglar alarms
• Medical equipment
• Instrumentation
  
• Alarms using piezoelectric ceramics as a transmitter generate standing waves and movement causes a Doppler shift in the standing waves, which is detected by a piezoelectric ceramic receiver. Once activated, the ultrasonic intrusion alarm is triggered. 

• FILTERS AND RESONATORS are found in the consumer electronics market, in equipment such as high definition TV, AM and FM radios, telephone answering devices, pagers, CB and long-haul communication equipment. They are more suitable for  wideband applications due to coupling factors which are large and the mechanical Q is moderate  compared to quartz. These devices' main advantages are good temperature and aging characteristics, small size, low impedance, rugged construction, and low cost

  Piezoelectric resonators are finding increased usage in microprocessor data, clock oscillators, automobile engine compartments, or where quartz crystals are too expensive on a cost performance basis.

• HIGH VOLTAGE DEVICES employ piezoelectric ceramics' capability of producing voltages to draw a spark across an electrodes gap. Such a spark can be used to ignite a fuel. Typically they are used as the igniter for gas grills and stoves, heaters, and cigarette lighters.

  Another high-voltage application is the transformer (PET). The PET is utilized  in both the direct and converse piezoelectric effect. The PET is not as efficient in voltage regulation as ordinary transformers, however they are small in size, stable to load charges, large in step-up ration and can be used in:

  • Electrostatic smoke removers
  • Electrostatic coating systems
  • Electronic copying machines
  • Air cleaners
  • Fuses
      

• PIEZOELECTRIC ACTUATORS are finding increased use in applications requiring small amounts of displacement (typically less than a few thousandths of an inch of displacement). These devices can be manufactured in a variety of configurations and fabrication techniques. The industry recognizes these devices as monomorphs, bimorphs, stacks, cofired actuators, and flexure elements. 

  There is a common point to the remaining devices: each has some form of laminated ceramic to ceramic, or ceramic to metal bonding whether by means of epoxy or thermal fusing. Regardless of the device, each have their own specific limitations. However, knowing the limitation, one can select a device best suited for a given application provided the application is within the scope of a piezoelectric actuator.

  • Stacks consist of a number of piezoelectric ceramic elements bonded together forming a monolithic structure. These devices provide increased displacement with high force at low voltages. In the past, primary applications were in military applications.
  • Cofired actuators are very similar to bonded stacks, except that the piezoelectric ceramic is cast as a thin sheet, blanked to a convenient size, screen printed with a precious metal, placed in a laminating die box, and finally sintered and machined to size.
  • Flexure elements, which include monomorphs and bimorphs, are fabricated by bonding a thin film (less than 0.010 inches thick) piezoelectric ceramic element to a metal membrane or to another element.
      

• ELECTRO OPTICS has become a growing market segment and has shown considerable increased activity. The patented, grooved electrode technique has definite advantages over surface electrodes and from a cost comparison, it appears that the grooved technique will have definite cost advantages.