Noise reduction of dental drill noise

Dental drills produce a characteristic noise that is uncomfortable for patients and is also known to be harmful to dentists under prolonged exposure. It is therefore desirable to protect the patient and dentist whilst allowing two-way communication, which will require a headphone - type system. Re-establishing good communication between the dentist and patient will be achieved through a combination of three noise cancellation technologies, namely, Passive Noise Control (PNC), Adaptive Filtering (AF) and Active Noise Control (ANC). This paper describes how far a test-rig has been developed to achieve sufficient noise reduction that the uncomfortable noise can no longer be heard

Testing medical drills for noise emissions

Copyright @ 2007 TUT PressA comparative study of drills from a range of manufacturers was carried out in the laboratory. These tests were made under a variety of loading conditions to assess the characteristics of the noise likely in the dentist’s surgery. Details of the test setup are given, and some of the issues in analysing the results considered. Simultaneous Recordings were made of the noise on a minidisk recorder, a hand held sound meter, and a sound analyser. The results from these are considered. These are significant for dentist’s hearing, and the patient’s perception of visiting the dentists. The performance of different designs of pneumatic drill varies much with type and load

Dental drill noise reduction using a combination of active noise control, passive noise control and adaptive filtering

Dental drills produce a characteristic high frequency, narrow band noise that is uncomfortable for patients and is also known to be harmful to dentists under prolonged exposure. It is therefore desirable to protect the patient and dentist whilst allowing two-way communication. A solution is to use a combination of the three main noise control methods, namely, Passive Noise Control (PNC), Adaptive Filtering (AF) and Active Noise Control (ANC). This paper discusses the application of the three methods to reduce dental drill noise while allowing two-way communication. Experimental setup for measuring the noise reduction by PNC is explained and results from different headphones and headphone types are presented. The implementation and results of an AF system using the Least Mean Square (LMS) algorithm are shown. ANC requires a modification of the LMS algorithm due to the introduction of the electro-acoustical cancellation path transfer function to compensate for the delays introduced by the control system. Therefore a cancellation path transfer function modeling method based on the filtered reference LMS (FXLMS) algorithm is presented along with preliminary results of the implementation

Active noise control on high frequency narrow band dental drill noise: Preliminary results

Dental drills produce a characteristic noise that is uncomfortable for patients and is also known to be harmful to dentists under prolonged exposure. It is therefore desirable to protect the patient and dentist whilst allowing two-way communication. A solution is to use a combination of the three main noise cancellation methods, namely, Passive Noise Control, Adaptive Filtering and Active Noise Control. Dental drill noise occurs at very high frequency ranges in relation to conventional ANC, typically 2kHz to 6kHz and it has a narrow band characteristic due to the direct relation of the noise to the rotational speed of the bearing. This paper presents a design of an experimental rig where first applications of ANC on dental drill noise are executed using the standard filtered reference Least Mean Square (FXLMS) algorithm. The secondary path is kept as simple as possible, due to the high frequency range of interest, and hence is chosen as the space between headphone loudspeaker and error microphone placed in the ear (input of the headphone loudspeaker and the output of the error microphone). A standard headphone loudspeaker is used for the control source and the microphone inside of an “Ear and Cheek Simulator Type 43AG” is used as the error microphone. The secondary path transfer function is obtained and preliminary results of the application of ANC are discussed

Active noise control for high frequencies

There are many applications that can benefit from Active Noise Control (ANC) such as in aircraft cabins and air conditioning ducts, i.e. in situations where technology interferes with human hearing in a harmful way or disrupts communication. Headsets with analogue ANC circuits have been used in the armed forces for attenuating frequencies below 1 kHz, which when combined with passive filtering offers protection across the whole frequency range of human hearing. A dental surgery is also a noisy environment; in which dental drill noise is commonly off-putting for many patients and is believed to harm the dentist’s hearing over a long period of time. However, dealing with dental drill noise is a different proposition from the applications mentioned above as the frequency range of the peak amplitudes goes from approximately 1.5 kHz to 12 kHz, whereas conventional ANC applications consider a maximum of 1.5 kHz. This paper will review the application of ANC at low frequencies and justify an approach for dealing with dental noise using digital technologies at higher frequencies. The limits of current ANC technologies will be highlighted and the means of improving performance for this dental application will be explored. In particular, technicalities of implementing filtering algorithms on a Digital Signal Processor will be addressed

Real-time adaptive filtering of dental drill noise using a digital signal processor

The application of noise reduction methods requires the integration of acoustics engineering and digital signal processing, which is well served by a mechatronic approach as described in this paper. The Normalised Least Mean Square (NLMS) algorithm is implemented on the Texas Instruments TMS320C6713 DSK Digital Signal Processor (DSP) as an adaptive digital filter for dental drill noise. Blocks within the Matlab/Simulink Signal Processing Blockset and the Embedded Target for TI C6000 DSP family are used. A working model of the algorithm is then transferred to the Code Composer Studio (CCS), where the desired code can be linked and transferred to the target DSP. The experimental rig comprises a noise reference microphone, a microphone for the desired signal, the DSK and loudspeakers. Different load situations of the dental drill are considered as the noise characteristics change when the drill load changes. The result is that annoying drill noise peaks, which occur in a frequency range from 1.5 kHz to 10 kHz, are filtered out adaptively by the DSP. Additionally a schematic design for its implementation in a dentist’s surgery will also be presented

A New Operation on Sequences: the Boustrouphedon Transform

A generalization of the Seidel-Entringer-Arnold method for calculating the alternating permutation numbers (or secant-tangent numbers) leads to a new operation on integer sequences, the Boustrophedon transform.Comment: very minor change: corrected typo in author list. June 24 2002: correction to a proof; additional reference

Arizona’s botched execution of Joseph Wood violated the Eighth Amendment and highlighted the U.S. lethal-injection problem—dwindling drug supplies and too much secrecy

Last week saw the controversial execution in Arizona of Joseph Wood by lethal injection. Nancy E. Millar argues that the procedure, which lasted for two hours, illustrates the major problems with the way that executions are now carried out in the U.S. She writes that the growing reluctance of pharmaceutical companies to provide the required drugs, in combination with the secrecy laws enacted by states over them and the staff who carry them out, puts those to be executed at risk of undergoing cruel and unusual punishment – a violation of the Eight Amendment to the Constitution

The U.S. Supreme Court is about to re-evaluate how some states carry out lethal injections.

Next month, the Supreme Court will hear oral arguments in a case which challenges Oklahoma’s use of “liquid fire” in executions. The drug – potassium chloride – is one of a cocktail of drugs currently used in some states to carry out death sentences, a cocktail that has led to botched executions. Nancy E. Millar comments on the upcoming case, which challenges the drug’s use under the Eighth Amendment’s prohibition of cruel and unusual punishment. She writes that while it is impossible to predict what the Court will decide, its previous decisions and statements might provide some indication of how the justices are leaning

The U.S. Supreme Court is about to re-evaluate how some states carry out lethal injections.

Next month, the Supreme Court will hear oral arguments in a case which challenges Oklahoma’s use of “liquid fire” in executions. The drug – potassium chloride – is one of a cocktail of drugs currently used in some states to carry out death sentences, a cocktail that has led to botched executions. Nancy E. Millar comments on the upcoming case, which challenges the drug’s use under the Eighth Amendment’s prohibition of cruel and unusual punishment. She writes that while it is impossible to predict what the Court will decide, its previous decisions and statements might provide some indication of how the justices are leaning